by nuovadarimpianti | 24-05-2026 | Technical Insights

Come Scegliere il Materiale Giusto per Pompe e Agitatori

PP vs PVC vs PVDF

PP vs PVC vs PVDF: Choosing the Right Material for Chemical Pumps and Agitators

In a chemical plant, the material choice is not a secondary decision — it is the decision that determines whether your pump or agitator will last years or weeks. A polypropylene pump body exposed to concentrated nitric acid degrades within hours. A PVC impeller used above 60°C deforms under load. Investing in PVDF where PP would suffice is an unnecessary cost.

Each thermoplastic material has a precise application range, defined by the combination of three factors: the type of chemical agent, its concentration and the operating temperature. This technical guide analyses in depth the properties, limitations and ideal applications of the three main polymers used in manufacturing pumps and agitators for corrosive environments: polypropylene (PP), polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF).

PP vs PVC vs PVDF material comparison for chemical pumps and agitators - Nuova Darimpianti

Molecular structure: why different materials resist different substances

To understand the chemical resistance differences between PP, PVC and PVDF, it helps to start with their molecular structure — because it is the polymer chemistry that determines vulnerability to chemical attack.

Polypropylene (PP)

Polypropylene is a hydrocarbon chain polymer with lateral methyl groups. Its structure consists exclusively of carbon and hydrogen, giving it excellent resistance to aqueous solutions of acids and bases, but poor resistance to organic solvents (which “dissolve” the similar hydrocarbon chains) and strong oxidising agents (which break the C-H bonds).

PVC (Polyvinyl chloride)

PVC replaces one hydrogen atom with a chlorine atom in each repeating unit. The chlorine gives the polymer greater rigidity and good chemical resistance to many acids and bases. However, the presence of chlorine makes PVC sensitive to thermal degradation: above 60°C the material starts to lose dimensional stability, and above 70°C degradation becomes rapid.

PVDF (Polyvinylidene fluoride)

PVDF replaces two hydrogen atoms with two fluorine atoms in each repeating unit. The carbon-fluorine bond is one of the strongest in organic chemistry (bond energy ~485 kJ/mol versus ~413 kJ/mol for the C-H bond). This extreme stability of the C-F bond is why PVDF resists concentrated acids, aggressive solvents and elevated temperatures where PP and PVC fail.

Understanding this molecular hierarchy explains why PVDF costs more: it is not simply an “upgrade” from PP, but a material with fundamentally different and superior chemistry in terms of chemical inertness.

Polypropylene (PP): the workhorse of the chemical industry

Polypropylene is the most widely used thermoplastic in the construction of pumps and agitators for corrosive fluids. The reason is straightforward: it offers an excellent balance between chemical resistance and cost, covering the majority of standard industrial applications.

Chemical resistance of PP

Polypropylene has excellent resistance to dilute inorganic acids (sulfuric up to 70%, hydrochloric up to 30%, phosphoric at all concentrations), strong bases (sodium and potassium hydroxide at all concentrations and temperatures up to 80°C), saline solutions (chlorides, sulfates, nitrates), alcohols (methanol, ethanol, isopropanol) and deionised and ultra-pure water.

Limitations of PP

Polypropylene does not resist strong oxidising acids such as concentrated nitric acid (>50%) and chromic acid, oxidising agents such as concentrated hydrogen peroxide (>30%) and high-concentration hypochlorite, chlorinated organic solvents (dichloromethane, chloroform, trichloroethylene), aromatic hydrocarbons (benzene, toluene, xylene) and free halogens (chlorine gas, bromine).

Mechanical and thermal properties

PP’s maximum operating temperature is 80-90°C (depending on grade and mechanical stress). PP has good impact resistance at ambient temperature but becomes brittle below 0°C. Its density of 0.90-0.91 g/cm³ makes it the lightest of the three polymers, resulting in easy-to-handle components.

CNC machinability

Polypropylene is an excellent material for solid-block machining. It cuts cleanly, produces neat chips and requires no lubrication during machining. Achievable tolerances are excellent. Nuova Darimpianti uses PP as the standard material for pump casings, impellers and agitator shafts machined on 3-axis and 5-axis CNC centres.

When to choose PP

PP is the correct choice for dilute acids and bases at moderate temperatures (<80°C), electroplating tanks with standard solutions, water treatment plants with non-oxidising reagents, washing and neutralisation solutions, and all applications where material cost is a determining factor.

PVC: the low-temperature specialist

PVC occupies a specific niche: it offers comparable performance to PP at ambient temperature, with a distinctive advantage in sodium hypochlorite resistance and superior rigidity that makes it ideal for structural components.

Chemical resistance of PVC

PVC has excellent resistance to dilute and medium-concentration inorganic acids (sulfuric up to 50%, hydrochloric up to 35%), sodium hypochlorite at all industrial-use concentrations (it is the preferred material for NaClO), dilute and medium-strength bases, saline solutions and seawater, and mineral oils and fats.

Limitations of PVC

PVC does not resist temperatures above 60°C (temperature is its main limitation), organic solvents (acetone, MEK, THF which dissolve it), chlorinated hydrocarbons, concentrated acids at even moderate temperatures, and concentrated amines and ammonia.

Mechanical and thermal properties

The maximum operating temperature is only 60°C — a significant limitation for many industrial processes. However, PVC has superior rigidity compared to PP and PE-HD at ambient temperature, good flame resistance (self-extinguishing due to chlorine content), and a density of 1.35-1.45 g/cm³.

When to choose PVC

PVC is the correct choice for sodium hypochlorite dosing and storage circuits, potable water treatment plants (where NaClO is the standard disinfectant), fume scrubbers for acid gas abatement at ambient temperature, tanks and vessels for dilute acid solutions in unheated environments, and applications where material rigidity is important.

PVDF: chemical resistance without compromise

PVDF is the premium material for pumps and agitators destined for the most aggressive applications. Its cost is 3-5 times higher than PP, but in many applications it is the only technically valid option.

Chemical resistance of PVDF

PVDF has excellent resistance to strong inorganic acids at any concentration (sulfuric up to 98%, hydrochloric at any concentration, nitric up to 65%), organic acids (acetic, formic, oxalic), halogens and halogenated acids (hydrofluoric acid, wet chlorine gas, bromine), hydrogen peroxide at moderate concentrations, polar organic solvents (acetone, MEK — unlike PP and PVC), and aggressive acid mixtures used in semiconductor manufacturing.

Limitations of PVDF

PVDF does not resist concentrated strong bases (NaOH > 30% at elevated temperatures — this is the critical difference from PP, which does resist), aliphatic amines (triethylamine, diethylamine), fuming sulfuric acid (oleum), some strongly basic solvents (DMF, DMSO under aggressive conditions), and concentrated nitric acid above 65% at elevated temperatures.

The poor resistance to strong bases is an often-overlooked aspect: for applications with hot concentrated caustic soda, PP is safer than PVDF.

Mechanical and thermal properties

The maximum operating temperature is 100-120°C (significantly higher than PP and PVC), with excellent dimensional stability under load even at elevated temperatures. The density is 1.75-1.78 g/cm³ (the heaviest of the three), and mechanical strength is superior to PP and PVC across the entire temperature range.

When to choose PVDF

PVDF is the mandatory choice for concentrated acids at elevated temperatures (>50°C), hydrofluoric acid at any concentration, applications involving strong oxidising agents, semiconductor industry (extreme purity requirements), pharmaceutical processes with aggressive solvents, magnetic drive pumps for highly hazardous fluids, and all applications where safety permits no compromise.

Other materials: PE-HD and Ebonite

Beyond the three main materials, Nuova Darimpianti uses two additional polymers for specific applications.

PE-HD (High-density polyethylene)

PE-HD has chemical resistance very similar to PP, but offers better environmental stress cracking resistance and greater flexibility at low temperatures. It is the preferred choice for applications with dilute hydrofluoric acid (where PP may present stress cracking issues) and for outdoor installations in cold climates.

PE-HD’s main limitations are its low maximum operating temperature (60-70°C) and lower rigidity compared to PP, which restricts its use in pressurised components.

Ebonite

Ebonite is a natural rubber vulcanised with a high sulfur content, offering excellent chemical resistance to hydrochloric acid at all concentrations, hydrofluoric acid and aggressive saline solutions. It is used as an internal lining for pumps and tanks in applications where the combination of chemical resistance and mechanical resilience is critical.

Chemical compatibility table: the most common cases

The following table summarises the compatibility of the three main materials with the most commonly used industrial chemicals. The classification uses three levels: R (resistant — safe for continuous use), PR (partially resistant — verify concentration and temperature), NR (not resistant — do not use).

Chemical agent	Conc.	Temp.	PP	PVC	PVDF
Sulfuric acid	<70%	60°C	R	R	R
Sulfuric acid	70-98%	60°C	NR	NR	R
Sulfuric acid	96%	80°C	NR	NR	R
Hydrochloric acid	<30%	60°C	R	R	R
Hydrochloric acid	37% (conc.)	60°C	PR	PR	R
Nitric acid	<30%	40°C	PR	PR	R
Nitric acid	>50%	any	NR	NR	R
Hydrofluoric acid	<50%	40°C	PR	NR	R
Hydrofluoric acid	any	60°C	NR	NR	R
Sodium hypochlorite	<15%	40°C	R	R	R
Sodium hypochlorite	concentrated	40°C	PR	R	PR
Sodium hydroxide (NaOH)	<50%	80°C	R	PR	R
Sodium hydroxide (NaOH)	>50%	80°C	R	NR	PR
Hydrogen peroxide	<30%	40°C	PR	PR	R
Hydrogen peroxide	>30%	40°C	NR	NR	R
Chromic acid	any	any	NR	NR	R
Ferric chloride	any	60°C	R	R	R
Acetone	pure	20°C	NR	NR	R
Methanol	pure	40°C	R	PR	R
Chloroform	pure	20°C	NR	NR	PR

Important note: this table is an orientative guide. Chemical resistance depends on the specific combination of concentration, temperature, exposure duration and mechanical stress. For critical applications, always consult the manufacturer’s complete compatibility tables and request a compatibility test.

Manufacturing method: why solid-block machining makes the difference

Material selection is a necessary but not sufficient condition for a reliable pump or agitator. The method by which the material is transformed into the finished component significantly affects its performance.

The limitations of moulding

Most manufacturers of plastic pumps and agitators use injection moulding or rotational moulding. These processes have economic advantages for high volumes, but introduce potential problems: residual internal stresses generated by non-uniform cooling can cause cracking under chemical stress (Environmental Stress Cracking), non-uniform wall thickness creates weak points where the material fails prematurely, and weld lines in moulded material are zones of reduced strength.

The advantage of solid-block CNC machining

Nuova Darimpianti manufactures all critical components (pump casings, impellers, agitator shafts, containment shells) by solid-block machining on 3-axis and 5-axis CNC machining centres. This means every part is machined from a solid bar or plate of extruded material, which by definition is free from moulding-induced thermal stresses.

The advantages include complete absence of residual internal stresses (the primary factor in stress cracking), precise wall thickness control (±0.1 mm on all surfaces), no weld lines or weak points, ability to optimise geometry without mould constraints, and full traceability of the material batch used.

In applications with concentrated acids at elevated temperatures, where the material is subjected to maximum chemical and mechanical stress, the difference between a moulded part and a solid-block machined one can mean years of additional service life.

Solid-block CNC machining of PVDF pump casing

How to choose: a practical decision tree

To simplify selection, here is a logical path in four questions.

Question 1: Is the fluid a strong oxidising acid (nitric, chromic) or an organic solvent? If yes → PVDF is the mandatory choice. If no → proceed to Question 2.

Question 2: Does the operating temperature exceed 60°C? If yes → exclude PVC, choose between PP (up to 80-90°C) and PVDF (up to 100-120°C). If no → proceed to Question 3.

Question 3: Is the fluid sodium hypochlorite? If yes → PVC is the preferred choice. If no → proceed to Question 4.

Question 4: Is the acid concentrated (>70% sulfuric, >37% hydrochloric, any concentration of HF)? If yes → PVDF. If no → PP (the economical choice for most standard applications).

This decision framework covers approximately 80% of applications. For the remainder (multi-component mixtures, cyclic conditions, simultaneous presence of multiple aggressive agents), a specific analysis accounting for all factors is required.

For further details on the pumps in which these materials are used, see HTM series, PMC series and the vertical pumps category. For agitators, see EV series and EVR series.

Material selection decision tree for pumps in corrosive environments

Frequently asked questions

Is PVDF always better than PP?

No. PVDF has superior chemical resistance in most cases, but PP resists concentrated strong bases (NaOH > 30% at elevated temperatures) better. Additionally, PVDF costs 3-5 times more than PP: using it where PP is perfectly adequate is an economic waste. The correct choice always depends on the specific fluid, concentration and temperature.

Can I use PVC for sulfuric acid?

Yes, but only for dilute solutions (up to 50%) at ambient temperature (maximum 60°C). For higher concentrations or elevated temperatures, PVC is not suitable. For concentrated sulfuric acid, only PVDF provides adequate resistance.

How do I know if my fluid is compatible with a given material?

The first step is to consult the manufacturer’s chemical compatibility tables. However, these tables refer to standard conditions. For critical applications (high temperatures, high concentrations, mixtures, thermal cycling), it is advisable to request an immersion test on the specific material under actual operating conditions.

Why doesn't Nuova Darimpianti use PTFE (Teflon)?

PTFE has virtually universal chemical resistance, but it cannot be machined from solid blocks like thermoplastics. PTFE cannot be melted and injected like PP or PVDF: it is sintered from powder, a process that limits achievable geometries. Nuova Darimpianti uses PVDF because it offers chemical resistance nearly comparable to PTFE but with excellent CNC machinability, enabling the production of complex geometries such as pump casings and impellers.

Is the O-ring material as important as the pump body material?

Absolutely. A pump with a PVDF body but incompatible O-rings will still leak. Seals must be selected with the same care as the pump body. Nuova Darimpianti uses FPM (Viton), EPDM or PTFE seals depending on the process fluid.

The right material for every application

Choosing the material for pumps and agitators in corrosive environments is not a question of “better” or “worse” in absolute terms, but of suitability for the specific application. PP covers most standard industrial needs at an accessible cost. PVC excels with hypochlorite and low-temperature applications. PVDF is irreplaceable where extreme chemical resistance and elevated temperatures are required.

Nuova Darimpianti manufactures centrifugal pumps (PMC, HTM series), vertical pumps (VSK, VGA, VL series) and agitators (EV, EVR, KVL, KVRL series) in all three materials, plus PE-HD and Ebonite for specific applications. Every component is machined from solid blocks on CNC centres to guarantee maximum reliability and service life.

Which material for your process fluid?

Nuova Darimpianti’s engineering team analyses your fluid (concentration, temperature, mixtures) and recommends the correct material and the right pump or agitator. Free compatibility analysis.

Request a compatibility analysis

The right material for every application

How to Choose an Industrial Agitator

by nuovadarimpianti | 21-05-2026 | Mixers

How to Choose an Industrial Agitator

Practical Sizing Guide

How to Choose an Industrial Agitator: A Practical Sizing Guide

Choosing an industrial agitator is not simply a matter of buying a motor with a propeller. An undersized agitator will leave dead zones in the tank where the product remains unmixed, causing process defects.

An oversized agitator will waste energy, generate excessive vibrations and shorten the service life of bearings and shaft.

Correct sizing requires a systematic analysis that starts from the fluid properties and process conditions and works towards the choice of impeller, rotational speed and motor power.

This technical guide covers every step of the selection process, with reference to the agitator series manufactured by Nuova Darimpianti for corrosive environments.

Agitatore industriale serie EVR montato su vasca per ambienti corrosivi - Nuova Darimpianti

Starting point: what the agitator needs to achieve

Before discussing impellers and motors, it is essential to clearly define the purpose of the agitation process. Different operations require very different approaches.

Homogeneous blending is the most common operation: uniformising the composition of a liquid within the tank, typically after a reagent addition. It requires good circulation of the entire volume with moderate turbulence.

Solid suspension requires the agitator to generate sufficient fluid velocity to prevent solid particles from settling on the tank bottom. The power needed depends on particle density and size distribution.

Gas-liquid dispersion applies to processes such as aeration in biological treatment or chemical reactions with gaseous reagents. It requires high-turbulence impellers capable of breaking gas bubbles into microbubbles to maximise the exchange surface area.

Heat transfer requires the agitator to maintain a constant flow along the tank walls where cooling or heating coils or jackets are installed.

Emulsification (creating stable liquid-liquid emulsions) requires high shear forces to reduce the droplet size of the dispersed phase.

Clearly defining the objective is the first step: the required flow pattern, the most suitable impeller and the power demand all follow from it.

The fluid properties that drive the selection

The two physical properties that most influence agitator sizing are viscosity and density.

Viscosity: the dominant parameter

Viscosity measures a fluid’s internal resistance to flow. A low-viscosity fluid such as water (1 cP) behaves radically differently from a heavy oil (10,000 cP) or a resin (100,000 cP).

For low-viscosity fluids (1–100 cP), such as aqueous solutions, dilute acids and solvents, the flow regime is easily turbulent and agitation is relatively straightforward. Small-diameter, high-speed impellers are sufficient (D/T ratio between 0.2 and 0.4, where D is the impeller diameter and T the tank diameter).

For medium-viscosity fluids (100–10,000 cP), such as concentrated suspensions, emulsions and polymer solutions, the transitional regime makes mixing more complex. Larger-diameter impellers (D/T between 0.4 and 0.6) at intermediate speeds are required.

For high-viscosity fluids (above 10,000 cP), such as pastes, gels, adhesives and resins, the regime is laminar and conventional impellers become ineffective. Large-diameter impellers that approach the tank walls (D/T between 0.6 and 0.95), such as anchors or helical ribbons, operating at very low speeds are needed.

Density: the effect on power

The fluid density (expressed in kg/m³) directly affects the power drawn by the agitator. All other parameters being equal, doubling the density doubles the required power. For concentrated acids (density 1,400–1,840 kg/m³ for sulfuric acid) the power demand is significantly higher than for aqueous solutions.

Rheological behaviour

Many industrial fluids do not have a constant viscosity — they are non-Newtonian fluids. Some become less viscous when agitated (pseudoplastic or shear-thinning fluids), others become more viscous (dilatant or shear-thickening fluids), and others have a yield stress that must be exceeded before the fluid moves (Bingham plastic fluids). Understanding the rheological behaviour is essential for correct agitator sizing.

The rotational Reynolds number: the sizing compass

The parameter that links fluid properties to agitator operating conditions is the rotational Reynolds number, defined as:

Re = (ρ × N × D²) / μ

where ρ is the fluid density (kg/m³), N the impeller rotational speed (revolutions per second), D the impeller diameter (m) and μ the dynamic viscosity (Pa·s).

The Reynolds number determines the flow regime inside the tank. At Re < 10, the regime is laminar: the fluid moves in ordered layers and mixing occurs mainly by molecular diffusion. At 10 < Re < 10,000, the regime is transitional: laminar and turbulent zones coexist, and mixing is uneven. At Re > 10,000, the regime is fully turbulent: mixing is rapid and efficient, with optimal mass and heat transfer.

The sizing objective is to select the impeller-speed combination that brings the Reynolds number into the desired regime for the specific process. For homogeneous blending in turbulent conditions, Re > 10,000 is the minimum target.

Impeller types: axial, radial and tangential flow

The impeller is the heart of the agitator. Its geometry determines the type of flow generated in the tank and, consequently, the effectiveness of the mixing process.

Axial flow impellers

Axial flow impellers drive the fluid parallel to the agitator shaft, generating a large recirculation loop that involves the entire tank volume. They are the most efficient for homogeneous blending and solid suspension, because they move large fluid volumes with relatively low energy consumption.

The main types include the three-blade marine propeller, the classic choice for low to medium-viscosity fluids. Nuova Darimpianti’s EV series features three-blade marine propeller impellers in PP, PVC or PVDF for corrosive environment applications, with rotational speeds up to 1,400 rpm. It is the quintessential high-speed agitator, ideal for blending, neutralisation and dilution tanks for acids and bases.

Pitched blade impellers combine a dominant axial component with a radial component, offering versatility in applications requiring both circulation and a degree of localised turbulence.

Radial flow impellers

Radial flow impellers drive the fluid perpendicular to the agitator shaft, towards the tank walls. They generate high shear forces in the zone immediately surrounding the impeller, making them ideal for gas-liquid dispersion, emulsification and solid dissolution.

The Cowles impeller (or sawtooth disc) is a disc with a serrated perimeter that generates an intense shear zone. It is the preferred choice for pigment dispersion in paints, emulsion preparation and mixing of fluids with very different viscosities. Nuova Darimpianti’s EVK series features Cowles-type impellers for applications requiring high shear in corrosive environments.

Flat blade turbines (Rushton type) generate intense radial flow and are the standard for gas-liquid dispersion in chemical reactors and bioreactors.

High-viscosity impellers

For high-viscosity fluids, conventional impellers (axial and radial) cannot generate adequate flow because turbulence does not propagate far from the impeller. In these cases, large-diameter impellers such as anchors and helical ribbons are used, operating at very low speeds (5–50 rpm) but involving the entire tank volume due to their proximity to the walls.

Schema flusso assiale e radiale nella miscelazione industriale

Axial and radial flow patterns in industrial mixing

Girante elica tripala marina in PVDF per agitatore veloce EV

Three-blade marine propeller impeller in PVDF for EV high-speed agitator

Girante tipo Cowles per agitatore ad alto shear serie EVK

High-speed and low-speed agitators: the Nuova Darimpianti range

Nuova Darimpianti classifies its agitators into two main families based on rotational speed, each designed for a specific application range.

High-speed series: EV, EVK, EVL, KVL

High-speed series agitators operate at high rotational speeds (typically 300 to 1,400 rpm) and feature impellers with a relatively small diameter compared to the tank.

The EV series is the standard high-speed agitator with a three-blade marine propeller impeller, ideal for homogeneous blending, dilution and neutralisation of low to medium-viscosity fluids. The EVK series features a Cowles-type impeller for high-shear applications such as pigment dispersion and emulsion preparation. The EVL series is the extended-shaft version for deep tanks. The *KVL series is the variant with an integrated epicyclic gear reducer for applications requiring higher torque at intermediate speed.

All high-speed models are available with shaft and impeller in PP, PVC, PVDF or AISI 316 stainless steel, and can be fitted with a three-phase electric or pneumatic motor.

Low-speed series: EVR, EVRK, EVRL, KVRL

Low-speed series agitators operate at reduced rotational speeds (5 to 380 rpm via a mechanical gear reducer) and feature larger-diameter impellers, generating a gentler but more penetrating flow throughout the tank volume.

The EVR series is the standard low-speed agitator with a four-blade pitched impeller, designed for gentle blending, suspension maintenance and slow recirculation of shear-sensitive fluids. The EVRK series features a Cowles-type impeller on a low-speed drive for applications requiring both a degree of shear and a long residence time. The EVRL series is the extended-shaft version. The KVRL series integrates an epicyclic gear reducer for high torque at very low speeds.

The low-speed series application range spans viscous solutions to suspensions with heavy solids, from electroplating to water treatment.

Side-entry series: LVO and LRO

For large-volume tanks where top-entry installation is not practical, Nuova Darimpianti offers side-entry agitators mounted on the tank wall. The LVO series is the high-speed version; the LRO series is the low-speed version with gear reducer. Both generate a helical flow pattern inside the tank that ensures effective mixing even in large-diameter cylindrical vessels.

Practical sizing: the parameters to define

Once the impeller type has been chosen, agitator sizing requires the determination of four fundamental parameters.

1. Impeller diameter

The D/T ratio (impeller diameter / tank diameter) is the first parameter to establish. For high-speed agitators with axial flow impellers, the typical ratio is 0.25–0.40. For low-speed agitators with pitched blade impellers, the ratio rises to 0.40–0.65. For anchor or ribbon impellers, it reaches 0.90–0.98.

2. Rotational speed

Speed is chosen based on the desired Reynolds regime and impeller type. High-speed impellers (propellers, turbines) operate between 300 and 1,400 rpm. Low-speed impellers (pitched blades) between 20 and 380 rpm. High-viscosity impellers between 5 and 50 rpm.

3. Motor power

The required power is calculated through the power number (Np), a dimensionless coefficient characteristic of each impeller type:

P = Np × ρ × N³ × D⁵

where P is power (W), Np the impeller power number, ρ the fluid density (kg/m³), N the rotational speed (rev/s) and D the impeller diameter (m).

The power number varies by impeller type: for a three-blade marine propeller it is approximately 0.3–0.5 in the turbulent regime, for a Rushton turbine approximately 4–6, and for a pitched blade impeller approximately 1.2–1.5.

A common mistake is selecting the motor based solely on rated kW. The critical parameter is the shaft torque (expressed in Nm), which determines the agitator’s ability to overcome fluid resistance. For viscous fluids, a powerful motor running at high speed may have less usable torque than a less powerful but slower motor fitted with a gear reducer.

4. Installation position and shaft length

The agitator must be correctly positioned within the tank. For axial flow impellers, the distance from the tank bottom should be approximately one impeller diameter. For tall tanks with a variable level, it may be necessary to install multiple impellers on the same shaft or to use the EVL/EVRL extended-shaft series.

Eccentric installation (with the agitator axis offset from the tank centre) or angled mounting is an effective alternative to baffles for preventing the central vortex in open tanks.

Material selection for corrosive environments

In environments where the fluid is chemically aggressive, the shaft and impeller material must be compatible with the process. Nuova Darimpianti manufactures agitators with shafts and impellers machined from solid blocks on CNC centres in the following thermoplastic materials.

Polypropylene (PP) is the standard choice for dilute acids, bases, saline solutions and electroplating baths up to 80°C. PVC is suitable for sodium hypochlorite and low-temperature solutions. PVDF offers superior chemical resistance for concentrated acids, solvents and oxidising environments up to 100°C. PE-HD (high-density polyethylene) is used for specific low-temperature applications.

Solid-block CNC machining ensures no internal stresses and precise dimensional tolerances — a critical advantage for impellers operating at high rotational speeds where even small imbalances generate excessive vibrations.

Common mistakes in agitator selection

Industry experience reveals several recurring errors in industrial agitator selection.

Selecting the agitator based on motor power rather than analysing the process. A 5 kW agitator with the wrong impeller can mix worse than a 1.5 kW unit with the correct one.

Ignoring viscosity changes during the process. Many processes involve viscosity variations during the cycle (for example during polymerisation or heating). The agitator must be sized for the most demanding condition.

Not accounting for variable tank level. If the tank is filled and emptied while the agitator is running, the impeller may be exposed above the liquid during low-level phases, causing vibrations, unwanted aeration and accelerated wear.

Underestimating the effect of baffles. In cylindrical tanks with axial impellers, the absence of baffles causes a central vortex that drastically reduces mixing effectiveness and can entrain air into the fluid.

For more information on suitable materials, see our guide to Corrosive Acid Pumps and the article on magnetic drive pumps.

Domande frequenti

What is the difference between a high-speed and a low-speed agitator?

A high-speed agitator typically operates between 300 and 1,400 rpm with a small impeller relative to the tank (D/T 0.2–0.4) and generates intense turbulent flow. A low-speed agitator operates between 5 and 380 rpm with a larger impeller (D/T 0.4–0.65) and generates a gentler but more extensive flow. The choice depends on fluid viscosity and the process type: high-speed for rapid mixing of low-viscosity fluids, low-speed for viscous or shear-sensitive fluids.

How do you calculate the power required for an agitator?

Power is calculated using the formula P = Np × ρ × N³ × D⁵, where Np is the impeller power number (a coefficient that depends on geometry), ρ the fluid density, N the speed and D the impeller diameter. The Np value is obtained from experimental correlations specific to each impeller type and Reynolds regime.

What happens if the fluid viscosity changes during the process?

The agitator must be sized for the most demanding condition. If viscosity increases during the process (for example in a polymerisation reaction), the agitator must be capable of generating sufficient torque even at maximum viscosities. A variable frequency drive (VFD) can be useful for adapting speed to different process stages.

Which materials are suitable for agitating acids in electroplating tanks?

For electroplating tanks with dilute acids and metal salt solutions, polypropylene (PP) is the standard choice. For baths containing chromic acid, hydrofluoric acid or strongly oxidising solutions, PVDF is required. Nuova Darimpianti manufactures shafts and impellers in PP, PVC, PVDF, PE-HD and Ebonite, all machined from solid blocks on CNC centres.

Can Nuova Darimpianti size the agitator for my specific application?

Yes. Correct sizing requires information about tank volume, fluid type and properties, process objective and operating conditions. Nuova Darimpianti’s engineering team analyses these data and proposes the optimal combination of series, impeller, material and motor for each application.

Choose the right agitator

Selecting an industrial agitator is a technical process requiring analysis of multiple factors: the process objective, fluid properties, the desired flow regime, tank geometry and operating conditions.

Nuova Darimpianti designs and manufactures high-speed agitators (EV, EVK, EVL, KVL series), low-speed agitators (EVR, EVRK, EVRL, KVRL series) and side-entry agitators (LVO, LRO series) in PP, PVC, PVDF and AISI 316 stainless steel, all with components machined from solid blocks on CNC centres. Every agitator can be custom-configured for the specific requirements of your plant.

Pumps for corrosive acids

by nuovadarimpianti | 20-05-2026 | Pumps

Pumps for Corrosive Acids: How to Choose the Right Material and Type

Pumps for Corrosive Acids Complete Guide

Transferring acids is one of the most critical operations in any chemical, electroplating or pharmaceutical plant. Choosing the wrong material or pump type does not simply result in mechanical failure — it can lead to hazardous spills, costly downtime and, in the worst cases, serious safety risks for operators.

The challenge is that no single pump works for every acid. Concentrated sulfuric acid at 98% demands a completely different approach than a dilute 5% hydrochloric acid solution. Temperature, concentration, the presence of suspended solids and required flow rate all influence the decision.

This technical guide covers the fundamental criteria for selecting the most suitable pump for each type of corrosive acid, comparing thermoplastic materials and construction types.

Why metal pumps fall short with acids

Stainless steel pumps (AISI 316) are often regarded as the “safe” choice for chemical duty. In practice, however, stainless steel has significant limitations when handling acids.

Hydrochloric acid attacks stainless steel even at very low concentrations, causing pitting corrosion that rapidly deteriorates the impeller and pump casing. Concentrated sulfuric acid at temperatures above 50°C causes generalised corrosion even on the most resistant grades. Hydrofluoric acid is incompatible with any iron-based alloy.

Furthermore, metallic corrosion contaminates the pumped fluid with metal ions — an unacceptable problem in pharmaceutical manufacturing, potable water treatment and semiconductor production.

For these reasons, thermoplastic pumps represent the most reliable and often most cost-effective solution for handling corrosive acids.

The three thermoplastic materials compared: PP, PVC and PVDF

Polypropylene (PP)

the most versatile option

Polypropylene is the most widely used thermoplastic in the manufacture of pumps for corrosive fluids, and for good reason. It offers excellent resistance to most dilute acids, saline solutions and bases, with a maximum operating temperature of 80–90°C.

PP is the ideal choice for dilute acids and bases in non-oxidising environments, galvanic solutions based on dilute sulfuric acid, saline solutions and pickling baths, and processes where material cost is a critical factor.

The main limitation of polypropylene is its poor resistance to strong oxidising agents (such as concentrated nitric acid and high-concentration hydrogen peroxide) and to chlorinated organic solvents.

PVC

the low-temperature specialist

PVC offers chemical resistance similar to PP for many acids, with one specific advantage: it is the material of choice for sodium hypochlorite, a reagent widely used in water treatment and electroplating plants.

However, its maximum operating temperature is limited to 60°C, restricting its use to processes at ambient temperature or slightly above. PVC is not suitable for organic solvents and aromatic hydrocarbons.

Typical applications include fume scrubbers, containment tanks and sodium hypochlorite dosing circuits.

PVDF

superior chemical resistance

Polyvinylidene fluoride is the highest-performing thermoplastic for aggressive acid applications. The presence of fluorine atoms in the polymer chain ensures more stable chemical bonds, providing exceptional resistance to concentrated strong acids.

PVDF withstands sulfuric acid up to 98% concentration, hydrochloric acid at any concentration, concentrated nitric acid and strong oxidising agents. Its maximum operating temperature reaches 100°C, with good dimensional stability under load.

The higher cost compared to PP and PVC is justified by longer service life in extreme environments and reduced downtime for maintenance.

PVDF is the mandatory choice for magnetic drive pumps handling concentrated acids, high-temperature concentrated sulfuric acid transfer, pharmaceutical processes where purity is critical, and applications involving hydrofluoric acid.

Quick comparison table

Property	PP	PVC	PVDF
Max. operating temp.	80-90°C	60°C	100°C
Dilute sulfuric acid	Excellent	Good	Excellent
Concentrated sulfuric acid	Poor	Poor	Excellent
Hydrochloric acid	Good	Good	Excellent
Nitric acid	Poor	Poor	Good
Sodium hypochlorite	Good	Excellent	Good
Organic solvents	Poor	Poor	Fair
Relative cost	Low	Low	High
CNC machinability	Excellent	Buona	Buona

Pump types for acids: which configuration to choose

Horizontal centrifugal pumps with mechanical seal

Horizontal centrifugal pumps are the most common type for transferring corrosive fluids. The fluid enters the impeller axially and is accelerated outward by centrifugal force, generating flow and head.

The mechanical seal is the most critical component: it is the interface between the rotating part (shaft) and the stationary part (casing), and must prevent any fluid leakage. Single seals are adequate for low-hazard fluids, while a double flushed seal adds a safety barrier with a barrier fluid between the two seal faces.

Nuova Darimpianti’s PMC series pumps feature casings and impellers machined from solid blocks of polymer on 3-axis and 5-axis CNC machining centres — a method that delivers tighter dimensional tolerances and higher internal pressure resistance compared to moulded pumps. The PMC-1 series is fitted with a single mechanical seal, while the PMC-2 series features a double flushed seal for maximum safety when pumping concentrated acids and hazardous liquids.

Magnetic drive pumps: zero leakage

Magnetic drive pumps completely eliminate the mechanical seal. Motion is transmitted from the motor shaft to the impeller through a pair of magnets separated by a containment shell. There is no physical contact between the drive side and the fluid.

This design guarantees absolute zero leakage — a decisive advantage when pumping concentrated acids, toxic solvents or fluids prone to crystallisation that would damage a traditional mechanical seal.

Nuova Darimpianti’s HTM series is a horizontal centrifugal magnetic drive pump available in PP, PVC and PVDF, designed specifically for strong acids, hazardous fluids and applications where safety is the top priority.

The limitations of magnetic pumps include sensitivity to dry running (which can demagnetise the magnets) and generally lower head than mechanically sealed pumps at the same power rating.

Vertical pumps: ideal for tank-mounted installation

Vertical pumps are installed directly on the edge of the tank or vessel, with the shaft and impeller submerged in the fluid. This configuration eliminates the mechanical seal problem entirely, as there is no fluid passage through external gaskets.

Nuova Darimpianti’s VSK series is a cantilever vertical pump without guide bushings: the absence of wetted sliding parts dramatically reduces wear, making it ideal for fluids containing suspended solids or abrasive particles.

Vertical pumps are particularly suited to galvanic tanks, acid storage vessels, scrubber recirculation systems and applications where floor space is limited.

Drum transfer pumps

For emptying drums and containers, portable and easy-to-handle solutions are required. PP and PVDF drum transfer pumps enable safe transfer of acids and bases from industrial drums without the need for tilting, reducing the risk of spills.

How to size the pump: key parameters

Selecting the right material and type is not enough — the pump must be correctly sized for the system’s operating conditions.

The key parameters are:

flow rate, the volume of fluid to be transferred per unit time, expressed in litres per minute or cubic metres per hour
head, the energy the pump must impart to the fluid to overcome the system’s friction losses and static height difference, expressed in metres of liquid column
and NPSH (Net Positive Suction Head), the parameter that determines whether the pump can draw fluid without cavitation occurring

Cavitation is a destructive phenomenon that occurs when suction pressure drops below the fluid’s vapour pressure, causing the formation and violent collapse of vapour bubbles on the impeller. In a plastic pump, cavitation can erode the impeller very rapidly.

A common mistake is sizing the pump based solely on motor power in HP or kW. The critical parameter is actually the torque transmitted to the shaft, which determines the pump’s ability to overcome fluid resistance. For viscous or dense fluids, a pump with a powerful motor but insufficient torque will not perform correctly.

Quick selection guide: which pump for which acid

To simplify the decision, here are the most common material-type combinations for the main industrial acids:

\Sulfuric acid (H₂SO₄):

For concentrations up to 70% and temperatures up to 80°C, the choice is PP with a horizontal centrifugal pump (PMC series). For concentrations above 70% or elevated temperatures, PVDF is necessary, preferably with a magnetic drive pump (HTM series) to eliminate leakage risk.

\Hydrochloric acid (HCl):

At any concentration, PVDF offers the best resistance. For dilute solutions at ambient temperature, PP is a valid and economical alternative. The vertical pump (VSK series) is ideal for direct suction from tanks.

\Nitric acid (HNO₃):

As a strong oxidiser, nitric acid attacks PP. PVDF is mandatory for concentrations above 40%. For dilute solutions, PVC may be adequate up to 60°C.

\Sodium hypochlorite (NaClO):

PVC is the preferred material for sodium hypochlorite. Vertical pumps for dosing from storage tanks or horizontal PMC pumps for distribution circuits.

\Hydrofluoric acid (HF):

Requires exclusively PVDF with a magnetic drive pump (HTM series) for maximum safety. Hydrofluoric acid is highly toxic and no leakage is acceptable.

The advantage of solid-block CNC machining

An often overlooked aspect when choosing an acid pump is the manufacturing method of the pump casing. Most manufacturers use injection moulding or rotational moulding — processes that can introduce internal stresses in the material and non-uniform wall thickness.

Nuova Darimpianti manufactures pump casings by solid-block machining: every component is machined from a solid block of polymer on 3-axis and 5-axis CNC machining centres.

This method guarantees no residual internal stresses, millimetre-precision dimensional tolerances, uniform and controlled wall thickness throughout the pump casing, and higher internal pressure resistance compared to moulded parts.

Frequently asked questions

Which material is better for sulfuric acid: PP or PVDF?

It depends on the concentration. PP performs well up to approximately 70% at ambient temperature. For higher concentrations or elevated temperatures, PVDF is essential due to its superior chemical resistance to strong oxidisers.

Can magnetic drive pumps run dry?

No, dry running is the main risk for magnetic pumps. The absence of fluid to lubricate and cool the internal bearings can cause overheating and demagnetisation of the magnets. Dry-run protection devices are essential.

How often should the mechanical seal be replaced on an acid pump?

Seal life depends on the fluid type, temperature and duty cycle. Under typical conditions, a mechanical seal on an acid pump lasts between 6 and 18 months. With the PMC-2 double flushed seal, the barrier fluid significantly extends seal life.

What happens if I choose the wrong material?

Chemical corrosion can manifest as polymer swelling, stress cracking, loss of mechanical strength or, in the worst cases, sudden casing failure with fluid spillage. This is why consulting chemical compatibility charts before selecting the material is essential.

Can Nuova Darimpianti build custom pumps?

Yes. Thanks to solid-block CNC manufacturing, Nuova Darimpianti builds pumps in custom configurations for material, dimensions, connections and accessories. Every pump can be engineered to the specific requirements of your plant.

Choose the right pump for your process

Need technical advice on choosing the right pump for your process?
Contact our engineers for a personalised quotation.

Correct selection of a pump for corrosive acids requires careful analysis of four factors: the type of acid and its concentration, the operating temperature, the required flow rate and head, and the safety level demanded.

Nuova Darimpianti designs and manufactures horizontal centrifugal pumps (PMC-1 and PMC-2 series), magnetic drive pumps (HTM series) and vertical pumps (VSK, VGA, VL series) in PP, PVC and PVDF, all machined from solid blocks using CNC technology.

Magnetic drive pumps

by nuovadarimpianti | 20-05-2026 | Pumps

Magnetic Drive Pumps

How They Work and When to Choose Them

Magnetic Drive Pumps: How They Work and When to Choose Them

Every mechanical seal, no matter how well engineered, is a compromise: a contact point between a rotating and a stationary part that will eventually fail. In a plant handling hydrofluoric acid, chlorinated solvents or toxic fluids, “eventually” is not acceptable.

Magnetic drive pumps eliminate the problem at its source. There is no mechanical seal, no contact point, no possibility of leakage. Motion is transmitted to the impeller through a magnetic field that passes through a sealed containment barrier, keeping the fluid completely isolated from the outside environment.

This technical guide explains how magnetic drive pumps work, analyses the real advantages and limitations of the technology, and helps identify the applications where magnetic coupling is the safest and most cost-effective choice.

Pompa a trascinamento magnetico serie HTM in PVDF - Nuova Darimpianti

How it works: transmitting motion without contact

Schema funzionamento pompa a trascinamento magnetico con magnete esterno, bicchiere di contenimento e magnete interno

The heart of a magnetic drive pump is the coupling system that replaces the traditional shaft seal. The mechanism is elegant in its simplicity.

The three key components

The system consists of three main elements. The outer magnet (or drive magnet) is connected to the electric motor shaft and rotates outside the pump casing. The inner magnet (or driven magnet) is attached to the impeller and is immersed in the pumped fluid. Between the two sits the containment shell, a sealed barrier made of non-magnetic material that physically separates the drive side from the hydraulic side.

How the drive works

When the electric motor rotates the outer magnet, the magnetic field passes through the containment shell wall and sets the inner magnet in rotation, which in turn drives the impeller. There is no physical contact between the dry side (motor) and the wet side (fluid). The only barrier between the fluid and the outside environment is the containment shell — a completely static component with no mechanical wear.

This principle guarantees an absolute hermetic seal for the entire service life of the pump, with no need for adjustments, periodic replacements or external lubrication.

The role of the containment shell

The containment shell is the most critical component from a design standpoint. It must be made of a material that simultaneously meets three requirements: magnetic transparency (it must not attenuate the field), chemical resistance to the pumped fluid, and mechanical strength to withstand internal pressure.

In metallic magnetic drive pumps, the containment shell is typically made of Hastelloy or austenitic stainless steel, but these materials generate eddy currents that reduce efficiency and heat the fluid. In thermoplastic pumps such as Nuova Darimpianti’s HTM series, the containment shell is made of engineering plastic, which generates no eddy currents and offers excellent chemical resistance. The result is superior magnetic efficiency and zero induced heating of the fluid.

Real advantages over mechanically sealed pumps

Choosing a magnetic drive pump goes beyond simply eliminating the mechanical seal. The advantages extend to plant safety, operating costs and process quality.

Zero fugitive emissions

European and international safety regulations (ATEX Directive, EPA Method 21, ISO 15848) impose increasingly stringent limits on fugitive emissions. Every mechanical seal is a potential emission source. Magnetic drive pumps, having no shaft penetration through the pump casing, meet the most restrictive regulations without the need for additional monitoring systems.

In ATEX-classified environments (zones with potentially explosive atmospheres), the absence of any leakage point drastically reduces ignition risk and simplifies risk assessment.

Reduced maintenance costs

The mechanical seal is the component that requires the most maintenance in a centrifugal pump. Replacing it involves plant downtime, partial pump disassembly and specialised personnel. In applications with concentrated acids, a mechanical seal typically lasts between 6 and 18 months.

By eliminating the mechanical seal, a magnetic drive pump reduces scheduled maintenance shutdowns, eliminates the need to stock seal spare parts, cuts technical intervention costs and extends the intervals between general overhauls. The slightly higher initial cost of a magnetic drive pump is typically recovered within 12–24 months through maintenance savings.

No fluid contamination

In mechanically sealed pumps, the seal faces release microscopic wear particles into the pumped fluid. In pharmaceutical applications, ultra-pure water treatment and semiconductor manufacturing, this contamination is unacceptable.

Magnetic drive pumps, having no sliding parts in contact with the fluid (except for the impeller support bearings), deliver a significantly higher level of fluid purity.

No barrier fluid consumption

Double mechanical seal pumps (such as Nuova Darimpianti’s PMC-2 series) require a barrier fluid that must be compatible with the process fluid, maintained at constant pressure and periodically topped up or replaced. The magnetic drive pump eliminates this requirement entirely, simplifying installation and reducing consumables.

Limitations and precautions: when a magnetic pump is not the right choice

No technology is universal. Magnetic drive pumps have specific limitations that must be carefully evaluated during the selection process.

The dry-running risk

The most critical limitation of magnetic drive pumps is their sensitivity to dry running. The internal bearings of the impeller are lubricated and cooled by the pumped fluid. If the pump operates without fluid, even for a few minutes, the bearings overheat and sustain damage, and in the worst cases the magnets lose their magnetic properties due to heat (demagnetisation).

To prevent this, it is essential to install level sensors in the suction vessel, provide dry-run protection (such as a thermal relay or flow sensor), and never start the pump with the discharge valve closed without a bypass line.

Transmissible torque and decoupling

The magnetic coupling has a maximum transmissible torque limit. If the fluid resistance exceeds this limit — due to a sudden blockage in the discharge line, excessive fluid viscosity or a foreign body in the impeller — the magnets “slip” and motion transmission stops. This phenomenon, known as magnetic decoupling, protects the motor from overload but requires manual intervention to restore operation.

For applications with viscous fluids (above 200–300 cP) or frequent sudden load variations, a mechanically sealed pump may be more appropriate.

Head and power

At the same size and motor power, magnetic drive pumps generally develop lower head than mechanically sealed pumps. This is because part of the energy is dissipated in the magnetic coupling (especially in metallic containment shells, less so in plastic versions). For applications requiring high head, a larger pump size must be selected.

Temperature and suspended solids

Permanent magnets lose magnetic strength as temperature increases. Above 200°C (in metallic versions) or 100°C (in plastic versions), transmissible torque decreases significantly. Additionally, fluids with suspended solid particles can damage internal bearings more rapidly than in a mechanically sealed pump.

Ideal applications for magnetic drive pumps

Magnetic coupling is the technically superior choice wherever the priority is absolute zero leakage. Here are the applications where this technology delivers the greatest value.

Chemical and petrochemical industry

Pumping concentrated acids (sulfuric, hydrochloric, hydrofluoric), chlorinated solvents, strong bases and toxic reagents is the classic application for magnetic drive pumps. Safety regulations classify many of these fluids as hazardous substances whose release must be prevented by all technically available means.

Surface treatment and electroplating

In electroplating plants, tanks contain acid and alkaline solutions at controlled temperatures that must be transferred without contamination or leakage. The magnetic drive pump is ideal for recirculation and transfer between galvanic baths based on chromic acid, sulfuric acid and hydrofluoric acid.

Pharmaceutical and food industry

Pumped fluid purity is a non-negotiable requirement. Magnetic drive pumps, releasing no particles from seals, meet the requirements of processes where contamination must be reduced to zero.

Water treatment and scrubbers

Dosing and transferring chemical reagents (sodium hypochlorite, sulfuric acid for pH correction, polyelectrolytes) in water treatment plants requires reliable, leak-free pumps — especially in outdoor installations or unattended facilities (see VSK pumps series).

Semiconductor manufacturing

The ultra-pure water and chemical reagents used in chip production must be transferred without any ionic contamination. PVDF magnetic drive pumps are the industry standard for these applications.

Nuova Darimpianti’s HTM series: magnetic drive in thermoplastic

The HTM series is the horizontal centrifugal magnetic drive pump designed and manufactured by Nuova Darimpianti specifically for corrosive and hazardous fluids.

Solid-block CNC construction

Unlike most magnetic drive pumps on the market, which are produced by injection moulding, the HTM series is manufactured by solid-block machining: every component — pump casing, impeller, containment shell — is machined from a solid block of polymer on 3-axis and 5-axis CNC machining centres.

This manufacturing method ensures no residual internal stresses in the material (which in moulded parts can cause cracking under chemical stress), precision dimensional tolerances that guarantee optimal coupling between magnets and containment shell, and uniform controlled wall thickness that maximises internal pressure resistance.

Available materials

The HTM series is available in three thermoplastic materials. Polypropylene (PP) is suitable for dilute acids, saline solutions and bases at temperatures up to 80°C — the most economical choice for non-oxidising fluids. PVC is ideal for sodium hypochlorite and ambient-temperature solutions up to 60°C. PVDF offers the highest chemical resistance for concentrated acids, solvents and oxidising fluids up to 100°C.

Key technical features

The HTM series covers flow rates from a few litres per minute up to significant industrial volumes, with head values suited to transfer and recirculation applications. The engineering-plastic containment shell eliminates the eddy current losses typical of metallic shells, improving overall pump efficiency.

Every HTM pump can be custom-configured for connection sizes, material type and motor power, thanks to the flexibility of solid-block CNC manufacturing.

Magnetic drive vs mechanical seal: a practical decision guide

The choice between magnetic coupling and mechanical seal is not always straightforward. Here are the practical criteria to guide the decision.

Choose the magnetic drive pump (HTM) when: the fluid is toxic, carcinogenic or highly hazardous; regulations require zero fugitive emissions; the fluid tends to crystallise (crystallisation destroys mechanical seals); the plant is not continuously manned and leakage cannot be tolerated; mechanical seal maintenance costs are excessive.

Choose the mechanically sealed pump (PMC-1 or PMC-2) when: high head is required that the magnetic version cannot achieve; the fluid contains suspended solids that would damage magnetic pump bearings; the temperature exceeds magnet limits; frequent load variations or unstable process conditions occur; fluid viscosity exceeds 200 cP.

Intermediate solution — double flushed seal (PMC-2): if the fluid is hazardous but operating conditions are not compatible with a magnetic drive pump, the PMC-2 series with double flushed seal offers a high level of safety, with the barrier fluid acting as an additional defence against leakage.

Frequently asked questions

What is the main difference between a magnetic drive pump and a mechanically sealed pump?

The fundamental difference is that in a magnetic drive pump there is no shaft penetration through the pump casing. Motion is transmitted through a magnetic field that passes through a sealed wall (the containment shell). This completely eliminates leakage risk, which in mechanically sealed pumps depends on the integrity of the seal faces.

Do magnetic drive pumps consume more energy?

In versions with a metallic containment shell, yes: eddy currents cause a power loss of 5–15%. In pumps with a plastic containment shell, such as Nuova Darimpianti’s HTM series, magnetic losses are negligible and efficiency is comparable to mechanically sealed pumps.

What happens if a magnetic drive pump runs dry?

Dry running is the primary risk for magnetic drive pumps. Without fluid to lubricate the internal bearings, rapid overheating occurs which can damage the bearings and, in severe cases, demagnetise the magnets. Dry-run protection (level sensors, thermal relays, flow sensors) is essential.

Which fluids are recommended for magnetic drive pumps?

Any fluid where a leak would be unacceptable: concentrated acids (sulfuric, hydrochloric, hydrofluoric, nitric), toxic solvents, carcinogenic fluids, expensive reagents, crystallising fluids and pharmaceutical solutions requiring absolute purity.

Can the HTM series be customised?

Yes. Being manufactured from solid blocks via CNC machining, the HTM series can be configured for material (PP, PVC, PVDF), connection sizes, flow rate and head. Nuova Darimpianti engineers custom solutions for specific plant requirements.

The safe choice for fluids that allow no compromise

Magnetic drive pumps are not the solution for every application, but when the fluid is hazardous, toxic or corrosive and zero leakage is not optional but a requirement, they represent the most reliable technology available.

Nuova Darimpianti’s HTM series combines the magnetic drive principle with solid-block CNC machining in thermoplastic materials, delivering a leak-free, corrosion-resistant pump built to precision tolerances that surpass moulded alternatives.