Diaphragm, peristaltic, solenoid and progressive-cavity pumps each have a sweet spot in chemical dosing. The decision involves chemistry, viscosity, pressure, accuracy, dose volume per stroke and maintainability. This page gives the technical comparison and a selection matrix.
Choosing a dosing pump is rarely about pick-best-from-catalogue. The right unit depends on (1) the chemical’s viscosity and corrosivity, (2) the discharge pressure required, (3) the dose volume and accuracy spec, (4) whether dose is steady or pulsed, and (5) how often the pump can be safely maintained. This page covers four common technologies, how they differ and a decision matrix to start the selection.
An electromagnetic coil pulls a diaphragm back rapidly, sucking liquid through a check valve; spring return pushes the diaphragm forward, discharging through a second check valve. Stroke length and frequency are electronically adjustable.
Best for: small-flow drinking-water and industrial dosing (chlorine, coagulants, pH), low-cost reliable duty.
Solenoid pumps deliver discrete dose pulses, not smooth flow. Combined with low strokes/min this produces jerky dose curves. Mitigation: pulsation dampener on discharge, or motorised diaphragm for higher flow.
Solenoid pumps lose prime if air enters the suction. Self-priming variants tolerate small air pockets; degas valves help in volatile chemistries (NaOCl).
An electric motor with eccentric drives one or two diaphragms via a connecting rod. Stroke length adjusts mechanically (manual knob or pneumatic actuator); flow turn-down via VFD on motor.
Best for: medium-to-large flow dosing, high-pressure applications (e.g., into pressurised distribution mains), continuous heavy-duty industrial.
| Material | Best for | Avoid with |
|---|---|---|
| PTFE (Teflon) | Acids, alkalis, solvents, ozone | Fluoride at high temp |
| EPDM | Water, dilute acids/alkalis | Hydrocarbons, oils |
| FKM (Viton) | Hydrocarbons, oils | Strong amines, MEK |
| Hypalon | Sulphuric, nitric, hypochlorite | Aromatic solvents |
| PVDF (Kynar) | Halogens, strong oxidisers | Strong caustic at temp |
A flexible hose is compressed by rotating rollers, pushing fluid through. The only wetted part is the hose itself — no valves, no diaphragms, no seals. The fluid never contacts pump mechanicals.
Best for: abrasive slurries (polymer slurry, lime milk, ferric chloride concentrate), shear-sensitive (polymers, biological), aggressive/corrosive chemistry, dirty fluids that would jam check valves.
The single moving wetted part — the hose — is also the only failure point. No check valves to clog; no diaphragms to crack; no seals to leak. Predictable PM. Particularly favoured for polymer feed (preserves long-chain polymer; no shear damage).
Natural rubber: cheapest, abrasion resistant, good for slurry.
NBR: oil/hydrocarbon compatible.
EPDM: acids/alkalis, ozone.
Hypalon: hypochlorite, peroxides.
PTFE-lined: most aggressive chemistry.
A helical steel rotor turns inside a flexible elastomer stator, creating sealed cavities that progress from suction to discharge. Smooth, non-pulsating flow; tolerates viscous and shear-sensitive fluids.
Best for: viscous fluids (polymer solutions, lime slurry, anti-foam emulsions), sludge feed to dewatering, shear-sensitive long-chain polymers, blended chemicals.
| Rotor | Stator | Best for |
|---|---|---|
| Chromed steel | NBR | General — oils, hydrocarbons |
| SS 316 | EPDM | Acids, alkalis, polymer solutions |
| Hardened SS | Hypalon | Hypochlorite, peroxide, mild abrasion |
| Ceramic-coated | FKM / EPDM | High abrasion + chemistry |
| Hardox / tungsten | Natural rubber | Heavy slurry, lime milk |
| Application | Recommended pump | Why |
|---|---|---|
| Sodium hypochlorite (15%) | Solenoid or motor-driven diaphragm | Low flow, accuracy, off-gas degas valve essential |
| Ferric chloride (40%) | Motor-driven diaphragm (PTFE) or peristaltic | Dense, corrosive, pressure-tolerant pump needed |
| PACl / alum | Motor-driven diaphragm or peristaltic | Moderate flow, dense liquid, valves can clog with crystals |
| Polymer (prepared, 0.05%) | Peristaltic or progressive cavity | Shear-sensitive, low pressure, viscous |
| Lime slurry / milk of lime | Peristaltic or progressive cavity | Abrasive, scaling, hose pump excels |
| Caustic (50%) | Motor-driven diaphragm (PVDF / Hastelloy) | Corrosive, viscous when cold, requires heated piping |
| Sulphuric acid (98%) | Motor-driven diaphragm (PVDF / Hastelloy C) | Aggressive, requires Hastelloy wetted parts |
| Peracetic acid | Solenoid or motor diaphragm (PTFE/FKM) | Strong oxidiser, hose pumps degrade quickly |
| Antifoam emulsion | Progressive cavity | Viscous, shear-sensitive |
| Coagulant aid (silica) | Solenoid diaphragm | Low flow, dilute solution, micro-dosing accuracy |
| Hydrogen peroxide (35%) | Motor diaphragm (PTFE / 316 SS) | Decomposes on contact with metals (not 316L); EPDM/Viton fine |
The wrong wetted-part material destroys a dosing pump in days.
Wetted: diaphragm, suction & discharge check valves, valve seats, valve balls, pump head. Each can be a different material to optimise cost. Manufacturer wetted-parts kit selection chart is the reference.
Wetted: hose material + connections. Hose is the only consumable; check chemistry compatibility chart and operating temperature window.
Wetted: rotor (steel coating), stator (elastomer), inlet/outlet flanges. Rotor coatings: hard chrome, tungsten carbide, ceramic for abrasion. Stator: NBR, EPDM, FKM, Hypalon, Buna.
Don’t forget the piping. PVC-U for low temp / non-aromatic; HDPE for moderate; PVDF (Kynar) for aggressive; PTFE-lined steel for extreme.
Wetted: plunger, packing/seals, suction & discharge valves and pump head. Ceramic or hard-coated plungers with PTFE packing handle high-pressure, mildly abrasive duty — verify seal chemistry against the dosed reagent.
The smallest wetted parts cause most failures. Match the elastomer to the chemistry: EPDM for acids and alkalis, FKM (Viton) for oxidisers and solvents, PTFE/FFKM for the most aggressive reagents and high temperatures.
Specified flow accuracy means nothing without periodic verification. Recommended calibration regime:
Stroke pump into a graduated cylinder; time 60 seconds. Calculate volume; compare with display. Most pumps can be tuned via stroke length adjustment or controller scaling.
For critical service, install a micro-motion flow meter on the discharge. Confirms actual delivered volume regardless of stroke calibration drift.
The pump is only as good as its connecting piping.
Flooded suction preferred (storage tank above pump). Foot valve + strainer to prevent debris & air ingress. Suction pipe sized 1.5× nominal pump size to limit NPSH.
Check valve at pump outlet to prevent back-flow during shutdown. Pressure-relief valve (PRV) routed to bund or scrubber. Pressure gauge with isolation cock.
If pump discharges below liquid level in receiving tank, install anti-syphon loop or vacuum breaker to prevent uncontrolled siphon during shutdown.
Graduated transparent cylinder upstream of pump inlet, valved to suction tank. Allows quick in-service volumetric calibration without removing piping.
Bladder-type accumulator on discharge of solenoid & small diaphragm pumps. Smooths pulse, reduces water-hammer in long discharge lines.
Stainless or PVDF quill projecting into the flow stream ensures the chemical injects into the centre of the main flow, not the wall — preventing local concentration spots.
Pump selection for ferric, alum and PACl duty.
Read MoreWhy peristaltic and progressive-cavity pumps dominate polymer duty.
Read MoreHypochlorite, chlorine dioxide and PAA — pump selection per chemistry.
Read MoreHow feedback / feed-forward / cascade control influences pump choice.
Read MoreHow the selected pump is packaged into a complete skid — day tanks, bunding, valves, calibration column and control.
Read MoreSize dose rate and pump capacity from your flow and target concentration.
Open CalculatorSend us your chemical, flow range, pressure, accuracy requirement and operating environment. We will recommend pump type, wetted materials and a full piping & control specification.
Our expertise spans multiple industries with sector-specific water treatment solutions.