Dosing Pump Type: What Kind of Pump Is a Dosing Pump?

A question we hear often: what type of pump is a dosing pump, centrifugal or something else? The short answer is that most dosing pumps are reciprocating positive displacement pumps. Getting this right explains a lot of what you see in selection and operation. Below we start from basic pump classification and show where each dosing pump type fits. For how the pump works in detail, see dosing pump working principle.

Basic Pump Classification

By working principle, pumps fall into three broad groups:

1. Rotodynamic pumps: an impeller transfers energy to the liquid, as in centrifugal, axial and mixed-flow pumps. High flow, smooth delivery, but flow changes strongly with discharge pressure.
2. Positive displacement pumps: a chamber changes volume cyclically to draw in and expel liquid, as in reciprocating, gear, screw and peristaltic pumps. Each cycle moves a nearly fixed volume.
3. Others such as jet pumps and hydraulic rams, rarely used for industrial dosing.

Positive displacement pumps split further into reciprocating pumps, driven by a piston, plunger or diaphragm, and rotary pumps, driven by gears, screws or rotors.

The Main Dosing Pump Type: Reciprocating Positive Displacement

Dosing means adding chemical by amount. Volumes are small, accuracy matters and the injection point is often under pressure. A centrifugal pump is inefficient at low flow and its output shifts with pressure, so it is hard to control. A positive displacement pump moves a fixed volume per stroke, so stroke length and rate set the flow, and discharge pressure has little effect.

That is why the dominant dosing pump type is the reciprocating positive displacement pump, usually called a metering pump.

Common Reciprocating Dosing Pumps

Solenoid Diaphragm Pumps

A solenoid drives the diaphragm. Compact and simple, this dosing pump type suits small flows at low to medium pressure and is the most common in water treatment.

Mechanical Diaphragm Pumps

A motor, gearbox and eccentric drive the diaphragm. Higher flow than solenoid pumps and steady operation make this dosing pump type a good fit for continuous medium-flow duties.

Hydraulic Diaphragm Pumps

A plunger moves hydraulic oil, which moves the diaphragm. Balanced pressure across the diaphragm allows high pressure and high accuracy with hazardous liquids.

Plunger Pumps

The plunger contacts the liquid directly and reaches very high pressure. Packing leaks slightly, so this dosing pump type is not suited to toxic or costly chemicals.

Rotary Pumps Used for Dosing

Some services use a rotary dosing pump type instead:

• Peristaltic pumps: the liquid touches only the hose. Good for slurries, crystallising or shear-sensitive chemicals.
• Gear pumps: for viscous, lubricating liquids such as some oil-based additives.
• Progressive cavity pumps: for viscous or solids-laden products such as sludge conditioners.

So there is no single answer, but the mainstream dosing pump type remains the reciprocating diaphragm metering pump.

Drive Options

Within reciprocating pumps there are further splits by drive. Solenoid drives are compact for small flows, motor drives give steady continuous output, and pneumatic drives suit hazardous areas or sites without power. Choosing a drive is the second decision after choosing the basic dosing pump type.

What the Classification Means in Use

Knowing the dosing pump type explains several rules:

1. Never run against a closed discharge: pressure in a positive displacement pump climbs fast with the outlet shut, so a relief valve is essential.
2. Output pulses: reciprocating motion delivers flow in pulses, so dampers are common.
3. Back-pressure valves are needed: with low discharge pressure or siphoning, flow runs high.
4. Gas sensitivity: gas in the chamber compresses and absorbs the stroke, so flow drops and the pump needs bleeding.

All of these are shared by reciprocating positive displacement pumps and differ greatly from centrifugal practice.

Why Not a Centrifugal Pump With a Control Valve?

Some engineers try to dose with a small centrifugal pump and a throttling valve. It looks cheaper on paper, but at very low flow the pump runs far from its best efficiency point, heats the liquid, and the valve must work almost closed, where control is poor and blockages are common. Any change in line pressure then changes the dose. A positive displacement pump avoids all of this because the volume per stroke stays nearly constant. For the same reason, a flow meter plus control loop around a centrifugal pump rarely matches the stability of a properly sized metering pump. In practice the centrifugal pump is better kept for transferring chemical into day tanks, while the metering pump handles the injection itself.

Dosing Pump or Metering Pump?

The terms are often used interchangeably. Metering pump describes function and design, dosing pump describes use. A metering pump used for chemical addition is a dosing pump, though not every dosing pump is a strict metering pump. See dosing pump vs metering pump.

Using This Knowledge in Selection

Small, accurate flows call for a diaphragm metering pump. High pressure with a benign chemical can use a plunger pump. Slurries and crystallising liquids suggest a peristaltic pump. Very viscous products point to gear or progressive cavity pumps. Matching the dosing pump type to the duty is the first step in the dosing pump selection steps.

FAQ

Can a centrifugal pump replace a dosing pump?

Generally not. At low flow it is hard to control and output shifts with pressure.

Is a dosing pump a positive displacement pump?

Mainstream dosing pumps are, and most are reciprocating diaphragm metering pumps.

Diaphragm or plunger: which is better?

It depends. Diaphragm pumps are leak-free for corrosive or hazardous chemicals. Plunger pumps handle higher pressure.

Why does a dosing pump need a relief valve?

Pressure rises quickly if the discharge is closed. The relief valve protects pump and pipework.

Is a peristaltic pump a dosing pump?

When used to add chemical, yes. It is a rotary positive displacement pump.

Conclusion

The main dosing pump type is the reciprocating positive displacement pump: solenoid diaphragm, mechanical diaphragm, hydraulic diaphragm and plunger metering pumps, with peristaltic, gear and screw pumps in special cases. Understanding the classification helps you install and select correctly. Browse our solenoid metering pumps and mechanical diaphragm pumps, or contact us.