Types of Metering Pumps: An overview of the most commonly used technologies

Types of Dosing Pumps: An overview of the most commonly used technologies

Metering pumps are devices used to add chemicals or liquids in a precise and controlled manner. These pumps are vital for industrial processes, water treatment, swimming pools, agriculture and more.

Over the years, different types of metering pumps have been developed and refined to suit various needs.

Below, we will review some of the most common types:

Diaphragm metering pumps

Diaphragm metering pumps are widely used because of their ability to provide accurate and consistent metering of liquids, even under certain pressure conditions.

These pumps consist of a flexible diaphragm or diaphragm, usually made of elastomer and PTFE (Teflon) coated, which is driven by a device against a chamber.

As the diaphragm moves forward, the check balls on the suction valves close and the balls on the discharge valves open to push the liquid through. As the diaphragm moves back, the balls of the discharge valve close against the check valves (seals) and the balls of the suction valves open to fill the head cavity again with liquid.

Different types of diaphragm metering pumps are available

Electromagnetic:

The membrane is attached to an electromagnet (or solenoid) which, when excited, moves the membrane forward. When it is no longer excited, internal springs move the membrane back to its initial position.

Electromagnetic with stroke adjustment:

They are exactly the same as the previous one, but a stem, normally with a setting of 10 to 100%, limits the diaphragm recoil to dose more or less quantity.

Electromechanical with spring return:

A motor, connected to an auger, rotates an eccentric where the axis of the membrane is located. This eccentric moves the membrane forward. A spring keeps the membrane attached to the eccentric, carrying out the movement of the membrane back to its initial position.

Electromechanical with mechanical recoil:

Also called a connecting rod, the axis of the diaphragm is attached to the eccentric, so that it moves as the eccentric moves. Both the forward and backward movement of the diaphragm is done mechanically, thanks to the movement of the connecting rod.

Double hydraulic membrane:

Hydraulic double diaphragm pumps are characterised by their ability to work at high pressures, to pump non-lubricating liquids or even liquids with small particles and to work dry without damaging the pump (no seals). A piston displaces a volume of oil into a chamber, which moves the diaphragm. In this circuit there is a safety valve. If the pressure exceeds the design pressure of the pump, it opens and the oil is returned to the chamber.

Advantages of diaphragm metering pumps:

Accurate dosing, on some API675 models
Suitable for corrosive or abrasive liquids, as it does not leak.
Silent operation.
Easy maintenance.

Disadvantages:

They may require periodic maintenance of the membrane.
They are not ideal for highly viscous chemicals, however, special valves with a spring can be supplied to ensure the closing of the valves with highly viscous chemicals. Consideration should also be given to the reduced flow rate in this case.

Piston dosing pumps

Piston metering pumps use a piston to move the liquid through a pumping chamber and then expel it with a high back pressure. They work in a similar way to diaphragm pumps, but in this case it is the piston that is in contact with the liquid to be dosed.

Advantages:

High precision and control in dosing.
Ability to handle high viscosity liquids.
Ability to work with high pressures.

Disadvantages:

They can be expensive and require more maintenance.
Not suitable for abrasive or corrosive liquids.
High maintenance as seals have to be changed regularly to avoid leakage in the piston area.

Peristaltic dosing pumps

Peristaltic metering pumps work by the repetitive compression and relaxation of a flexible "C" shaped tube. Liquid is drawn into the tube when it relaxes and is displaced forward when it is compressed, creating a unidirectional flow. This continuous compression/relaxation cycle is performed by the rotary motion of rollers. This type of pump does not need suction and delivery valves, as the movement of the roller causes a positive displacement. Moreover, the return of the liquid is impossible because the compression movement of the tube causes its sealing.

Advantages:

Easy to maintain and clean, as the liquid only comes into contact with the tube.
Suitable for handling viscous, abrasive and gaseous liquids.
No additional valves are required, which simplifies the design.
High precision, and regulation 1:1000.

Disadvantages:

They require periodic replacement of the tube.

Pneumatic dosing pumps

Pneumatic pumps consist of two pumping chambers and two diaphragms connected by a central shaft, called a distributor. The injection of compressed air causes the displacement of these diaphragms with an alternating compression/suction movement in each of the two chambers: when the shaft is moved to one side, the diaphragm on that side is compressed against its respective pumping chamber, pushing the liquid forward, while on the opposite side the opposite happens, sucking the liquid in. Each of the chambers is equipped with suction and discharge valves to allow unidirectional movement of the liquid.

Advantages:

They can run dry without damage.
They accept liquids of very high viscosity, even with solids in suspension.
Self-priming. High suction capacity.
They do not require electricity, making them ideal for hazardous environments.

Disadvantages:

Less precision compared to other types of metering pumps.
They may be less energy efficient.
Higher noise level.

These are just some of the most common types of metering pumps used in a variety of industries and applications. Choosing the right pump will depend on factors such as the type of liquid to be dosed, the required accuracy, the working environment and the available budget. It is important to select the pump that best suits the specific needs of each application to ensure optimum performance and successful results.

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