Metering pumps are positive displacement pumps designed to dispense precise amounts of fluids and measured flow control. They feature a high level of repetitive accuracy and are capable of pumping a wide range of chemicals including acids, bases, corrosives, or viscous liquids and slurries.

Operation

Metering pumps are positive displacement pumps, meaning they use expanding and contracting cavities to move fluids. This method of operation provides the steady flow and consistent volume characteristics of metering pumps, and also makes it more apt to handling viscous liquids and slurries which generate more resistance. For more information on positive displacement pumps, visit the Positive Displacement Pump Specification Guide on Engineering360.

Animation of metering pump operation.

Video Credit: Fluid Metering, Inc. / CC BY 3.0

Metering pumps transfer media in two stages: the intake stroke and the output stroke. During the intake stroke, liquid is pulled into the pump cavity past the inlet check valve. During the output stroke, the inlet valve closes, the outlet valve opens, and the fluid is forced out. The flow may be varied by changing the stroke length or by adjusting the cycle frequency.

Metering pumps are usually driven by a constant speed AC motor, although different drive mechanisms may be used depending upon the application at hand. Some of these include fixed speed, variable speed, electric drive, solenoid drive, and magnetic drive. The drive mechanism translates the rotary motion of the driver into reciprocating movement. Industrial duty metering pumps will submerge this portion of the pump in an oil bath to assure sufficient lubrication and reliability during continuous operation.

Pump Types

There are a number of different pump types that can be configured for metering applications. The different types are listed below. To learn more about selecting these types of pumps, click on the corresponding links.

• Bellows pumps use a compressible container with an outlet nozzle (called a bellows device) to move fluid through a piping system. They have the ability to pump both liquids and gases and do not require seals.

• Diaphragm pumps use the reciprocating action of a flexible membrane (diaphragm) to move fluid in and out of the pumping chamber. These pumps require no seals.

• Peristaltic pumps (also called hose pumps) use a roller device to move fluid through a tube or hose. Because the fluid is contained in the tube, it does not come in contact with the pump or outside environment.

• Piston pumps move fluid using one or more reciprocating pistons inside a cylinder (chamber), normally driven through the use of a crankshaft and connecting rod. These pumps require a seal to prevent leaks and should not handle abrasive media.

• Syringe pumps deliver small amounts of fluid through a syringe using a pusher block connected to a plunger. Flow is managed through a screw attached to the pusher block, typically operated by a corresponding controller.

This chart provides a summary of the properties of these different types of metering pumps:

Table Credit Cole Parmer

Specifications

The primary specifications to consider when selecting metering pumps are flowrate, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature. These specifications are described in detail in the Pump Flow page on Engineering360.

Flow Adjustment

Pump flow rate is adjustable by varying stroke length, effective stroke length or stroking speed. Some metering pumps are supplied with a micrometer screw adjustment. An electronic or pneumatic actuator may be used to replace the micrometer if the pump flow rate needs to be altered in response to a process signal. Changing the number of pump heads in use by the device is another way to increase pump flow rate. Metering pumps with two heads can double the flow capacity of a single pump device. Pumps are also available with three or more heads to maximize flow rate.

Applications

Metering pumps are generally used in applications with one or more of the following conditions: low flow rates required; high accuracy feed required; high system pressure; corrosive, hazardous, or high temperature media; slurry or high viscosity media; and controlled dosing (by computer, microprocessor, PLC, or DCS).

Engineering360's Pump Applications page provides an overview of pump types designed for specific applications.

References

Cole Parmer - Metering Pump Selection Guide

Pump Scout - Industrial Pump Types

Image credits:

GRI Pumps (A Gorman-Rupp Company) | OMEGA Engineering, Inc.