Metering Pumps are positive displacement chemical dosing devices with the ability to vary capacity manually or automatically, as process conditions require. Metering pumps 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. Metering pumps are usually driven by a constant speed AC motor, although different drive mechanisms may be used depending upon the application at hand including 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 reliability during continuous operation. Pump flow rate is adjustable by varying stroke length, effective stroke length or stroking speed.
Most 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. 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 generally used in applications where one or more of the following conditions exist: low flow rates in mL/hr or GPH are required; high accuracy feed is required; high system pressure; corrosive, hazardous, or high temperature media is being transported; the media has a high viscosity or is a slurry; dosing is controlled by computer, microprocessor, DCS, PLC, or flow proportioning.