A pump is basically a device or machine that moves or raises something through suction and pressure forces. This mechanical object is usually used to transfer liquids or gases from one location to another. One of the essential pump types used is the metering type.
A metering pump is a type of pump that is used if one wants to transfer liquids in constant and precise flow rates for a designated time frame. This type of pump is typically used in chemical plants where specific pump rates are needed. Characteristic of pumps like this is that they are able to pump liquids at high discharge rates. Therefore many of these pumps have specifications indicating their maximum discharge rates.
A typical pump of this kind is made up of two major parts: the motor and the pump head. The pump head is made up of a chamber with a piston fitting almost exactly into a chamber. The chamber has two holes with outward protrusions, one serving as the inlet and the other one, opposite it serves as the outlet. The motor is what drives and moves the piston in and out of the chamber.
The typical process that occurs when a metering pump functions starts when the motor pulls out the piston out of the chamber; this movement sucks the liquid through the inlet hole thus filling the chamber with the liquid. As the motor pushes the piston back into the chamber, the liquid and air between the end of the piston and the bottom of the chamber gets compressed. The compressed air and liquid is therefore being forced out and thus leads to it flowing out into the outlet hole. Overflow onto the outlet during the suction process and backflow into the inlet during the pressurization are controlled by two check valves, one on the inlet side and the other on the outlet side. Check valves are devices that allow fluids to flow only in one direction.
The typical metering pump uses a single-piston system where discharge to the outlet pipe happens only during the pressurization process. However, there are pumps of this type which use multiple pistons. Pumps with multiple pistons allow both filling of the chamber and discharging to happen almost simultaneously during a single action of the connected motor.
There are instances however that instead of using a piston pump for metering, a diaphragm type is used. The acting forces in a diaphragm pump are similar to a piston pump. However, instead of using a piston to create suction and pressure, a flexible membrane or cover is used on top of a chamber. It is this top which a motor or pressurizer pushes or pulls to create the required forces to act within the chamber. This is type of pump is used for metering purposes when the liquids to be transferred are toxic and hazardous.