Metering pumps move the small but accurate volume of liquid into other vessels. Metering pumps are also known as dosing or proportioning pumps. Metering is the process of delivery of fluids at accurate adjustable flow rates. Metering pumps are adjusted to deliver fluids at a constant flow rate. They pump water or other chemicals into a high discharge pressure. A metering pump consists of a pump head and a motor. The liquid gets pumped into the head and enters through the inlet line and leaves through the outlet line. The motor is just an electric motor that drives the head of the metering pump. 

Applications of the metering pumps

• The metering pump is used to:
• Maintain a constant flow rate
• Inject a discrete dose
• Deliver variable flow to maintain parameters such as ph
• Metering pumps are used in many industries such as:
• Pharmaceuticals 
• Waste treatment 
• Chemical processing 
• Petrochemicals 
• Power generation
• Oil extraction
• Gas extraction
• Food and drinks production 

Types of Metering Pumps

There are many types of metering pumps such as:

•Piston and Plunger pumps: The piston pump is used to draw a definite amount of liquid into the pump on the suction stroke. The fluid is delivered on the compression stroke. In the plunger pump, the volume of the liquid which is delivered depends upon the size of the plunger. 

Advantages: The volume of the fluid which is delivered is known to be precise.

Disadvantages: During the suction stroke of the cycle, no fluid is delivered. This leads to pulsation. Pulsation causes damaging vibrations into the discharge system. 

•Diaphragm pumps: Diaphragm pumps consists of a flexible membrane that pushes the liquid. They do not have a piston or a plunger. When the diaphragm expands, the volume of the pumping chamber increases, the pressure decreases, and hence the fluid is drawn in. When the diaphragm is compressed, the volume decreases, and the fluid is expelled out.

Advantages: The diaphragm pumps have an airtight sealing so they can be used to pump hazardous fluids. 

Disadvantages: In diaphragm pumps, the accuracy of delivery depends upon the performance of discharge and suction. Pulsation can also occur in this case, but it can be minimized using two or more diaphragms.

•Peristalticpumps: Peristaltic pumps deliver the fluid by mechanical squeezing. They are widely used as a metering pump in medical laboratories.

Advantages: The fluid pumped through peristaltic pumps never comes in contact with the pump mechanism. For this reason, it is ideal to be used in laboratories for medical applications where hygiene is important. 

Disadvantages: The flexible element used in the peristaltic pumps may wear out, so it needs to be replaced to avoid an issue.

•Gear pumps: Gear pumps use the rotating element to move fluids. The rotating element has a liquid seal with the pump casing over it which creates a suction at the inlet pump.

Advantages: They are simple and cheap. Gear pumps can withstand high pressures. They are ideal to be used for high viscosity liquids. Pulsation is rarely observed in gear pumps.

Disadvantages: Wear and tear of the gear teeth can occur in some time which will finally lead to leakage. Gradually, the efficiency of the gear pump will decrease.  Traditionally, piston and plunger pumps, diaphragm, and peristaltic pumps were used for metering. With the increase in technology, gear pumps are being developed which are being used these days. The dual precision series pumps are also available in the market which have high precision and are used for sensitive applications.