Piston Pump Vs. Diaphragm Pump

Pumps are omnipresent, and are one of the most widely used machines in the world. Even the human heart is a kind of pump, pumping blood through blood vessels throughout the body. Several different types of pumps are used in various day-to-day and industrial activities, such as agriculture/irrigation, power plants, sewage and waste recycle plants, oil rigs, as well as cars, air-conditioning and refrigeration systems, etc. Because of such varied usage, they come in all shapes and sizes. They are capable of handling very high volume and can withstand very high pressure as well. It would be difficult to imagine life without pumps, they are the lifeline and backbone of the industrial world.

There are mainly three different kinds of pumps, the positive displacement pumps, gravity pumps, and direct lift pumps. Piston pumps and Diaphragm pumps use the Positive Displacement technique. They trap liquids and then force them into a pipe, which helps in transferring the liquids. Positive displacement pumps can be further divided into two classes:

• Reciprocating: These pumps have an expanding hollow chamber on one side from where the fluid is sucked in, and a collapsible chamber on the other end from where the fluid is discharged.
• Rotary: These pumps transfer fluids using the rotation principle. When the pump shaft inside rotates, it creates a vacuum which then draws in the fluid.

Category	Piston Pumps	Diaphragm Pumps
Definition	The piston moves back and forth inside a cylinder, which pushes the liquid out of the cylinder. The soap dispenser so commonly used is an example of this kind of pump.	Use diaphragm and check valves to push a liquid out. Liquid can move only in one direction. Sewage handling pumps are an example of diaphragm pumps.
Characteristics	Used to transfer both gases and liquids. Can withstand very high discharge pressure. The pistons repeatedly move in a back and forth manner, thus transferring the fluid by drawing it in and forcing it out a discharge port, thus using the Reciprocating technique. The pump and its internal parts come in direct contact with the liquids and gases.	Used mainly for liquids and slurries, especially those that have high viscosity. Can withstand very high discharge pressure. In this, the fluids are transferred with the help of a flexible membrane which acts as an obstruction to displace the fluids, making use of the Reciprocating technique. Only certain internal parts of the pump come in contact with the processing liquid.
Types	Axial Piston Pumps Multiple cylinders are arranged within a cylindrical block, each in turn attached to a rotating shaft. These kinds of pumps are used in torpedoes and earth-moving machines. Radial Piston Pumps The pistons are arranged radially inside cylinders around a pintle, which acts a valve. These are highly efficient and reliable kind of piston pumps with very low noise level. Such pumps are widely used in the automobile sectors and test rigs. Both axial and radial piston pumps are hydraulic pumps.	Hydraulic Diaphragm Pumps In these, the diaphragm acts as a divider between the fluid that needs to be pumped and the fluid that is pumped. The arrangement of pistons in such pumps makes them suitable for use in transferring highly inflammable or explosive liquids. Air-operated Diaphragm Pumps These pumps are divided by two chambers, which are in turn again subdivided into two by two flexible diaphragms. It consists of a valve which controls a steady supply of pressurized air into one chamber, which pushes the fluids out through the other chamber.
Advantages	Can be highly efficient and require low maintenance.	Can handle all kinds of liquids, ranging from the most viscous to the highly corrosive sorts.
Disadvantages	Cannot be used for transfer of highly viscous fluids. Manufacturing costs can be high. It can result in a low volume of flow.	Cannot run at a very high speed. Maintenance costs can be very high. Are not always energy-efficient.

Thus, depending upon the application involved, a piston pump or diaphragm pump can be used accordingly, keeping in mind the density of fluids and manufacturing costs involved.