There are many different types of pumps, depending on their intended use and function. Choosing the right pump can be complex, as it depends on factors such as the type of liquid to be pumped and the distance it needs to be transported. Pumps can also be categorized based on their design and operation. To simplify the selection process, pumps are generally classified into two main types, which operate in very different ways and reflect most of their design characteristics: centrifugal pumps and positive displacement pumps.
Types of Pumps and Their Uses
Centrifugal and positive displacement pumps are the two main categories commonly used. Both types serve the primary purpose of moving liquid from one point to another, but they operate differently. Centrifugal pumps transfer the motor’s kinetic energy to the liquid using a rotating impeller, increasing the discharge speed and pressure. With a constant motor speed, the discharge rate remains constant.
Positive displacement pumps, on the other hand, capture a fixed volume of liquid in their chamber and force it out at the pump outlet. Positive displacement pumps can be rotary, piston, or diaphragm types. Centrifugal pumps typically have high capacity but relatively low discharge pressure, while positive displacement pumps have lower capacity but can achieve higher discharge pressure.
Centrifugal Pump Types
Centrifugal pumps can be further classified based on the mechanism driving the diaphragm:
- Mechanical Actuated: These pumps use a mechanical linkage directly connected to the diaphragm. A gear system or other mechanical mechanism converts motor rotation into the diaphragm’s back-and-forth motion. Flow can be adjusted by changing the stroke length or pump speed.
- Hydraulic Actuated: These pumps use an intermediate hydraulic fluid on the non-product side of the diaphragm to move it. The hydraulic fluid is pressurized by a piston, which indirectly moves the diaphragm. Flow is adjusted by changing pump speed or the amount of hydraulic fluid.
- Solenoid Actuated: These pumps use a solenoid powered intermittently by electricity. The solenoid creates an electromagnetic force that moves a metal component in the diaphragm, causing it to flex. Flow is adjusted by changing the pump speed.
Positive Displacement Pump Types
Positive displacement pumps create a suction space on the inlet and a compression space on the outlet, applying enough force to move a fixed amount of liquid. They are divided into:
- Piston Pumps: These pumps use a piston that draws in and pushes out liquid. Valves ensure flow moves in only one direction, producing a pulsed flow.
- Rotary Pumps: These pumps use interlocking gears to push liquid through the discharge side, generating high pressure.
Differences Between Centrifugal and Positive Displacement Pumps
Both pump types move liquids, but they operate differently. Centrifugal pumps increase liquid velocity to generate pressure at the outlet, while positive displacement pumps capture a fixed amount of liquid and transfer it from the inlet to the outlet. In centrifugal pumps, flow depends on changing pressure, whereas positive displacement pumps maintain consistent flow regardless of pressure changes. Both types can regulate flow by adjusting speed. Positive displacement pumps are less affected by viscosity and high pressure, whereas centrifugal pump efficiency decreases with high viscosity and extreme pressure levels.
Centrifugal pumps are generally not used for liquids above 850 cSt, and performance drops significantly above 100 cSt. In contrast, positive displacement pumps become more efficient with increasing viscosity and pressure.
Many pump types are available to meet industrial needs, including booster pumps, multistage pumps, and end-suction pumps. Choosing the right pump ensures high performance, long service life, and efficiency for specific applications.