Positive VS. Non-Positive Displacement Pump

 When it comes to choosing the right industrial pump to match your expectations, it is very important to be aware of which type of pumps you are using for your industrial needs and if they are suitable or not. There are similarities and important differences between positive & non-positive displacement systems. Let us know the actual difference between them. 

What is a Positive Displacement Pump?

A positive displacement pump provides a constant flow at fixed speed, regardless of any change in the pressure.

The pump transfers the fluid by trapping a fixed amount and forces the volume into the discharge pipe. The liquid flows into the pump when the cavity on the suction side opens or expands, whilst the liquid flows into the discharge when the cavity closes or decreases. Through every cycle of operation, the volume is the same.

These are some examples of positive displacement pumps:

●     Diaphragm Pumps

●     Helical Rotor or Progressive Cavity Pumps

●     Peristaltic Hose Pumps

●     Piston Pumps

●     Rotary Lobe or Gear Pumps 

What is a Non-Positive Displacement Pump?

A non-positive displacement pump’s output flow rate can be changed in response to the pressure on the outlet. This Pump uses Newton’s first law of motion to transfer fluid against the system resistance. Although it provides smooth and continuous flow - its flow output is reduced when system resistance is increased.  Non-positive pumps have their own problems related to fluid viscosity, system pressure and temperature, but they are different from positive displacement pumps.

These are some examples of non-positive displacement pumps:

●     Centrifugal pumps

●     Multi-stage pumps

●     Axial (propeller) pumps

Key Differences Between Positive and Non-Positive Displacement Pumps!

Pressure - Positive displacement pumps work for high pressure applications, the pressure might go upto 800 bar. Non-positive displacement pumps are basically used for low pressure applications and are designed to work for a maximum pressure of 18 to 20 bar.

Efficiency -  In positive displacement pumps, the efficiency increases with increasing pressure. Whereas in non-positive displacement pumps, efficiency peaks at best-efficiency-point. At higher or lower pressure, efficiency decreases.

Viscosity - In positive displacement pumps, efficiency increases with increasing viscosity. On the other hand in non-positive displacement pumps, efficiency decreases with increasing viscosity due to frictional losses inside the pump.

Performance - The flow is constant with changing pressure in positive displacement pumps whereas in non-displacement pumps, flow varies with changing pressure.

 Now that you are made aware of the most basic differences between positive and non-positive displacement pumps, choosing the right pump for your industry should be easier. If not, Fluorolined Equipment Pvt. Ltd. offers a wide range of industrial pumps that are designed to perform well and offer the highest standard of services. For more information on positive or non-positive displacement pumps, contact our team of experts.  

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