Skid mounted pumps typically include a driver such as a diesel engine or an electric motor, and a pump installed on a common steel base. Positive displacement and centrifugal pumps are the two popular types. Read on to learn more about them and what makes them different in order to choose the right one for your needs.
An Overview of Centrifugal & Positive Displacement Pumps
There are two types:
- Radial Flow Pump
It comes with a rotating impeller that looks like a fan to create a vacuum and help move the fluid. The impeller reduces pressure at the inlet and drives the liquid outside of the pump.
- Axial Flow Centrifugal Pump
It uses an impeller in the shape of a curved propeller and helps to move the fluids by drawing them towards its axis. The impeller then propels the liquids out of the pump.
Positive Displacement (PD) Pumps
PD pumps come in many types such as piston, lobe, gear, screw, and more. They have a segment at the inlet where they can draw the fluids and move them to the outlet for discharge. They typically use a rotary or diaphragm method to help the liquid flow in the required direction.
Difference Between a Centrifugal Pump and a Positive Displacement Pump
The main difference between centrifugal and positive displacement pumps is that regardless of the pressure on the inlet, the later can move fluids at the same speed while the former cannot. In addition to this, while a centrifugal pump loses flow with an increase in viscosity, the flow in a PD pump improves as viscosity goes up.
Choosing Centrifugal & Positive Displacement Water Pump Skids
|Pump Selection Factors||Right Choice of Pump|
|High Viscosity||A modest change in viscosity affects the efficiency of a pump. Thus, PD pumps are better in this scenario.|
|Middle of the Curve||Since PD pumps can operate at any point on their curve without affecting the performance, they are a wiser choice.|
|Variations in Pressure||PD pumps can sustain their efficiency and flow rate even with notable changes in pressure. Thus, it is a better choice in this scenario.|
|Alterations in Viscosity||Depending on temperature, the viscosity of liquids can change, making PD pumps a better choice as compared to centrifugal pumps.|
|High Pressure||Although centrifugal pumps can operate in series to increase the pressure, the capability for a PD pump to produce pressure is greater.|
|Shear-Sensitive Liquids||Since centrifugal pumps are high-speed pumps, they tend to shear liquids which is why PD pumps are a better choice.|
|Suction Lift||PD pumps are capable of producing a vacuum on the inlet end, which is why they are the ideal choice in this case.|
Importance of NPSH for Pump Selection
Net Positive Suction Head is essential when installing a pump.
- NPSHa, where ‘a’ indicates available. It refers to the pressure of a liquid at the pump’s inlet as reduced by its vapour pressure.
- NPSHr, where ‘r’ indicates required. It is used to describe the loss of energy that occurs within pumps when the volume of the fluid increases.
Pumps have different NPSH specifications depending on a variety of factors such as the pump speed, impeller design and diameter, liquid flow rate, more. To choose the right size of the pump and ensure it works correctly, it is crucial to know the NPSHa and make sure it matches the NPSHr of the pump.
Choose Us for Skid Mounted Pumps & Packages
At Crimtech Services Ltd., we offer a variety of pumps such as produced water injection pump, water pump skids, produced water filter packages, chemical pump packages, and more. We can help you by providing accurate solutions according to your specifications.