A pump well-fitted for your needs will enhance its lifetime and reduce its maintenance. There are lot of different pump types out there and understanding which one is right for you is not always clear. Here we will discuss the working principles and compare three common pump types: positive displacement, centrifugal, and turbine pumps.
Positive displacement pumps come in two main classes: reciprocating and rotary vane pumps.
General working principals of rotary vane (left) and reciprocating (right) positive displacement pumps.
Rotary vane pumps contain one or two rotating parts that move in a manner which creates suction. This draws in liquid which moves with the rotation, building up pressure as it passed through the pump. As the pump moves it pulls in liquid at the same speed at which it is expelled creating a constant and regular flow. This consistency makes it a good pump for pumping a wide range of non-corrosive liquids. The liquids should contain no solid particles as they may cause the rotating parts to block.
Reciprocating pumps work based on a different mechanism and here alternating force and suction action creates flow. The pump contains a chamber that expand and contracts, often through movement of a piston or diaphragm, creating a pulsing flow. This powerful set up is recommended for application in which viscous liquids are pumped.
Positive displacement pumps are desirable for constant flow applications and can often handle high viscosity liquids. They create high output pressures while operation at low suction pressures. To prevent over pressurization of the system a pressure relief valve should be installed on the line through which the liquid is pumped.
Centrifugal pumps are less powerful than positive displacement pumps and are therefore less suitable for pumping high-viscosity liquids. They are generally cheaper than positive displacement pumps and require less maintenance. Their working principle is based on one or more impellers which rotate with the shaft moving the liquid through the pump consistently. Due to its layout, the rotating rate increases and decreases with pressure making them unfit for systems with variable internal pressure. They are the most commonly used pump type and are excellent for low viscosity and high flow rate applications.
General working principals of centrifugal (left) and turbine (right) pumps.
Turbine pumps have characteristics of both centrifugal and positive displacement pumps. They contain a rotating impeller similar to centrifugal pumps, the difference being that the turbine pump has a turbine-like impeller. This design leads to a buildup of pressure while the fluid moves through the pump creating a powerful discharge. Due to this layout, the rotating rate does not vary much with changing pressure. Turbine pumps are good for applications where high head and low flow are needed.
When you are running your circulator and/or chiller with water at a constant pressure you will need a pump that provides a good flow rate. In this situation a centrifugal or rotary vane pump will do well. If, however, you use one pump for multiple systems, use a high viscous cooling or heating liquid, or have varying internal pressure a more powerful positive displacement or turbine pump should be considered instead.