Everything You Need To Get Started With Centrifugal Pumps
Your team is right on top of things. Everyone has the latest information on all the equipment you use. Pumps included. But what if they’re not? Or what if you have new members come in who are not as familiar with centrifugal pumps?
Here’s a quick overview of the terminology and basic definitions for centrifugal pumps, all in one place.
How does a centrifugal pump work?
Liquids typically flow from areas of high pressure to areas of lower pressure. Pumps work by lowering pressure at the point of input, allowing liquid in and then pushing it out with a motor.
At its most basic, a centrifugal pump has an impeller, which rotates within a casing. This impeller accelerates liquid and pushes it out of a discharge port using centrifugal force (the liquid is pushed away from the center or the impeller – hence centrifugal). As the liquid is pushed out, it creates a reduced pressure zone near the impeller, which serves to draw in more liquid through a suction port. This loop continues, and you have a centrifugal pump!
Here are some commonly used terms:
The capacity of a pump is defined as the volume of liquid that moves through the pump at a given time. Capacity is typically measured in a unit called GPM, which stands for gallons per minute. To calculate GPM, you take the flow (usually in pounds per hour) and divide it by 500 times the specific gravity of the liquid.
Pressure is visualized as a column of liquid. The height of this column is called static head and is usually measured in number of feet. To arrive at the head in feet, you need to take the pressure of the liquid in PSI and multiply it by 2.31 and then divide the resulting number by the liquid’s specific gravity.
There are several terms used in relation to head.
With flooded suction, liquid flows from a level above the pump without the pressure falling below the atmospheric pressure at any given point.
Suction lift exists in the opposite scenario, i.e., when the source of the liquid is below the pump, and the pressure is below atmospheric pressure. Static suction lift or static discharge head is measured by taking the distance in feet from the center line of the pump down to the surface of the liquid to be pumped.
When liquid flows, friction is lost due to the impact of its viscosity. Friction head is the head (in feet) required to overcome the resistance to the flow in the pipes and surrounding fittings.
Pressure head comes into play when the liquid is in a pressurized container (other than atmospheric pressure). When either the suction or discharge tank is a vacuum, less pressure is available to the pump. The head required to overcome this is defined as pressure head.
Total dynamic or total dynamic head (TDH) is calculated as the sum of the static discharge head, discharge pressure head, and friction, minus suction head, or plus suction lift. It is the total height the liquid is to be pumped, taking into account the loss of friction in the pipe.
Note: All definitions are simplified from information contained in technical manuals for the products sold by Vissers Sales Corp. – in this case, Pulsafeeder’s Eastern pumps.