20 pump industry terms you should know
Understanding the important pump industry terms will save you a lot of time when working through the pump buying process. Here are some of the more common terms that will likely come up during your conversations with pump suppliers.
Head: A measure of pressure, expressed in feet of head for centrifugal pumps. Water is used as the default where 10 meters (33.9 ft.) of water equals one atmosphere (14.7 psi. or 1 bar).
Flow: A measure of the liquid volume capacity of a pump. Given in gallons per hour (GPH), gallons per minute (GPM), liters per minute (L/min), or milliliters per minute (mL/min).
Pump performance curve: A diagram provided by the pump manufacturer to explain the relationship between the head and the flow rate of a pump using various size impellers. The curve also includes efficiency, NPSH required, and horse power consumption as a function of flow.
Pipe friction loss: The positive head loss from the friction resistance between the pipe walls and the moving liquid.
Friction head: The pressure expressed in pounds per square inch or feet of liquid needed to overcome the resistance to the flow in the pipe and fittings.
Total Head / Total Dynamic Head: The amount of head produced by the pump. Calculated by summing the static head, friction head, pressure head, and velocity head.
Pressure: The force exerted on the walls of a pipe by a liquid. Normally measured in pounds per square inch (psi).
Pressure drop: Referring to the loss of pressure between two points in a pipeline system. Generally occurs because of pipe friction loss of differences in elevation between the two points.
Efficiency: A ratio of total power output to the total power input, expressed as a percent.
Best Efficiency Point (BEP): The BEP is the point where the power coming out of the pump is the closest to the power coming into the pump. In other words the BEP is the point at which the head (pressure) and flow converge to produce the greatest amount of output for the least amount of energy.
Net Positive Suction Head Available (NPSHa): The NPSHa available to prevent cavitation of the pump. To calculate the NPSHa, you take the [Static Suction Head] plus [Suction Vessel Surface Pressure Head] minus [vapor pressure of your product] minus [friction losses in the suction piping, valves and fittings].
Net Positive Suction Head Required (NPSHr): The NPSHr to stop a pump from cavitating. The NPSHr is generally supplied to you by the pump manufacturer.
Cavitation: Process in which cavities or bubbles form in the fluid low-pressure area and collapse in a higher pressure area of the pump - causing noise, damage to the pump, and loss of efficiency because it distorts the flow pattern. Occurs in centrifugal pumps when NPSHa < NPSHr.
Specific Gravity (Liquid): The ratio of the weight of a given volume of liquid to pure water. Pumping heavy liquids (specific gravity greater than 1.0) will require more horsepower.
Viscosity: A measure of a liquid's resistance to flow. Essentially it’s a how thick the liquid is. The viscosity determines the type of pump used, the speed it can run at, and with gear pumps, the internal clearances required.
Brake Horsepower (BHP): The BHP is the actual amount of horsepower being consumed by the pump as measured on a pony brake or dynamometer.
Flooded Suction: In a flooded suction system, the liquid flows to the pump inlet from an elevated source by means of gravity. This is generally recommended for centrifugal pumps.
Suction head: Condition that occurs when the liquid source is above the centerline of the pump.
Suction lift: Condition that occurs when the liquid source is below the centerline of the pump.
Specific speed: A formula that describes the shape of a pump impeller. The higher the specific speed the less N.P.S.H. required.
Pump impeller: The moving element in a centrifugal pump that drives the fluid.