Pump curve basics. In this video we take a look at pump charts to understand the basics of how to read a pump chart. We look at basic pump curve, head pressure, flow rate, pump performance, impeller size, efficiency, npsh, multi-speed pumps, VFD's, rotational speed, voltage, frequency and phases to help you learn hvac, hvacr and mechanical engineering.
With manufacturing lead times growing, selecting the right pump the first time is more important than ever. At the same time, understanding the full range of each pump's capabilities under specific operating conditions gives you a window to your options, so you're not locked in to just a few choices during the selection process.
Also called a pump selection curve, pump efficiency curve, or pump performance curve, a pump curve chart gives you the information you need to determine a pump's ability to produce flow under the conditions that affect pump performance. Reading pump curves accurately helps you choose the right pump based on application variables such as:
head (water pressure)
Flow (the volume of liquid you have to move in a given time period)
A pump has to produce enough pressure differential to overcome head loss created in pipe systems by friction, valves, and fittings. A pump curve shows the two performance factors on the X, Y axis so you can see the volume of fluids a pump can transfer under various pressure conditions.
This pump curve explanation also discusses variables such as:
RPM
Impeller size, as they relate to pump performance
Power
Efficiency
Net Positive Suction Head (NPSH) in centrifugal and positive displacement pumps
For example, if you know the flow rate your application requires, you find the gallons per minute (or hour) rate along the bottom horizontal line of the curve and then draw a line up to the head/PSI you require. The curve will show you if the pump you have chosen will perform in that application.
1. HOW TO READ A CENTRIFUGAL PUMP PERFORMANCE CURVE?
Curves typically include performance metrics based on pressure, flow, horsepower, impeller trim, and Net Positive Suction Head Required (NPSHr).
Centrifugal pump curves are useful because they show pump performance metrics based on head (pressure) produced by the pump and water-flow through the pump. Flow rates depend on pump speed, impeller diameter, and head.
WHAT IS HEAD?
Head is the height to which a pump can raise water straight up. Water creates pressure or resistance, at predictable rates, so we can calculate head as the differential pressure that a pump has to overcome in order to raise the water.
Common units are feet of head and pounds per square inch. (A pump curve calculator might offer different units such as Bar or meters of head). As Figure 1 illustrates, every 2.31 feet of head equals 1 PSI.
THE FORMULA FOR PSI: FEET OF HEAD/2.31 = PSI
Flow is the volume of water a pump can move at a given pressure. Flow is indicated on the horizontal axis in units like gallons per minute, or gallons per hour, as shown in Figure 2.
WHAT IS TOTAL DYNAMIC HEAD?
While pump curves help you select the right pump for the job, you first have to know the total dynamic head for the application.
Total Dynamic Head (TDH) is the amount of head or pressure on the suction side of the pump (also called static lift), plus the total of 1) height that a fluid is to be pumped plus 2) friction loss caused by internal pipe roughness or corrosion.
TDH = Static Height + Static Lift + Friction Loss
Static Lift is the height the water will rise before arriving at the suction side of the pump.
Static Height is the maximum height reached by the pipe on the discharge side of the pump.
Friction Loss (or Head Loss) are the losses due to friction in the pipe at a given flow rate.
Learn more about centrifugal pumps and key calculations.
HOW TO USE PERFORMANCE PUMP CURVES IN SELECTING EQUIPMENT: THE BASICS
Let's say you want to know the flow rate you can achieve from the pump in Figure 3 at 60 Hz when the design pressure is 80 PSI. In this case, the curve shows that the pump can achieve a flow rate of 1321 gallons per hour at 80 PSI of discharge pressure.
READING CENTRIFUGAL PUMP CURVES THAT CONTAIN ADDITIONAL INFORMATION
Because some centrifugal pumps operate across a range of horsepower, their curves will include additional information. Figure 4, for example, features a pump that can operate from 2 to 10 horsepower depending on desired performance.
IMPELLER TRIM SIZE
Impeller size is another variable for meeting performance requirements. The curve above shows impeller trim sizes, at the right end of each curve, ranging from a minimum of 4.33" to a maximum of 6.42".
Reducing impeller size enables you to limit the pump to specific performance requirements. The curve above shows maximum pump performance with a full-trim impeller, minimum pump performance with a minimum-trim impeller, and performance delivered by the design-trim impeller, or the r trim closest to the design condition. Impellers are typically trimmed 0.20 inches (or 5mm) at a time.
Impeller size is also a factor when handling shear sensitive liquids, or liquids that change viscosity when under pressure.
NET POSITIVE SUCTION HEAD REQUIRED/AVAILABLE
In addition to pressure and flow, the curve at the bottom of Figure 4 indicates NPSHr, which stands for Net Positive Suction Head Required. NPSHr is the minimum amount of pressure required on the suction side of the pump to avoid cavitation, or the introduction of air into the fluid stream. NPSHr is determined by the pump. You always want NPSHa>NPSHr.
Pump curve basics. In this video we take a look at pump charts to understand the basics of how to read a pump chart. We look at basic pump curve, head pressure, flow rate, pump performance, impeller size, efficiency, npsh, multi-speed pumps, VFD's, rotational speed, voltage, frequency and phases to help you learn hvac, hvacr and mechanical engineering.
With manufacturing lead times growing, selecting the right pump the first time is more important than ever. At the same time, understanding the full range of each pump's capabilities under specific operating conditions gives you a window to your options, so you're not locked in to just a few choices during the selection process.
Also called a pump selection curve, pump efficiency curve, or pump performance curve, a pump curve chart gives you the information you need to determine a pump's ability to produce flow under the conditions that affect pump performance. Reading pump curves accurately helps you choose the right pump based on application variables such as:
head (water pressure)
Flow (the volume of liquid you have to move in a given time period)
A pump has to produce enough pressure differential to overcome head loss created in pipe systems by friction, valves, and fittings. A pump curve shows the two performance factors on the X, Y axis so you can see the volume of fluids a pump can transfer under various pressure conditions.
This pump curve explanation also discusses variables such as:
RPM
Impeller size, as they relate to pump performance
Power
Efficiency
Net Positive Suction Head (NPSH) in centrifugal and positive displacement pumps
For example, if you know the flow rate your application requires, you find the gallons per minute (or hour) rate along the bottom horizontal line of the curve and then draw a line up to the head/PSI you require. The curve will show you if the pump you have chosen will perform in that application.
1. HOW TO READ A CENTRIFUGAL PUMP PERFORMANCE CURVE?
Curves typically include performance metrics based on pressure, flow, horsepower, impeller trim, and Net Positive Suction Head Required (NPSHr).
Centrifugal pump curves are useful because they show pump performance metrics based on head (pressure) produced by the pump and water-flow through the pump. Flow rates depend on pump speed, impeller diameter, and head.
WHAT IS HEAD?
Head is the height to which a pump can raise water straight up. Water creates pressure or resistance, at predictable rates, so we can calculate head as the differential pressure that a pump has to overcome in order to raise the water.
Common units are feet of head and pounds per square inch. (A pump curve calculator might offer different units such as Bar or meters of head). As Figure 1 illustrates, every 2.31 feet of head equals 1 PSI.
THE FORMULA FOR PSI: FEET OF HEAD/2.31 = PSI
Flow is the volume of water a pump can move at a given pressure. Flow is indicated on the horizontal axis in units like gallons per minute, or gallons per hour, as shown in Figure 2.
WHAT IS TOTAL DYNAMIC HEAD?
While pump curves help you select the right pump for the job, you first have to know the total dynamic head for the application.
Total Dynamic Head (TDH) is the amount of head or pressure on the suction side of the pump (also called static lift), plus the total of 1) height that a fluid is to be pumped plus 2) friction loss caused by internal pipe roughness or corrosion.
TDH = Static Height + Static Lift + Friction Loss
Static Lift is the height the water will rise before arriving at the suction side of the pump.
Static Height is the maximum height reached by the pipe on the discharge side of the pump.
Friction Loss (or Head Loss) are the losses due to friction in the pipe at a given flow rate.
Learn more about centrifugal pumps and key calculations.
HOW TO USE PERFORMANCE PUMP CURVES IN SELECTING EQUIPMENT: THE BASICS
Let's say you want to know the flow rate you can achieve from the pump in Figure 3 at 60 Hz when the design pressure is 80 PSI. In this case, the curve shows that the pump can achieve a flow rate of 1321 gallons per hour at 80 PSI of discharge pressure.
READING CENTRIFUGAL PUMP CURVES THAT CONTAIN ADDITIONAL INFORMATION
Because some centrifugal pumps operate across a range of horsepower, their curves will include additional information. Figure 4, for example, features a pump that can operate from 2 to 10 horsepower depending on desired performance.
IMPELLER TRIM SIZE
Impeller size is another variable for meeting performance requirements. The curve above shows impeller trim sizes, at the right end of each curve, ranging from a minimum of 4.33" to a maximum of 6.42".
Reducing impeller size enables you to limit the pump to specific performance requirements. The curve above shows maximum pump performance with a full-trim impeller, minimum pump performance with a minimum-trim impeller, and performance delivered by the design-trim impeller, or the r trim closest to the design condition. Impellers are typically trimmed 0.20 inches (or 5mm) at a time.
Impeller size is also a factor when handling shear sensitive liquids, or liquids that change viscosity when under pressure.
NET POSITIVE SUCTION HEAD REQUIRED/AVAILABLE
In addition to pressure and flow, the curve at the bottom of Figure 4 indicates NPSHr, which stands for Net Positive Suction Head Required. NPSHr is the minimum amount of pressure required on the suction side of the pump to avoid cavitation, or the introduction of air into the fluid stream. NPSHr is determined by the pump. You always want NPSHa>NPSHr.
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