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Welcome back to another exciting edition of Inspector Pumphead’s Video Classroom! In this feature, I, Inspector Pumphead, will tackle a common question about pumps, parts or water systems using fun visual aids. This video is designed for those who like visual learning or enjoy a bit of fun in the classroom!

In today’s feature, my assistant Mike, will explain how to read a pump curve chart. The pump curve is something you should be able to find in the corresponding literature for any pump we sell. It is simply a visual representation of the pump’s performance. The graph may be confusing or intimidating to those who don’t consider themselves technically savvy, but fear not! This isn’t a replay of calculus; curves are actually pretty simple to read.

The above video will discuss the most basic type of curve which identifies pump performance through two variables: flow rate (or capacity) and total dynamic head. Those are the two basic things you need to know to identify what pump goes with your system. In the above example, Mike uses a curve from a Goulds WW05 3872 sewage pump.

For those of you that like a written guide to go with your videos, read on below for a repost of a previous blog about pump curves. It goes into a little more detail and talks about more advanced curves as well. A Pumphead Classic all right!

A common question that customers ask Pump Products application engineers is, “What am I looking at?” in reference to the pump curve charts you can often find in technical manuals and brochures.

The pump curve is simply a visual representation of the conditions in which the pump ca

n operate. At the most basic level the relationship between flow (plotted on the x-axis) and head (y-axis) is displayed. Thus, if you know the total dynamic head capability of the pump, you can easily determine how many gallons per minute the pump can move.

Knowing how to read a pump curve chart can help you pick the most efficient pump for your application, keep that pump running in optimal condition, and ensure a long operating life. If you need to replace a pump, the information can also help estimate flow rates for an existing system.

Put simply, understanding the information on a pump curve chart can save you time, money, and a lot of maintenance effort in the long run.

In this blog post, we will walk you through reading a basic flow-head curve and give a primer on reading more intermediate and advanced curves as well.

Basic Pump Curve

Above is a basic chart giving the curves for the Goulds WE series of submersible effluent pumps. Each specific model in the series, designated by the SKU number on the left, has its own curve. The box in the upper right hand identifies the series or model. Other information such as the diameter of waste solids the pumps can handle and the rotations per minute of the motor shaft are included.

Highlighted in yellow on the x-axis is the capacity or water flow rate, expressed in gallons per minute. The highlighted y-axis gives the TDH in feet. Determine the value of these two variables for your system requirements and find the point on the chart where they intersect. Whichever pump curve passes through that point, signals the right model for your needs. Points on or to the left of the curve will be sufficient. Any points to the right of the curve will not work.

(If you need a refresher on these concepts watch these videos: How to Calculate GPM for Potable Water and Wastewater / How to Calculate TDH).

Of course, there are points where curves will intersect. Look at the point circled in red above where the WE15H and the WE15HH meet. In that case, you can use other variables (HP, voltage) to make your choice.

In the chart above, three different series of Goulds MC centrifugal pumps (1MS, 2MS, 3MS), are highlighted. The top highlighted curve is the maximum curve for the series, while the bottom curve is the minimum. All models in the series fall within these ranges. This type of chart is useful if you are examining a pump family that features multiple series. The range chart gives a visualization of the difference between series.

Pump Curve Efficiency

The above chart shows curves for a Goulds 3656 end-suction pump. The u-shaped curves (one highlighted in red) intersect with the flow-head curves (the various flow-head curves signify the 3656’s performance at different impeller trims; we’ll get to those). These u-shaped curves represent the pump’s efficiency, which is defined as the ratio of water energy output from the pump to the shaft to energy input from the motor. The number at the top of the efficiency curve (40% boxed in gold above) is the percent efficiency.

Pumps have high-efficiency areas (the u curve labelled with 67 at the points) and in the middle of that area is the best efficiency point (BEP, marked in blue). The BEP represents the point where the pump will operate with the least possible interference from outside forces, such as vibrations. Operating at or near the BEP will also save save energy. You should look for flow-head settings that intersect with the BEP. As a general rule of thumb, a deviation of 10% on either side of the point is acceptable.

Brake Horsepower Curve

The dotted lines highlighted above are brake horsepower lines for the Goulds 3656. The lines simply represent the horsepower required at the shaft. If the flow-head curve of your selected pump falls under that line, your pump requires the HP value displayed on the line.

Impeller Trim Curve

The highlighted letters display the impeller type while the highlighted numbers signify the impeller trim or impeller diameter (in inches) options for this model pump. Because of physics, changing the type and diameter of the impeller will change the produced flow and head of the pump. The flow-head curves for each impeller option are displayed.

NPSHR Curve

The chart above shows the various Net Positive Suction Head Required (NPSHR) ratings for the Goulds 3656. The NPSHR ratings are represented in the highlighted lines that intersect with the flow-head capacity curves. NPSHR is simply the minimum amount of pressure required at the suction side of the pump to overcome the pressure losses at the pump’s intake port. These losses are due to the water moving through the smaller diameter of the intake port.

NPSHR is measured in positive feet of water. Looking at the chart above, the numbers over the highlighted lines tell you the minimum required head for a flow rate to the left of the line. Track your desired GPM along the x-axis of the chart and move up to see the required NPSHR. For instance, if you need to pump at 80 GPM, 6 feet of head is the bare minimum NPSHR.

Minimum Flow Curve

The thick blue line above represents the minimum flow needed for this specific model pump. If a minimum is included, make sure to never operate your pump at a flow point to the left of this line. Doing so will cause the pump to cycle improperly – meaning it will shut on and off continuously and burn out. Typically one minute per cycle is the minimum run time.

It should be noted that more advanced curve charts might look different from the above examples depending on pump type and application. Hopefully this blog post has given you an understanding of the fundamentals of reading a pump curve chart. Understanding this information before you purchase a pump will save you time and money. If you have trouble with a curve or pump sizing, be sure to call Pump Products at (800) 429-0800 to have a qualified expert assist you.

Pump Products application engineers are standing by to help you find the right pump, as well as to provide price quotes, stocking availability and shipping information. Call our toll free number 1-800-429-0800 to speak to an expert today.