How to Read a Pump Curve
Choosing the right centrifugal pump for your application is vital for maximizing its performance. The wrong pump that isn’t suited to the application or underlying conditions won’t operate efficiently, and it could prematurely fail.
So how do you choose the right pump or make sure the pump you have is appropriate for your needs? This starts by examining the pump curve. Here is what you need to know about pump curves, the elements of a curve, and how to read a pump curve properly.
What Is a Pump Curve?
A pump curve is a graphical representation of a pump’s performance. It indicates how a pump will perform relative to pressure head and flow at specific operating speeds and inlet/outlet diameters. The proper interpretation of data provided by a pump curve is the best way to make informed decisions about the type of pump, size of motor, power consumption, and other factors that will impact your business.
The Goal of a Pump Curve
When you use a pump curve, your goal will be to get as close to the Best Efficiency Point (BEP) as possible. The BEP is an operating point on the pump curve illustrating the highest efficiency point for a particular pump diameter.
In a perfect world, your industrial pump will run at the BEP constantly. But this isn’t the case for most real-world applications. Systems experience fluctuations, leading pumps to operate outside these optimal conditions. Some common terms you might encounter include the following.
- Operating away from BEP — The pump is operating at flow rates lower or greater than BEP.
- Operating to the left of BEP — The pump is operating at a lower flow rate than the BEP.
- Operating to the right of BEP — The pump is operating at a higher flow rate than the BEP.
Where your pump operates relative to BEP matters because running your pump consistently higher or lower than BEP can result in a variety of challenges. These include cavitation, excessive vibration, premature wear on parts, lubrication breakdown, and even failure.
Elements of a Pump Curve
If you’re looking at a pump curve, there’s a lot of information depicted. Here is a breakdown of the different elements of data you’ll find on a basic pump curve.
1. Title Box
Most pump curve charges will have a title box at the top. This should provide information about the pump model, speed, size, and any other identifying data that is specific to the pump being measured. If you are measuring the performance of an existing pump, ensure you match the pump to the correct curve.
Identify the amount of flow required from your pump. This will be depicted on the horizontal axis of the pump curve.
You should also determine the total head your pump must overcome at the required flow. Head refers to the height to which a pump can move water straight up. Water creates resistance or pressure at rates that are predictable, so you can calculate head as the pressure the pump needs to overcome to raise water.
4. Impeller Trim
Performance points may not always be achievable with maximum impeller sizes. Many centrifugal pumps allow for trimmed impellers to accommodate these issues. When you reduce your impeller size, it limits the pump to your specified performance parameters. On the left side of the curve, you’ll see impeller diameters listed as well as the performance for each trim size.
There will be a dotted line across the curve indicating the horsepower. You will need to ensure that your pump has the required to power to rotate the parts of the pump and overcome discharge pressure.
The Net Positive Suction Head Required (NPSHR) is essential for efficient pump operation. This refers to the minimum amount of pressure needed on the suction end of the pump to overcome pump entrance losses.
The pump curve will identify the NPSHR of the pump. If there isn’t a sufficient level met, you are likely to get cavitation, which will impact the pump’s performance and useful life.
Efficiency will be one of your most important factors when selecting the best centrifugal pump. On the pump curve, you can view the efficiency of the pump as the ratio of energy supplied by the pump to the energy delivered to it. The less energy required to operate the pump at a certain performance point, the more efficient it is. Efficiency numbers ranging from 60-80% are typical.
8. Minimum Flow
Centrifugal pumps require a minimum flow to move through them to dissipate the heat they create. Minimum flow is depicted on the left side of the pump curve by a bold, vertical line. Any pump operation to the left of this line isn’t recommended as it can damage the pump.
How to Read a Pump Curve
The different elements listed above should give you a good start on reading a pump curve. Basically, a pump curve tells you how a pump is going to perform in regards to flow and pressure head.
The curve is defined for a particular operating speed (RPM) and a specific outlet/inlet diameter. But several curves on the same chart will tell you how performance changes for those different impeller diameters.
Pump flow is on the chart’s x-axis, and pressure/head is depicted on the y-axis. Typically, pumps will give you a higher flow rate as the head pressure decreases. The pump curve also shows you optimum efficiency points, which are vital. Specifically, the efficiency curve on the chart will intersect with the head-flow curves and show you the pump’s efficiency percentage.
Get the Right Industrial Pump from C&B Equipment
Whether your business needs a new industrial pump or would like to get the best performance out of its existing equipment, C&B Equipment can help. We offer a wide range of centrifugal pumps for industrial use that can handle a variety of applications and processes. Our team also offers preventative maintenance, service, and repair services to improve your productivity, uptime, and profitability.
C&B provides services throughout Kansas, Oklahoma, Missouri, Arkansas, and the Texas Panhandle. We serve clients in a variety of industries. Contact us today for more information about our products and services.