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Home » Pumps » Why should you Learn to Read a Pump Curve & How to Do It?

Why should you Learn to Read a Pump Curve & How to Do It?

Posted: 25/11/2017
Category: Pumps

If you’re new to pump terminology, then reading a pump curve may seem like a daunting task. What with all the lines and numbers, how do you make sense of them? Put your fears to rest! Here, at Sintech Pumps, we often get plenty of questions regarding pump curves and how to interpret them, both from beginners as well as experienced mechanics. This is why we decided to make this post a “How-To” on reading pump curves. By the time, you finish reading this, you’ll no longer be intimidated by Pump curve diagrams. Let’s get started! What is a Pump Curve? It’s one of the first things that you usually look at before your purchase the right pump for your project. Additionally, the pump curve is also a handy tool that guides you in the usage of the pump. To phrase it a nutshell, “the pump curve is a graphical representation of the pump’s performance. It’s what is to be expected from the pump, based on the testing conditions of the manufacturer.” Every pump has its own performance curve, and this curve varies significantly from one pump to another. Even the same type of pump will have different curves based on the manufacturer. The performance of a pump is dependent on the following three major factors:

  • Horsepower
  • Impeller size
  • Shape of the Impeller
Why use a Pump Curve? When you’re able to read and interpret a pump curve, you can quickly select the right pump for a specific application. Finding the right pump is essential if you want to extend the life of your pump by operating it at maximum efficiency. Additionally, reading a pump curve will also help you identify the limitations of the pump. Operating a pump beyond its given range not only damages the pump, but also leads to unnecessary downtime, which becomes expensive in the long run. Now, we come to the big question, How to Make Sense of a Pump Curve Aka How to Read It? Pump curves are nothing but graphical data that denotes a pump’s ability to produce flow against a specific head. Generally, the flow rate is on the X-axis (top and bottom), while the height required to push is on the Y-axis (sides). If you want to achieve a particular flow rate for your application, locate the required numbers on the chart. Then draw a line from top to bottom, that passes through your desired flow rate. Now, select your desired height by drawing a line to the right. You must now choose a pump, whose performance curve lies just above the intersecting point. Yes, it’s as simple as that. To help you understand better, here are a few terminologies used by Pump Curves:
  • Flow
This is the rate at which the liquid moves through your system. It’s measured in litre per minute or metre per hour in SI Units. In the US system, it’s estimated in gallon per minute. Different liquids have varying viscosities, which impacts the flow. Too much flow leads to noise and mechanical damage, while too little causes insufficient output. So, the key here is to find the right flow amount. Flow is denoted on the horizontal axis (X-Axis).
  • Head
It’s the total mechanical energy of the fluid at any given point in the piping system. The pressure in the system is measured as a pound per square inch. However, the hydronic pressure is measured as the head-loss. For your pump to displace the liquid through the system, it must produce a sufficient pressure differential, to avoid head loss. Head-loss is created due to friction between the valves and other fittings in the system. In SI Units, the head is measured in metres. In the US system, it’s measured in feet.
  • Performance Curves
A multistage centrifugal pump uses several impellers to create high pressures over several flows. The g curve on the chart represent the capacity & head developed by one single Impeller. To achieve the desired head, one has to divide the head required by the head developed by lone impeller. In multi stage pumps with say 5m stages the CAPACITY REMAINS SAME & ONLTY THE HEAD INCREASES.
  • Horsepower
Once you have identified the correct performance point, you can determine the right amount of horsepower that the system requires. On the left side of the curve, you can find the HP/Stage. This is a measure of how much horsepower the system needs at every stage.
  • Net Positive Suction Head (NPSHR)
This is a vital factor that plays a crucial role in proper pump operation. This is the minimum amount of pressure that you must input on the suction side to meet the positive pressure/head required by a particular type of impeller. This is called the NET POSITIVE HEAD REQUIRED(NPSHR). If the NPSH AVAILABLE isn’t adequate, you run the risks of cavitation’s, which affect the pump’s life and performance.
  • Efficiency
Efficiency plays a significant role in the selection of the best pump that is suited for a particular application. This indicates the percentage of the motor energy that is being expended for useful work. Low efficiency means that the energy is lost from the system as heat. There are several reasons for this loss like cavitation, friction, and recirculation.
  • Minimum Flow
All multistage and centrifugal pumps require a minimum amount of flow to dissipate the heat generated in the system. When you operate your pump, below this value, it causes severe damage to your pump components. Now, how do you find the Best Efficiency Point of a Pump? The general rule of thumb is the BEP (Best Efficiency Point) is 80% of the shutoff head. Ideally, you should aim to operate your point to as close to the BEP as possible. The BEP is mentioned in the pump curve. If you can’t find it, you can contact your pump manufacturer to get the value. Conclusion Knowing how to read and interpret your pump curve is essential if you want your pump to operate at maximum efficiency. Running your pump higher or lower than the curve, not only damages the pump and its components but also leads to excessive energy consumption, causing deterioration in the performance of the overall system. Have further questions about your pump curve? Get in touch with our Pump experts by giving us a call @ +91-120-4176000 or dropping in a line @ Sintech is India’s leading commercial and industrial pump supplier, and we can provide you with the best pumps that are perfectly suited for your requirements.

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