Best Efficiency Point Of A Pump – Our team of experienced technical sales engineers are here to support you and provide expert advice on product selection. Contact us.
If you work with, service, or specialize in centrifugal pumps, you’ve probably at least heard of the pump curve. Simply put, it tells you what pump performance/flow you can expect at a given pressure. As the pressure the centrifugal pump faces in the installation increases, the flow rate decreases until it effectively stops producing product. On the other hand, if there was no pressure in the system, the pump could deliver the maximum possible flow. When plotted, these points form what we know as the pump performance curve.
Best Efficiency Point Of A Pump
To answer this question, let’s do a simple car comparison. A car has a lot of gear, and while first gear can get you from zero to 40 mph, it would be bad for the engine to go 40 mph in first gear. It’s also not good for the engine if a car is going 10 mph in third gear, even though the engine can run at those speeds. Using this analogy, although the pump curve shows the various flow rates and pressures that the pump can operate with, it does not mean that the pump must operate at all points on the curve. So, where exactly should the pump be operated?
Increasing Pump Capacity
As the name suggests, a pump’s Best Operating Point, or BEP, is the conditions specified by the pump under which the pump operates most efficiently, giving the user the longest life and least maintenance. Operating a pump at a capacity less than its BEP is known as “pump left” and similarly operating at more capacity is called “pigeon right”.
Although it is not always possible to obtain the exact BEP point, it is recommended that the pump be operated within 10% of this point. Most pump operators and even pump specifiers only see the optimum point in terms of energy consumption and cost. However, as you can see in this illustration, jumping too far to the left or right for a long time can cause problems and expensive failures, in addition to wasting energy…
Here, the pump is operating at a level below its optimal design. When it runs low enough for a significant period of time, it causes the fluid to not flow properly through the pump and backflow can occur at the suction and discharge points of the pump. The instability the rotor faces when this happens is premature wear and damage to the mechanical seal, which leads to pump maintenance and durability.
Another issue to consider is overheating. Overheating of the pump due to low flow conditions causing friction between the impeller and pump housing can damage components. However, in the worst case scenario, if the pressure sustained for a long period of time is such that the pump casing can no longer withstand it, an explosion may occur.
Pumps & Systems
As the centrifugal pump flow greatly exceeds the BEP, the probability that the net positive suction head required will exceed the available head is much greater. Here something called cavitation occurs. Cavitation is when the pressure of the pumped liquid drops below its vapor pressure, resulting in bubbles that explode as they return to the higher pressure region. The force of those cuts creates shock waves that punch holes in the impeller and eventually destroy the pump.
The hydraulic imbalance in the impeller caused by cavitation also creates excessive vibration, which puts more stress on the shaft and bearings. Not only can this cause a loss of efficiency, but it also creates the risk of component failure.
When choosing a centrifugal pump, it is important to consider the manufacturer’s recommended optimum efficiency point and whether it is reasonable for your system to operate around this. As you can see, if this is not done, the total cost of running the pump can be very high, including maintenance, downtime and energy consumption.
Choosing a pumping solution is a complex decision and our technical sales engineers can help you find the right solution for your system. For over 10 years we have provided carefully selected pump solutions for the marine and industrial markets and have helped hundreds of customers find the right pump for their applications. The key to achieving optimal overall performance is to ensure that each pump in the system is operating as close to its BEP as possible. This will not only give you the best return on your energy costs, but also reduce maintenance costs. Pumps work best and have the longest life when they are operating near their BEP.
Understanding Pump Curves #8
How do you know if your pump is getting close enough to optimum efficiency? First, determine your operating point by finding the intersection of pump performance and system curve. The pump manufacturer will provide you with a pump casing, but it is up to you to determine the casing for your system. You will need to calculate this using a number of variables such as pressure, unit, voltage and resistance.
Once you have the pump curve and the system curve, you can find your operating point where the two curves meet. The pump manufacturer specifies where the BEP is on the pump curve. The relationship between your operating point and your BEP can tell you a lot about what you can expect from your pump and the system around it. The graph below shows that if you move to the left of your BEP, you can expect all kinds of system symptoms from cavitation and overheating to regurgitation depending on how far you are from BEP. If you fall to the right of BEP, your pump may require more maintenance and parts replacement than it should, or in more extreme cases, is experiencing cavitation. As shown in the graph below, the best practice is to be between 10% to the left of BEP and 5% to the right.
Of course, choosing the right pump for your system is very important, but it does not guarantee that your pump will still operate close to BEP. In real life, systems change over time. System demand increases or decreases, and corrosion or sediment build-up in pipes can increase flow and require different pressures. Additional accessories such as valves, hoses or flanges before or after the pump can also change the curve of your system.
If your system is experiencing some of the symptoms listed above and you expect your pump to operate close to BEP, or if you know your system has changed significantly since your pump selection, we can help get you back on track! SES (System Operations Services) can provide a deep understanding of what is happening in your system, and our experienced engineers can interpret this information into actionable recommendations that not only reduce maintenance requirements, but also increase efficiency. They also increase the energy of your system. Another option that can actually change the pump’s torque and BEP closer to your operating point without replacing the entire pump is to cut the valve.
Match Pumps To System Requirements
If you want to improve the efficiency of your system or have any other questions, do not hesitate to contact us. We built our business on helping customers like you get the most out of their systems. Assessment of the hydropower potential of the Torisa River and its energy use in the process of reducing energy poverty in local communities
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