Pump Power Calculator

This Calculator provides a very "superficial" estimate of a pump’s average power consumption based on its pressure, flowrate and efficiency. This estimation may be helpful for sizing of cables and circuit breakers / isolator points for the pumps at the initial stages of design.

(Reference: www.engineeringtoolbox.com)

For unit conversion:

Note: Use Unit Conversion Table above as reference for Pump Flowrate & Pressure Head Unit Conversion

Look for Value '1' in the source unit & multiply with the factor in destination unit

Example:

Understanding Pump Curve and System Curve

The following article will help you understand Pump Curve and System Curve in the simplest understandable ways.

System curve is also referred to as system resistance curve. It is a function of Pressure Loss (Resistance of fluid) and Flow of a hydraulic system. A typical system curve shows that when flow increases, pressure loss increases as well.

To visualize this, imagine that when you turn your water tap on to the maximum to force a large flow of water through a pipe, the frictional force of the water against the pipe’s inner surface will rise, resulting in a higher pressure loss (or pressure drop). The term “Pressure loss” or “Pressure drop” used can be rather confusing, just bear in mind that they resemble the “resistance” of flow. The word “loss” or “drop” are common industrial terminologies because those resistances introduce “loss” to the pressure head of a fan or pump. They need extra “work” (in terms of pressure) to overcome those “losses” used to overcome friction along the system’s "wall".

The same goes to an ACMV (Air-conditioning & Mechanical Ventilation) ducting system. A fixed size of duct will experience higher frictional loss, hence higher pressure drop when we introduce an increased flowrate of air across it. The friction against the duct’s inner surface also result in higher noise pressure level. Therefore, when the airflow is increased to an extent that it exceeds a threshold of maximum allowable frictional loss or pressure drop, we need to upsize the duct.

The same applies whether the fluid is water over a pipe, or air over a duct.

When we upsize a duct or a pipe, the system curve becomes less steep.

This means that with a bigger pipe size, the increase in flow of water inflict less significant resistance. In other words, when flow increases, pressure (pressure drop) increases, but in a gentler manner compared to that in smaller pipes.

When the size of pipe is increased further, pressure drop becomes insignificant even if flowrate is increased even further.

Pump Curve

A pump curve, on the other hand, may look like this.

The pump’s pressure head is required to overcome the “pressure loss” we were discussing about, that is introduced by the system, with application-adapted pressure required at discharge. For instance, when we downsize a pipe or duct, we are anticipating that the pump or fan has to overcome a higher pressure loss due to friction, hence the output pressure head has to be increased.

Different pumps or fans exhibit different properties. Nonetheless, a typical pump curve shows that when flow increases, the pressure head it can offer reduces. A good analogy for a better understanding of the pump curve would be the torque and speed relationship in motor vehicles. A car’s gear can resemble the pumping system. When the gear is set for low speed, we can achieve higher torque. This is why you should always engage a low speed gear when your vehicle goes uphill, because you need the torque to start the acceleration. The pump is quite a similar application. When the pump starts, you need higher pressure head before desired flowrate can be achieved. When flowrate is at operating point, the required pressure head will be lesser. Similarly, when your car is running fast on a highway, you need lesser torque to maintain the speed.

Depending on the types of application, you can define a pump as “better” if the pump is able to maintain its pressure head at high flowrates. Whether or not this is necessary shall be based upon case to case application. Most pumps, like cars, do not need high pressure head (Torque for car) at high flow (Speed for car). However, certain pumps have to anticipate high pressure loss in the system, especially when the system has undersized or scaled pipes, or is fitted with many loss-inducing valves or accessories. They are just like the trucks or trailers, needing higher torques to expect higher drag or resistance. Similarly, certain fans need to have higher static pressure to overcome pressure losses across heavy filters, for example.

One thing for sure, if you are expecting your pump to have high pressure head even at high speed, you should be prepared for the higher electricity consumption. For certain, F1 racing cars equipped with powerful torque to accelerate even at high speed, consumes much more fuel and requires much more maintenance.

Pump Operating Point

The point where the system curve and the pump curve intersect one another is known as the operating point.

For example, a Hosereel System is designed with an operating point at 120 L/min of flow and 120 feet H2O of pressure head. If we introduce a restriction to the flow of our system, an increase in the pressure drop (resistance) from the system will follow. This means an increase of the pressure head of the pump will be required to overcome that loss. For instance, if you install a nozzle at the outlet of the hosereel pipe or a shower head at your bathroom tap, or reduce the pipe size of your system, or simply restrict the water discharge at the outlet by blocking out part of the discharge using your finger, pressure loss is experienced at the restriction area (prior to discharge). A portion of the pressure provided by the pump is lost while trying to overcome the restriction introduced at those narrow-neck fittings or at your finger. A new system curve is observed to the left of the old curve before restriction is introduced, as shown in the figure below.

At this point, your pump pressure head needs to rise to 180 feet. The operating point shifts upward and toward the left (OP2). Using the same set of pump, you will notice that this increase of pressure head comes at the expense of the flowrate. As a result of that, the flow is also reduced. If this flowrate (80 L/min) is not acceptable by your application, you need to “upgrade” your pump. Similarly, at an increased carrying load (higher drag), if I cannot accept my trailer to only be able to run at 20 km/hr. The only thing I can do is to upgrade my engine performance.

In this case, extrapolated system curve shows that to force 120 litres of fluid through the restricted system in one minute, much higher pressure loss (500 feet) will be resulted. Now, I have to improve my pump in order to maintain a 120 L/min flowrate, to the ability of delivering in this case, 500 feet head pressure across the restricted system. This marks our new operating point at OP3. From this pressure drop value, we can gauge that this restriction is impeding the flow severely.

Therefore, another approach is to relook into the restriction that was being introduced. For example, use nozzles with larger openings, filters or coils that allow more air to pass or grilles with larger free areas. If the improvised restriction now adds a much lesser pressure loss to the system, the system curve shall appear to be less steep (orange). Now, to maintain a flowrate of 120 L/min, only additional 10 feet pressure loss (190 feet) is required to push the fluid through the restriction.