How to Size a Pump

Getting the right size industrial pump shouldn’t be an afterthought. In other words, you don’t want to purchase and install a pump only to find out later that it’s under or overpowered for its intended purpose. 

Using the wrong pump can result in inefficiencies and unnecessary costs. So how do you find the right size? First, you’ll want to understand the basic pump types and then have some practical insight into figuring out pump sizing. 

What Are the Different Pump Types?

Pumps move fluid from Point A to Point B by increasing pressure to produce a flow. Before you can size a pump, you need to choose what type you plan to use. The two basic types of pumps are rotodynamic and positive displacement pumps. 

A rotodynamic pump uses a rotating impeller to create energy. The most common type is a centrifugal pump. A positive displacement pump traps some of the fluid before forcing it through the pump. A gear pump is one example of this. 

How to Size a Pump

Most industrial pumps are rotodynamic pumps, so you should understand how to size these properly. If you are using any other type of pump, the considerations might be similar, but a pump specialist can ensure you get the right size. You’ll need to consider these five factors when sizing an industrial pump.

1. Differential Pressure

Differential pressure is the difference in pressure at the pump inlet and pump outlet. The Net Positive Suction Head (NPSHa) is the amount of pressure available on the inlet side of the pump. It is determined by multiple factors in your system. 

Things like line sizes, line lengths, filters, and valves all impact the NPSHs as fluid tries to make its way into your pump. Once the fluid enters the pump, the pump’s mechanics will produce the necessary pressure to push them through to the outlet side. The differential pressure is the difference between the two. 

Every pump has a minimum pressure required for the inlet to work correctly. This is referred to as the Net Positive Suction Head required (NPSHr). If it is lower, you will risk cavitation, which is the formation of air pockets or cavities within a pump. 

In a centrifugal pump, pressure is added to the pump through the constant rotational speed of the impeller. The pump needs to operate efficiently to transfer the right amount of energy and fluid, or you risk cavitation and damage. 

2. Fluid Temperature

The flow properties of fluids can change when their temperatures shift. Temperature is one element that can impact a product’s viscosity as it moves through heat exchangers, pipes, pumps, and other system components. There will be more flow resistance as higher viscosity and vice versa. 

Some products will be processed at higher or lower temperatures than room temperature. For example, heated honey will flow faster than it will at room temperature, as will many food sauces. 

3. Fluid Viscosity

In addition to temperature changes, some fluids will change viscosity in response to pressure changes. The idea is that some liquids will get thicker or thinner when they are under pressure or stress, such as when they come into contact with a pump’s impeller. 

This can be a complex issue that your pump expert can help figure out if you are unsure about pump sizing. A pump company can perform rheology testing on a product sample to measure its viscosity and help you choose the right pump. 

4. Flow Rate

Flow rate refers to the volume of liquid moving through a pump in a particular time frame. Usually, this is something like liters per second or gallons per minute. For example, a pump that moves 25 gallons of fluid per minute has a flow rate of 25 GPM. 

The formula to calculate flow rate is:  Volume of fluid moved/  duration of flow = flow rate

If you don’t have a flow rate meter on your pump, you can test your flow rate by:

• Placing a 5-gallon bucket at the outflow of your pump
• Starting a timer as you open the pump and stopping the pump at one minute
• Calculating the flow rate using the provided formula

One of the factors that you’ll have to consider with flow rate is friction loss. This refers to a reduction in flow through your system when something isn’t optimized. This can be caused by pipe length, pipe turns, pipe materials, the age of the pipe, and other issues. 

5. Water Velocity

Depending on the purpose of your pump, water velocity might be a concern. This refers to a minimum scouring velocity in your pump to prevent debris buildup. For example, when a pump shuts down and material stops flowing, solids can settle in the pipe. If there isn’t enough water velocity, those solids can begin to clog your pipes and lead to friction loss. 

6. Density

A fluid’s weight by volume is its density. The more a fluid weighs, the denser it is. This means that, given a certain volume, a more dense fluid is likely to be more resistant to flow. For example, a jar of honey will weigh more than a jar of water. That’s because the fluid is thicker or more dense. Understanding fluid density compared to water is one of the factors that can help you choose the right pump. 

Get Help Choosing the Right Industrial Pump Size

Having the right size industrial pump for your business is critical. Even with the above information, you might still have some questions. C&B Equipment would be happy to help. 

Our team of factory-trained technicians can help you choose the right pump and keep your pump operating as it should. We have decades of experience installing, troubleshooting, and repairing all types of industrial pumps. Contact us today to find out how our services can help your business improve its efficiency and profitability.