(215) 244-4300
RSS Feed

How to select the correct pump


Updated: Tue, 9 Aug 2011

Selecting a pump can be confusing but it is critical that the proper pump is chosen to ensure longevity and trouble free performance. Following are several things to keep in mind when selecting a pump:
How to select the correct pump

Waterflow

How Much Volume Do You Need?

It takes approximately 36 gallons per minute to make a waterfall 1' wide x 1" deep (1" deep water is considered an average depth for residential applications). The first step in determining how much water you need is to multiply the width of the waterfall in feet x 36 = gallons per minute needed to make 1" thick water over your falls.

Example: A 3' wide waterfall would need 108 gallons per minute to be 1" thick.

Next, determine how much head (lift) there is from the surface of the pond to the top of the waterfall. On a small, simple waterfall the vertical lift is all you need, however, on large applications you also need to factor in friction loss from the pipe as well as each fitting to get the total head.

This Determines Head Pressure...

Head Pressure Chart

Now that we know water volume needed and the head height it is needed at, it makes selecting a pump much easier. Start by looking at our pump comparison chart below. This chart lists all of our popular submersible pumps on one page. Look in the grey box on the right side of the chart - find the column of head closest to your application then follow that column down until you find a pump that delivers the gallons per minute (GPM) you need.

The depth of the water where the pump is located does not count towards ft. of head. Ft. of head is the distance the water is lifted above the pond's surface.

Pump Comparison Chart
(Click on the image above to view a larger chart)

Click here for the EasyPro pumps shown in the graph

If you have a unique application, are using an external pump or just want our help please do not hesitate to call. Improper pump application is the leading cause of pump failure - we want to help you select the best pump for your application. When calling we need to know the GPM needed, voltage and phase of power available, the length of the pipe run and the diameter of the pipe (if already installed).

Knowing the application and selecting the correct pump for the job will increase the overall performance of the feature and decrease the frustration of frequent call backs and unhappy customers.

External Pumps

Using an external pump raises several questions regarding proper pump selection.

Self Priming - A self priming pump can sit higher than the water level being pumped by a few feet (depends on the model) and will displace the air in the suction line to prime itself.

Non-Self Priming - These pumps must either sit below the water level being pumped or must have a check valve installed at the end of the suction line to keep water in the system after being primed the first time.

All external pumps are designed to push water, not pull it. This means the pumps should sit as close to the pond as possible!

Proper Plumbing is Important!

Your pump can only perform as well as your plumbing system allows it to! Very often contractors use pipe that is too small and then cannot figure out why a larger pump doesn't give them more water. Always size your plumbing for the amount of water you are pumping regardless of the outlet size of the pump!

Maximum water flow for a pipe size of:

1" = 25 GPM 2" = 90 GPM 6" = 700 GPM
1.25" = 45 GPM 3" = 225 GPM 8" = 1500 GPM
1.5" = 60 GPM 4" = 350 GPM 10" = 2500 GPM

If your pump delivers more water than your pipe can handle you will not get the pump's rated amount - you will get the pipe's rated amount!

Example: Frequently contractors use 3" flex pipe when installing a WQ1502 pump. This pump has a 3" discharge but pumps 295 GPM at 5' of head. Since 3" pipe can handle a maximum of 225 GPM the pump does not deliver the amount of water it is capable of! Always size your pipe for the amount of water being pumped.

Fittings can also reduce flow - 90º elbows should be avoided if at all possible (use two 45º elbows).

Proper Electrical Supply is Critical

Inadequate power supply is one of the biggest contributions to reduced pump service life, poor performance and premature pump failure. Low voltage caused by undersized wiring, having too many items running on the same line and not double checking the voltage/amp draw once the pump is operating are common mistakes that lead to problems. All pumps need a certain amount of back pressure to operate correctly. Often times a ball valve is needed on the outlet side of the pump to create the needed back pressure. Without this back pressure the impeller will pump more water than the motor is rated for creating high amp draw and excessive heat. This will lead to shortened motor life and premature failure. By closing the valve a small amount, back pressure is increased and the motor operates within its designed service factor.

Important Pump Info - Please Read and Understand This!!

Kill-A-Watt Meter

The life of any pump is directly related to the operating conditions it works under. One of the most common causes of premature pump failure is LOW head. Pumps are designed to work under a certain amount of load. In low head applications not enough back pressure is put on the pump and is spins too freely. This causes the motors to run hot and shortens their life considerably.

In every plumbing system you should incorporate a valve somewhere in the discharge line. This valve can then be closed part way to simulate backpressure if not enough natural pressure is created.

Plastic Pipe: Friction Loss (In Feet of Head) Per 100 Feet of Pipe

Feet of head is typically measured in terms of vertical lift. However, the diameter and length of pipe can have a significant effect on the performance of the pump as well (especially if the pipe diameter is too small). A pump must have the power to not only push the water up to the vertical height of the waterfall, but to also overcome the friction loss created by the pipe. Total Dynamic Head is the feet of head (lift) added to the friction loss created by the pipe. In most small ponds, with short pipe runs, friction loss is not typically a problem. However, in a feature with long streams or high flow rates, friction loss can have a big impact on the performance of the pump. To determine the Total Dynamic head you would add the feet of head and the friction loss. The chart at the right lists the feet of head equivalent created by flow and pipe diameter (figures show are based on a 100' length of pipe).

Example: We are pumping 70 GPM (4200 GPH). The chart shows that 70 GPM through 100' of 2" pipe equals 7.76' of head while a 3" pipe only equals 1.13' of head. If your waterfall is 10' high and 100' away, you will have a total head of 17.76' using 2" pipe but only 11.13' using 3" pipe.

 

  10.00' Vertical Lift   10.00' Vertical Lift
+ 7.76' Friction Loss + 1.13' Friction
= 17.76' Total Dynamic Head = 11.13' Total Dynamic Head

Pipe Comparison

Many people mistakenly think that there really isn't much difference between (for example) 1.5" pipe and 2" pipe or between 3" pipe and 4" pipe. The chart to the right shows how many square inches of surface area are on the inside of flexible PVC pipe.

As you can see, there is a big difference between 1.5" and 2" pipe - almost 80% more space! This shows why using the correct size pipe is important to the output of your pump.


Description: