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This post is intended to pass along some good information regarding water pumps and plumbing – things you should be aware of. This is another good post to bookmark as this information will come in handy later.

The Basics
Pumps are usually rated in flow, either Gallons per minuter (GPM) or Gallons per hour (GPH). To convert from GPM to GPH simply x 60. To convert from GPH to GPM just divide by 60.

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.

A 3′ wide waterfall would need 108 gallons per minute to be 1″ thick.

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.

Now that we know water volume needed and the head height it is needed at, it makes selecting a pump much easier. Matching feet of head with a pump that delivers the gallons per minute (GPM) you need.

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

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
1.25″ = 45 GPM
1.5″ = 60 GPM
2″ = 90 GPM
3″ = 225 GPM
4″ = 350 GPM
6″ = 700 GPM
8″ = 1500 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!

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 instead). Use flex PVC with sweeping curves where ever possible.

Friction Loss (click on the chart to read it more clearly)

I hope this was helpful and informative. Call us and we will walk you through everything and make sure you have the right setup.
Paul Cole

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