What is "foot valve",why it prevents loss of prime

[bcarwell]

I have a new cheapo non-self-priming water pump. Instructions say to install a "foot valve" on the input side, and that this will prevent loss of prime.

What exactly IS a "foot valve" ? And why would it prevent loss of prime ?

Bob

 

[beenthere]

As I understand it is like a one-way flapper valve that holds a column of water in the pipe. It as the lower end so holds that column of water above it.

http://www.inspectapedia.com/water/Foot_Valves.htm

 

[Chilly807]

The foot valve goes at the "foot" of the piping in your well/cistern/lake, etc. It acts as a one-way valve to prevent water from draining out of the pipe when the pump isn't running.

Sean

 

[rjmack]

check valve.

 

[Mace Canute]

If you Google "foot valve" you will find many entries that describe what it is and how it works with several pictures and illustrations.

 

[Qapla]

The foot valve goes at the "foot" of the piping in your well/cistern/lake, etc. It acts as a one-way valve to prevent water from draining out of the pipe when the pump isn't running.

This is correct. Keep in mind that a "check valve" is a "one way valve" that keeps the water from returning to the source. The main difference in the "check" and the "foot" valve is the location. A "foot valve" is technically a "check valve" that is located at the bottom of the well drop pipe - thus the name "foot".

A check valve can be installed near the pump since it is mostly a safety device. A "foot" valve is installed on the "bottom" of the drop pipe.

Since a check valve will also stop the water from going back down the well, you might wonder why you need the foot valve.

The main reason for the foot valve being at the bottom of the well is to maintain a drop pipe that is filled with water. The weight of the water in the pipe will help keep the valve closed when the pump is off and keeps the pipe full. This way, when the pump turns on, the water in the pipe helps keep the pump from losing it's prime while starting a flow of water.

If you only have a check valve at the top, it is true that the water in the storage tank won't drain back down the well, but gravity will leach the water from the drop pipe. When the pump turns on, there may not be enough water in the pipe to maintain the prime while the pump pulls a fresh flow. Even if it does prime, you will most likely send a pipe full of air into your storage tank. A few starts like that and you will replace the water in the tank with only air.

If you have no check or foot valve, there will be no water available for the pump to prime itself.

 

[bcarwell]

Ahhhh. Thanks to all, now I understand. Since I am running my pump from a (house) pressurized input source (e.g. a garden spigot located right next to the pump) I assume that I can dispense with the "foot" valve once I've primed the pump.

Thanks again for all your help !

Bob

 

[Egon]

With a pressurized suction line no foot valve/check valve should be required.:thumbsup:

 

[Argosy]

With a pressurized suction line no foot valve/check valve should be required.:thumbsup:

Maybe I'm missing something. What would maintain the pressure in the line when the pump shut off if it was open on the end? And if the suction line was pressurized wouldn't it be a discharge line?

 

[J_J]

The weight of the water helps to keep the check or foot valve closed. The stand pipe is not pressurized by the pump. You need a check valve to keep water in the tank and the suction side of the pump. There is pressure on one side of the check, and a vacuum on the other side. If you have both valves, the pressure on the foot valve is only the weight of the water in the stand pipe. The pressure on the upper check valve is the tank pressure.

I think What Egon is saying is, that if you only have a foot valve, then the pressure from the tank is on the top of the foot valve, and therefore, the suction side has tank pressure. You have to have a check of some kind, unless it is an artesian well.

Most shallow well pumps, can draw from about 25 ft.