pressure switch question

[jas2218]

I understand different pressure switches, or settings, will effect the amount of drawdown of water in the pressure tank. Does the pressure switch effect the water pressure I will have at the shower, faucet, etc..? I currently have a 20 gal. tank with a pressure switch that is set at 48/68 and the water pressure is OK. I'm going to replace this with a 62 gal. or more tank. Do I just pick a pressure switch that will cause my pump to run for at least one minute? Will a 50/70 switch give me better water pressure than a 30/50 switch?
Thank you.

 

[Valveman]

At 50/70 a 20 gallon tank only holds 4.62 gallons of water. So if your pump delivers 4.62 gallons per minute, that size tank will give you one minute of run time. If you pump delivers 9.24 GPM, you will only have 30 seconds of run time, and so on.

At 50/70 a 60 gallon tank holds about 14 gallons. So you would get one minute of run time if you have a 14 GPM pump. A pressure switch setting of 48/68 is basically the same, so adjusting up to 50/70 is not going to make much difference in the pressure in the house.

I am sure the pump cycling on and off between 48 and 68 is why the pressure is just OK. You probably notice good pressure for a few seconds just before the pump shuts off at 68. Then you probably notice low pressure for a few seconds just before the pump restarts at 48 PSI.
With a 50/70 pressure switch you have an average pressure of 60 PSI. However the pressure keeps swinging from 50 to 70 and 70 to 50 as the pump cycles on and off. Holding a constant 60 PSI would deliver much better pressure to the house. Using a 60 PSI Cycle Stop Valve to maintain this pressure constant has several advantages. First the pump would no longer be cycling itself to death. Second the 60 PSI constant pressure is much better in the house. And third you can use a much smaller pressure tank because cycling and run time are no longer a problem. A smaller tank, such as the 4.4 gallon tank in the picture above is all you need. Then you would not have to wait long for the pump to start, and the pressure to come up and maintain a constant 60 PSI. The bigger the tank, the longer you will see low pressure before the pump starts.

 

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[jas2218]

How do I size a CSV with a pressure tank? My pump produces 6 gpm.
Thnak you.

 

[Valveman]

You need to check if the pump is cycling on and off while the shower is on. If it is cycling then a CSV1W will work with the tank you have, and give you constant pressure in the shower. If the pump is already running steady while the shower is on, then the 6 GPM pump is just not enough to keep up, and adding a CSV will not give you better pressure in the house.

 

[Gary Slusser]

How do I size a CSV with a pressure tank? My pump produces 6 gpm.
Thnak you.

How do you know you have a 6 gpm pump? And if you do have a 6 gpm pump, I think you mistakenly think you can ony get 6 gpm in the house.

 

[jas2218]

Valveman; the pump is cycling on and off with the shower running. Its on until the pressure tank fills up, then off until the shower drains it and back down and then on again, etc. So I can use a CSV1W valve and a smaller tank. I have an 18 year old rusted 20 gallon tank that needs to be replaced, so I can replace it with a similar or smaller size?

Gary: I filled the pressure tank, opened a faucet before the filters and filled a five gallon bucket. When the pump clicked on, I turned off the faucet and timed the refill of the presure tank. It tool 40 seconds and I got 4 gallons of water. Isn't that 6 gpm? Doesn't that mean my pump produces 6 gpm?

Thank you both.

 

[Gary Slusser]

No it doesn't, it means the draw down of your pressure tank is 6 gpm and your pump is not getting the minimum 60 seconds off between starts. Which means as is the tank is too small for the pump.

 

[Valveman]

Valveman; the pump is cycling on and off with the shower running. Its on until the pressure tank fills up, then off until the shower drains it and back down and then on again, etc. So I can use a CSV1W valve and a smaller tank. I have an 18 year old rusted 20 gallon tank that needs to be replaced, so I can replace it with a similar or smaller size?

Yes! With the CSV1W you only need a 4.4 gallon tank like the one pictured in the picture above. Then the pump will stay on and hold a constant 50 PSI while the shower is running, which will give you much better shower pressure.

 

[jas2218]

Gary, a web site gave me that info on how to figure out my pumps gpm. I'm glad you're telling me its wrong. What would be the right way of finding the gpm? I do know it's a 3/4 hp pump, that's it. I need this info when I buy a new softner and acid tank to figure in the backwash rate of the control heads. Thank you.

 

[NHmaster]

Valveman; the pump is cycling on and off with the shower running. Its on until the pressure tank fills up, then off until the shower drains it and back down and then on again, etc. So I can use a CSV1W valve and a smaller tank. I have an 18 year old rusted 20 gallon tank that needs to be replaced, so I can replace it with a similar or smaller size?

Gary: I filled the pressure tank, opened a faucet before the filters and filled a five gallon bucket. When the pump clicked on, I turned off the faucet and timed the refill of the presure tank. It tool 40 seconds and I got 4 gallons of water. Isn't that 6 gpm? Doesn't that mean my pump produces 6 gpm?

Thank you both.

Yes and no. At the point where you are drawing water you are getting 6 gpm. That does not mean it's a 6 gpm pump though. Pipe size, friction loss and well depth all factor in.

 

[Gary Slusser]

The biggest factor is getting the 6 gpm through a 1/2" or at best, a 3/4" valve when the pipe from the well is at least 1" and can be 1.25".

 

[jas2218]

Ok, so I am drawing 6 gpm from my pressure tank, which doesn't mean my pump is producing 6 gpm. And my pressure tank is to small for the pump. I am going to replace the tank, softner and acid tank. How do I figure the GPM rating to properly size the softner and acid tank when they backwash? Since it is 6 gpm now, with an under sized pressure tank, will it go up if I increase the tank, to say, 44 or 62 gallon tank?

 

[Gary Slusser]

Ok, so I am drawing 6 gpm from my pressure tank, which doesn't mean my pump is producing 6 gpm. And my pressure tank is to small for the pump. I am going to replace the tank, softner and acid tank. How do I figure the GPM rating to properly size the softner and acid tank when they backwash? Since it is 6 gpm now, with an under sized pressure tank, will it go up if I increase the tank, to say, 44 or 62 gallon tank?

Your pump is putting out/delivering 6 gpm now because that's all the water that you got because of the size of the pressure tank and the switch settings, after the pump filled the pressure tank but...

Although many guys, and web sites, mistakenly think you can't get more gpm from the pump/system than the gpm rating of the wet end of a pump you can BUT, you don't size softeners and filters based on the output gpm of the pump or well system.

You size the softener etc. based on the peak demand gpm the family size, number of bathrooms and the type of fixtures in them actually use. That's not the same as turning every water using thing on in the house at once.

That dictates the constant SFR (service flow rate) gpm the softener must have and that is based on the cuft volume of resin in the resin tank.

The cuft volume of resin dictates the size of the resin tank and that dictates what control valve can be used and the tank size dictates how many gpm is required to successfully backwash the softener etc..

All softeners and filters have a DLFC (drain line flow control) that is rated in gpm and the gpm depends on the volume and type of resin or mineral used and as an example, normally a softener DLFC gpm will not exceed like 5 gpm; the vast majority are 1.5 to 3 gpm. An AN filter like 7-10 gpm depending on size. They don't use water at the same time and most times not on the same night and no other water is being used while either one is using water. So it is very rare for a pump/system to not be able to deliver the volume of water at the pressure required.

I suggest a very small pressure tank and a CSV, and then Clack WS-1 control valves on the softener and filter. To learn much more about sizing click here.
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