Where to place a pressure switch?

[Stuartl]

I use surface water with small Gould pump and precharged tank 10 ft above the river bed (the main lot is 40 ft above the river bed). I am thinking of moving the pressure tank to the top of the lot - should the switch move with the tank, or stay by the motor? I realize I would have to adjust the system to operate on lower pressures because of the increase height.

Thanks for any advice!

Stuart

 

[Rancher]

I am thinking of moving the pressure tank to the top of the lot - should the switch move with the tank, or stay by the motor?

the switch needs to be at the tank.

I realize I would have to adjust the system to operate on lower pressures because of the increase height.

Unless your pump can do higher pressures.

Rancher

 

[Sponsor]

 

[Gary Slusser]

IMO it has to be at the pump, and the pressure tank should be there too but... the pump may not have the ability to reach the pressure needed in the system 40' higher, plus any additional elevation in the building. A better choice would have been a 1/2 hp 10-13 gpm submersible pump set up properly in the river.

 

[Rancher]

If the pump currently has the power to reach a usable pressure at the building site, then nothing has changed in the water head pressure, just the location of the tank.

If you don't have the switch at the tank, you will have rapid switch cycling.

Rancher

 

[Gary Slusser]

I realize I would have to adjust the system to operate on lower pressures because of the increase height.

If you move the switch up 40', you must run the pump at HIGHER pressures; not lower. Most jet pumps can not go above 50-60 psi consistently.

 

[Bob NH]

If you move the tank and switch 30 ft higher, and reduce the switch settings by 13 psi (30 ft/2.31 = 13 psi), then you will have virtually the same conditions that you now have with the following small variations:

1. You will eliminate the pressure loss that now exists from tank to user when you have high flows.

2. There will be a virtually unmeasurable increase in pressure at the pump at the shutoff point due to the pressure loss in the pipe as it is filling the tank. That pressure loss will be small because the pump is pumping at its lowest flow rate as it approaches shutoff pressure.

If the pump has some pressure margin then you can select a pressure setting between the existing setting and the "13 psi lower" setting.

If you are using surface water for drinking it should be filtered and disinfected. You may not have a problem because you are accustomed to the biological thingies that are often in surface waters, such as cryptosporidium, giardia, and coliform bacteria. However, your guests might be susceptible to those things.

If you want to find out about crypto, Google cryprosporidium milwaukee and cryptosporidium seneca lake

 

[Gary Slusser]

Stuart said: I use surface water with small Gould pump and precharged tank 10 ft above the river bed (the main lot is 40 ft above the river bed).

I read a jet pump, a shallow well single line Gould's jet pump, sucking 10' above the bottom of the river.

I mistakenly have been saying 40' when it would be 30' but... I suspect Stuart is having a problem with delivery of water at a usable pressure and flow, hence his wanting to improve the system by moving the tank up the hill; and maybe the pressure switch AND the reason he posted here!

The normal jet pump isn't going to work well sucking water from 10' or a bit less and then pumping it 30' up hill and then to whatever water uses there may be with their associated pressure losses without raising the operating pressures of the pump. Regardless where the switch or tank is but...

Reducing the switch settings by 13 psi works well on paper, but please try it on your pump and tank where it is now Stuart and let us know how it works in real life.

And don't forget to reduce the air pressure in the tank accordingly. 30/50 switch settings now goes to 17/37 psi and that gets 16-15 psi captive air pressure in a bladder tank with no water in it. If 40/60, I'm sure you can do the math. And I suggest not using less than a 20 lb differential.

The best place for the tank and switch is at/with the jet pump down by the river but get rid of the jet and throw a 1/2 hp 10-13 gpm submersible in the river, or float it on the water in the river with the inlet screen under water at all times. Set the switch and tank for say 40/60 or 50/70. Then you can put the tank and switch anywhere up on the lot you want to and use a lot more water than any jet pump will supply.

 

[Bob NH]

I was responding to the original inquiry by Stuartl. I described what would be the effect of moving the tank 30 ft higher, and the change of switch settings that would produce the same pressure at the point of use.

Stuartl did not specify the pressure setting for the switch at the lake. Whatever it is, reducing the setting at the switch by 13 psi when the tank is moved up the hill will have only an insignificant change on the pressure at the pump.

The Goulds J5SH, J7S, J10S, and J15S are all rated for 60 psi discharge pressure with 10 ft of lift. With the tank up the hill they could have switch settings of 27/47 psi with tank precharge of 25 psi.

The J5S is rated at only 50 psi with 61 psi shutoff and is probably inadequate for the described application.

A submersible is always a better choice where it it is possible to install one.

One advantage of putting the tank up the hill with 13 psi lower settings is that the available drawdown is increased because the ratio of absolute STOP/START pressures is greater for the case at the top of the hill.