Press. Tank, Press. Switch Question

[jimainiac]

I'm going to winterize a seasonal cottage, and need to relocate the water line that comes in from the well to a different location. I plan to put the pressure tank where the pipe comes in, about 40 feet from where it does now. It's going from the kitchen to a bathroom, so the plumbing will still be connected inside the house. I wonder if I can leave the pressure switch where it is, to avoid a bunch of rewiring? Is there any rule about the pressure switch being within a certain distance of the pressure tank? The way I see it, the whole system will have about the same pressure, so it shouldn't matter, but maybe I'm missing something?

 

[Steve_Miller]

Depending on the pipe size and the draw that will occur when a tap or valve opens. There will be a pressure drop of some value, if this drop is enough to activate the pressure switch, you may trigger the pump to start each time this occurs and quickly turn off again when the tap closes. It may happen or it may not, you'll have to experiment with the setup. If there are no offtakes between the switch and the pressure tank this will probably not occur through as the tank will absorb the initial drop. Hope this makes some sense as my descriptions don't always make sense the way I try to portray them.

Steve

 

[jimainiac]

Thank you for your reply, your rationale makes sense. I don't have 100% confidence that it will function properly, either. It's just that to change the routing of the wires from the pump in the well I'll have to make connections underground, in the trench, that hopefully will stand up to the elements down there. Or I could extend the wires the extra 40 feet along with the pipe to the pressure tank, inside the house. Don't know if running the extra length of wire would be detrimental.

 

[GaryQWA]

It is best to have the switch at the pressure tank.

All you need for the electrical connection for the splice is a water proof splice kit and a piece of conduit like sch 40 PVC tubing to protect the splice kit material. You get the kit at any pump supply house, hardware or big box store that sells pumps.

Gary
Quality Water Associates

 

[LarryD]

I'm certainly no expert here but I can't see a problem with the pressure switch located "in the general vicinity" of the tank. Is a few feet going to make a difference?

The pressure tank is there to buffer any surge when the pump comes on. I can't see a big difference in the line pressure over a few feet, of course my pressure switch is only a foot away from the pressure tank.

Maybe a pump guy will chime in, the question has me curious.

 

[jimainiac]

I thought that in theory it shouldn't be too bad to seperate the tank and switch, but when I move the tank it will be about 30' away horizontally, plus 8' up and then 8' back down. Unfortunately, it's getting out of the "general vicinity". I just thought that, since you can't compress a liquid, the pressure should be about the same in the whole system and I might be able to get away with it.

 

[TMcD_in_MI]

I just thought that, since you can't compress a liquid, the pressure should be about the same in the whole system and I might be able to get away with it.

Yup, Pascal's Principle tells us that exact thing, and it works for any enclosed fluid, compressible or not. But that's only true (1) if measured at the same depth (height) and (2) if the fluid is stationary. Once the fluid starts moving, the pressure is going to drop more and more as you get farther and farther from the pump, as Steve mentioned. Will the pressure drop enough to matter? I don't know if that's a question anyone can answer for sure because it depends on how much resistance the pipe offers to the water. Why not just give it a try and see if the pump comes on almost immediately when you turn the shower on. If not, you're probably good to go, although I think I would be inclined to move the pressure switch just to keep a nice tidy installation.

Tom

 

[_RaT_]

Yup, Pascal's Principle tells us that exact thing, and it works for any enclosed fluid, compressible or not. But that's only true (1) if measured at the same depth (height) and (2) if the fluid is stationary. Once the fluid starts moving, the pressure is going to drop more and more as you get farther and farther from the pump, as Steve mentioned. Will the pressure drop enough to matter? I don't know if that's a question anyone can answer for sure because it depends on how much resistance the pipe offers to the water. Why not just give it a try and see if the pump comes on almost immediately when you turn the shower on. If not, you're probably good to go, although I think I would be inclined to move the pressure switch just to keep a nice tidy installation.

Tom

Great comments. You can minimize the effect of a pressure drop in this instance by oversizing the pipe thus minimizing the pressure drop by reducing the velocity of the water at least in the section between the pressure tank and the switch, But then, if you have to upgrade the pipe size, you might as well redo the wiring and keep the tank and switch in the same vicinity and preferably as close to the point of use as possible for accurate pressure settings.

 

[jimainiac]

That's a good idea to use a larger pipe size. I can do that, since the addition isn't built yet, and it never hurts to use a larger pipe for better flow volume, anyway.
I really could extend the wires, but I thought that the extra 40' of hot wire to the switch, and extra 40' of wire from pump to switch would give extra resistance, and maybe votage drop. Maybe I shouldn't worry about that.

 

[Steve_Miller]

Electricity flow is similar to water flow, the smaller the water/pipe the more resistance to flow occurs, the bigger the better to a certain extent.

Steve