What PSI should be in my well expansion tank?

[Valveman]

Valveman, thanks for your post. I was going to say the same thing, got down to the end of the thread and you already said it a and better than I would have.

One concern I have about my well pump, which is set deep due to declining water table is the wear on the thrust beating. Granted it cycles less and is under less electrical load but I think there may be a tradeoff with thrust bearing life.

Actually no again. A Kingsbury type thrust bearing is completely friction-less. There is a film of water between the thrust pads and the plate as long as the pump is spinning at least 50% of full speed. So the only wear on a thrust bearing is during start up until the motor gets to 50% speed. I have a pump supplying a stock tank that hasn't shut off in 17 years. Pumps are made for continuous operation. And the thrust bearing is made to handle the full load of the pump, even at shut off condition. The pump won't put more thrust on the bearing than it can handle. As long as there is sufficient flow past the motor, (at least 2/10s of a GPM) to keep the thrust bearing cool, its life it dependent on how many starts it has on it. Every time the pump is started, the bearing runs dry for a split second until the motor is up to 50% of full speed.

Here is a short video of pump cooling requirements. It is a little technical, but basically shows that restricting the flow from a pump will reduce the amps and make it run cooler. This is just the opposite of what most people think. Restricting the flow from the pump does put more weight on the thrust bearing, but not more than it can handle. As long as there is enough flow to keep the motor cool and you don't let it cycle on/off too many times per day a thrust bearing will last a life time. An example is the bearings on the turbines at the Hoover Dam. Those Kingsbury thrust bearings where inspected after 75 years of service, and the tech said they have at least another 75 years of life in them. Kingsbury thrust bearings just don't wear unless the water gets hot or unless you run them dry on start up too many times.

VFD does not cool pump as good as CSV Technical Explanation on Vimeo

 

[turnkey4099]

when I had a low flow shower head, it took me at least twice as long to shower, so that didn't work out!..

Same here. As for the other 'save water at low pressure' that is cured by just closing the faucet a bit if the very minor savings is really critical.

 

[turnkey4099]

I disagree. 30/50 or 40/60, both being a 20# differential, the pump will turn on the same amount of times.

Exacty - it is the volume of water used not the pressure that counts as far as 'how often'

 

[Valveman]

Same here. As for the other 'save water at low pressure' that is cured by just closing the faucet a bit if the very minor savings is really critical.

Exactly! Any faucet is a variable flow faucet. Just don't open it more than needed. And yes it is the volume of water used that counts on "how often", not the pressure.

At 40/60 a pressure tank holds less water than at 30/50, so with the same size tank the pump will cycle more often at 40/60. However, at 40/60 the pump is producing less water. So depending on the pump curve, the fill cycle could take longer at 40/60 than at 30/50. Pretty much a wash either way, just get the pressure you want. No sense living with low pressure just because you think it cycles the pump less.

 

[BoylermanCT]

Make sure you turn off the well power at the breaker panel before opening the pressure switch cover. Mine is 220V, so you don't want to go banging around there with your screwdriver!

 

[CobyRupert]

At 40/60 a pressure tank holds less water than at 30/50, so with the same size tank the pump will cycle more often at 40/60. However, at 40/60 the pump is producing less water. So depending on the pump curve, the fill cycle could take longer at 40/60 than at 30/50. Pretty much a wash either way, just get the pressure you want. No sense living with low pressure just because you think it cycles the pump less.

Yes, I agree 30/50 gets you more water, less cycling. But I realize I'm thinking in terms of a pump cycling when people are using a couple gallons here and there (toilet flush, cooking, glass of water, brushing teeth, etc...) over the course of the day, that is, taking out quantities less than the ballast tank capacity. And at 30/50 thy can take out more water than at 40/60 before pump cycles.
I think others here are thinking about cycling if you are continuously drawing water out in large quantities in excess of the ballast tank (say showering, or filling a stock tank). Then yes, the pump would cycle less because it's staying on more, because it's replenishing water more slowly.

 

[Valveman]

With all the variable speed (VFD) and other types of "on demand" pump controls now available, pump companies have learned that cycling a pump for intermittent uses doesn't add up to much. It doesn't hurt if the pump comes on every time you flush or wash your hands. Pumps can survive between 100 and 300 cycles per day. How many times per day would a toilet be flushed anyway? But cycling while using water for long terms like irrigation and heat pumps must be eliminated for the pump to survive.

In the old days, a quarter of a century or so ago, I would have recommended as large a pressure tank as you can get. But there are several problems with the old pressure tank only method, most importantly being at low pressure in the house for long times waiting on the tank to drain. Times have changed and there are better ways of controlling pumps now. Constant pressure systems have many benefits over the old pressure tank method. A constant pressure valve will keep the pump from cycling as long as you are using more than 1 GPM. So for showers, sprinklers, heat pumps, etc, this is the way to go. The small tank normally used with a constant pressure valve will cause the pump to cycle for each toilet flush, but having eliminated all cycles for long term uses, adding back a cycle for each toilet flush will have little to no effect on the life of the pump.
How a Pressure Tank Works and why you need a Cycle Stop Valve on Vimeo

 

[gary49]

Yes, I agree 30/50 gets you more water, less cycling. But I realize I'm thinking in terms of a pump cycling when people are using a couple gallons here and there (toilet flush, cooking, glass of water, brushing teeth, etc...) over the course of the day, that is, taking out quantities less than the ballast tank capacity. And at 30/50 thy can take out more water than at 40/60 before pump cycles.
I think others here are thinking about cycling if you are continuously drawing water out in large quantities in excess of the ballast tank (say showering, or filling a stock tank). Then yes, the pump would cycle less because it's staying on more, because it's replenishing water more slowly.

Whew! This thread's gotten pretty far off in the weeds.��Hope the OP has gotten his problem fixed. My experience with submersible pumps is that they're pretty robust and can tolerate a lot of abuse. I pull more pumps where the problem is the cable wearing through from start/ stop cycles than the pump and/or motor having failed. Still a good reason to make sure the pressure tank is functioning correctly. I use a torque arrestor and cable guards when I do installs which seems to greatly reduce the cable wear issues. I can see where the thrust bearing could be more of a problem in areas here wells are extremely deep. I rarely see wells here in central Virginia that are much over 400' and most are 300' or less.

 

[CobyRupert]

I think OP has his answer: 2 psi below cut-in when water pressure is zero.
But should that be 28 psi (for 30/50) or 38psi (40/60) and what are pro/cons of each range?
Hey, we're not THAT far out in the weeds.
You got something against weed?

 

[Valveman]

I use a torque arrestor and cable guards when I do installs which seems to greatly reduce the cable wear issues. I can see where the thrust bearing could be more of a problem in areas here wells are extremely deep. I rarely see wells here in central Virginia that are much over 400' and most are 300' or less.

Again, depth or back pressure has nothing to do with thrust bearing wear. I have set pumps as deep as 2200' and no problem with the thrust bearing. It is the cycling on/off and lack of cooling flow that causes thrust bearing damage and a lot of other problems. I don't like torque arrestors or cable guards (standoffs) in the well either, as they are just additional (unnecessary) equipment that can come loose and fall in the well or stick so the pump cannot be removed from the well. A constant pressure valve will limit the cycling, and with double jacketed wire there is no chaffing and no need for torque arrestors or cable guards.