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Thread: What are the trade-offs in setting pump pressure?

  1. #1
    DIY Senior Member guy48065's Avatar
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    Default What are the trade-offs in setting pump pressure?

    30-50, 40-60...What guidelines are there for choosing system pressure? Is higher always better? Can I hold down the pressure switch to see where the pump tops out and then set the pressure maybe 10psi below that maximum?

    I'm looking for the reasons & to get a better understanding.
    Romeo and Atlanta, MI

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    Sprinkler Guy Wet_Boots's Avatar
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    You will only blow the pressure relief valve if you hold the switch contacts closed. My trade is the one most responsible for the switch settings needing to be increased, and we regularly go beyond 40-60, and approach 50-70, because we need to see good pressures in our sprinkler systems, even after 20 psi gets lost through electric valves and backflow preventer.

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    DIY Senior Member Reach4's Avatar
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    The the main reason for lower pressure would be to use less power. So if 30 PSI does everything you want, 30-50 would have that advantage.

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    DIY Senior Member guy48065's Avatar
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    My "test" assumes you would close the main valve so as to not stress anything downstream.
    Romeo and Atlanta, MI

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    DIYer, not in the trades LLigetfa's Avatar
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    A lot depends on the well depth to static level and draw versus recovery. If you set it too high and the level drops, the pump could deadhead and meltdown.

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    DIY Senior Member craigpump's Avatar
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    If you plug the PRV and close off the valves you can turn the tank into a rocket provided the pump is big enough and the well is full of water.

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    DIY Senior Member guy48065's Avatar
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    Quote Originally Posted by LLigetfa
    A lot depends on the well depth to static level and draw versus recovery. If you set it too high and the level drops, the pump could deadhead and meltdown.
    That's a volume issue.
    Last edited by guy48065; 11-19-2013 at 05:14 PM.
    Romeo and Atlanta, MI

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    DIY Senior Member guy48065's Avatar
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    OK so far we have the one single determining factor is the average cost is higher to pump to a higher pressure.
    I guess I thought there was more to it than that.

    Do I consider myself schooled? Sure--if we're in about the 4th grade. C'mon you guys can provide more insight than this. Pretend it's a test question. There ARE questions like this to get a license, aren't there?
    Romeo and Atlanta, MI

  9. #9
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by guy48065 View Post
    Do I consider myself schooled? Sure--if we're in about the 4th grade. C'mon you guys can provide more insight than this
    A fourth grade question gets a fourth grade answer.

    You say nothing about what pump you have, stats on the well, etc. If you override the pressure switch until the pressure max's out, it could get high enough to rupture the pipe or tank.

  10. #10
    Moderator valveman's Avatar
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    Everybody is giving you good answers. It is not a volume problem. If the water level is low enough and/or the pressure switch is adjusted too high, the pump may not be able to reach that pressure and will be destroyed from deadheading.

    If the water level is high and the pump can build lots of pressure, blocking off the pressure relief could send your tank through the roof like a rocket.

    And it doesn't use more electricity to produce higher pressure, unless you install a larger HP pump to do so. As a matter of fact, the higher the pressure the less the amp draw will be. It is counter-intuitive. The higher the pressure, the lower the volume, and the lower the amp draw.

    Let us know the pump model number and the depth to water in the well and we can tell you how high you can turn up the pressure switch.

    You never said what you are trying to accomplish, but I am guessing you want better pressure in the house. You don’t usually have to increase the pressure switch setting to get higher pressure in the house. Even if you increase from 30/50 to 40/60, the pressure will still be at 40 PSI a lot of the time, which is why the pressure seems low. If you hold the pressure at a constant 50 PSI, it will seem like you greatly increased the pressure setting. A constant 50 PSI is much stronger in the shower than an average 50 PSI that happens when the pump is continually cycling on and off between 40 and 60.
    Last edited by valveman; 11-20-2013 at 12:27 PM.

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    DIY Senior Member guy48065's Avatar
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    Actually it was your product and Youtube videos that spurred me to ask the question. If a CSV can be adjusted to maintain a 50psi flow is there any reason it can't manage 60?

    My question is in general (and sorry about the bypassed switch thing--it really muddied the water so I didn't get the pressure question answered). I have 2 houses--one with a submersible pump in 130' well (don't know the water depth), and a shallow well pump on a 35' well with water at 20'. On either I wouldn't be foolish enough to hold the switch until something blows up--I just want to see if I can get 10psi more and still have enough margin so I never run into a problem with a weakening pump that burns itself out because it can't open the switch.
    Neither system has a PRV.

    So in the end I really still don't know why a well guy would choose a 30/50 setting if the pump is capable of 100psi (just examples--don't shoot me).
    Romeo and Atlanta, MI

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    Test, Don't Guess! cacher_chick's Avatar
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    I'm no expert on the subject, but anytime the pressure is increased there has to be increased wear on the thrust bearings of the pump and/or motor. If the pump/motor or piping system is already on it's last legs, increasing the pressure might be enough to finish it off.

  13. #13
    Moderator valveman's Avatar
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    Increasing backpressure does not increase wear on the thrust or radial bearings. The thrust bearing is a Kingsbury type, frictionless bearing. The thrust bearing and the radial bearings in the pump are water lubricated and cooled. As long as there is sufficient RPM, there is a film of water between the shoes and plate. It is a hydroplaning effect that only happens when the RPM gets above 50% of full speed. So it is the starting of the pump, when there is no water between the plates that causes wear. When the pump is up and running, the film of water eliminates wear between the plate and shoes.

    Since water is not compressible, this film of water stays in place even when the load on the thrust bearing increases. So increasing the load does not increase wear on the bearings. It is just the opposite of what you might think. Increasing backpressure will decrease the flow rate. Decreasing the flow rate will decrease the amp draw. Decreasing the amp draw will decrease the heat produced. Decreasing the heat produced will decrease the wear on the motor.

    It is only during that split second when the pump is first started and there is no film of water in the bearings that wear occurs. So the fewer times the pump starts, the longer it will last.


    Sorry, back to the question. Yes you can hold down the pressure switch until the pressure comes up 10 PSI. Then you can adjust the pressure switch as such. But later if the water level in the well drops, the pump may not be able to build enough pressure to shut itself off. So you need to make sure the pump can build enough pressure to shut itself off at the pump setting or the lowest level you will see in the well.

  14. #14
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by valveman View Post
    And it does use more electricity to produce higher pressure, unless you install a larger HP pump to do so. As a matter of fact, the higher the pressure the less the amp draw will be. It is counter-intuitive. The higher the pressure, the lower the volume, and the lower the amp draw...
    Did you mean to write doesn't?

    There is an economy curve that equates to a higher cost per gallon.

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by guy48065 View Post
    ...and a shallow well pump on a 35' well with water at 20'.
    That one stands a greater chance of deadheading. Static water levels in a shallow well often have a higher propensity to change and jet pumps have much less total head.

    As for the deep well, the static level, model of pump, and depth it is set at will factor on what margin of safety you may need.

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