What are the trade-offs in setting pump pressure?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by guy48065, Nov 19, 2013.

  1. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    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.
  2. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    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.
  3. Reach4

    Reach4 Active Member

    Messages:
    2,303
    Location:
    IL
    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.
  4. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    My "test" assumes you would close the main valve so as to not stress anything downstream.
  5. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,004
    Location:
    NW Ontario, Canada
    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.
  6. craigpump

    craigpump Member

    Messages:
    950
    Location:
    ct
    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.
  7. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    That's a volume issue.
    Last edited: Nov 19, 2013
  8. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    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?
  9. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,004
    Location:
    NW Ontario, Canada
    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. valveman

    valveman Moderator Staff Member

    Messages:
    4,473
    Location:
    Lubbock, Texas
    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: Nov 20, 2013
  11. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    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).
  12. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,248
    Location:
    Land of Cheese
    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. valveman

    valveman Moderator Staff Member

    Messages:
    4,473
    Location:
    Lubbock, Texas
    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. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,004
    Location:
    NW Ontario, Canada
    Did you mean to write doesn't?

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

    LLigetfa DIYer, not in the trades

    Messages:
    4,004
    Location:
    NW Ontario, Canada
    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.
  16. Reach4

    Reach4 Active Member

    Messages:
    2,303
    Location:
    IL
    A higher head/pressure will take more power to move a given amount of water.
  17. valveman

    valveman Moderator Staff Member

    Messages:
    4,473
    Location:
    Lubbock, Texas
    The difference in energy use per gallon produced between 30/50 and 40/60 is negligible. The pump will have to run slightly longer at 40/60 to produce the same amount of water produced at 30/50. But while it is running longer, it is drawing less amperage and running cooler.

    Thanks LL, Yes “doesn’t” and now it has been corrected.
  18. Reach4

    Reach4 Active Member

    Messages:
    2,303
    Location:
    IL
    A pump in a basement pumping to a second floor might be set to a higher pressure to compensate for the pressure loss with height.
    Last edited: Nov 20, 2013
  19. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Strictly on a dollars-per-gallon basis, you go with lower pressures and make do with it. For as much as I liked the effect of steamy hot water blowing from a shower head of 50 years ago with 90 psi behind it, a massaging shower head of today works on half the pressure and half the flow. Technology at work.
  20. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    "Make do" aint getting it. Is this what you tell customers?
    I do miss the forceful showers when I was on city water but now running 30/50 no matter what fancy shower head I try I feel like I'm being peed on in the upstairs shower. Amazing how 8 more feet of lift can kill the pressure.
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