Diagnosing water pressure issue

Discussion in 'Pumps and Tanks Well Forum & Blog' started by MCO_970, Jul 22, 2008.

  1. MCO_970

    MCO_970 New Member

    Messages:
    4
    Hi,

    I'm a new member who has been browsing your site to learn about well issues. I am trying to determine if the water pressure problem we have is the pump or the waterlines, so please bear with me.

    We have a 3' deep well on a spring with a 3/4 HP Jacuzzi jet pump. The well is about 500' from our house, and it also feeds the neighbor's house (she's about 800' from the well). The line is 50+ year old galvanized pipe, probably 1". The line goes up a hill (~40' lift) then it flattens out as it goes toward the house - so maybe 50' of lift max.

    We have a pressure tank at the house with a booster pump - I just figured out that it it runs way too much (kicks on about every 15 seconds when water is used).

    The outside irrigation water pressure, which is not boosted, is really bad. Anytime someone turns on water anywhere, the pressure drops to zero and a single sprinkler will barely function. The standing pressure on that line is about 20#, and it's the same on all the irrigation spigots. If I run one low-flow sprinkler, the standing pressure will drop to about 12-15#.

    So I went down the hill and looked at the pump. It shows pressure at all times from 55# to 70#. It does not cut on very often. The pump is, however, about 10 years old. I am going to have it checked soon just in-case. There is a big Well X-trol pressure tank at the pump.

    I considered insufficient supply, but even during our worst drought, the well level never dropped more than 12" despite the area water table falling pretty low. And that was with my neighbor watering her lawn 24x7 :mad:

    I am thinking the problem is the 50+ year old galvanized water lines, and that the booster pump is spending too much time trying to suck water though blocked lines. And the irrigation pressure falls to zero because there is insufficient flow to the house. Is this correct? Is there anything else I can do to diagnose the problem before I spend all my dough on a new waterline?

    Thanks!
    Michelle

    (who used to live on Union Hill in Redmond :) when I worked for the Empire)
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,522
    Location:
    Lubbock, Texas
    You can push a lot of water through a small and corroded water line, if your pump will delivr enough pressure. Changing the water line will not help with static pressure, which is pressure when there is no flow. Larger and smoother water lines will help reduce friction loss when there is water flowing. 20 PSI at static and 12 PSI with one sprinkler running tells me there is 8 PSI of friction loss in that pipe, even with just about 2 GPM flow.

    I would replace the pump. Maybe go with a submersible that could be set at 80/100. This will give you 30 PSI more static pressure. Then if the pressure falls too low when running sprinklers or using water, you may still want to install new and larger lines. New lines first, will only give you 8 PSI more during use, and no extra pressure when static.
  3. MCO_970

    MCO_970 New Member

    Messages:
    4
    A few more questions -

    Can I temporarily increase the pressure that my current pump delivers to test how much pressure I can gain during use? I know how to do it, but is it OK to do it?

    Can a submersible be installed in a 3' deep well?

    Will the added pressure possibly damage the old crufty water lines?

    There is an unoccupied mobile home at the top of the hill, 200' from the well. I thought about checking the static pressure there (I'd have to crawl under it and turn on the water). If the pressure is OK there, could I replace the line from my house to there, AND replace the pump to get things in spectacular working order? That would be the easy section of line to replace, as it's flat from there to my house.

    Thx,
    Michelle
  4. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Something doesn't fit.

    Fifty ft of elevation accounts for about 22 psi loss of pressure so the static pressure when the tank is at 55 should be 33 psi. It would be lower if your neighbor is drawing water; especially with a booster pump.

    The easiest way to solve the problem would be to put a pressure tank at your place with the booster pump set to maintain the pressure. You would have a check valve in your system so it doesn't back-flow to the place farther along when the pressure drops in the line.

    I would put a tank of at least 40 gallons actual volume at your place and set the pressure switch to shut off at 60 psi with the minimum differential on the switch so it would operate from about 48 to 60 psi. You would still get good service with pressure down to 35 psi.

    The air precharge should be at the lowest pressure that you want for your household use, so if that is 35 psi that is what the air precharge should be.

    The tank will not help for irrigation flows but if you take them off the boosted pressure you can probably get reasonable flow.

    The setup will put you at some advantage over your higher/farther neighbor because you will be taking water first and reducing the pressure up the line.

    Based on your description of the problem I suspect that your neighbor is using a boosted system for irrigation.

    Do not get one of those switches that must be reset if pressure drops too low because if your neighbor is drawing water the booster pump may occasionally fail to keep up.

    The situation at the well seems to be OK. If the pump can reliably deliver higher pressure it could be increased, keeping the differential at the minimum value for the pressure switch.

    Are you the controller of the well and pump system? When two people are using the same well you should have water meters so you can sort out who is abusing the system. You can get rebuilt 5/8" water meters with brass adapter couplings for less than $60 each.
  5. MCO_970

    MCO_970 New Member

    Messages:
    4
    Just to follow up...

    We tweaked the well pressure last night and only had to bump it up a few # to get the system working better.

    We also found out that the lateral line under the house that feeds the sprinkler spigot is an old black iron pipe and had major corrosion. So my tests at that lateral made the system look worse than it was... Anywhere else that I tested the static pressure when the sprinklers were running had OK (20#) pressure, versus the pressure being cut in half on the bad lateral line.

    Between bypassing the bad lateral and bumping the pressure, it's working much better. I am still going to price a submersible pump and my brother can put in a new water line for me (better just do it while his backhoe is working!).
  6. MCO_970

    MCO_970 New Member

    Messages:
    4
    pps. we do have a pressure tank in our house, neighbor does not. Somewhere we are still losing a lot of pressure.

    Side story - our really dumb previous neighbor had a line freeze and asked to attach a new water line from her house onto our spigot near her house. They were short on parts and didn't want to drive to town, and asked us for a nipple. All we had on hand was a 3/8", and they used that to kludge their main water line! We told them it was a bad idea, but they thought it would be OK. So the current neighbor has really poor water pressure - but she is supposed to be installing her own domestic well one of these days.

    I did check at the empty house atop the hill (200' from the well) and the pressure is about 22# - a tiny bit more static pressure than at the house. We turned on a sprinkler at my house, and the pressure at the empty house stayed at about 20#.

    My brother pointed out to me that the gauge on well pump might be damaged and not reading right. That would be one possibility.

    We checked the pressure tank at the well and it's got 40#.

    It will be interesting to replace the line running down the hill and see how much that helps. If it's badly corroded, couldn't it create more line friction and loss than the charts show?
  7. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    It isn't static pressure when ANYTHING is running. Static means stopped, not moving.

    Check the pressure when no water is being withdrawn from the pipe, anywhere at your place or at the neighbor's place, and no booster pumps running. Compare that to the pressure at the pump house. That gives you the difference caused by differences in elevation.

    Then, when you are running water the difference between the pump-house pressure and the pressure at your place is the total loss due to elevation AND flow. That is used to determine the line loss which depends on condition and size of the pipe and the flow (GPM). Each doubling of the flow will increase the pressure loss by a multiple of about 3.6, so quadrupling the flow will increase the pressure loss by a factor of about 13.

    Example:

    1. With all water off and pressure at the well = 55 psi, and pressure at your house 33 psi. The difference is 22 psi. That is the static pressure difference due to the difference in elevation.

    2. With water flowing through your irrigation system or a hose, but the booster pump not running, measure the flow (GPM) and the pressure somewhere in the pipe at the house.
    If the pump-house pressure = 50 psi, and the measured pressure = 20 psi, and the flow = 3 GPM:
    Total pressure loss = 50 - 20 = 30 psi
    Pressure loss due to flow = 30 psi - 22 psi static difference = 8 psi at 3 GPM.
    If that is for 500 ft of steel pipe that is the equivalent of a pipe smaller than 3/4" and larger than 1/2". A new 1" pipe, 500 ft long, would have less than 2 psi loss due to flow at 3 GPM.

    If you want less than 5 psi loss due to flow at 10 GPM you should install 1 1/4" poly pipe. If you are digging a trench the larger pipe is negligable cost.
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