11

The problem

I just ran a 650 foot 1-1/4 inch pipe from my water source, up a hill, where the rise is about 35 ft. I expected some water pressure loss, but I have much more loss than I was expecting. This water line will eventually run into a residential home.

I don't have the water pressure exact numbers, but at the bottom of the hill the water company says they are about at 55-60psi. At the top of the hill, I can place my hand over the hose and stop the water. It barely trickles out of a hose. I put a pressure reader on it, and it didn't move. I'm not sure if there's 0-1 psi, or if what I bought is broke, but either way it's very small.

Possible solutions and their issues

  1. I can get a more direct pipe to make it shorter. I could go from 650 ft to about 450 ft, but with how low the pressure is now, I don't know how much that would help.
  2. I've looked into getting a pump at the bottom of the hill, but at the moment, I can't get power down there.
  3. I know there are systems to pressurize the water once it's in the house lines, but that doesn't help now.
  4. We do have power at the top of the hill, so I could put a pump up here, to pump up the hill, but I've read that's not a great idea past 20ft in elevation.
  5. I talked to the water authority and they said most people in the area that have this issue just put a tank up the hill. I'm not sure if he means a separate tank so the water comes from the same level as the house, or if he meant something else.

What are some other options I'm not thinking of?

1
  • 2
    Put a pressure gauge on the supply: easy done then you will know if you start with 55psi.
    – Solar Mike
    Apr 11, 2023 at 7:57

4 Answers 4

18

If there's 55 PSI at the bottom of a 35 foot rise, and no pressure at the top, there's got to be a leak between those points, or the height is (much) greater than guessimated, or the pressure is (much) lower.

55PSI is 126.898 feet of head. 35 feet of head is 15.169 PSI.

If there isn't something very close to 40PSI at the top of the hill with no flow, there's a leak between the top and the bottom, or the numbers are very much not as stated.

With zero flow, any length and diameter of pipe, there should be 40 PSI. With 10 gallons per minute in 650 feet of 1.25" plastic (smooth) pipe, there should be 33PSI. 5 GPM / 38 PSI. It's not the length of the pipe causing the problem. Should do 25 gallons per minute at 3.5 PSI, or 26.3 GPM at no pressure (open pipe)

2
  • 2
    Thanks, I'm going to test the PSI at the bottom, as that's where I think the mistake is. When I asked the water authority in my area how they measured the pressure at the bottom, the tech I talked to said he "eyeballed it". That's ludicrous of course, but it does look like a decent amount of water coming out. But thank you for your excellent answer. Apr 11, 2023 at 1:38
  • 9
    @trueCamelType - Measure the water pressure at the bottom with all flow closed off. You want to measure the static water pressure there.
    – Michael Karas
    Apr 11, 2023 at 3:17
13

I believe the idea of the tank at the top of the hill is that you feed the low pressure water line into the tank via an automatic shutoff valve. The automatic valve is designed to sense the water level in the tank and shut off the incoming water flow when the tank is full. The concept is that the incoming water flow is larger than the outtake usage over the average. The tank needs to be large enough to supply immediate needs and yet still fill from the low pressure line between the bursts of immediate needs.

If the pressure drop is mostly due to the dynamic pressure loss in the pipe when water is flowing then it could very well be a benefit to work with a larger diameter pipe. The larger diameter pipe will provide greater flow rate at the low pressure making it take less time to keep the tank full.

If the pressure drop is caused by the altitude difference then you are going to have little choice but to put a pump at the bottom of the hill to push the water up the 35 feet altitude difference. This would operate very similar to how a pump is placed at the bottom of a well to bring water up out of the earth.

The chart below will go a good ways toward showing what part of the basic problem is here. Consider your uphill pipe as an equivalent of a 35 feet high water column. The chart shows that the pressure of such column, as produced by gravity on the water, at the bottom will be in excess of 14.2 psi. This means that you immediately lose 15 to 16 psi just to overcome the static pressure caused by the water in the pipe.

enter image description here

Picture Source

2
  • Thank you, this makes sense. I think they're wrong about how much pressure is at the bottom, but it doesn't seem so low at the bottom that I should be at nearly 0. I will say, that the flow seems heavy at the top with just a 1-1/4 pipe, but when I reduce it to a 3/4 at the top it almost seems to stop any flow. The 3/4 at the top is only like 4 feet at this point, so it can't be an issue with the pipe. Apr 11, 2023 at 1:43
  • "automatic shutoff valve" -- think toilet tank...
    – arne
    Apr 13, 2023 at 6:37
10

Check for air locks.

If the pipe goes up and down repeatedly, there can be air trapped in each “hill” that reduces the pressure.

To Test

If the line is still accessible you can pick up the pipe at a hill section and shake it to hear a sloshing sound, and feel the pipe is lighter.

Fixing

Rearrange the pipe route so the pipe constantly rises.

Temporary checks

If convenient you can pump to force the air out temporarily. But gases will tend to accumulate again.

Also, you can start at the source and walk to the top, lifting a section of pipe as you go. Effectively, walking along with the pipe over your shoulder.

I have spent many hours doing this for newly installed gravity fed irrigation pipe; as the cold water warms in the pipe, the gases come out of solution, and if the flow rate is not high enough the gases accumulate and the flow stops.

6

So the tank idea is simple.

You put a tank above your property at just below the limit of head available. Then the supply has 24hrs to fill the tank per day.

The idea is that you size this to use less than that. The height of the tank above your property gives the constant head for your house supply.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.