Just replaced last 120 feet of home water supply line. Old line was 1" galvanized, new line is 3/4" PEX. Lines are six feet underground here in our mountain location and must feed upstairs bathroom along with the usual downstairs fixtures. Most lines under house are 1/2" copper. Have experienced unacceptable pressure loss with new 3/4" line. Now is time to fix as haven't covered trench yet. Do I need to go back to 1" line and if so will 1" PEX give us our previous pressure? Prior to new line, pressure was always very good. Water supply is from spring 1/2 mile above house, gravity supplies pressure with 2" poly pipe main line from spring.
Plumbing – pressure loss going from 1“ supply to 3/4” supply to home, 120 feet length
plumbing
Related Solutions
It's a trick question, you can never get 4 bar of pressure with only a 20 m head.
The pressure due to a vertical column of liquid is equal to the density x height of the column x the acceleration due to gravity (little g = 9.8 m/s2).
Your height is 20m
Density of water is 1000 kg/m3
g = 9.8
So, pressure is 196,000 Pascals
100,000 Pascal per bar, so you have 1.96 bar as the max pressure you could get, independent of flow rate or pipe size.
The Pressure gauge reading cycles between the pump cut-in and cut-out pressures. Sounds like the gauge is dead and permanently stuck at 24psi.
Often, the cut-in and cut-out pressures will be listed on the pressure switch and commonly are 20psi cut-in and 40psi cut-out. So your water pressure on the gauge will cycle between 20 and 40psi during water usage.
The tank has a built-in bladder that is pre-charged to 30psi when your gauge reading is 0psi (pump breaker turned off, water tank drained). There should be a faucet somewhere on the pump manifold system that allows you to drain the pressure tank of water so you can check the bladder air pressure.
To repair the gauge, I would switch the power to the pump off, drain the tank and simultaneously, replace the gauge and check the bladder pressure and top it off if needed. Then power the pump back up.
If there is a lever on the side of the pressure switch (image below), it is a low pressure cutout to prevent the pump from operating if the well runs dry. Pull it up till the pump turns on and hold till the pump stays on (about 10-15psi). With no low pressure cutout, just power the pump on and it will automatically do the rest.
Once you have a working gauge, you can start to determine whether it is a pump pressure supply issue, or if you have something more serious like a restriction in the house supply line or a leak.
Do you have any sort of sedimentation filter in your water system? Sounds like it may have clogged and if a screen, needs flushed or replaced if it's one of those string filters.
Related Topic
- Plumbing – Low water pressure in both kitchen lines –
- Plumbing – Pex Plumbing System w/ Manifold (Entire House)
- Plumbing – Can a new water heater cause a Aquatherm heating system to fail
- Plumbing – install water filters in parallel to abate pressure loss
- Plumbing – Should this section of water line be replaced
- Plumbing – What causes this brown discoloration in residential water supply
- Plumbing – Is a bleeder-valve to let air into the water line necessary when the plumber put in a frost-free valve? Should a bleeder-valve leak if kept open
Best Answer
As you now realize, going from 1" steel pipe to 3/4" PEX is a big step down. 1" steel pipe has an actual ID of 1.05" and 3/4" PEX has an actual ID of 0.68". At a flow of 8 gallons per minute, the pressure loss for 1" steel is 1.9 PSI/100' and the pressure loss for 3/4" PEX at that flow is 12.3 PSI/100'. What you did was the equivalent of stepping down approximately two sizes.
1" PEX will still give less than your previous pipe but it might be acceptable. The pressure loss of 1" PEX at 8 GPM is 4.2 PSI/100' and the pressure loss of 1-1/4" PEX at 8 GPM is 1.6 PSI/100'. You will have to decide what you want as far as price vs. performance.
EDIT: You might consider if another material would be suitable, such as 1" SCH 40 PVC. 1" SCH 40 PVC has losses similar to 1" galvanized.