• Please be sure to read the rules and adhere to them. Some banned members have complained that they are not spammers. But they spammed us. Some even tried to redirect our members to other forums. Duh. Be smart. Read the rules and adhere to them and we will all get along just fine. Cheers. :beer: Link to the rules: https://www.forumsforums.com/threads/forum-rules-info.2974/

Pressure drop after moving main feed?

T

Trav4011

New member
Hey,

Trying to figure out if I screwed up. I have an old single story house that has copper in the slab. 1" main running to 3/4" copper going into the slab. 3/4" copper with 1/2" branches in the main wet wall going back down into the slab and all over the house. One 3/4 from the main that goes up to the attic to the water heater, then back down to feed branches in the same wall going all over the house.

During the remodel, that wall had to go. I slowly ran new PEX-B overhead and ran drops to all of my faucets. Well, the last step was to re-run the main. I disconnected at the slab outside, bored a hole into my bricks, and ran a 1" pipe inside, then 90'd up the wall going back to 3/4" PEX-B. From there, it's 1/2" drops to each faucet.

Well, I noticed immediately that when I open a faucet, the pressure and flow is fine, but it drops down to about 75% of its normal flow after a few seconds. Turning on multiple faucets makes it drop as much as 50%. Didn't have this issue before the re-plumb. Is the 9 foot vertical rise an issue going up the wall? Can this be fixed with larger pipe and bigger manifolds? Or am I looking at having to find a way to keep the main and feeds close to ground level?

Thanks for any any advice!
 
This is my 1" PEX-B main feed coming in, then going down to 3/4" PEX-B. Excuse the temporary Skarkbite fitting. It feeds the old hose barb outside until I can get a new one and convert to PEX.
 

Attachments

  • 20250428_204150.jpg
    20250428_204150.jpg
    1.1 MB · Views: 4
waybomb said:
I assume you installed a new valve or valves. Did you use full port valves?
Click to expand...
I replaced the ones inside with the same style. The one outside near the meter is the same one (full port). Everything ran on the old copper feed temporarily as I was remodeling. I just recently replaced the water main feed overhead so I could tear out the last wall. So, everything was working fine until I moved the main up the wall 9 feet and into the attic.
 
This is classic.
I am willing to suggest the drop to 3/4" feeding across the top is restricting flow.
It should remain at 1.0". At 3/4" you have only 75% of flow over 1.0"
Diameter restricts, flow not pressure. Fine in static mode, no faucets running. But, in active mode, restricted flow will lower pressure.
 
FrancSevin said:
This is classic.
I am willing to suggest the drop to 3/4" feeding across the top is restricting flow.
It should remain at 1.0". At 3/4" you have only 75% of flow over 1.0"
Diameter restricts, flow not pressure. Fine in static mode, no faucets running. But, in active mode, restricted flow will lower pressure.
Click to expand...
So I assume that the 9 foot rise brought this on? (Since the issue wasn't there when the main was at ground level with a 3/4" pipe in the slab) I can increase the size to 1" up to the attic. I can probably go 1.25" if I really wanted to. Once on the attic, should I split that into (2) 1" manifolds with (4) half inch drops down to each faucet? I have the water heater, 2 showers, 1 bathtub, 3 vanities, 1 kitchen sink, dishwasher, washing machine, and 2 outdoor faucets.
 
Trav4011 said:
So I assume that the 9 foot rise brought this on? (Since the issue wasn't there when the main was at ground level with a 3/4" pipe in the slab) I can increase the size to 1" up to the attic. I can probably go 1.25" if I really wanted to. Once on the attic, should I split that into (2) 1" manifolds with (4) half inch drops down to each faucet? I have the water heater, 2 showers, 1 bathtub, 3 vanities, 1 kitchen sink, dishwasher, washing machine, and 2 outdoor faucets.
Click to expand...
First, the 9 foot rise is unlikely the problem. The water pressure from the utility is more than adequate.
1.0" should be enough. Also your idea to create a two-line manifold will also improve flow. Here's a tip. Connect both lines at the end creating a complete oval loop. You will be amazed at the improvement of flow. And therefore pressure.
 
FrancSevin said:
First, the 9 foot rise is unlikely the problem. The water pressure from the utility is more than adequate.
1.0" should be enough. Also your idea to create a two-line manifold will also improve flow. Here's a tip. Connect both lines at the end creating a complete oval loop. You will be amazed at the improvement of flow. And therefore pressure.
Click to expand...
I appreciate the tips! I'm a metal fabricator by trade.. If I'm constructing my own manifolds, what material is best? Food grade stainless? I have the ability to do sanitary welds. So, 1" feed, split with a Tee to dual 1" manifolds, 1/2" drops, and then loop the ends around to each other?
 
Trav4011 said:
I appreciate the tips! I'm a metal fabricator by trade.. If I'm constructing my own manifolds, what material is best? Food grade stainless? I have the ability to do sanitary welds. So, 1" feed, split with a Tee to dual 1" manifolds, 1/2" drops, and then loop the ends around to each other?
Click to expand...
Copper pipe is fine but SS steel? Have at it.

You do understand that by closing the ends to a loop the water will flow both ways depending on what valves are open. This could actually work using the existing line and just adding to it. Your problem is that each outlet "thief's" off some of the water. Each time allowing less to proceed to the next outlet. A loop allows it to flow from either source.

That said, 1.0" should suffice.

I have done a system where all the lines came to one loop barely 8X4 feet in size. 1.0 " in diameter copper pipe. Flawless.
 
FrancSevin said:
Copper pipe is fine but SS steel? Have at it.

You do understand that by closing the ends to a loop the water will flow both ways depending on what valves are open. This could actually work using the existing line and just adding to it. Your problem is that each outlet "thief's" off some of the water. Each time allowing less to proceed to the next outlet. A loop allows it to flow from either source.

That said, 1.0" should suffice.

I have done a system where all the lines came to one loop barely 8X4 feet in size. 1.0 " in diameter copper pipe. Flawless.
Click to expand...
So, I dug further back, and the PVC pipe from the main is actually 1.5". About a 50 foot run (same elevation). 3 feet before the house, it necks down to 1" PVC, then they had it reduced again to 3/4" copper going into the slab. Not sure why it was done like this.

If I tee into the exist 1" or 1.5" at ground level and run a second 3/4" per line up parallel with the first one I ran up, would that be enough? Run manifolds on each, and loop them? So, 1.5 or 1" PVC split at ground level to dual 3/4" parallel PEX, each into a 4 port manifold, then loop the back ends of the 3 manifolds together with 1" or so?
 
waybomb said:
I believe a 1" pipe will flow almost twice as much as 3/4. Or 3/4 about 50% of 1".
Click to expand...
So ditch the single 3/4" and go with dual 1" on the vertical run? Or would dual 3/4" work? I have 1.5" PVC underground up until 3 feet from the house, where they necked it down to 1" PVC. So, my options are pretty wide open.
 
Is there any chance you kinked off a piece of your new install? If the only thing different is your vertical pipe and everything has been kept the same size it shouldn't have reduced your flow.

You guys run 1 inch water lines in your house? Standard here is 1/2 inch, some newer buildings have 3/4. How much water do you use that you need a 1 inch line??
 
Actually, I don't think the diameter of the line is the problem. The problem is having all the tee offs in series and on one line.
As water passes each Tee off, it thieves' water for the next valve. Pressure remains high in a closed system if it has enough diameter to flow. 1.0"should be enough. 1.5"would certainly suffice.
 
You must log in or register to reply here.
Top