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Old 11-29-2007, 08:49 AM   #1
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Flow not Pressure problem???


I'm on a well. The pressure is well above 35. I currently have copper (schedule M) but am going to replumb to Pex (separate issue) because my water is aggressive and I'm getting pitting and pin hole leaks.

I'm hoping the replumb with a homerun system will also help my flow problem. When I currently flush the toilet with only the hot water running in the bathroom, I notice about a 50% decrease in the flow with no other water use in the house! Why would I see any change in the hot water flow when I flush the toilet???

What exactly causes and cures a flow problem?

Thanks
Don

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Old 11-29-2007, 09:44 AM   #2
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Flow not Pressure problem???


The flow of hot water is detemined by the pressure at heater's outlet. And pressure at outlet is detemine by pressure at inlet. In other words, hot water is pushed out at about the same rate as cold water is pushed in. Toilet fill valve is a full-bore thing, so when tank is refilling, it can drop the pressure throughout the system by quite a bit. In an ~80psi setup, this drop is not enough to reduce flow to other fixtures, but in your case it is. Moving to PEX is not going to cure it.

What you need is pressure booster

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Old 11-29-2007, 09:53 AM   #3
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Flow not Pressure problem???


It might also help to turn down the supply valve into the toilet. It'll take an extra minute to cycle, but it won't rob your other supplies quite so much.
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Old 11-29-2007, 10:04 AM   #4
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Flow not Pressure problem???


The hot water supply is controlled by the cold water inlet pressure. It sounds like you have a bad main feed line supplying the fixtures. Perhaps a 1/2" mainline with 1/2" takeoffs to each fixture, including the water heater. I like to run at least 3/4" mainline and then use 1/2" for the takeoffs. The fixtures are then reduced further by 3/8" supply valves. When any fixture is supplied by the same size pipe as the main feed line, the pressure will drop when a fixture is used.
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Old 11-29-2007, 10:14 AM   #5
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Flow not Pressure problem???


Quote:
Originally Posted by majakdragon View Post
The hot water supply is controlled by the cold water inlet pressure. It sounds like you have a bad main feed line supplying the fixtures. Perhaps a 1/2" mainline with 1/2" takeoffs to each fixture, including the water heater. I like to run at least 3/4" mainline and then use 1/2" for the takeoffs. The fixtures are then reduced further by 3/8" supply valves. When any fixture is supplied by the same size pipe as the main feed line, the pressure will drop when a fixture is used.
I have a 3/4" main line- The "takeoff" is 1/2"- so I don't think that is the problem.
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Old 11-29-2007, 05:53 PM   #6
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Flow not Pressure problem???


How big is the house? I've seen four story mansions plumbed in 3/4 galv. and they wonder why they aren't getting pressure in their new bathroom with two shower heads, four body sprays and a hand held.

Do you have any old gate valves? I've seen them clog or fail reducing volume and in some cases cutting off flow completely.

35lbs is pretty low pressure too.

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