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# Low Water Pressure

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• #272932
MasterPlumbers
Keymaster

In the process of buying a home and home inspection revealed low water pressure (about 1 1/2 gallons a minute at outside faucets). The home owner stated he got a bid from a plumber for a booster system, but would only guarantee 5GPM. System is part of a shared community well (10-20 houses) and the booster pump to be installed in basement.

Question is, what can I reasonably expect for water flow, and what components make up an ideal setup to fix this problem?

Thanks

• #286568
SylvanLMP
Participant

Actually all you need is enough pressure to reach the top floor fixture plus 15-25 PSI.

To get a rough idea of the pressure you need all you have to do is measure from your top floor fixture to your water main piping and times this by the constant .434 height, this will give you a no flow hydrostatic pressure.

For example if we assume your top floor is 25 ft above the water main you would get a no flow reading of 10.85 pounds BUT to have any pressure we would add another 30 to 40 pounds to over come friction losses of piping and fittings.

To convert pressure to feet all you do is take 2.31 the pressure (figure 50 PSI in this case) 50 2.31 = 165.55 feet BUT we must then take off the friction loss factor and the actual PSI demand of the fixture to operate properly (like a flushometer requires a min of 25 PSI)

The problems associated with too much pressure is erosion and hydraulic shock waves BOTH are detrimental to plumbing systems (especially on hot water) and who wants to hear their plumbing make unnecessary noises?

Ideally you want a flow rate of about 6 FPS based on piping and pressure.The GPM rate is governed not only by pressure available BUT the internal diameter of your piping

If you get just your building height from the main and contact any 2nd or 3rd year plumbing apprentice they can give you an exact pressure requirement.

This may seem more complicated than it is. Like I stated any United Association apprentice could rattle off formulas all day long relating to plumbing and piping lay outs and they would be more than happy to help you with your friction loss calculations Try this site http://www.masterplumbers.com/plumbing/plumbviews/watersupply.html

Good luck

SylvanLMP
[Edited by SylvanLMP on 10 May 2000]