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Old 08-14-2009, 09:36 AM   #1
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Water Pressure Question


HI,

I have 2 hose bibs outside my house, 1 up front, 1 in back. The one up front is reduced from 3/4" to 1/2" just as it connects to the hose bib,this one is also close to the meter, and does not make lots of 90's between where the water comes in and where it connect to the bib. This one has a lot of water volume / pressure.

All of my pipes are copper.

The one on the back of my house, is run on 1/2". It makes a number of 90's and travels 60' in the house before it gets to the hose bib. This hose bib has much lower volume / pressure than the front one.

So basically does the one up front have more volume / pressure because it is reduced down to 1/2" just as it connects to the hose bib? And the one in the back is 1/2" for quite a distance?

It just gets a bit confusing to me if both hose bib's are 1/2" themselves, then why does the size of the pipe to connects to that matter? Does the water pressure get slowed down / reduced by the number of elbows and the 3/4" helps compensate for this?

If I want the additional pressure in back, Would my only solution be to rip out the 1/2" and run new 3/4" all the way out there?

Thanks

Jamie

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Old 08-14-2009, 09:48 AM   #2
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Jamie, your pressure is the same throughout the house regardless of the pipe size. What differs is the actual volume of water passing through the pipes and fixtures.

There's a possibility that your pipe could be somehow obstructed due to corrosion, reducing the volume greatly downstream of the obstruction. I'd rule out the hose bib itself first, and then start replacing plumbing from there. Less bends is good but probably won't make or break you. Running 3/4" to a 1/2" hose bib isn't going to do much...The 1/2" pipe will only allow a certain amount of volume through at the given pressure of your home's water supply.

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Old 08-14-2009, 09:51 AM   #3
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You're good at electrical, look at it this way:

Your water pressure is voltage...The same way the 110v is a constant in a circuit in your house.

Your water flow is amperage...The amount of water that is being called for by the valve is what is being delivered.
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Old 08-14-2009, 10:08 AM   #4
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Quote:
Originally Posted by thekctermite View Post
Jamie, your pressure is the same throughout the house regardless of the pipe size. What differs is the actual volume of water passing through the pipes and fixtures.

There's a possibility that your pipe could be somehow obstructed due to corrosion, reducing the volume greatly downstream of the obstruction. I'd rule out the hose bib itself first, and then start replacing plumbing from there. Less bends is good but probably won't make or break you. Running 3/4" to a 1/2" hose bib isn't going to do much...The 1/2" pipe will only allow a certain amount of volume through at the given pressure of your home's water supply.
Thank you. So I have just a volume problem, not a pressure problem. There is a S/O just inside the house from this hose bib, but likely has not been turned in many years. I tried to turn it, but it was pretty stuck. It's within feet of my electrical panels, so I will need to cover them with plastic before I mess further with that valve or the bib.

Thanks very much for the information and sending me in the right direction.

Jamie
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Old 08-14-2009, 08:48 PM   #5
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Water Pressure Question


http://www.engineeringtoolbox.com/da...ion-d_646.html
The fitting losses may be somewhere else on this site.

Quote:
Originally Posted by jamiedolan View Post
I have 2 hose bibs outside my house, 1 up front
This one has a lot of water volume / pressure.

The one on the back of my house, is run on 1/2".
This hose bib has much lower volume / pressure than the front one.

If I want the additional pressure in back, Would my only solution be to rip out the 1/2" and run new 3/4" all the way out there?
If you have a pressure meter (voltmeter) and a flow meter (ammeter) and you hook up each at several different points along the way from front to back you can find the point of high resistance (possibly due to an obstruction).

Water is incompressible so the GPM in must equal the GPM out, just like total amps in must equal total amps out.

I've done this analysis/measurement on many elec. circuits but never on a hydraulic system.

For straight runs you can use the formula above to find the expected PSI reduction (resistor value).

You might look up "pump curves".
I'd think the water supply to your house follows a similar curve. It's not a perfect pressure source [delivers constant pressure no matter how big the pipe is] or a perfect flow source [delivers constant GPM no matter how small the pipe is].

Last edited by Yoyizit; 08-15-2009 at 10:16 AM.
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Old 08-16-2009, 12:01 PM   #6
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http://www.engineeringtoolbox.com/pe...oss-d_619.html
Cold water in plastic pipe,
ID = 0.5", 4.8 GPM, 5 ft/sec, 8.8 psi drop per 100'

http://www.engineeringtoolbox.com/pv...ngs-d_801.html
90 elbow 0.5" ID, 1.5'
gatevalve 0.5" ID, 0.3'
tee-flow branch 0.5" ID, 4'

Let's say at your resi. water entrance you have 20 PSI @ 4.8 GPM.
60' downstream with a gate valve off of a tee, you should have 8.8(64.3/100) = 5.7 PSI at the same 4.8 GPM.

You can measure the GPM with a large container and a stopwatch.

Last edited by Yoyizit; 08-16-2009 at 12:04 PM.
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Old 08-16-2009, 12:43 PM   #7
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Jamie, This tool has helped me troubleshoot TPR problems on my hot water tank that both times turned out to be the Water Pressure Regulator
http://www.amazon.com/Toro-Flow-Pres.../dp/B000O5SP80

If you have a Pressure Regulator similar to this one you may be able to make small adjustments to the regulated line pressure but this could be very hazardous to old pipes. Pressure regulators when new are factory adjusted to 50-60 PSI. When my regulator failed (both times) the pressure shot up to 160 PSI (Street Pressure)

http://www.watts.com/pro/_productsFu...pid=6690&ref=2


Luckily my 1954 house was all re-plumbed 20 years ago with all copper so I had no leaks over the 2 weeks before I found that the hot water tank TPR valve was leaking. When I replaced the whole house Pressure Regulator the pressure immediately dropped to the factory set 60 PSI.
.

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