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Water Flow With 1/4" Reducer?

 
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Old 03-19-2019, 08:44 PM   #1
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Water Flow With 1/4" Reducer?


I'm building an RV parking area, and for my main water lines I ran 1 1/2" pvc to each of the 4 RV spaces. The PVC switches to pex right before coming out of the ground to the pedastals. In my town (for some reason) I can only find 1/2" pex faucet pieces. I really wanted to run 3/4" pex because the 1/2" pex fittings have such tiny inside diameters it looks like. Is this worth hunting down or ordering 3/4 pex faucet fittings, or will the RV even have a noticeable drop of pressure with the 1/2? Just hate to ruin a whole decent sized water system with trying to feed water through a pinhole. If this was a single sink or shower, I'm sure 1/2 would be acceptable, but what about 1/2 compared to 3/4 to feed a whole RV?
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Old 03-19-2019, 09:12 PM   #2
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Re: Water Flow With 1/4" Reducer?


An RV is not a house, with three teenagers taking 30 minute showers simultaneously. You should be just fine with 1/2".

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Old 03-19-2019, 09:35 PM   #3
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Re: Water Flow With 1/4" Reducer?


Flow isn't reduced much by a short bottleneck. Flow resistance is linear to length. A fire hose has a pretty small orifice but needs a giant hose to feed it over the full length.
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Old 03-19-2019, 09:48 PM   #4
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Re: Water Flow With 1/4" Reducer?


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Flow isn't reduced much by a short bottleneck. Flow resistance is linear to length. A fire hose has a pretty small orifice but needs a giant hose to feed it over the full length.
water hydraulics.

talk to an engineer on a fire truck & he can explain it best.

friction loss and the need for volume & pressure.
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Old 03-19-2019, 09:55 PM   #5
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Re: Water Flow With 1/4" Reducer?


Great, if this is the case, I'll stick with my 1/2 fittings. Just didnt want complaints about "no water pressure here". 👍
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Old 03-30-2019, 02:59 AM   #6
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Re: Water Flow With 1/4" Reducer?


Also depends on what is feeding these lines. Is it city water or coming from a well? Bigger pipe means more volume less pressure also.
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Old 03-30-2019, 01:04 PM   #7
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Re: Water Flow With 1/4" Reducer?


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Flow isn't reduced much by a short bottleneck. Flow resistance is linear to length. A fire hose has a pretty small orifice but needs a giant hose to feed it over the full length.
I disagree.
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Old 03-30-2019, 02:46 PM   #8
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Re: Water Flow With 1/4" Reducer?


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I disagree.
Feel like elaborating without using anecdotes?
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Old 03-30-2019, 02:56 PM   #9
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Re: Water Flow With 1/4" Reducer?


For example, 50 GPM at 60 psi through 1/2":

https://www.firehosedirect.com/1-1-2...ss-hose-nozzle
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Old 03-30-2019, 02:58 PM   #10
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Re: Water Flow With 1/4" Reducer?


Think of a faucet. When you open it full blast you get the most water. When you shut it down some the water slows too.

Put the same restriction in the middle of a pipe, what makes you think the same thing wouldn't happen?
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Old 03-30-2019, 03:13 PM   #11
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Re: Water Flow With 1/4" Reducer?


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Think of a faucet. When you open it full blast you get the most water. When you shut it down some the water slows too.

Put the same restriction in the middle of a pipe, what makes you think the same thing wouldn't happen?
The simple difference is shutting down a faucet to supply, say 1/2 of its rated 2.5gpm at 60 psi, there is a MUCH smaller orifice than what a 1/2" pex valve has.

In reality, a 1/2" pex valve easily supplies 5 gpm. Which is plenty for an RV.
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Old 03-30-2019, 03:48 PM   #12
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Re: Water Flow With 1/4" Reducer?


But that's not what we're discussing.

Quote:
Flow isn't reduced much by a short bottleneck. Flow resistance is linear to length. A fire hose has a pretty small orifice but needs a giant hose to feed it over the full length.
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Old 03-30-2019, 05:32 PM   #13
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Re: Water Flow With 1/4" Reducer?


Quote:
Originally Posted by Leo G View Post
But that's not what we're discussing.
https://www.tlv.com/global/US/calcul...gh-piping.html

You'll notice that 50 feet of pipe has 10 times the pressure drop as 5 feet of pipe. Flow resistance is linear to length.

Also that 50 feet of 1/2"NPS at 5GPM has far more pressure drop than 1 foot of 1/4" nps at 5 gpm. Flow isn't reduced much by a short bottle neck.
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Old 03-30-2019, 05:34 PM   #14
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Re: Water Flow With 1/4" Reducer?


At a constant pressure it does.

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