Question about water pressure in relation to valve and feeder pipe diameters...

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I think you've received sufficient answers, but I wanted to reinforce what others have stated. It isn't the pressure, its the shower head. I switched my shower head to a low pressure model and right away I noticed a huge difference in how the show "felt". It took some experimenting to be sure, but I wouldn't trade my current one for nothing - and I've had it for years now. Going to 3/4" is just going to make you hate life - especially considering that you'll have to neck it down to 1/2" anyways at the shower head - so all that 3/4" inch pipe won't make any difference anyway.
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wrote:

My $.02
Not to be argumentative with other posters, but 3/4 pipe has less resistance to flow than 1/2, so for a given flow rate and pipe length there *will* be less pressure drop, resulting in higher pressure available at the shower head. But unless you have a very long run it's won't be enough difference to make it worthwhile. BTW, this is true even if your valve is 1/2, but the flow resistance of the valve may very well cancel out the gain from upping the pipe size.
Others have made good suggestions, let me add another point: If your showers are on higher floors, you loose a lot a pressure overcoming gravity. This exacerbates the problem, especially if your pressure is marginal to begin with.
A more practical solution than re-piping may be to add a booster pump. If your main supply pressure is truly marginal, a booster pump will work wonders. They are available as packaged solutions with a pump, controls, and a very small pressure tank. Placed inline with your cold water supply, it will help both cold and hot pressure throughout your home.
HTH,
Paul
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Paul Franklin wrote:

Yes, this is what I'm thinking could be the case. But I would like to find out for more certain.

This shower's on the lower floor.

Yes I've thought of this. But I'm not comfortable with the idea of increasing the pressure for the entire household. If one of my neighbors learned I was doing this during the summer months when water restrictions are in effect (and inexplicably, water pressure for everybody in the neighborhood always seems to be much lower than during the rest of the year), I'm pretty sure I'd soon receive a visitor from the city abruptly ordering me to 'shut er down' due to some bureaucratic bylaw prohibiting such. (Hey, in this city where I now live it's even illegal to use a sump pump, because -silly as it may seem- that is considered to be abuse of public sewer system capacity.)
Ken
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"My shower lacks pressure so I want to replace the existing 1/2 inch copper pipe that leads up to it with 3/4 inch copper pipe. Obviously, if done
correctly this will increase the water pressure available at my shower."
The first paragraph of your post is incorrect and untrue. It makes me wonder how you could be so judgemental of everyone's response when you don't have a clue of what your asking yourself.
kenny b
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kenny

Now Kenny, is that the way we plumbers write? You're going to give everyone the impression that we're a little harsh.
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Mike Grooms wrote:

Sorry I'm trying to stay away from the 4 letter words that come so easy to us every day, it's the new me.
kenny b
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Measure the pressure available - if it is low, that is your problem. If not, raising the heater temp may help because then more cold would be added to it to get the right temp - reducing pressure losses in the hot pipe.
Did you have the problem before installing the balsance valve?
Bob
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I haven't installed the balance valve yet.
Ken
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Ken,
I noticed everyone and his mother has been giving you advice. This is coming from the plumbing newsgroup.
Increasing the feed pipes to 3/4" won't help. Incidentally, since water is not compressible, the smallest pipe or port in the system affects whatever's after it.
Here's three thoughts..
#1 Is the shower the only place in your house where this low pressure occurs? If this problem exists elsewhere, write back for more advice.
#2 Since the problem isn't a clogged shower head (which was the first thing to check), then, assuming some rust hasn't lodged in the valve body, I'd suspect the balancing valve itself. If you're handy enough, take the valve out and see if that doesn't increase the pressure. If it does, then just get a new valve. BTW, you shouldn't need a balancing valve. Something is awry somewhere. Perhaps you'll end up repiping the main arteries that feed the fixtures.
#3 Don't ask plumbing questions in the "alt.home.repair" group, unless you want a bunch of amateurish, faulty advice.
First do what I've suggested, then write the plumbing group if you need more advice. Sice we're not there to look at things ourselves, it might take a message or two.
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Mike Grooms wrote:

Thanks. Finally a response suggesting credibility.

Okay, this appears on the surface to be saying exactly what others before you have been saying. Am I to be sure then that you mean to be saying here that using 3/4" pipe in place of the current 1/2" pipe *won't* result in less pressure loss (in relation to the main supply line into the house)? If so, maybe you could indulge my curiosity and explain how this can be so in light of the many references that appear to say otherwise (such as the "Bob Villa" reference I quoted, for example)? But somehow I'm inclined to to think you don't mean to be saying this at all, but rather could be somewhat misunderstanding my original post.

Thank you!. So a reduction in pipe diameter from, say 3/4" to 1/2" for a travel distance of, say, 4" (the length of my PB valve) and then back again, would definitely limit the pressure at the end to what it would be if the entire line were just 1/2" in diameter to begin with?

No, the pressure is low throughout the house. (Bear in mind, however, that when I say "low", I don't mean abnormally low; just lower than what I've been used to from older dwellings I've lived in prior. I can write back later and give you the actual psi value since my memory is not so numerically precise, but I will tell you now that I recall checking the water pressure at an outside faucet in the past and finding it to be within the lower end of the normal range.)

Okay, I don't have the valve installed yet. When I bought this house there were no pressure balance valves installed whatsoever. Since the time it was built however, local laws have come into effect that require these be installed for each shower in all new (as well as legal rental) dwellings. I have bought an inline pressure-balance valve still waiting for me to install. But it's openings are only standard 1/2", as opposed to the 3/4" piping I have more recently been thinking of installing for a separate and totally distinct reason (i.e. my personal preference for increased overall pressure to shower - think 'President Lyndon Johnson with his 100 PSI shower in the White House...', though not necessarily that extreme <g>)..., thus prompting my original question.

This comes to me as a surprise. In every house I've ever lived in prior to, as well as including, this one, people have had to time their showers (or tell others before showering) in order to avoid being scalded or cold-shocked while showering. I remember my Dad turning down the thermostat of a new hot water tank that had just been installed in his house, as a safety precaution to decrease the chance of somebody getting seriously injured while showering in the event that somebody opened or closed a tap somewhere unawares during.

Okay, thanks for your helpful feedback.
Ken
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Pressure and volume are different things. Increasing the pipe size will NOT increase the pressure. Can't happen. Won't happen. Put in a 6" pipe and you won't get any more pressure If your feed from the street is corroded, you may get better flow by replacing it, but putting in a section of larger pipe will do nothing.
If you want to increase the pressure, the first step is to find what pressure is at the street. Then you compare that to your house. If they are the same, nothing you do will increase it. If you get a big pressure drop, it may be from a flow restriction on the main to the house. What size and type of pipe is it? If it is an old galvanzied pipe it may be corroded or have buildup inside and giving restriction. This is a different scenario than what you are suggesting. Replacing a section inside will do nothing.
If you want a high pressure shower, move to the town that I work in. We have 110 psi feed.
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In the original post increasing the size won't do anything measurable, "Can't happen. Won't happen" I don't think so. In theory and in practice with long runs pressure drops will add up and increasing the pipe diameter will increase the pressure at the output end.
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Increasing pipe diameter reduces restriction on the flow. Static pressure remains exactly the same. There will be less pressure drop once the flow is started. But pressure is never increased by larger pipes.
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wrote:

it comes to taking a shower. Who cares?
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And thus less pressure drop.

Agreed
Which is the condition when actually using your plumbing.

The above is totally misleading. The only pressure that is relevant to the OP is during flow, so that if you wanted to stay relevant then you should of said.
"The pressure can be increased by larger pipes"
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snipped-for-privacy@mucks.net wrote:

Static - no residual - yes
kenny b
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No, it can not. Restrictions are removed, but pressure is not increased, just decreased less.
Think about that for a minute and once you know the difference, you can cure the problems easier. Along the same lines, can you make something colder? No. You can, however, remove heat. The physical differences is of the utmost importance when dealing with changing pressures or temperatures. Unless you know what characteristics are the ones affecting your situation, it is a crap shoot to find a cure.
Bigger pipes do not make more pressure. This is not my opinion, this is the laws of physics. I didn't write them, but we all must abide by them.
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Edwin Pawlowski wrote:

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Oh my! So you really weren't just trying to be a wise ass in your reponse to my original post after all! You really do believe what you so clearly misrepresent here as having been suggested!

Ya think?
Ken
"The emperor has no clothes..." -Hans Christian Andersen
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Oh my! You came here knowing nothing and now you disparage comments by others. Just what is misrepresented?
No one has yet explained or proven that a larger pipe will INCREASE pressure. The only way to increase pressure is to have a higher head or mechanically, as with a pump. There are ways of reducing pressure drop, but that is a different method all together.
Did you understand my analogy of making cold?
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Edwin Pawlowski wrote:

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Oh my! So you really weren't just trying to be a wise ass in your reponse to my original post after all! You really do believe what you so clearly misrepresent here as having been suggested!

Ya think?
Ken
"The emperor has no clothes..." -Hans Christian Andersen
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