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

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Maybe that's the reason why he was able to see the problem I was having integrating what I had read (about pipe diameter affecting pressure) with what I was merely "being told" in black-and-white terms as being otherwise (without explanation or discussion). The plumbers were completely silent in response to my implied requests for help in reconciling what they were telling me, with what I had read and recalled for them, such as, "The plumber and the plumbing designer rely on the internal diameter of the water delivery pipes to control water pressure" (Bob Vila). By giving me the raw, not paternalistically oversimplified, theoretical information [i.e not merely what the 'doctors' judged to be all that the little 'patient' need concern himself with] Paul was able to help me make logical sense of what I was "being told" with respect with what I had previously read.

I think Paul's explanation made this quite apparent.

It was to clarify specifically just this question that I posted my query here in the first place.

Was it not you who said that larger pipes will nonetheless deliver greater volume (providing the corresponding capacity valves, etc.)?

Yes, that is the industry standard here in Canada too (for houses). But I've long noticed in commercial buildings (like the hospital where I work) they have 1" pipes leading directly to things like toilets. These toilets (without a tank) flush prodigious amounts of water in just a second or two. Unless there is more to these systems than meets my eye, it would appear to me that larger diameter pipes do allow more water to get through quicker.

Being strapped with paying on a huge mortgage (huge only because entry level property values are staggeringly high here in Vancouver) while earning only a very modest income, I just can't afford to hire a reputable plumber for anything that isn't an emergency. So I have little choice but to just try my best at being as handy and knowledgeable a 'jack-of-all-trades' as I can be in responding to my house's needs.
Ken
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There's a lot of misinformation and incomplete information in this thread. Let's bring some citations and facts to the game. You wanted details and facts, here you go.
At least part of the mess here is due to confusing static pressure and dynamic pressure. In this context, static pressure is the pressure at a specified point in the system when flow is zero. Dynamic pressure is pressure at a specified point in the system when water is flowing at some non-zero rate.
What you asked about is the dynamic pressure at the showerhead when the water is flowing at whatever rate it flows when you have the shower on. The greater the dynamic pressure at that point, the more forceful the shower stream will seem, for a given showerhead. Yes, as many posters have pointed out, different showerheads will feel better or worse all else being the same, but for a given showerhead, the higher the dynamic pressure at the showerhead, the more forceful feel the water streams will have.
So first a word about static pressure. The static pressure at the shower head is determined by the static pressure at the point your water pipe enters your house, minus 0.433 lbs for every foot of elevation difference between the entry point and the shower head, assuming your showerhead is higher than the entry point and you don't have a pressure regulator valve. So if the static pressure at the entry point is 50 lbs, and your showerhead is 10 feet higher than the entry point, the static pressure at the showerhead will be 45.67 lbs.
Note that pipe size (within reason), number of turns, fittings, etc., does not enter into this. So when a previous poster says pipe size doesn't affect pressure, they are talking about static pressure (or they are wrong, see below).
For a good explanation of static pressure, see:
http://www.nationaldriller.com/CDA/Archives/e125cc2ce4197010VgnVCM100000f932a8c0____
On to dynamic pressure. When water flows through a pipe, a pressure drop occurs along the pipe due to the energy that is required to overcome the friction between the pipe and the flowing water. Pressure drop in a pipe is affected by flow rate, the viscosity of the liquid, the diameter of the pipe, and how smooth the pipe interior is (corrosion and deposits increase pressure drop).
Fittings such as els, tees, shutoffs, etc., also cause a pressure drop, and for the same reason. Pressure drop for fittings is often expressed as the length of equal diameter pipe that would cause the same pressure drop at the same flow rate.
For an example, a 1/2 inch copper el has a pressure drop equivilent to 2 inches of 1/2 copper pipe. A 3/4 copper el has a pressure drop equivilent to 3 inches of 3/4 copper pipe.
Pressure drop is usually expressed as lbs per 100 feet of pipe at a given flow rate. For an example, water flowing at 2 gpm through 1/2 copper pipe will have a pressure drop of 2.6 lbs per hundred feet. For 3/4 copper pipe under the same 2.0 gpm flow, the pressure drop is 0.5 lbs per hundred feet.
For a good explanation of pressure drop and tables for pipe and fittings see:
http://www.nationaldriller.com/CDA/Archives/0dbf5d7935197010VgnVCM100000f932a8c0____
What does all this mean for your shower?
Let assume the pressure at the entry point to your house is 50lbs. Lets assume you have 4 elbows and 100 feet of total pipe length (not counting the elbows) between the entry and your showerhead, and that the showerhead is 10 feet higher than the entry point. Let's also assume copper pipe and a flow rate of 2 gpm. What will be the dynamic pressure at the showerhead with both 1/2 inch and 3/4 inch pipe?
Dynamic pressure at showerhead equals static pressure at entry, minus static pressure drop due to change in elevation, minus dynamic pressure drop in pipe, minus dynamic pressure drop in fittings.
For 1/2 inch this is:
50 - (.433 x 10) - 2.6 - (((4 x 2) / 1200) x 2.6) = 43.0527lbs
For 3/4 inch this is:
50 - (.433 x 10) - 0.5 - (((4 x 3) / 1200) x 0.5) = 45.165
All the figures come from the cited references.
The complicated term is the number of ells times the equivilent length of pipe in inches divided by the number of inches in 100 feet, times the pressure drop of pipe per 100 feet.
So for the above example, the dynamic pressure will be a little over two lbs greater for 3/4 pipe compared to 1/2 pipe. Will you notice it standing in the shower? I doubt it.
You will notice that the pressure drop due to elevation change is the major factor, followed by the dynamic drop of the 100 feet of pipe. The elbows contribute only a tiny amount.
Sticking a valve in the pipe will add a dynamic pressure drop term to the calculation. The magnitude of the term will depend on the valve and the flow rate but it will be the same for the two cases, so you will still be better off (albeit only a tiny bit) with 3/4 pipe.
For completeness I will mention one complicating factor. The above calculations assume the same flow rate in both cases. However, in practice this won't quite be true, because the dynamic pressure is higher in the 3/4 case. This will mean the flow rate will be slightly higher, which will increase all the pressure drops slightly. The net affect is that the difference in practice will be even less than shown above.
I hope this helps clear up some of the confusion.
Paul Franklin
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http://www.nationaldriller.com/CDA/Archives/e125cc2ce4197010VgnVCM100000f932a8c0____
http://www.nationaldriller.com/CDA/Archives/0dbf5d7935197010VgnVCM100000f932a8c0____
This is a real good and complete explanation of the situation. I had noticed that some posters were referring to static pressure and others to dynamic pressure without stating which.
I agree with the conclusion that increasing the pipe size is very unlikely to satisfactorily solve the problem. The 1/2 inch pipe is adequate for the service and is pretty much standard in the plumbing systems I have come in contact with. I suspect low source pressure, a faulty reducing valve, a localized restriction such as a clogged screen, obstruction in the pipe, or obstruction in the valve. It is also possible that the pathway has generalized obstruction caused by deposits in the piping. If there is another restriction, then increasing the pipe size will theoretically and actually increase the water flow, but it is unlikely to be any significant amount of increase.
Don Young
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Paul Franklin wrote:

You've hit the nail right on the head! A lot of "incomplete information" and/or incomplete communication (which I'll admit to being a part of, as well).

http://www.nationaldriller.com/CDA/Archives/e125cc2ce4197010VgnVCM100000f932a8c0____
http://www.nationaldriller.com/CDA/Archives/0dbf5d7935197010VgnVCM100000f932a8c0____
That slight of a pressure difference, eh? Now it's all beginning to make sense to me.

Yes, yes. I see it now.

This has most certainly done so for me. My questions are now finally satisified. I thank you very much, Paul.
Ken
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Ken Moiarty wrote:

Hi, I think you posted to argue, not to gather information. Simple answer to your original question, increasing pipe diameter as you stated won't make any difference. May make things worse. I thought water saver shower head was a good idea. I live in Calgary in a house with 4 bath rooms. All my plumbing is done to save water and our water is on meter. Remember water is becoming scarce and we have to do everything to conserve it. My son is in water conservation and waste water recycling. According to him, the outlook is pretty grim for good water supply in the coming years. Sounds like you have this idea of your own and trying to justify it to try. Then just go ahead and try and come back here to report the result.
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My apologies. I replied to your message last night from my work computer, through Google Groups (since it doesn't have direct newsgroup access), and forgot that my display name is slightly different there ("Ken" instead of "Ken Moiarty"). So I'll paste and resubmit my reply to you below.
--

Mike Grooms wrote:
> Ken,
  Click to see the full signature.
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I've never lived in a house with such a problem, and I've seen some pretty corroded galvanized pipes. It would take a significant constriction in the cold line to make this a problem if you have reasonable supply pressure.
You really need to be looking at your static water pressure and make sure all valves in the supply are open fully.
Bob
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Bob F wrote:

Wow! This is like a paradigm shift (so to speak) for me. Got any suggestions as to what to search for in order to learn more about this? Apparently production housing contractors in my part of the country are either all helplessly second rate, or are colluding to 'pull the wool' over consumers' eyes in this matter. (Based on my long-held displeasure due to a lack of attention to quality _in general_ from these "slap-n-tack" outfits, I'm personally inclined to believe the latter.)
Ken
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If you increase the pipe size you can increase the flow rate / pressure. I run 3/4 right up to every shower. I especially do it on well pressure.
If you are on city water with good pressure then you must have an obstruction.
I would need to know how many psi we have to size the pipe to get the right gpm at your pressure.

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Ken Moiarty wrote:

Increasing diameter increases flow, not pressure. Pressure is determined by head, or height of fixture relative to height of water source if no pumps are used. Increase pressure by having your town buy a new water tower.
Increasing to 3/4" would be useful for multiple showerhead fixtures.
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Father Haskell wrote:

I hadn't mentioned it for simplicity's sake, but since you've brought this up, the idea of having multiple showerhead fixtures (actually, purchasing and installing one of those "super shower" systems) at some point in the near future, is also a consideration leading to my intentions here.
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