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Good idea to fit 1/2' pipe to 3/4' valve?

17 years ago

I am planning on installing a custom shower system. Due to the reason I do not want to switch out my polished brass sink faucets I am having a difficult time in doing this.

1. The Kohler system has a shower head, handheld shower, 2 body sprays, with K670-ks & K672-k 3/4" valves. One plumber said it is ok to fit the 3/4" w/ 1/2" pipe, another plumber and friend said that would diminish the water performance plus it would causes issues down the road. So who is correct?!

If the 3/4" valve with 1/2" pipe does not work I am thinking of getting the Moen 255CGPC, which has 1/2" vlave. The only thing is this system comes in 2 showerheads, handheld shower, 4 body sprays. I will be wasting a lot of money and parts.

Suggestions on which direction I should go?

2. My bathroom is on the third floor. Which has 1st bathroom, 2nd bathroom, laundry room, 3rd bathroom - since it is two floors above the water heater, are there any chance there is a 3/4" pipe on this third floor?

3. One plumber said he would do a GPM test prior to install any system. Four other plumbers did not offer to test, and one of them said he did not know how to test. I would like to hire the one that would test GPM, but he does not work in my area (traffic issue).

Is this test important? How do I test it myself?

I apprecaite your assistance. I am planning to have this install next week and am so confuse with what to go. Believe it or not I started this a year ago and decided on the Delta 1800 Jetted Shower. When I went to place an order last week, the sales person told me a customer just had it installed and did not like it a bit. So this turned everything around for me. I have to get this done next week or the following week is because of my work. This is the third time I had to reschedule this project and my manager is losing his patience!!

Please HELP!!!

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Comments (3)

lazypup
17 years ago
Why not select the Kohler K680KS valve which is the same type of valve with identical function but already set up for a 1/2" input?
mym2222
Original Author
17 years ago
I called Kohler and they told me to use the same size on both valves.
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I have 10 gpm flow (measured at a peak time...8am on a hot day). Any recommendations on using 1/2" vs 3/4" (option #1 or #3 above)? I like 1/2" because my hose bib and sprinkler heads are 1/2" and it's simple. Yet I like 3/4" since it gives room for expansion (though now unforeseen) and small extra cost. I just wonder if there are any potential disadvantages to using 3/4" in this application?
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The other part of that question is "do you have sufficient flow at the 3/4" part of the system." Here's the deal: If there is a flow restriction anywhere upstream it will limit the amount of gpm that can flow through the system. So, if you have the ability to move 4gpm through the main - because of some type of restriction - you will be fine when you turn on the first faucet at 2 gpm, but you will really notice flow falls off when you turn on the second faucet. A 1/2" pipe, if it doesn't have restrictions, will generally supply two standard faucets without significant drop in flow. You should not be seeing "greatly reduced" flow with two standard faucets (not a hose bib, tub or washing machine). If you are seeing that, I would insert a tee shortly after the main shutoff and 3/4 full flow ball valve. Then I would turn on the water, full flow, into a large container just to see what kind of flow there was right at the main. I would bet you have some other restriction.
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lazypup
17 years ago
My greater concern here would be "Dynamic Pressure" which is the working pressure under flow.

This bathroom is on the third floor so if this structure is on slab the vertical rise from the water main to the shower mixer will be approximately 24' and with a basement it could be as much as 32' or perhaps more. That would be a 10.3 to 13.8psig loss to vertical head. While the code required minimum dynamic head pressure for a standard shower mixer is only 8psig a temperture controlled shower mixer is required a minimum 20psig dynamic pressure. This means you would need between 30.3 and 33.8psig dynamic pressure at the main under full flow.

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