View Full Version : Water supply and pressure with Kohler Rite Temp valve.

10-23-2010, 01:35 PM
I have the master bath set up to have 2 shower heads, 1 stationary head which is the primary, and a hand shower which would be the secondary. I have 3/4 PEX supply running all the way to the valve, then a 3/4 PEX line up to a 3/4 x 1/2 x 1/2 tee. From there, 1 tee goes to the main head, 1 tee goes to a on/off volume valve for the hand shower.

This is a well system with a 40/60 switch. The valve is a Kohler Rite-Temp K-304.

The main shower head running by itself seams pretty good, not great pressure, but pretty good. When I open the volume valve for the secondary head, the volume of water from the primary head drops significantly, and the second head is about the same.

Is the valve not large enough to supply the 2 heads? It is the smaller of the 2 Rite Temp valves that Kohler makes, but it states it can supply up to 2 heads. It is "supplying" them, just not very good.

I noticed the thread the other guy posted with the Delta valve and 2 head setup, I wondered if he will have flow problems. I have attached the flow chart from Kohler:

10-23-2010, 02:43 PM
Those flows assume copper pipe...pex has a smaller ID so the curve would be flatter and more horizontal. The pex could be part of the problem. 3/4" pex is about the same ID as 1/2" copper, so 1/2" pex is closer to 3/8" copper. If you can access things, and switched the pex to 3/4", you might notice a difference when running both. I don't think you'd need to change the valve to a 3/4". Actually, if you made the connections after the valve with copper, it would probably be best.

10-23-2010, 07:00 PM
I do have 3/4" ran to the valve, which I switched from 1/2". Didn't really make much of a difference if any. The only place I have 1/2" is after the valve from a tee which is fed by 3/4". That chart shows the valve can flow 7 gpm even at 40 psi. That can't be the hold up. Really confused now. How much pressure loss could I be losing from the tank all the way to the valve? It's quite a long run, about 70 feet horizontal and 15 feet vertically.

10-24-2010, 10:58 AM
Those charts assume COPPER pipe input...pex is smaller ID. So, look at the 1/2" (copper) flow curve, and move it over about the same as from the 3/4" to 1/2", and you'll see what 1/2" pex can flow. At your pressure, you've about maxed it out with two showerheads. And, when there's no excessive pressure, the output of the showerhead isn't as vigerous. Think a hose, then put your finger over the end. If the showerheads don't create that backpressure, they don't work as well. Replace the piping after the valve with copper, and you'll get closer to the 1/2" copper flows. Having 3/4" coming into it should be fine, but is closer to a 1/2" supply than 3/4" copper.

10-26-2010, 05:11 PM
Yes, I understand the the size difference from PEX to copper. With the 3/4" PEX I have as a supply to the valve, I can assume that it is around the same as 1/2" copper. The chart I believe is giving you the flow THROUGH the valve, not upstream or downstream of it. The 1/2" valve can flow 7.0 gpm, and that I'm sure they are assuming that the supply is from 1/2" copper.

I am going to put a pressure valve at the showerhead and see what kind of pressure is actually being seen there.

10-26-2010, 07:11 PM
With everything off, the pressure will be identical whether you have a fire hose or a soda straw...it only changes once flow is initiated...your lines after the valve are too small to support the flow of two showerheads at once with enough pressure. You want that flow to exceed the flow of the showerheads, so that it does not drop off. When the heads can flow as much as the supply, it's like using a hose without a nozzle on it. Two heads are probably 5 gpm. 1/2" pex is about maxed out at that flow.

10-27-2010, 02:36 PM
The chart is giving you the resistance to flow, and it varies with the flow rate because pipe/fluid friction varies with the speed of the water through the pipe or valve.

1 GPM in half-inch pipe implies the fluid goes 100' in one minute, 1.6' per second. Usually fluid velocity is kept below 5' per second to minimize pipe friction.

The valve should have a TEL, Total Equivalent Length [of pipe]. The TEL for a valve is probably several feet of straight pipe.

For city water, 40 PSI @ 16 GPM is adequate and 5 PSI @ 6 GPM is lousy. I'm waiting on two water companies to tell me their benchmarks for good flow, bad flow and questionable flow. Above 16 GPM probably implies good PSI.