Can someone tell me if using check valves in my bathroom piping is a good idea or not?

Question

The supplier says they are used all the time and should be ok. The plumber is hesitant. If I don't use them I have to spend more money buying other fixtures.

Here is what I have: one thermostatic mixer with volume control and an one-input-three-output diverter, one shower head and one hand-held shower. The goal is to be able to use the shower head and the hand-held independently or at the same time. The original design was to have the diverter to feed the shower head, when set to 1st position, feed the hand-held shower when in 2nd position, and feed both when in 3rd. But for the last situation to work, we have to t-off the main pipes of the showers which will cause the water to go back to other shower when we intend to only use one of them. Basically the problem is if we don't use the check valves we would have waters in both showers at all times.

Answer 1

I experienced a similar situation when installing a therapy tub with a hand held shower and spout. I know it may seem a bit counter-intuitive but the check valves may be prone to chattering. This may initiate a water hammer effect which may damage your expensive components or just make a hell of a lot of noise. In steady-state operation, the check valves shouldn't be a problem but your system will see many transient conditions such as switching from position 1 to 2 to 3. Our solution was pretty simple. We installed (2) separate volume controls on the common output of the T-stat valve. The volume controls regulated flow to the hand held and spout independently. If I remember correctly, the (2) volume controls and volume-less T-stat costs less than the diverter and T-stat with volume. Whatever you decide to do, be sure to test it all out before you seal up the wall.

Answer 2

If you have one of those long flexible hose type shower heads, that is long enough for the shower head to get below the maximum water line in the tub, then you should install check valves. Even if you might get a hose-type head in the future, you should install check valves, now.

If you just have fixed showere heads, then you don't need check valves.

All it would take is one time where the shower head is sitting in dirty bath water, and a pressure-drop occurs (very rare but possible), and you have a MAJOR mess of contaminated water for you and your neighbors.
.