I'd like to compare the shower flow between PEX bend brackets and 90-degree elbow connections to the shower valve.
With the test cap on and turning on the hot and cold, will that correlate to having the cartridge installed, or does the cartridge restrict the flow to a large degree?
I would run into a bucket to check GPM and take a pressure test.

The reason I am asking is that I did a mock-up and the bends are snug up against the studs. I could move the studs and inch or so if necessary.



Edited 1 times.

That will have little relevance to the "real world" because the greatest restriction will be in the flow FROM the "handle" to the shower head, which is after the point where you are testing. There will be very little difference between the two methods you are testing.

Then, the true test would be to install the cartridge and handle in each setup?

why are you fretting over this?
there is no question that a gradual bend has less resistance than a sharp 90.
how much difference , i don't know.
as hj says "very little".
the fact that the bend support is hard up against a stud is means nothing.
if it bothers you, bring the pex up in the next stud bay and drill a 1 inch hole to push the pex thru.

You have to install the cartridge to get proper flow numbers.

I just want to compare it to another identical valve and trim in my other bath. Should give me a quick check on my pex efficiency. If the gpm and psi at the shower arm are close, then I can button it up.

the gpm is limited by the federally MANDATED limiting device in the showerhead itself

SHEEEZ

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Thanks for making that point Sheeze.
All I'm trying to do is compare the gpm and psi of the existing shower system, which works well, with the one I'm plumbing out now. With the cartridge installed, turn the water on, run the water into a bucket to check gpm and then connect a shower adaptor and connect a psi gauge.

Because the new shower is at the end of the line, very tight stud bays and this section of house transitioned to pex off 3/4" copper in a 30" high crawlspace, I'd rather know now, than find out after I button up and tile.

a PSI gauge will tell you what kind of pressure drop you have when you turn on the shower. but it is useless for standing pressure. you will have the exact same standing pressure whether the valve is piped with 1/4 inch tubing with 15 elbows or if it is piped with 2 inch pex with no elbows.
obviously if the valve was piped with 1/4 inch then when you turn it on the pressure will drop dramatically.
if it is piped with 2 inch the pressure drop would be extremely small.

If, repeat if, you have 'normal' conventional valves and NOT 3/4" supply rain-shower and body-nozzle set-ups the flow is limited by the (relative to the supply pipe ID) small 'ports' in the cartridges and/or seats.


Simply pipe it out and enjoy.

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638