try it before you permanently install it:
if shower water is much like electricity, some people like a 220 volt
shower at 200 amps.
the shower's comfort level is based on available pounds per square inch
[volts] and available gallons per minute [amps].
incoming from the street with city water measure the psi anywhere on
the same floor and it's generally the same. but the farther you go from
the main past restrictive straight stops and valves and elbows and
reducers that do not permit 100 percent flow, the less water there is.
compared to the present shower, the device you wish to install may have
significant flow restriction in it even though it may be easily
connected with adapters. regardless of the label of gallons per minute
on the package, many of these devices ate measuresd at 80 psi. you can
buy an inexpensive water pressure meter and make the tests or just use
a 5 gallon pail and clock with a second hand. if you measure the
gallons per minute from the showerhead, then without the showerhead to
compare what's available. then adapter the new valve into the
showerhead pipe and check the gallons per minute thru it. add the
showerhead and measure again. or compare how many seconds it takes to
fill a known size container each of the four ways.
a half-inch versus a 3/4" device could be identical in flow restriction
and delivery of gpm.
this is based on lots of fooling around over the years with only 42 psi
coming into the house we upgraded from 3/4" to 1" service pipe and a 1"
water meter and run 3/4" to the second floor showers using gate valves.
I think he is talking about one of these http://www.leonardvalve.com/ .