I am reviewing a set of construction documents that show the inspector test valve right off the main.  This is a single story building so I am not as concerned about its location relative to the riser base.

If this were a, say, 4 story building, shouldn't the test valve be located on the highest level to ensure adequate pressure to trip the flow switch?

You do not think the 39' hydrostatic head will reduce the flow, perhaps enough to not trigger the paddle in the flow switch?

If the inspector's test outlet was 39' in the air an argument might be made that it *might* but the 1" valve is located 5' above the floor with the outlet 1" above the floor it the height of the system wouldn't matter.

Take a building 200' high with a 60 psi static and 59 residual pressure and it's obvious you wouldn't get a drop of water from an open sprinkler head as the column of water would only reach 138' high.  But what if we were able to completely fill the system using a test pump expelling all trapped air in the process? If the system was totally filled in this manner you would get a normal flow from the inspector's test regardless of the height of the building because the system would be acting just like a siphon hose on a can of gasoline.  If you installed pressure gages located 5' above the floor on the riser and just above the inspector's test valve they would both read around 58 psi but a gage 200' up on a branch line would read a negative or minus 29 psi but water would still flow due to the siphon effect.

Given these conditions if a sprinkler head were to discharge the vacuum would be broken and your sprinkler head would suck air until the water column reached 138' at what point it would stabilize all assuming the system didn't have a check valve at the riser.

I recognize this is a stupid analogy only to prove a point.

The best setup would be to have the inspector's test valve