Final Acceptance Testing of a Wet System and Standpipe
A new 13 system in a six-story office building is ready for final acceptance. The hydrostatic test was conducted at 200 psi for two hours. The gauge started at 200 psi and ended at 186 psi; the ambient temperature dropped 18 degrees F during the test. The contractor says the drop is thermal contraction and wants the test accepted. The main drain test at the riser shows a static pressure of 72 psi and a residual of 64 psi. The flow switch on the riser actuated 65 seconds after the inspector's test connection was opened. The standpipe flow test at the topmost outlet produced 250 gpm with a residual pressure of 48 psi, and the calculated demand at that outlet is 250 gpm at 45 psi. The building official must decide whether to sign the acceptance certificate or require retesting.
1. Should the 14 psi hydrostatic drop be accepted as thermal contraction? What procedure should the AHJ require?
Read the worked answer
A 14 psi drop over two hours is not automatically thermal contraction. Water contracting 18 degrees F in a 10,000-gallon system can change pressure, but the effect depends on the amount of trapped air and the system volume; the contractor must calculate it, not assert it. The proper response is to calibrate the gauge, inspect every joint and valve for leakage, isolate sections if necessary, purge trapped air, and retest at 200 psi for two hours. The standard requires the system to withstand the test without leakage. If the gauge is accurate and there is no leak, a small drop may be explained by temperature, but the burden is on the contractor to document it. Do not sign the acceptance certificate on the thermal claim alone.
2. Evaluate the main drain result and the 65-second flow switch actuation.
Read the worked answer
The main drain test shows 72 psi static and 64 psi residual, an 8 psi drop, or 11.1 percent. A drop of more than about 10 percent from static suggests an obstruction, a partially closed valve, or a supply problem. On a new system the drop should be small. The inspector should verify the main drain valve is fully open, check the service main and backflow preventer, and compare with the original flow test. The flow switch actuated in 65 seconds, which is within the 90-second waterflow alarm requirement, so that part is acceptable, but the switch should be tested at the inspector's test connection with the correct orifice and the alarm should be verified at the fire alarm panel. The main drain result requires investigation before acceptance.
3. Evaluate the standpipe flow test result and state what records the AHJ should require before signing off.
Read the worked answer
The standpipe flow test produced 250 gpm at 48 psi, and the calculated demand at that outlet is 250 gpm at 45 psi. The available pressure exceeds the demand by 3 psi, which is a very thin margin; gauge error alone could erase it. The test should be run at the topmost outlet with the required hose stream and the residual pressure recorded at the correct elevation, then compared with the hydraulic calculation. If the margin is only 3 psi, the AHJ may require a retest with calibrated gauges or a review of the calculation. The contractor must also submit the material and test certificate, the hydrostatic test record, the flow test data, and the alarm test results. Acceptance testing does not replace the initial ITM program; the owner needs a baseline and a schedule for gauges, main drains, and alarm devices.