Water distribution piping is to be hydrostatically tested. Take these criteria as given for this project: the test pressure must be at least 1.5 times the system's working pressure and in no case less than 100 pounds per square inch. The system's working pressure is 78 pounds per square inch. What is the minimum acceptable test pressure?
- A78 pounds per square inch
Testing at working pressure proves the system survives normal service but leaves no margin, and the project criteria plainly ask for more.
- B100 pounds per square inch
The 100 pound figure is a floor that applies when the multiplier produces something smaller. Here the multiplier is larger, so the floor is not the answer.
- 117 pounds per square inch
- D156 pounds per square inch
Doubling the working pressure is a criterion from other kinds of testing and overstresses fittings, gauges and any device left in the line.
Why C is correct
Two criteria are given and both must be satisfied, so the larger number controls. One and a half times 78 is 117, which is above the 100 pound floor, making 117 the minimum acceptable test pressure.
What this question is testing
Whether the candidate can apply a two-part test criterion and select the governing value rather than defaulting to the stated minimum.
On the job
Before you pump anything up, isolate or remove what cannot take the pressure: relief valves, expansion tanks, backflow assemblies, gauges and any appliance connection. Choose a gauge whose range puts the test pressure near mid-scale so a small drop is visible. Write the start pressure, the time and the ambient temperature on the tag, because temperature swings move a gauge on a long test and you will want the record when somebody questions the result.
Memory technique
Multiplier or floor, whichever is bigger, wins.
Exam tip
When a rule gives a multiplier and a floor, compute the multiplier first, then take the larger of the two.
Where to look it up
IPC Chapter 3, tests and inspections, for the required tests on water supply and drainage systems. Test pressures and durations differ between the IPC and the UPC and are frequently amended locally, so read them from your adopted code and the project specification.