Perform the required main drain test on sprinkler system risers

Steps

1. Determine required frequency: annual for standard system risers, but quarterly for any main drain downstream of a system whose sole water supply passes through a backflow preventer and/or pressure-reducing valve
2. Record static pressure at the supply-side gauge before opening the drain
3. Fully open the main drain valve and record the resulting residual pressure once it stabilizes
4. Close the drain slowly and confirm pressure returns to the original static reading, checking for water hammer or slow return that could indicate a check-valve or PRV issue
5. Compare the residual reading to previous tests and the original baseline, investigating any pressure loss of roughly 10% or more as a possible supply obstruction
6. Record results, noting that any PRV or backflow preventer feeding the riser has its own separate periodic testing requirement