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NOTE: This is an unformatted excerpt from our online fire protection training library.

Automatic Sprinkler Inspection, Testing & Maintenance

Main Drain Test

The main system drain is located at the sprinkler system alarm valve, dry pipe valve or deluge valve. It's main purpose is to be the point where almost all of the water in a sprinkler system drains from the system piping. It is usually 2-inch, but can be 1-1/4 - inch on smaller systems. A main drain test provides an indication of major blockages that approach 80-90 percent blockage of the supply piping. Blockage could be due to things like a mostly closed valve, or debris, such as stones, in the piping.Smaller obstructions will not be revealed through a main drain test. A main drain test is required at least annually and after any closed sprinkler control valve is reopened. Conduct a main drain test on a sprinkler system(all wet and dry pipe systems, and all deluge and preaction systems) as follows:
Record the static water pressure: Use the gauge on the supply side of the sprinkler riser to record the pressure with the main drain valve closed. The supply side gauge will be tapped below the sprinkler system valve - i.e alarm check valve - or into the lower part of the valve body. Close the alarm line valve: Conducting a main drain test without closing the alarm line valve will result in actuation of the local alarms and possibly the building fire alarm system. The alarm line valve may remain open if all appropriate personnel and agencies have been notified of the testing. Fully open the main drain valve: Check the location to which the main drain empties to make sure the water will not cause any damage. Then fully open the main drain valve. Allow the water to flow until the pressure stabilizes on the sprinkler system gauges. Record the residual water pressure: Use the gauge on the supply side of the sprinkler riser to record the pressure with the main drain valve fully open. It may take a few seconds for the pressure to stabilize after the main drain is opened. The pressure recorded is the residual pressure. Shut the main drain valve: After reading and recording the residual pressure, close the main drain valve. When the valve is fully closed the water pressure registered on the sprinkler riser gauge should rise quickly. A gauge that very slowly rises could be an indication of an obstruction in the water supply line, or in the small diameter piping supplying the pressure gauge. Record the static water pressure: Allow the water pressure in the system to stabilize after closing the main drain. Using the same pressure gauge used to read the residual pressure, record the static water pressure, or the pressure with no water flowing. Compare this value to the value you obtained by reading the gauge in the first step of this procedure. Make note of any difference between the two static pressure readings. Open the alarm line valve: If the alarm line valve was closed before the test, reopen the valve. Failure to reopen the alarm line valve impairs the waterflow switch and prevents actuation of both the local water flow alarms and the building fire alarm system signal if the sprinkler system actuates. Analyze the results: Subtract the residual pressure (flowing pressure) from the static pressure (no flow pressure). The difference between these two pressures represents the fiction loss or pressure loss in the system with the main drain fully open. This difference should be compared to previous and subsequent main drain tests. The difference should remain relatively constant over time. If future tests show a marked increase in the difference between the static and residual pressures, it could indicate a significant problem in the water supply piping to the sprinkler system.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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