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Two Inch Drain Tests – Valuable Data on Your System’s Health


One of the most common ways that a property can lose sprinkler credits from insurance rating services is failure to perform routine testing. The most evident test result used by many rating services is a 2-inch drain test. What is this test and why is it so important?


The 2-inch drain or main drain test is used to evaluate the condition of the water supply for the sprinklers system. By imposing a high flow rate on the supply, you can measure the pressure drop and the time to recover the pressure. A slow recovery or a large pressure drop may indicate an impairment or fundamental change to the water supply.


The Main Drain Test is Conducted by:


  1. First checking to see that the discharge of water will not cause damage. Look for loose soil, adjacent vehicles, or pedestrians.

  2. If the sprinkler system is connected to an alarm service or panel, make sure to alert the service that you are doing testing. Be prepared to silence any alarms on premises.

  3. Record the starting pressure (static) from the lower water supply pressure gauge on the riser.

  4. Open the main drain slowly and completely. Let the pressure on the lowest gauge stabilize and record that pressure (residual).

  5. Slowly close the main drain valve. The pressure should recover to a value close to the original pressure quickly.


A valuable way to measure system health is to compare drain tests results across time. A gradual decrease in static or residual pressures may indicate that the water supply is being reduced by other demands. This can be an important consideration in area experiencing significant development. A change of 10% in residual pressure from prior tests should warrant and investigation.


A slow recovery of water pressure may indicate an impairment to the water supply. You should check all valves between the city supply and the riser in question to see that all valves are wide open. A partially closed valve may allow sufficient water for domestic purposes, but not allow flow needed for the fire sprinklers.


An extremely low residual pressure may also indicate an impaired water supply. You may need to involve the water district or city to investigate valves off of your premises. A 4-story hotel had a residual pressure of 14 psi. Insufficient water pressure to get water to the top floor of the building. The city identified a valve down the street that was over 80% closed was the culprit. Our questioning the test results led to this impairment being resolved.


Drain tests were formerly done quarterly. The codes have changed to require an annual test. If the risers are downstream from a backflow preventer or pressure reduction valve, the frequency should be quarterly, and tested after any time system valves are closed.


The Driehaus Difference


We have the risk management experience and knowledge to help you understand fire protection system maintenance, testing and inspections. We can work with insurance companies and rating bureaus to assure you get the credits you deserve. Call us at 513-977-6860 or reach out to us via our website www.driehausins.com

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