Residual PSI at BOR and Main drain test

[SpcFoor]

Question: Does the main drain test and the residual psi at bor on the hydraulic data plate have any relation to each other?

 

[TravisMack]

Not necessarily. A main drain test in and of itself is pretty useless. My understanding is that it is a way to see if the water supply has been stable over the years or not. If you have steadily had 60 psi at the riser during main drain testing, then you all of a sudden see a 50 psi reading, then you have a problem in your water supply.

For comparing to the BOR info, it is not a great idea. If you have a light hazard system where the demand is 100 gpm and you do a full open main drain test where you may be flowing 200-400 gpm (just made up numbers), then your main drain test should have a lower residual than what is at the base of the riser requirement for the system.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[Sdpaddler50]

A main drain test can also be used to check for obstructions. Example, I watched a main drain go from 80 static to 15 psi residual. Turns out the butterfly valve on the riser that had an indicator noting it was open, was actually about 80 closed. This was discovered when the contractor removed the valve. False sense of security. Same thing can happen on PIV,s and I have seen that as we'll.

 

[chicopee]

To add to Sdpaddler50, such test can also detect if the shutoff valve on the supply line is fully opened or partially closed. A drain test test can also estimate the water supply adequacy for sprinkler systems as attested by insurance representatives periodically performing such tests of commercial properties.