NFPA 25 - Main Drain Test
NFPA 25 - Main Drain Test
(OP)
Hello,
Per NFPA 25 Table 13.1 Main Drain Tests are required Annually/ Quarterly.
We are trying to size the floor drain/sewer line to drain water from the Main Drain during the test.
The confusion is how much water flows from the 2" drain when its fully open. The city won't let the main drain to flow to the sidewalk.
Any insight on how the test is carried out if there is flooding issue during the test would be helpful.
Is it any good to size the floor drains/ sewer line for this particular test (taking in consideration the volume of water)? Also P-trap would slow down the flow.
Thanks !
Per NFPA 25 Table 13.1 Main Drain Tests are required Annually/ Quarterly.
We are trying to size the floor drain/sewer line to drain water from the Main Drain during the test.
The confusion is how much water flows from the 2" drain when its fully open. The city won't let the main drain to flow to the sidewalk.
Any insight on how the test is carried out if there is flooding issue during the test would be helpful.
Is it any good to size the floor drains/ sewer line for this particular test (taking in consideration the volume of water)? Also P-trap would slow down the flow.
Thanks !





RE: NFPA 25 - Main Drain Test
I know RPz backflow preventor drains can get quite big when properly sized. It's not uncommon to see a 6" drain piped to outside underneath the port of a 4" rpz depending on the water pressure.
RE: NFPA 25 - Main Drain Test
Most floor drains cannot handle just opening the valve with the pipe over the floor drain
Forgot if 13 allows direct connection. I am thinking that not directly to the sewer connection, but like in a multi story bldg the floor taps are tied into a drain line, so seem like you could do that with the main drain
RE: NFPA 25 - Main Drain Test
RE: NFPA 25 - Main Drain Test
First test I witnessed was followed in about 10 seconds with screams from the basement ladies' room. Turned all the toilets into geysers. We payed the ladies a healthy sum later on to compensate. We had the drains cleaned and tried again when the store was closed. This time no geysers. Policy from then on was: 1) clean the drains before sprinkler testing; and, 2) test only after hours, and make sure the restrooms are empty.
Get some confirmation from a good plumbing engineer -- this post is just memories from an EE.
Good on ya,
Goober Dave
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RE: NFPA 25 - Main Drain Test
Jon
RE: NFPA 25 - Main Drain Test
Throwing something together quick I think most standard 2" main drains (angle valve with 7' of pipe with single 90 deg elbow and 45 deg elbow) will have a K-factor of between 50 and 60.
To be conservative using a k-factor of 60 a 2" main drain will discharge 300 gpm @ a 25 psi residual pressure and 600 gpm @ 100 psi residual pressure.
I think this is a little on the high side but we would want to error that direction if we would dare to tell someone what we think a full flow main drain would produce. In actual practice I think the flows would be closer to 250 gpm @ 25 psi and 500 gpm for 100 psi residual pressures.
I used a 130 c-value on pipe and .90 discharge coefficient through a circular orifice .... both introduce a conservative margin which is why I think the actual k-factor is closer to 50 than 60.
Am I close or off base?
For the record I would not tell anyone what I thought the flows would be... I would avoid any liability by letting the civil or project engineers figure this one out.
RE: NFPA 25 - Main Drain Test
Perhaps you could jury-rig a series of 50 gal.plastic drums piped together with 4” PVC as low down as possible with a 3” discharge directly over a 4” floor drain. No guarantees though.