I am working on a project where there is a fairly large demand. The EOR
has determined there are to be (3) 3000 gpm pumps. These are all
installed parallel. One of the pumps is to be a backup pump. The design
has not been finalized, but the system demand (overhead sprinklers and
grate foam nozzles) is somewhere around 6000 gpm. That is why we have
two 3000 gpm pumps in parallel to create a 6000 gpm pumping capacity.
There were some errors in the EOR pump room design that led to a few
other questions. We are getting conflicting information from the EOR
and the pump guys. The arrangement is that the pumps share a common
suction header and a common discharge header.
Per NFPA 20, a 3000 gpm pump needs a 12" discharge. The EOR showed 10"
discharge piping and equipment, so this is what flagged some questions
with the pump room design. The questions are now:
1 - Should the test header be sized to accommodate a 6000 gpm pump, or a
3000 gpm pump? The pump guy says that the common discharge header must
be sized for the combined pumping capacity. The EOR states that it is
only based on 1 pump flowing. I seem to agree with the pump guy, in
that you need to test with both pumps flowing so you can test your water
supply as well to show you can get the full 150% flow from the water
supply. It is easy to size the piping so that the recommended
velocities in NFPA 20 are not exceeded. It is just a question as to
what is the basis.
2 - Should the common discharge header that the pumps tie in to be sized
based on 3000 gpm pump or 6000 gpm pump? I believe that the common
piping (after the pump discharge valve) only needs to be sized based on
hydraulic calculations.
3 - These are diesel pumps. The individual relief valves are tied into
a common discharge header. How should this be sized? Based on 3000 or
6000 gpm pumps?
We are awaiting input from the authority having jurisdiction as well on
this topic. The biggest issue is the pump test header and relief valve
discharge piping. There are more issues of now trying to fit 12"
valves/pipe/fittings on the discharge side of a pump in a room that was
tight to begin with and was designed for 10" discharge equipment.
Part of the issue is that NFPA 20 only goes to 5000 gpm tables for
sizing pump room piping/equipment. The EOR is stating that the NICET
tech is to correct anything in the pump room and provide it per NFPA
20. However, since we have a 6000 gpm total capacity, it is not
possible to size things based on the summary table in NFPA 20 if it is
to be based on 6000 gpm.
I am just interested as to the thoughts of the guys on this forum.
--
Travis Mack, SET
MFP Design, LLC
2508 E Lodgepole Drive
Gilbert, AZ 85298
480-505-9271
fax: 866-430-6107
email:[email protected]
http://www.mfpdesign.com
https://www.facebook.com/pages/MFP-Design-LLC/92218417692
Send large files to us via: https://www.hightail.com/u/MFPDesign
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