We did just get directed to the following section from NFPA 20, 2010
edition that explicitly addresses this:
14.2.5.2.3.1 Where simultaneous operation of multiple pumps is possible
or required as part of a system design, the acceptance test shall
include a flow test of all pumps operating simultaneously.
So, it looks like the EOR will be looking to re-design a few of the
components.
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
On 3/26/2015 1:32 PM, [email protected] wrote:
With 3 pumps, 2 needed and one backup the suction and discharge header should be
sized for 2 pumps. 16" pipe would result in a suction velocity of less than 10
fps, I believe that is the recommended limit in NFPA 20. All common pipe subject to
the full flow of two pumps should be sized accordingly.
Ron F
-----Original Message-----
From: Sprinklerforum [mailto:[email protected]] On
Behalf Of Travis Mack
Sent: Thursday, March 26, 2015 12:25 PM
To: [email protected]
Subject: Large pumping capacity
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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