I have a job where there are two existing diesel fire pumps that serve an existing warehouse (2 million sq. ft +).
The building is surrounded by an existing 12" underground fire supply loop. The two diesel pumps serve the space. According to the property manager the system operate as follows: (1) Pressure is maintained at 160-175 psi. (2) Below 160 psi the jockey pump turns on to maintain 160-175 psi. (3) Fire Pump #1 turns on when pressure drops below 150 psi to maintain 175 PSI. (Fire Pump - Static: 165 PSI ; Residual: 134 PSI @ 2000 gpm). (4) Fire Pump #2 turns on when pressure drops below 140 psi to maintain 175 PSI (Fire Pump - Static: 190 PSI; Residual: 174 PSI @ 2000 gpm). The pumps are provided by a municipal supply and a back-up private lake dedicated for the fire service. The pumps are in parallel, so you would add the flows. And to my knowledge the higher pressure would overtake the smaller pressure. My question is, how do you determine how to calculate the system hydraulically? If I only use fire pump #1 for water supply, it will not be an accurate representation on how the system operates. In this case it also is very difficult to get the system to work hydraulically off of one fire pump. I appreciate any input! Submitted anonymously and posted for discussion. Discuss This | Submit Your Question | Subscribe
6 Comments
Brian Gerdwagen FPE
9/18/2020 10:34:06 am
This is a fun question. The simple answer is that you would add the flows at the lower pressure. But it is in reality much more complicated.
Reply
Ivonn
9/18/2020 11:49:00 am
Pumps are operated in parallel as a means of flow control and for emergency back up (installed spare). However, if the pumps are not properly selected for parallel operation, or operated in the most optimum combinations, pump reliability can be compromised. Operating the wrong pumps in parallel can even cause one of the pumps to operate at shut off, resulting in over heating and failure.
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Pete D.
9/18/2020 11:57:14 am
Use the primary pump curve and calculate to the discharge flange.
Reply
SK
9/18/2020 06:52:55 pm
This post is real fun. I agree with Brian and will not repeat what mentioned already but I'll try to add bit more based on my limited understanding and conclude as below;
Reply
Franck
9/20/2020 07:50:42 am
As already indicated, fire pumps ate normally one in duty and one in back up.
Reply
Tony C
9/22/2020 06:05:08 pm
Thank you all for your valuable input and insight! Thank you MeyerFire for putting this topic out there for discussion.
Reply
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