Jockey Pump Design 3

[Ribicki]

Hello everyone,

My name is Vinícius, I'm an engineer in Brazil.

I have a question regarding a sprinkler project for a warehouse, following the NFPA-13 and 20 codes. The system calculations required 170 psi for my remote area, speaking with the pump representative, they indicated a pump rated for 175 psi @ 2550 GPM, with a churn pressure of 200 psi.
As my pump churn is above 175 psi, I'll use a pressure relief valve after the pump discharge to maintain the system below this pressure. For the jockey pump the NFPA 20 code says: 'The jockey pump stop point should be equal to the pump churn pressure plus the minimum static supply pressure', so my question is: should I consider the start point of the jockey at 175 psi? considering that I'll use the pressure relief valve to protect the system, or should I adopt 200 psi and be above the 175 psi limit?

Thanks in advance

 

[MGXFP]

4.7.7.2 says not to use relief valves to meet the requirements of the shutoff head being the pump churn plus the minimum suction head to avoid pressures exceeding what the components are rated. You can also figure in the working pressure where the sprinkler are. If the sprinklers are high in the air, you can deduct the elevation head to check if their working pressure will be exceeded.

 

[Ribicki]

I'm aware of this restriction, but I don't have much choice in this case, the local Brazillian code doesn't specify those scenarios, so we follow as much as we can the NFPA 13/20 codes. My sprinkler heads are rated to 175 psi, the highest sprinkler heads in my design will be under a pressure of 180 psi (warehouse), and the lowest 195 psi (loading bay).

 

[MGXFP]

Not sure what type of fire sprinklers you are using but many are available in high pressure, up to 250 psi. ESFR and CMSA are usually not available in high pressure but CMDA typically are.

 

[LittleInch]

If NFPA 20 says " should be", that gives you room to set it lower for your particular requirements surely?

So you can set the start and stop pressure where you need to.

The whole purpose of a jockey pump is to keep the system pressurised enough so that when a demand is made the pump can't maintain it and the pressure falls below the start point of the jockey pump which is above main pumps start pressure and then the main pumps kick in. Max pressure is really up to you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Ribicki]

I'm using ESFR heads. I'll set the pumps similar to what I read from this post, limiting the system up to 175 psi. I'll have to use the relief valve for this purpose anyway. Thanks.

 

[TravisMack]

You can get your demand pressures lower so you can get your churn requirements down. But that will require larger pipe sizing and such. If you say there is no other way, then use a VFD or PLD to keep your churn pressure below 175. It is not cheap, but a relief valve is not allowed in NFPA 20 as it is considered poor practice and there are many other ways to accomplish what you are striving for.

Travis Mack, SET, RME-G,
MEPCad, Inc
AutoSPRINK | AutoSPRINK FAB | AutoSPRINK RVT

 

[MJCronin]

LI and Travis offer good advice ... I agree

MJCronin
Sr. Process Engineer

 

[Ribicki]

I agree with the advice, but as Travis said, it's not cheap to change the system to be under 175 psi and I'm already using large pipes because it's a huge warehouse, and I can't change the heads for higher pressure ones. In the end, it all comes to the cost, as we are not obliged to follow 100% of the NFPA code in my country it's almost impossible to justify to the warehouse owners spending more when there is a more affordable 'solution'.

 

[cdafd]

What is the sq ft/ size of the building??

How many risers will there be?

 

[Ribicki]

645000 sqft (~60000 m²), 16 risers.

 

[cdafd]

Ok so sounds like maxing out each riser.

 

[Ribicki]

Yeah, some of them are a little bit over 40000 sqft.

 

[SprinklerDesigner2]

Maybe I missed it but what is the sprinkler design criteria?

 

[Ribicki]

10x ESFR 25.2 heads @ 75psi (5.2 bar)

 

[SprinklerDesigner2]

Appears to be an FM Global job.

Yes, your pipe will be large but you have no options with the design criteria given.

I would look at a 2,000 gpm pump rated at 160 psi which should provide a churn of 165 to 170 psi.

I assume the pump will be supplied by a ground storage tank.

Yep, you might end up with 3" or maybe 4" branch lines but so what?