Increasing fire jocky pump flow rate..impact on system....?

[ukupul]

I'm working in a High rise building project in Dubai, Our design fire main pump is 1000 gpm(duty + standby) & jockey pump is 26 gpm, head is 20 bar. but fire sub contractor has submitted jockey pump material submittal with 100gpm flow rate. submitted main pump is ok.(capacity & head)

I want to know what is the impact on the system of increasing jockey pump capacity,( of cause kw rating gone up)

Please advice on this.............

 

[quark]

Unless you have some regulations, jockey pump just maintains the pressure of a hydrant system when not in use. This is to take care of leakage while the system is pressurised.

 

[PEDARRIN2]

The jockey pump is there so that when little leaks or drops in pressure occur, the main fire pump doesn't start and stop very quickly. It is there to maintain the pressure in the system.

Typically jockey pumps are low flow and rated for a little higher head than the main pump.

With a higher flow jockey pump, you will likely get a much quicker on/off cycling of the pump. This will likely cause failure of the pump sooner than with the lower flow pump..

I would reject the submittal and require the specified pump.

 

[rshayesteh]

According to PEDARRIN2's interpretation, the pump will turn off more quickly. But the number of pump starts will remain the same during the life cycle of the system. So the total working duration of the pump will decrease.
Hence if the new pump working duration in each start/stop cycle would not be very short to prevent full pump running (which depends on the pump start/stop setpoints), it may not have a bad effect on failure rate of the pump.
Also the electric consumption would not be increased due to shorter working time.
Therefor if the pump cost is not a problem, it is reasonable to think on keeping the new pump.

Reza

 

[MortenA]

Your system must have a bleed with an orifice to allow continuos flow. Normally an orifice will limit the flow - in you case to 26 gpm at 20 bar (funny mixing of units).

Assuming that you new pump is a centrifugal pump - then it will NOT be 100 gpm - but the pressure in the system will go up and the flow will be somewhere inbetween 26-100 gpm.

Best regards

Morten

 

[BigInch]

Moten, Its a firewater system... no continuous flow, no orifice.

10% of flow capacity is too high for a jockey pump. Don't accept it.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[Artisi]

Is the jockey pump rated 100gpm at 20 bar or are they quoting full capability of the pump at some lower pressure? -- but I would agree, if it is 100/20 there is no need for such a big jockey pump.

 

[MortenA]

Biginch

But it a water filled system with a jockey - dosnt you normally have a bleed so that the jockey dont have shut in head and no flow?

Best regards

Morten

 

[ukupul]

Appreciate replyies of all guys,

I'd like to add something here, this is FIRE system (stand pipe, hydrant, hose, sprinkler) as Bigmach mentioned.

1) my design fire jockey pump is 15.4gpm, 20bar(disign done by other party, i don't have any contact with them now)

2)contractor fist submit 26gpm, 20bar (which i rejected because of low efficiency of the pump)

3)again he submitted 100gpm(10% very big), 20bar

what I'm struggling is , i couldn't find base for selection of fire jockey pupm.

[NFPA 20 mentions -Pressure maintenance (jockey or make-up) pumps should be used where it is desirable to maintain a uniform or relatively high pressure on the fire protection system. A jockey pump should be sized to make up the allowable leakage rate within 10 minutes or 1 gpm (3.8 L/min), whichever is larger.]

if any body knows about selection criteria for fire jockey pump out of NFPA, please advice me. (because i feel leakage rate is depent on system water volume and no. of fittings)

I'm suspecting , sypplier can not meet our desing jockey pump parameters(high head)

 

[Artisi]

Seems you are really confusing the issue with this fire pump system.

Is is a NFPA approved system or are you trying to use NFPA as a guide.

The effficiency of the jockey pump is a non-issue, it will (or should)only run infrequently if you have a leak proof system - its role is only to maintain a set system pressure usually slighlty above the upper limit on the main fire pump, therefore flow and efficiency are secondary issues with the NFPA comment re jockey pumps a recommendation.

 

[quark]

Morten,

The jockey pump shut off head will be more than the operating pressure, so no issues.

ukupul,

1. For example, if you operate the jockey pump between 6 and 7 bar pressures, the densities are 995.916 and 995.961 kg/cu.mtr respectively. If you have a system volume of 1 cu.mtr then you have to pump in 0.045 liters and a pump of 15.4 gpm flowrate takes about a fraction of a second to actually raise the pressure. However, the actual time will be more than this due to inertia and pressure switch response.

2. Forget about the efficiency. Irrespective of size of the system, you have serious leakage, if your jockey pump runs more than once in an hour.

 

[BigInch]

Morten, no (as Quark says) it simply compresses the water some and ... expands the pipe too.

I had a very long (8 km) firewater system installed in three levels of an underground storage facility with multiple loops on each level that they were trying to run on one firewater jockey pump. Due to all the compression of the water and the expansion of the pipe, they could never get it to hold the right pressures in any given location. There were always too many transients running around. We eventually had to break it up into several systems, each with their own jockey pumps to keep pressures constant and within acceptable ranges.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[ukupul]

Thanks for quick replies,

Artisi - specification & issued for construction drawing manetioned , design based on NFPA.

quark - I got an idea about size of jockey pump, my system volume is 7.75 m3,

my jockey pump stop(cut out) pressure setting will be 22.7bar(shut off head) + delta (flooded suction ... tank is very near to pump suction)

jockey pump start pressure setting will be 22.7bar(cut out pressure) - 0.7bar(10psi)

but sitll we can't get the jockey pump capacity,can't we?

but I was thinking about jockey pump capacity relates to one sprinkler flow rate.(19.5gpm sprinkler flow rate in my system) jockey pump capacity is to compensate leackage but it is below one sprinkler flow rate.(because in case of fire, main duty fire pump should come to operation) - my guess

Any advices.......

 

[BigInch]

The capacity isn't too very important as long as it is a few times the overall true minimum leak rate. If twice the capacity of the true leak rate, it will run half the time, so you're looking for something like 10 times the true leak rate, which BTW should be much much less than (est. 1/100th maximum? of) the capacity of one sprinkler. 10 times the true leak rate would be 6 minutes operating every hour. But it also depends on the volume and pressure contained within the system, so you might want to increase it, if the system is very large.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

Couple of things.

AT 20 bar with typical 1/2" sprinklers, the flow from the first sprinkler at a lower floor level would be something over 80 gpm. If one wants an alarm from fire pump start, the 100 gpm pump would keep the fire pump from running.

When you think of makeup time, don't forget that there will be considerable air in the system. Maybe about 1/20th of the 7.74 m3 system volume.

If the piping is all overhead, you can expect leakage to be next to none. Maybe only what leaks back through check valves.

Sprinkler system parts, pipe and fittings are usually rated at only 175 psi, much less than 20 bar. Hopefully, standpipe valve pressures will be controlled to safe working pressure for firefighters.

 

[ukupul]

Guys

Thanks all for replying.

Finally i fond some useful information from Armstrong web site,
Please read STEP 6 - Selecting Jockey pump.

thanks

 

[Artisi]

You have now answered your own question and without re-reading all the posts was probably answered by others much earlier.