14 replies to this topic

[imtinan mohsin]

i am working on finding the deficiencies in the fire water system at bulk plant as per NFPA 20.
In that system, Jockey pumps are installed without any pressure sensing lines (no pressure actuated switches). So these jockey pumps are in operation for 24 hours/day.
But NFPA 20 states that there must be pressure sensing line at the discharge line of jockey pump. The jockey pump will stop when its set point of pressure is reached.

This fire system is also connected with utility system.
So, If a pressure actuated switch is installed at the discharge line of jockey pump then its operation will be pulsating due to drop in pressure by usage of water in the utility.
It will create load on the motor winding due to high starting current and chances of burning the winding is very imminent.

please advice that pressure sensing lines with pressure actuated switches for jockey pumps are required or not ?

[ankur2061]

Imtinan,

Check out this earlier post on firewater pumps and discussed with great clarity and insight by one of our senior members 'gvdlans'. You may find your answer in this post.

http://www.cheresour...?showtopic=7516

Regards,
Ankur.

[imtinan mohsin]

My question is that
" Can i use the jockey pump without the pressure sensing lines in the existing system coz it will cost us a lot?"

[fallah]

My question is that
" Can i use the jockey pump without the pressure sensing lines in the existing system coz it will cost us a lot?"

No, because the jokey pump should maintain the pressure of fire water network and, in this way, must sense the line/network pressure.

[Art Montemayor]

Fallah´s answer is precisely correct in the spirit and the scope of what a jockey pump is intended to furnish and to ensure: The constant, secure, and 100% availability of sufficient fire water supply at the moment a fire is detected. The manner in which a jockey pump ensures that its scope is maintained is by maintaining a constant and continuous water pressure in the fire water headers around a process. By maintaining a constant and continuous water pressure, the jockey pump makes available a definite pressure drop the moment a fire hydrant and/or sprinkler system is activated. This pressure drop availability is the driving force required to ensure the sufficient flow of fire water upon the fire source.

Therefore, in order to ensure a constant and continuous pressure in the fire water headers, one must be able to continuously monitor and measure the existing pressure in the same headers. As a result, common sense dictates that a constant availabilty of pressure-detecting must be ensured 100% of the time in the form of pressure sensing and measuring devices. These devices are usually reliable and accurate pressure transmitters and they are, undoubtedly, expensive. You either are willing to protect yourself and your investment from a fire, or you are not. You are free to select either option.

[imtinan mohsin]

can i operate it 24 hours/day coz fire water system is connected to utilities?
It will make jockey pump operation pulsating.

[imtinan mohsin]

thanks Mr. Art,
the purpose of the jockey pump is maintain the pressure in the fire water system.
For this, a pressure sensing line (with pressure actuating switch) is installed which causes the jockey pump to stop when the set pressure in the fire water system reached.
In our existing system, there is no pressure sensing line (pressure actuating switch).There fore it will never stop and remain in operation 24 hours/day.
But our fire water system is also connected with utility lines.

If we install the pressure actuated switch, then the operation of jockey pump will become on/off.
it will put load on motor winding and the risk of its burning is high.

would you suggest to install pressure actuated switches at the discharge lines of jockey pump?

[gvdlans]

I cannot give a definitive answer. I would say there is nothing wrong with having a continuously running jockey pump, with a small overflow line for providing some minimum flow to the pump. That way you ensure that the system is always pressurized. For fighting fires, your main pumps are important, not your jockey pump. I have seen that design quite often, a.o. in the Middle East. Actually, I have never seen a design with a jockey pump that is switched on and off...

Since you are located in Saudi Arabia, I expect that you have some freedom to deviate from NFPA 20.

I don't have the exact text from NFPA 20 here and now to check it.

Whether you can connect your firewater system (a safety critical system) with a utility system I cannot say with the information I have now. You must ensure that this connection does not reduce the availability of your fire water system.

[Qalander (Chem)]

Dear Imtinan,

May I first of all say that a lot is already very reliably intimated to you by our M/S Art, Guidoo, Ankur, and Fallah.

However I add few practically observed points from my previous employer's last assignment as Manager Fire protection;that you may find useful/helping.

1) It was a usual observation that sometimes unauthorisedly one or more remotely located fire hydrants were operated upon from the whole Fire water network in spite of strong vigilance maintained and and patrolling physically to shut remote point hydrant (if any opened).

2) accordingly we kept slightly oversized specs for our Jockey pumps ordered i.e around 10~15% excess; in order to cater for small initial usages in emergency and avoidance of Main fire water pump cutting-in too frequently if no real need existed.

3)Accurate Pressure sensing and control logic was also in-place/ aligned to ensure ample firewater flow availability in-need

through Two jockey pumps,

Two Electric Motor Driven(Main) Fire pumps and

Two Diesel Engine driven(main)Fire Pumps(However one needed major overhauls etc. was not in proper service when I left)

4)As regards Pressure controls we had bleeding out to main reservoir through marginal back if header pressure went beyond the set point of 7.0~7.5 barg(if correctly recalled)

As regards the hook-up/interconnection with utility; that did exist but was always kept closed/ car-sealed;

with only extra ordinary circumstance usage under specific special permission from AHJ and intimation to the operating staff and stakeholders and never without intimation/ special permission from fire protection staff.

Hope this helps in way forward!

[Qalander (Chem)]

It was Noticed though, that almost 75~80% of the 24 Hours period Jockey pumps remained operative(except in late evening and Night hours when they stopped for very short intervals;15~20 minutes in many splits.

Even many a times they operated on 24 Hours basis and this should never become an issue if the cost of safeguarded assets can be imagined even very roughly against whatever could be the cost(s) involved with fire protection/fire suppression top quality systems.

Since I have been and still I am a very strong believer/advocate of

'Very High Reliability Fire Fighting/ Fire suppression arrangements must always be employed and maintained'

Since "Fire" is nothing,but a consequence of Failure of all other Preventive/ Protective measures already in-place.

Sorry if too harsh in any way here!

[gvdlans]

But NFPA 20 states that there must be pressure sensing line at the discharge line of jockey pump. The jockey pump will stop when its set point of pressure is reached.

Can you give a reference to the section in NFPA 20 where this requirement can be found?

Section 5.24 Pressure maintenance (jockey or make-up) pumps does not contain this requirement.

In section 5.29 Pressure sensing lines it is stated that "For all pump installations, including jockey pumps, each controller shall have its own individual pressure-sensing line.". It is my understanding that if the jockey pump is switched on and off, it must have its own pressure sensing line, independent of pressure sensing lines for the main pumps.

[imtinan mohsin]

it is the reference (5.29) on which my assumption is based.
i am assumed that it is must.
Also i have seen jockey pump control panel instrument diagram of Patterson and other companies.
They are mentioning the pressure switch for jockey pumps as per NFPA 20.

[gvdlans]

Well that is not my interpretation of section 5.29.

As I wrote, I have seen many P&IDs of firewater systems, from many different, reputable companies, and none of these had a jockey pump that was switched on and off by a pressure switch. Also I don't see what would be the problem with a continuous running jockey pump and a continuous overflow line...

[Qalander (Chem)]

Well that is not my interpretation of section 5.29.

As I wrote, I have seen many P&IDs of firewater systems, from many different, reputable companies, and none of these had a jockey pump that was switched on and off by a pressure switch. Also I don't see what would be the problem with a continuous running jockey pump and a continuous overflow line...

Dears,

I do not exactly recall the automatic operation with header pressure triggered switching on& off of the jockey pumps at my previous employer's my last assignment (Probably we used manually switching them on & off for change-overs etc.)

However definitely the main Fire pumps were controlled with NFPA 20's referred philosophy including the Lastly Procured(Patterson's Fire Pump) driven by 'Cummins' diesel engine.

I'm not sure how much this proves helpful in way forward;however this my humble info submission.

[fallah]

Well that is not my interpretation of section 5.29.

As I wrote, I have seen many P&IDs of firewater systems, from many different, reputable companies, and none of these had a jockey pump that was switched on and off by a pressure switch. Also I don't see what would be the problem with a continuous running jockey pump and a continuous overflow line...

Agreed........

Those cases i have seen consist of continuous running jockey pump whose discharge pressure would be maintained by a PCV that its outlet is connected to continuous overflow line.