Question: Jockey Pump 101

[SkaMan]

Here is a question for you all. I need some educating on the typical use and setup for a jockey pump. A client of mine has asked me to evaluate whenther a jockey pump would be appropraite for his system.

I have reviewed Karassik and the explanation in there is pretty sparse - it's briefly discussed in the Fire Pumps section. As I understand it, the typical use of a jockey pump is to maintain the normal operating system pressure of a closed piping network that needs to remain at operating pressure during times of no flow or no demand from the system. The idea is that the jockey pump keeps the system pressured up, and when a valve is opened (i.e. a demand is made on the system), the resulting pressure drop trips a pressure switch or transmitter, which then notifies the control system, shuts off the jockey pump, and starts the main pump(s). Is this correct?

OK, why is the jockey pump even needed? If there's no demand, and no leaks in the system, why do I need the jockey pump at all? Is it to get around the time delay from the time when the pressure drop is detected in the piping system, to the time when the main pump starts and comes up to pressure, which shouldn't be more that a few seconds?

Since the flowrate required to keep the system pressured up is very small, don't I have to bypass some of the jockey pump's discharge back to the suction, or maybe to waste, to keep from deadheading the jockey pump?

Thanks very much for your time and for any help or insight. I'm always learning!!!

 

[DeltaCascade]

This isn'nt my specialty, but:
- if you had no jockey pump, to maintain pressure wouldn't you have to block the system in? Blocking the system in is likely undesirable for a number of reasons? We'd need more info on you actual application (fire system? other system with special control needs?)
- doesn't a jockey pump also maintain circulation? Up here in Canada, at least, this is handy to at least prevent freezing in fire systems. If this is a fire system, I'd bet that NFPA codes would shed more light.
Hope you get more expert postings! Cheers//

 

[quark]

Skaman!

What you said is correct. A jockey pump is used in a fire hydrant system to maintain constant pressure. If you are using your main hydrant pump after fire occurs, initially it cannot deliver the required pressure to put the water jet to the required height.

A smaller size jockey pump (specific)which will work for lower minimum flows. It will just push water and stops so that no overheating happens. As the pipelines are laid underground generally, we cannot say when the leakage takes place. That is why as a precautionary measure the jockey pumps are installed.

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[MJCronin]

SkaMan,

All of the comments/responses made to your question are correct...... however a couple of other points should be noted.

- Jockey pumps are frequently required by the "governing authorities" in selected fire protection systems.

- The NFPA-25 standard governs the design, inspection and performance requirements for all kinds of fire protection pumps including jockey pumps. You should read and become familiar with this standard as well as the particular system design requirements

- Jockey pumps are a good choice in systems that, over the years, are expected to develop small leaks or would be difficult to inspect (read "underground piping&quot. Frequent on-off cycling and even jockey pump replacement is more desireble from an owner's standpoint rather than digging up fire water mains.

Consider contacting "PEERLESS Pump" for more information

http://www.sterlingfluidsystems.com/

Consider posting this question in the NFPA section of the website.....

Good Luck.....

MJC

 

[SkaMan]

Guys thanks for your replies.

This is not in fact a firewater system. The system is a well kill system. Water is pumped from a central tank/pump site, through several miles of pipe, to manifolds where oil wells are manifolded together. The kill water is used to fill the wellbore, thus providing a static head of water against the formation so the well does not kick back during well servicing operations.

The current system consists of two 150 hp ANSI pumps, tank, and controls. The pumps are activated and staged on and off from the PLC via a pressure transmitter in the main discharge header. The system is supposed to maintain about 260 psig at all times; however, due to small leaks out in the piping system, the pressure bleeds off, causing one pump to run all the time and to bypass nearly all of its discharge back to the tank because the rate required to maintain system pressure is WAY below the pump's minimum flow; hence, the jockey pump idea to save some energy.

MJC - your point is well-taken about systems being difficult to inspect; this system falls squarely in that category.

Thanks!
Pete