jockey pump

[mouse123]

Greetings,
I am reffering to a typical fire fighting sprinkler piping system acc to NFPA 13 or NFPA 20.

For example, the permanent pressurization of the ff piping system is required in order to prevent the main fire pumps from unnecessary start. This may be done by adding a centrifugal type jockey pump. We can also assume that there is no hydraulic accumulator is the piping system. Knowing the water is an incompressible fluid I can conclude following:

1. In a standby mode, the jockey pump should operate continuously(24hr/day) because if the jockey pump stops the system pressure will drop simultaneously to atmospheric pressure because the water is considered incompressible and none of the hydraulic accumulator fitted in the system.

2. We know that centrifugal pumps should not operate with flow below minimum required i.e. shutt-off valve on discharge should be kept open. So the flow through jockey pump should be led back to the water tank by means of a baypass or orifice valve.

Is above true or I missed something?

Tnx.

 

[Artisi]

1. there is a non-return valve between the jacking pump and the pipe system - the jacking pump will only run whenever the pressure drops below the setpoint due to any slight leak in the system.

2. Don't really understand the second quetsion.

 

[mouse123]

Artisi,

1. I know that there is a non-return valve in the discharge side if the jockey. But, if we consider following statements:
a.Water is a non compressible fluid,
b.None hydraulic accumulator fitted in the piping system,
c. steel piping considered as a rigid body/non deformable
In that case, I believe it is not possible to maintain the pressure in the piping system without the jockey pump running?

2. Every centrifugal pump should operate with flow above minimum required in order to prevent the overheating of the pump, also it should not operate against closed discharge valve.

 

[Artisi]

Ok, if this is a sprinkler system, I believe that the code does not allow for a a hydraulic accumulator - there is no need as the system MUST be leak free. So therefore once the system is jacked up to its set pressure it will maintain the pressure, if not them the system is faulty.
I suggest you contact the local NFPA authority and discus this with them.

 

[mouse123]

Hm...if you are true about the set pressure, then the only way to keep the pressure in the piping system without running the jockey pump, is that the pipes deforms a little in order to store the pressure energy, i.e. the pipes acts as some kind of hydraulic accumulators...

 

[mouse123]

or the water compresses a little...

 

[BigInch]

Good afterthought. Actually it's both and leakage across the valves and out the valve packings, flanges and pinholes, etc. in the pipe reduces it, temperature variations increase or decrease it.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[mouse123]

This could be true but I think that reliability of such system would be on low level which couldn't be acceptable for a fire fighting system, i.e. there must be an accumulator fitted in the system, see link below:

http://www.ultrafog.se/Technology/Systemdescription/tabid/126/language/en-US/Default.aspx

 

[Artisi]

Entirely upto you - but you have now introduced the comment "......acceptable for a fire fighting system, .." My earlier comment stands, contact the local NFPA representative if this is an NFPA installtion or contact the fire authority underwriting the insurance and see what they consider as "acceptable"

 

[786392]

I have again have a thought that sometimes considered fairly small contributor; usually neglected factor coming-in
i.e. improper geometrical piping lay-out's inducing air pockets factor

getting in a way dissolved/pressurized into water bulk also eat-up partially the pressure of jockey pupms as occassionally might be witnessed at some high point hydrant's intial flow-out

emitting lot of tiny air bubbles while being released into open atmosphere.

Hope this is helpful/fairly considerable real scenario!

Best Regards
Qalander(Chem)