What does a Jockey Pump Expansion Tank Do?

5/1/2025

I have a private fire main serving a large manufacturing building. The fire main is served by a city connection and has an electric and diesel fire pump before returning underground and surrounding our building. The jockey pumps have a connection to a Jockey Pump Expansion Tank, and I have no idea what this is intended to do.

Does anyone have similar equipment or know what a Jockey Pump Expansion tank does?

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3 Comments

Jack G

5/1/2025 09:56:28 am

Hydropnematic , surge or expansion tank?
Expansion tanks help regulate pressure on a closed system due temperature changes. High pressures are absorbed due to system /trapped air in the system. Boyles law?)
Hydro pneumatic tanks are used to maintain a higher pressure on the system ( like a well pump bladder tank) ) without the use of a pump .
Surge tanks are used to protect a system on pump start up due to
Water hammer which is a sudden pressure wave that can occur when the flow of water is abruptly stopped.
Expansion tanks are placed near the jockey or similar pumps to extend its life.
With the underground piping, NFPA 13 allows “ permissible leakage “ which will drop the pressure in the system, and would require the jockey pump to operate to maintain the system pressure.
Since the system involves underground, a larger size jockey pump would be required, due to system volume ( takes shorter run times to maintain pressure to fill)
I ve used 15 to 45 gpm pumps (/specified) to support the pressure and volume in the system ( been involved in Fire Protection for 57;years) . — capacity of fire pump - usually about 1%. So a 1500 gpm fire pump may need a 15 gpm jockey pump.
I would say this does not appear likely to be hydropnematic.
Air release mechanisms can be installed on underground with elevation changes ( clay valve ) and should be installed on system branches at the highest elevation .

Pete H

5/1/2025 12:44:01 pm

Wouldn't it prevent the pump from cycling?

Phil W

5/2/2025 08:43:31 am

I have used these in delivery headers in the past where we were experiencing water hammer from the jockey pump which were probably oversized and check valves that were non-dampening.

Its a kind of surge dampener really with an internal diaphragm; compressed air on one side, water the other.

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What does a Jockey Pump Expansion Tank Do?

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