Why fire systems don't use a hydropneumatic tank? 1

[jejaram]

According to the large amount of information on the web about hydropneumatic tanks and their large use in industrial hydraulic applications I got to wonder, why is it that fire systems (for sprinklers and/or hoses) do not use them? Is there a dissadvantage if one would use them?

 

[Artisi]

Why would you require one in the system?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[MikeHalloran]

I think he's suggesting that it could replace the jockey pump.

I have read just enough NFPA documents to realize that some non-obvious reasoning is behind many of the requirements. ... and not enough to comment on why an accumulator is atypical.




Mike Halloran
Pembroke Pines, FL, USA

 

[lilliput1]

Expansion tank is for closed liquid system were expansion of the liquid can cause pressure rise above the design pressure limit of piping or equipment. The expansion tank accepts the expanded volume. A pressure relief valve is also provided to make sure design pressure is not exceeded.

 

[jejaram]

As said before and stated in several articles on the web, hydropneumatic tanks control pressure sudden changes. It does not replace the jockey pump, because it can not increase the pressure, it can just maintain it.

So if there are advantages in using such tanks, why aren't they common in fire systems?

 

[Artisi]

Mike: You can't replace the jacking pump with an accumulator, how would you keep the system up to pressure as an accumulator can not recharge itself to replace water loss and pressure, that is the function of the jacking pump -- maybe a dedicated jacking pump to keep the accumulator up to pressure .

lilliput1: in a fire system, what would cause the design pressure to exceed its design, maybe a bit of thermal expansion but then the system would or should be designed for this likelihood. For interest, a sprinkler / hose reel system is maintained at a higher standby pressure than the operating system anyway - jacking pumps are set to cut in / out above the sprinkler hose reel operating pressure.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[bimr]

Hydropneumatic tank are not storage vessels and do not provide storage capacity. If you desire to control the flow or pressure, it would be more economical to accomplish it with valves.

 

[LittleInch]

jejeram,

In some systems you will find accumulators, but I'm still not sure what advantages you think they bring to the party.

Accumulators are common and well used on re-circulating systems where the contents don't leak out and are not intended to leak out and where expansion and contraction occur due to thermal expansion of the fluid.

Fire systems are different.

Sprinklers are often just connected to the mains water and float on the mains water pressure - no need for an accumulator. Ditto fire systems in buildings and other places connected to mains water.

The thermal expansion and contraction are very low.

Standalone systems such as plants and refineries etc with fire water ponds and pumps tend to have large systems which in essence act as the accumulator. Whilst water is almost incompressible it's not a solid and neither is the pipes (often buried PE) so some expansion is possible when the jockey pump kicks in.

Large systems often end up with small leaks or are used for washing things down or supplying test water etc. In either case an accumulator does not really add anything to the party.

The systems are setup so that if either the fire alarm is pressed the main pumps start or if you just turn on a hose or hydrant the pressure falls until the jockey pump can't cope and then the main pumps swing into life. The volume available in an accumaultor is not enough to make any difference in these circumstances.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chicopee]

In response to the OP, you have a limited amount of water in such tanks and these pressure tanks will be economically constructed up to a certain size. Although you may have let's say, a 20,000 gallon tank, the amount of water stored will be for argument sake 70% since the vapor space will be reserved for the air pressure. You have to strike a balance within such tank between the quantity of water and the volume of pressurized air. Such tank will be found only in places where availability of water either from lake or from municipalities is non existent or when the premises are considered to present minimal fire risk to life and/or property.

 

[jejaram]

Thank you LittleInch, that was very informative.