We have a hydrant system with most pipes exposed on a power plant with a regular jockey pump. We think the size of the jockey pump is fine (15gpm-3hp).

We have met problems setting the on-off values of the jockey pump (goes on&off very often), and with the fire pump start setting. Maybe due to the size and configuration of the system, trapped air, daily heat-cooling cycle on exposed pipes, leaks, etc.

When we vent air on hydrants and fill the system systematically, we solve the problem, and it looks that there are no leaks. But after some days we found the jockey pump starting very often again, and the fire pump may start unexpectedly or not. The plant operator does not thrust the automatic start mode and sets the fire pump to manual.

Thinking of options. I´ve seen a plant with a fire pump NFPA 20/FM system designed and provided by Europeans that uses a jockey pump that includes a small hydroneumatic tank system, they say that it is used by them when they have a relatively big system to prevent problems with fire pump start settings, and to have a jockey pump working better.

Have you seen such systems, what do you think?

Do you know if there is a fire pump manufacturer/provider in U.S. that include such an option, I mean to avoid going on a special designs or to make it easy to buy/specify as an accessory package as when you buy a regular jockey pump.

I'm not familiar with a hydropneumatic tank for fire pumps, but I'll try to  help address the issue of your jockey pump cycling  and your fire pump starting.

Does the pump supply hydrants only? What is the difference between the  start pressure for your jockey pump, and the start pressure for your fire pump? Is it possible that someone is using water from a hydrant and kicking your pump on? Is there a pressure relief valve anywhere on the system?

I've also found a leaking check valve in either the jockey pump  discharge piping, or the supply by-pass to be a common cause of cycling. Though I've never seen it do it on some days, but not others, it's fairly easy to determine if those valves are the culprit, so it's worth checking into. I hope this helps.
 

The plant consists of aprox. 4 blocks of facilities and there are a lot of 10-8-6 pipes that feed hydrants, spray systems to cool fuel storage tanks, bladder tank foam systems. The pipes are buried (AWWAC900)and exposed carbon steel (ASTM A53).

I guess nobody is taking water, but you never know, pressure reliefs: just main pressure relief valves on the pumps.

There is a plan to change the old pumps, so I´m considering if we have a chance to specify a "better" pressure maintaining system.

I think a leaking check valve could be a possibility. Thanks for the point.

Somewhere,you are losing water pressure in your lines and air is entering the lines.