Fire Pump/Jockey Pump Question?

Question

I need your help. Briefly explain to me the roles of a jockey pump and a diesel engine fire pump in a high rise building. This would be for a five story 100,000 sq ft structure with it's sprinkler water supply coming from the city's main line. Which of these 2 pumps would need to have backup battery or generator power in case of an outage. And if the city water line was broken(hurricane Katrina) how could this cause the diesel pump to run itself dry until it overheated(the oil in the engine was like tar). Just need to know the basics for an interview. Thank you Thank you.

Answer 1

This article
http://en.wikipedia.org/wiki/Fire_pump
discusses fire pumps and way down at bottom mentions the purpose of jockey pumps. It appears both would have to have backups because the jockey pressure allows the fire pump to sense opening.
Basically the problem the fire pump is solving is that while the city lines can deliver volume, the pressure is only nominal, especially at the top of a building. A fire sprinkler, especially if several are open, is like an open pipe so the pressure will drop considerably if it isn't kept up so the fire pump takes the (almost) limitless supply and jams it into the smaller system pipes.
If the diesel depended on the water supply for cooling, then it would run way hot and cook the oil if that failed. It should have had a cut off switch since without incoming water it was pretty useless.

Answer 2

For a brief explanation of fire pump and jockey pump go to http://en.wikipedia.org/wiki/Fire_pump.

The diesel engine fire pump is driven by a diesel engine that works on diesel fuel, so there is no concern with electrical outages with this pump.

Pumps require a minimum flow when operating in order to preclude damage to the pump internals. If the city main line is broken, the fire pump would be running dry since it takes a suction from the city main line. Therefore, the fire pump would overheat and depending on the amount of time running in these conditions can become damaged. Usually, pumps trip when the motor currents or temperature reach a certain setpoint. The oil in the engine may have been like tar for other reasons (i.e., poor maintenance).

Hope this is an entry level position; otherwise you'd be in big trouble if you don't know the very basics. Good luck with the interview.

Answer 3

Both pumps are considered emergency equipment, and so, are designed to provide protection to the building & its occupants rather than to protect themselves.
This explains the behavior of the diesel pump.
The main fire pump is designed to provide the required system flow & pressure. If electrically driven it would have been required to have back-up power.
The jockey pump, to fill the sysytem and to and "trim" pressure in operation.
The jockey pumpis required by most codes to have back-up power if it is electrically driven.
( Due to the size of the load, batteries are not a good option for powering fire pumps.)

Answer 4

go to www.corncobupurs.com