Steve S
The "jockey pump" was used to make up for very small pressure drops (leaks) in the fire suppression system.
Here's the way I recall it being set up. (I may have the pressures not exact, but you'll get the point):
fire suppression water pressure > 120 psi = no pump on
water pressure drops below 120 psi then the jockey pump would come on to keep those small leaks satisfied. The jockey pump should be able to cover all nuisance leaks so as to not burden (or bring on) the rest of the system. Jockey pumps have to be "sized" for each system; too much or too little will cause operational issues.
water pressure drops below 110 psi the then big 100 HP, 480/3ph electric motor kicks in. This is presuming that a sprinkler head, or fire line, has been opened. If only a line or two, then the 100 HP electric motor can easily keep the 110 psi satisfied.
As the pressure continues to drop (more volume is demanded than the system is supplying), each fossil-fuel'd motor kicks in:
motor 1 at 100 psi
motor 2 at 90 psi
motor 3 at 80 psi
I cannot recall the total volume the system could move, but it was astounding.
True story:
We actually had them all come on at once. The main fire suppression feed loop ruptured in the ground beneath the plant cafeteria! All the pumps came on because the pressure dropped immediately (as you would suspect when a 14" line blows apart from 40 years of neglect underground). The amount of water that filled that part of the plant was STUNNING to say the least! The floor quite literally blew upward and struck the ceiling with all the force/volume. And then it PUMPED and PUMPED and PUMPED. If you know anything about fire suppression systems, you know that they are made big-and-manly with no regard for the equipment. The philosophy is that water is needed and no one can stop it, short of manual power shutdowns (shut off the electric power or defeat the fuel pumps). The electric motor was not even fused; it was wired straight to the panel. You don't need to worry about motor life in a burning building! Buring up a motor is a pitance compared to the whole facility, after all. The same concept applied to the engines; you'd rather melt one down from internal destruction than skimp on water supply! The DD motors came on a full tilt and it was LOUD. But, I must say, when those motors were running it made you tingle at the thought of all that emense power. (I don't recall the models, but I'm sure that there was a LOT of torque in that room.) NOTHING makes noise like 2-stroke DDs when fully loaded. I often think of those things going from a dead sleep at 50 degrees F to running full-song WOT in a matter of 5 seconds, and then contrast that to some of our BITOG members that cringe if they don't "warm up" their little daily commuter.
Here's the ironic part to the water explosion. For weeks we were getting "nuisance" alarms because if the Jockey pump did not keep up, an alarm sounded in security when the 100 HP electric motor came on. Well - it started coming on every once in a while every day or two. As soon as it came on, it stayed on, and had to be shut down manually, and then pressure gage reset after the presure came back up. But because the "leak" wasn't large enough yet, it kept the pressue easily above the next set point where the first motor would come on. So, the Jockey was constantly on, and every once in a while the electric 100 HP would bump on. Then someone would go shut it back down.
Hmmmmmmmmmm ... Gee - that ought to tell you something, shouldn't it? I told my boss that we've got a major leak developing and it could get ugly. Wow! What fore-sight! They thought I was being overly dramatic. Until the floor exploded a few weeks later. I'm sure the "I told you so" look was pasted on my face for about a week.
Back on topic of sorts. My experience is that the DDs really bleed fuel unless they are run at a good load and warmed up and run continuously. That's why our UOAs showed favorable changes when we started running them weekly, and having them pump the water from/to the storage tanks.