A jockey pump is a small pump whose only job is to keep a pressurized system topped up, so the big main pump stays asleep until it is genuinely needed. In a fire protection system it holds the sprinkler and standpipe network at a standby pressure and makes up the tiny losses from fittings and minor leaks; without it, every small pressure drop would start the large fire pump, which is meant to run only in a real fire. The same idea appears on booster and pressure-maintenance systems. This page explains how the jockey's cut-in and cut-out pressure setpoints are arranged relative to the main pump, and why watching how often the jockey runs is a powerful early warning of leaks and failed check valves.
Jockey Pump in one line: A jockey pump is a small pressure-maintenance pump that keeps a fire or booster system at its standby pressure by making up the small losses from minor leaks and pressure decay. It runs briefly and often, cutting in at a pressure set above the main pump's start pressure and cutting out when pressure is restored, so normal small drops are handled by the jockey and the large main pump stays off until demand is real. Tracking how frequently the jockey cycles reveals developing leaks or a leaking check valve long before they become a problem.
A fire protection system sits pressurized and idle almost all the time, waiting for a sprinkler to open or a hose valve to be used. That standing pressure slowly bleeds away through tiny leaks at fittings, valves, and gauges, and through normal thermal changes, so left alone the system pressure would gradually sag. The main fire pump is a large machine designed to deliver big flow at fire-fighting pressure, and it is not meant to start and stop for a trivial pressure drop, both because that wear is undesirable and because a starting fire pump is treated as a significant event.
The jockey pump solves this by handling the small stuff. It is sized to make up leakage and minor demand, not fire flow, so it is a small pump that switches on for a few seconds, restores the standby pressure, and switches off again. Because it absorbs the routine losses, the system pressure stays up and the main fire pump is never called upon for anything but an actual fire, when a real demand pulls the pressure down past even the jockey's ability to hold it. This keeps the main pump rested and its starts meaningful.
The same pattern is used on booster and pressure-maintenance systems that must hold a standing pressure with occasional small draw. A small maintenance pump covers the trickle demand and keeps the large pumps off during quiet periods, so the big pumps only stage on when genuine demand arrives. In every case the jockey is the buffer between constant small losses and the large pumps, and its whole purpose is to keep those large pumps from short-cycling.
The jockey and the main pump are coordinated by their pressure setpoints, arranged so the jockey always acts first. The jockey has a cut-in pressure at which it starts and a cut-out pressure at which it stops, and both sit above the main pump's start pressure. When a small leak drops the pressure to the jockey's cut-in, the jockey starts, pumps the pressure back up to its cut-out, and stops. The main pump's own start pressure is set lower still, so it only starts if the pressure keeps falling past the jockey's cut-in, which happens when the demand is larger than the jockey can supply.
That ordering is the whole logic of the arrangement. A minor leak that the jockey can handle never pulls the pressure down far enough to reach the main pump's start point, so the jockey deals with it alone. A real fire opens sprinklers and drops the pressure fast and far, straight past the jockey's cut-in and on down to the main pump's start pressure, so the main pump starts and stays running to fight the fire. Where more than one main pump exists, each has a progressively lower start pressure so they stage on in order as demand grows.
Getting the setpoints and the pressure band right matters in practice. The gap between the jockey's cut-in and cut-out sets how long it runs each cycle; too narrow a band and it short-cycles on every tiny fluctuation, too wide and the pressure swings more than desired. The margin between the jockey's cut-in and the main pump's start pressure has to be wide enough that normal jockey operation never nuisance-starts the main pump, but not so wide that a real demand is slow to bring the main pump on. These settings are chosen to fit the system and its applicable design rules.
The jockey pump is one of the most useful diagnostic signals in the whole system, because how often it runs is a direct measure of how leaky the system is. In a tight, healthy system the jockey cuts in only occasionally, running for a short burst now and then to make up slow thermal and fitting losses. When it starts running more often, or its cycles get longer, something is bleeding pressure faster than before, and that trend is visible long before the leak grows large enough to threaten the system's readiness.
That makes jockey run frequency a leak detector. A steady increase in cycles per hour points to a developing leak somewhere in the piping, a weeping valve, or a fitting that has loosened. A jockey that suddenly starts cycling continuously usually means a real leak has opened or, importantly, that a check valve is passing, letting pressure bleed backward so the jockey can never quite satisfy the system. A leaking discharge check valve on the main pump is a classic cause of a jockey that runs far more than it should, and it is exactly the kind of quiet fault that goes unnoticed until someone looks at the run pattern.
This is where remote monitoring earns its place on systems that are visited rarely and must simply be ready when needed. A cloud SCADA platform such as Merobix can log every jockey start and stop, trend the cycle rate over days and weeks, and alarm when the frequency climbs above its normal baseline, sending an alert to maintenance while the leak is still small. Watching the pump that is supposed to run occasionally, and flagging when it starts running too much, turns an invisible developing leak or a failed check valve into an early, actionable warning rather than a discovery made during an inspection or, worse, during an emergency.
The main fire pump is a large machine meant to run only in a real fire, so it should not start and stop for the small pressure drops caused by minor leaks and thermal changes. A jockey pump is a small pressure-maintenance pump that makes up those routine losses and holds the standby pressure, keeping the main pump rested and reserving its starts for genuine fire demand.
The jockey cuts in and cuts out at pressures set above the main pump's start pressure, so the jockey always acts first. A small leak drops pressure only to the jockey's cut-in, which the jockey restores, while a real fire drops pressure fast and far, past the jockey's cut-in and down to the main pump's lower start pressure, starting the main pump. This ordering ensures small losses are handled by the jockey and the main pump only runs on real demand.
It means the system is losing pressure faster than normal, which usually points to a developing leak, a weeping valve, or a check valve that is passing and letting pressure bleed backward. A jockey that suddenly runs almost continuously often means a real leak has opened or the main pump's discharge check valve is leaking. Trending jockey run frequency and alarming when it rises above its baseline catches these faults early.
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