A jockey pump is a small pump that maintains pressure in a fire protection piping system so the main fire pump doesn’t have to run. It compensates for minor pressure losses caused by small leaks and temperature changes, keeping the system pressurized and ready at all times. Without it, every tiny drop in pressure would trigger the main fire pump, wasting energy and wearing out critical emergency equipment.
How a Jockey Pump Keeps Pressure Steady
Fire sprinkler systems are filled with pressurized water at all times. Over hours and days, that pressure slowly drops. Pipe joints seep slightly. Check valves allow tiny amounts of backflow. Temperature shifts cause water to contract. These losses are small, but left unchecked, they’d eventually pull system pressure low enough to trigger the main fire pump.
The jockey pump watches for these small drops and corrects them automatically. A pressure switch monitors the system. When pressure falls to a preset “cut-in” point, the jockey pump kicks on and pushes a small amount of water into the piping until pressure climbs back to its “cut-out” point. The pump then shuts off and waits. This cycle might happen a few times a day in a well-sealed system, or more frequently in older buildings with more leakage.
The key design principle: the jockey pump’s discharge pressure must exceed the main fire pump’s shutoff pressure by at least 10 psi. This gap ensures the jockey pump can restore normal system pressure on its own, without the main pump ever waking up. If a sprinkler head actually opens during a fire, the water demand far exceeds what the jockey pump can supply, pressure continues to fall past the jockey pump’s range, and the main fire pump starts as intended.
Jockey Pump vs. Main Fire Pump
The difference between a jockey pump and the main fire pump comes down to scale. A main fire pump might deliver hundreds of gallons per minute at over 100 psi, powered by a large electric motor or diesel engine. A jockey pump, by contrast, is deliberately small. Its flow capacity is typically around 1% of the main fire pump’s rated capacity. If the main pump is rated for 500 gallons per minute, the jockey pump might move just 5 gallons per minute.
That small size is the whole point. The jockey pump is designed to be overwhelmed when real water demand occurs. When a sprinkler head opens, it flows far more water than the jockey pump can replace, so system pressure keeps dropping until it crosses the threshold that activates the main pump. The jockey pump can’t fight a fire, and it’s not supposed to. It just keeps the system primed and ready so the main pump can respond instantly when it matters.
Turbine-style pumps are a common choice for this role because they generate high pressures at low flow rates without needing much horsepower. Centrifugal pumps are also used. Either way, the required horsepower is modest since both the flow rate and the pressure boost are relatively small.
What a Jockey Pump Protects Against
The most obvious benefit is preventing unnecessary starts of the main fire pump. Every time a large pump motor starts up, it draws a surge of electrical current and puts mechanical stress on bearings, seals, and couplings. A main fire pump that cycles on and off repeatedly because of minor leaks will wear out far sooner than one that only runs during actual emergencies or scheduled tests. The jockey pump absorbs all that routine duty instead.
Jockey pumps also help prevent water hammer, which is the damaging shock wave that travels through pipes when water flow changes suddenly. By keeping pressure consistent and topping off the system gradually, the jockey pump avoids the abrupt pressure swings that come with a large pump starting and stopping. This protects pipe joints, fittings, and valves from the kind of repeated stress that leads to leaks and failures over time.
Core Components of a Jockey Pump Setup
A jockey pump installation includes several pieces working together:
- The pump itself: a small centrifugal or turbine pump sized for low flow and high pressure.
- An electric motor: typically a fraction of the main fire pump motor’s horsepower.
- A controller: receives signals from the pressure switch and tells the pump when to start and stop.
- A pressure sensing line: a small-diameter pipe that connects the system piping to the pressure switch, allowing the controller to monitor real-time system pressure.
The controller is the brain of the operation. It reads the pressure, compares it against the programmed cut-in and cut-out settings, and manages the pump accordingly. In a properly configured system, the jockey pump controller, the main fire pump controller, and the pressure sensing lines all work in a coordinated sequence: the jockey pump gets first crack at restoring pressure, and the main pump only starts if the jockey pump can’t keep up.
Sizing Guidelines
Jockey pumps are sized based on the system’s expected leak rate, not its fire flow demand. NFPA 20, the standard governing fire pump installations, specifies that the jockey pump should compensate only for normal leakage and minor pressure drops. It should never be large enough to maintain pressure if a sprinkler head opens.
A widely used rule of thumb is to size the jockey pump at 1% of the main fire pump’s rated capacity. For systems with underground piping, NFPA 24 allows some leakage in underground mains, and the guideline is to select a pump that can replenish the allowable leakage rate in 10 minutes or deliver at least 1 gallon per minute, whichever is larger. Oversizing creates problems: a jockey pump that flows too much water can mask a genuine sprinkler activation, delaying the main pump start when seconds count.
Common Problems and Warning Signs
Because jockey pumps run in short, automated cycles with no one watching, problems can go unnoticed until they cascade into bigger issues. The most common failures fall into a few categories.
Frequent short cycling, where the pump starts and stops every few minutes, usually points to either a pressure switch with too narrow a gap between its on and off settings or a jockey pump that’s oversized for the system. Each start-stop cycle stresses the motor, and dozens of cycles per hour will burn it out quickly. If you notice the jockey pump running far more often than usual, it can also indicate a new leak somewhere in the system that deserves investigation.
A jockey pump that runs continuously and never shuts off is a more urgent sign. This typically means the pump can’t build enough pressure to reach its cut-out point. The cause might be a failed pressure switch, a significant system leak, or an open test valve that someone forgot to close. Continuous running leads to motor overheating, which can destroy the pump entirely and leave the system unprotected against nuisance main pump starts.
On the other end, a jockey pump that fails to start at all, usually due to motor failure or a faulty pressure switch, means the main fire pump will take over pressure maintenance duties. The main pump will run more often than it should, accelerating wear on the equipment you most need to be reliable during a real fire.