1. The jockey pump function: small adjustments, great reliability
Imagine a newly installed fire-fighting system, pressurized to 7 bar, with all valves closed. After a few days, pressure starts dropping slowly — perhaps 0.1 bar per day. This is not a catastrophic failure; it is expected behavior of any piping network with dozens or hundreds of threaded joints, flanges, check valves and sprinklers.
Each of these points has an acceptable level of microscopic leakage not visible nor measurable with common instruments, but summing a pressure loss over time. Without any replenishment mechanism, pressure would continuously drop until reaching the main pump start setpoint, which would then activate, restore pressure, stop, and the cycle would restart.
This repeated main pump starting is exactly what the jockey pump exists to prevent. Positioned in the circuit as a secondary supply point, it operates with setpoints much higher than the main pump: typically starts at 6.5 bar and stops at 7.0 bar (assuming a system rated at 7 bar).
Whenever pressure drops to 6.5 bar due to accumulated microscopic leakage, the jockey starts, delivers a very small volume of water to the system to restore pressure, and shuts off on its own when reaching 7.0 bar. The cycle may repeat several times a day in a normally leaking system, or once a day in a very well-sealed system — but the main pump is never activated for this reason, remaining intact and available for real combat.
2. Sizing at 1% of main flow: the rule of thumb
NFPA 20 Annex A section A.4.26 explicitly recommends sizing the jockey pump at approximately 1% of main pump rated flow.
This rule is simple and well-founded: a too-small jockey cannot compensate for normal leaks and allows pressure to drop to the main pump setpoint; a too-large jockey, on the contrary, is capable of delivering enough flow to fight small fires, which is undesirable because it masks the need to activate the main pump and prevents the pressure-drop detection system from working as designed.
For a 1,500 gpm main pump, the correct jockey is approximately 15 gpm. For a 500 gpm pump, the jockey is 5 gpm. For a 3,000 gpm pump, the jockey is 30 gpm.
Jockey discharge pressure should be about 10% higher than main pump discharge pressure, to ensure the shutoff setpoint is above system static pressure. In a 7 bar system, this means a jockey sized to deliver approximately 7.7 bar at operating point — sufficient to maintain full water column at any piping point, including the tallest building sprinkler.
For tall vertical buildings, jockey pressure must additionally compensate for building static column, which can raise the requirement to 10, 12 or even 15 bar for multi-story residential towers.
3. Vertical multi-stage stainless construction
The typical construction of a jockey pump for a fire-fighting system is vertical multi-stage in stainless steel — a specific geometry quite different from the horizontal centrifugal pumps used as the main pump.
The vertical multi-stage pump can generate high pressures (up to 20 bar or more) with small flow in a compact casing, which is exactly the profile needed for a jockey. 304 or 316 stainless steel construction is standard because fire system water frequently sits stagnant for long periods, and a cast iron body would suffer surface corrosion that would eventually contaminate the water with oxide particles.
The choice between 304 and 316 depends on water quality. For treated potable water or clean reservoir water, 304 fully meets requirements and is the more economical option. For brackish water (intake in coastal regions with saltwater infiltration), water with chlorides above 300 mg/L, or environments with salt atmosphere, 316 is recommended for better pitting resistance.
For extreme environments (direct seawater intake), the choice would be duplex — but this is rare in Brazilian fire-fighting systems, which typically draw from a dedicated reservoir. FB Bombas integrates the jockey pump into the skid already sized, wired and configured with correct setpoints, eliminating the need for the designer to specify and procure this component separately.
4. Continuous operation as a serious leak indicator
An important characteristic of jockey pump operation is that it is not designed for continuous service. On the contrary, its continuous-regime operation is a clear alert of system problems. Under normal conditions, the jockey should operate intermittently — perhaps a few minutes per hour, or a few cycles per day, depending on the normal leakage level of the system.
If the operator or the monitoring system detects that the jockey is on all the time, this means accumulated leakage in the system is above what the jockey can compensate, or there is a serious point leak somewhere that needs identification and immediate repair.
For this reason, the main pump controller in well-designed systems includes a jockey operation-hour counter and an alarm triggered when this counter exceeds a configured limit (for example, more than 30 continuous minutes, or more than two total hours in a 24-hour period). When the alarm triggers, maintenance staff must investigate the cause before the leak grows to the point of affecting the main pump.
It is a proactive protection layer that avoids surprises: the system signals the problem before it becomes serious.
5. Integration with the main pump controller
In a complete FB Bombas fire-fighting skid, the jockey pump does not have its own controller: it is controlled by the same panel as the main pump, with integrated logic respecting each pump's setpoints. This integration simplifies operation and centralizes monitoring — all alarms, hour counts and events appear in a single interface.
Internal logic is simple: when pressure drops to the jockey setpoint (6.5 bar), the controller energizes only the jockey; if pressure continues to drop and reaches the main setpoint (6.0 bar), the controller energizes the main pump in parallel with the jockey. The jockey may continue operating or be automatically stopped per controller programming.
An important distinction compared to the main pump: the jockey has automatic shutoff. When pressure reaches the shutoff setpoint (7.0 bar), the jockey simply turns off on its own, without need for manual command. This is acceptable because the jockey is not the combat component — it is the maintenance component. The mandatory manual shutoff of NFPA 20 section 10.5.2.1 applies only to the main pump, which is the one actually fighting the fire.
The jockey can turn on and off dozens of times a day without any human intervention, and this is normal expected operation.
