A jockey pump is a small pressure-maintenance pump installed in fire protection systems to keep piping pressurized without running the main fire pump. It compensates for minor leakage, thermal expansion, and pressure drift so the primary pump starts only during actual fire demand. Sizing requires coordination between jockey pump capacity, pressure switch setpoints, main pump activation logic, and system leakage rates. A properly configured jockey pump prevents nuisance starts and protects the main pump from short-cycling, but an oversized unit can mask dangerous leaks or delay main pump response during real fire events.
In fixed fire suppression systems—wet pipe sprinklers, standpipes, foam systems, and high-rise risers—the jockey pump runs frequently while the main pump remains on standby. Selection depends on normal leakage rate, acceptable pressure band,suction arrangement, control sequence, and whether the system uses NFPA 20, FM Global, or local fire codes. Field performance ties directly to switch calibration, check valve condition, air removal, and maintenance access.
要点
- A jockey pump maintains fire system pressure between the main pump cutoff point and the activation setpoint, covering leakage without triggering the main pump.
- Capacity should exceed normal leakage but remain small enough that it cannot satisfy fire flow demand, ensuring the main pump starts during real events.
- Pressure switch settings control the operating band: jockey pump start pressure sits above main pump start pressure, with a narrow band to limit cycle frequency.
- Oversizing creates two problems: it can supply enough flow to delay main pump activation, and it hides leaks that should trigger investigation.
- Suction arrangement, check valve placement, air elimination, and controller coordination determine whether the system meets code acceptance tests.
How Jockey Pumps Fit Fire Protection Control Logic
Fire pump systems use staged pressure control. The main fire pump activates at a setpoint that indicates real demand—typically 5 to 10 psi below system design pressure. The jockey pump operates in a higher, narrower band to handle minor pressure loss. When system pressure drops to the jockey pump start point, the jockey pump runs until pressure recovers to its stop point. If pressure continues to fall and reaches the main pump start setpoint, the main pump takes over and the jockey pump stops or continues running depending on controller logic.
Typical setpoint layering looks like this: system design pressure 125 psi, jockey pump stop at 130 psi, jockey pump start at 120 psi, main pump start at 115 psi. The 10 psi jockey band covers thermal expansion, seal weepage, and small air leaks. If a sprinkler head opens or a hose valve is pulled, pressure drops through the jockey band into the main pump activation zone within seconds, ensuring fire flow begins before the jockey pump can compensate.
Controller coordination matters because some systems stop the jockey pump when the main pump runs, while others let both operate. Stopping the jockey pump during fire events reduces electrical load and simplifies diagnostics. Running both pumps can speed repressurization after the event ends, but it complicates flow testing and can create check valve chatter if the jockey pump discharge ties into the same header without proper isolation.
Sizing and Selection Criteria
The standard approach sizes jockey pump flow to replace system leakage with a safety margin, typically 1 to 3 gpm for small systems and up to 10 gpm for large high-rise or industrial installations. Head requirement matches the system pressure plus friction loss through the jockey pump piping and check valve. Motor power rarely exceeds 2 hp for standard commercial systems.
Selection also depends on suction source. If the jockey pump draws from the same suction tank as the main fire pump, it needs enough suction head to avoid cavitation at its operating pressure. Vertical turbine jockeys work when the tank is below grade. Horizontal centrifugal jockeys work with flooded suction or when the tank sits above the pump. Vertical inline jockeys save floor space but require overhead clearance for motor removal.
Materials and seal arrangements follow fire pump standards. Bronze or stainless-steel construction handles clean water systems. Mechanical seals with external flush lines prevent seal failures from dry running during maintenance or testing. Cast iron pumps cost less but may not meet aggressive water chemistry or seismic requirements depending on local amendments to NFPA 20.
| Selection Factor | Typical Range | Why It Matters |
|---|---|---|
| Flow capacity | 1 to 10 gpm | Must exceed leakage but not mask fire demand |
| Pressure rise | 10 to 30 psi above suction | Defines operating band and switch settings |
| Jockey band | 5 to 15 psi | Narrower band reduces cycles, wider band tolerates sensor drift |
| Suction arrangement | Flooded or lift up to 10 ft | Affects pump type and cavitation risk |
| モーター出力 | 0.5 to 2 hp | Result of flow, head, and efficiency, not a starting point |
Installation and Commissioning Checks
Jockey pump installations fail most often at the suction side, pressure switch calibration, and check valve sequencing. Suction piping should be short, direct, and free of air pockets. If the jockey pump shares a suction line with the main pump, the connection must not create turbulence or reduce available NPSH for either pump. Gate valves on both suction and discharge allow isolation for service without draining the system.
Pressure switches need field calibration because factory settings rarely match final system conditions. Use calibrated test gauges to verify start and stop points under no-flow conditions, then confirm that the jockey pump can lift system pressure into the stop band within a reasonable time. If the jockey pump runs continuously without reaching stop pressure, check for excessive leakage, undersized pump, or faulty pressure sensing.
Check valves prevent backflow from the system into the jockey pump when it stops. A failed or stuck check valve causes the jockey pump to short-cycle or allows the main pump to send high-pressure flow backward through the jockey pump. Some systems use a separate jockey pump discharge line with its own check valve to avoid interaction with the main pump check valve, especially when the main pump operates at pressures significantly higher than jockey pump shutoff.
Code acceptance testing requires running the jockey pump to verify it reaches the correct pressure band, then bleeding off system pressure to confirm the main pump starts at its setpoint without interference. Inspectors also check that the jockey pump cannot deliver fire flow—this is verified by observing that system pressure drops rapidly when a test valve simulating sprinkler demand is opened, triggering main pump activation before the jockey pump compensates.
Common Problems and Field Fixes
Frequent jockey pump cycling indicates leakage beyond normal rates. Check PRV weepage, test drain valves left partially open, malfunctioning air compressors on dry pipe systems, and packing leaks on OS&Y valves. If leakage is within acceptable limits but cycling remains excessive, widen the pressure band by adjusting the stop setpoint upward or the start setpoint downward, staying within code limits.
Jockey pump failure to maintain pressure can result from worn impellers, clogged suction strainers, air binding, or check valve leakage. Verify discharge pressure under no-flow conditions using a test gauge at the pump. If shutoff pressure is low, inspect the impeller and pump internals. If shutoff pressure is correct but system pressure still drops, the problem lies downstream—leaking valves, faulty pressure switches, or excessive system demand.
Oversized jockey pumps delay main pump starts during fire events, especially in systems with marginal design margins. If flow testing reveals the jockey pump can supply partial sprinkler demand, reduce capacity by throttling the discharge valve, replacing the impeller with a smaller diameter, or installing a smaller pump. Do not rely on pressure switch adjustments alone to fix oversizing—they can mask the problem without solving it.
Maintenance and Documentation
Jockey pumps run more frequently than main fire pumps, so wear patterns differ. Inspect seals, bearings, and couplings quarterly. Log run time, cycle count, and any pressure anomalies to identify trends before failures occur. Suction strainers should be checked monthly in new installations and quarterly in stable systems. Motor current draw should remain steady; increasing current suggests bearing wear or impeller fouling.
Document the original setpoints, flow capacity, head at duty point, suction arrangement, and piping layout. When troubleshooting or replacing the pump, this baseline reveals whether the system changed or the pump degraded. Include pressure switch model numbers and calibration dates so future technicians can verify settings without guessing.
Annual testing should include a full cycle test: bleed system pressure to start the jockey pump, verify it reaches stop pressure, continue bleeding to trigger the main pump, and confirm both pumps interact correctly. Record the time required for the jockey pump to restore pressure and compare it to the original commissioning data. Significant increases in restoration time indicate leakage growth or pump degradation.
よくある質問
Can I use a jockey pump on a dry pipe or deluge system?
Yes, but the jockey pump maintains air or nitrogen pressure in the supervised piping, not water pressure. Dry pipe systems use air compressors as the primary maintenance device, with jockey pumps serving as backup or in hybrid wet-dry configurations. Deluge systems remain unpressurized until activation, so jockey pumps apply only to the pilot or priming lines, not the main distribution piping.
What happens if the jockey pump runs continuously?
Continuous running means the pump cannot overcome system leakage or reach its stop setpoint. Check for open test drains, PRV leaks, failed check valves, or undersized pump capacity. If leakage is within acceptable limits, verify the pressure switch is calibrated correctly and the pump delivers its rated shutoff pressure. Prolonged continuous operation will overheat the motor and damage seals.
Should the jockey pump and main pump share the same suction line?
They can share suction if the piping is sized to provide adequate flow and NPSH for both pumps simultaneously, though this is rare since they typically do not run together during fire events. Separate suction lines simplify troubleshooting and allow jockey pump maintenance without affecting main pump availability. Code does not prohibit shared suction, but it must meet hydraulic requirements for both pumps.
How do I know if my jockey pump is oversized?
Open a test valve simulating one or two sprinkler heads. If system pressure drops slowly and the jockey pump keeps running without triggering the main pump, it is oversized. The jockey pump should lose the pressure battle within 30 to 60 seconds of significant demand, forcing main pump activation. Flow testing during commissioning should confirm this behavior.
Do I need a separate controller for the jockey pump?
Most fire pump controllers include jockey pump control as an integrated function, with dedicated pressure switches and starter contacts. Separate jockey pump controllers are used in retrofit installations or when the main controller lacks jockey pump provisions. Either approach works if the control logic correctly sequences jockey start, jockey stop, main start, and alarm functions.
結論
A jockey pump solves a specific control problem: it keeps fire protection systems pressurized without wearing out the main pump through unnecessary starts. Correct application depends on understanding the pressure band, leakage profile, control sequence, and code requirements that govern fire pump installations. Sizing must balance leakage compensation against the risk of masking fire demand. Installation must address suction conditions, check valve placement, and switch calibration. Maintenance must track cycle frequency and pressure trends to catch problems before they compromise system readiness. When these factors align, the jockey pump extends main pump life and reduces nuisance alarms. When they conflict, the result is short-cycling, delayed activation, or hidden leaks that threaten fire protection reliability.