Many people looking at a fire pump station for the first time ask the same question:
Why does the main fire pump not start immediately?
After all, it is the most powerful unit in the system. It provides the required fire flow and pressure. Why should a smaller pump respond first?
The answer lies in one of the basic principles of fire pump system design:
Not every pressure drop means there is a fire.
For this reason, many fire pump installations use a jockey pump to manage minor pressure losses while keeping the main fire pump ready for significant system demand.
Not Every Pressure Drop Is an Emergency
Pressure inside a water-based fire protection system can change for several reasons.
Possible causes include:
- Minor leakage
- Valve seepage
- Temperature-related volume changes
- Testing activities
- Pressure-sensing tolerances
- Small losses over time
If the main fire pump responded to every minor pressure change, it could start unnecessarily.
This may lead to:
- Additional motor or engine starts
- Increased mechanical stress
- Pressure surges
- Unnecessary alarm activity
- Greater maintenance requirements
- Difficulty identifying abnormal system behaviour
A separate pressure-maintenance pump prevents the main fire pump from responding to conditions that do not require fire-flow capacity.
What Is a Jockey Pump?
A jockey pump is a small pressure-maintenance pump installed as part of a fire protection system.
Its primary function is to maintain normal system pressure and compensate for minor losses without starting the main fire pump.
A jockey pump can help:
- Restore pressure after small losses
- Compensate for minor leakage
- Keep the fire protection network pressurised
- Reduce unnecessary main pump starts
- Maintain system readiness
Although smaller than the main fire pump, its role is critical to the operating logic of the station.
A Jockey Pump Is Not Designed to Fight a Fire
The jockey pump is not intended to provide the required sprinkler, hydrant, hose, or standpipe flow.
Its capacity is limited because its role is pressure maintenance—not firefighting.
If genuine fire demand occurs, the amount of water leaving the system exceeds the jockey pump’s capacity. Pressure therefore continues to fall until the main fire pump reaches its start setpoint.
An oversized jockey pump could potentially delay main pump activation by satisfying more demand than intended. Its capacity and settings must therefore be selected carefully.
How Does the Fire Pump Starting Sequence Work?
A typical pressure-based sequence may operate as follows:
- A minor pressure loss occurs.
- System pressure reaches the jockey pump’s start setpoint.
- The jockey pump starts and attempts to restore pressure.
- If the demand is small, pressure recovers.
- The jockey pump reaches its stop setting and stops.
- If demand is too great, pressure continues to fall.
- The main fire pump reaches its lower start setpoint.
- The main pump starts and supplies the required fire flow.
The exact settings and operating sequence must follow the approved project design and applicable requirements.
Does the Jockey Pump Always Start First in a Real Fire?
Not necessarily in a clearly separated sequence.
If a large sprinkler, hydrant, or hose demand develops quickly, system pressure may pass through the jockey pump’s start point and reach the main fire pump’s setting within a very short time.
The jockey pump may receive the earlier pressure signal, but it cannot meet genuine fire demand. The main fire pump starts as pressure continues to fall.
The system does not identify fire through human-like analysis. It responds to predefined hydraulic pressure setpoints.
When Does the Main Fire Pump Start?
The main fire pump starts when system pressure falls to its defined activation point.
This may occur because of:
- Sprinkler operation
- Fire hose demand
- Standpipe use
- Hydrant demand
- System testing
- A major pipe failure
- Another substantial water discharge
A pressure drop can activate the main pump even if the cause is not a fire. The controller responds to the hydraulic condition—not directly to flames or smoke.
Why Are the Pressure Settings Different?
The jockey pump’s start pressure is typically set higher than the main fire pump’s start pressure.
This creates an operating hierarchy:
- Normal maintained pressure
- Jockey pump start pressure
- Main fire pump start pressure
- Additional pump start settings where required
The separation between setpoints helps prevent simultaneous or unnecessary starts.
Setpoints should be determined using:
- Static water-supply pressure
- Pump curves
- Required system pressure
- Building elevation
- Pressure-sensing arrangement
- Controller characteristics
- Applicable fire protection requirements
They should not be selected through a universal rule without project-specific engineering.
Why Protect the Main Fire Pump from Unnecessary Starts?
The main fire pump’s role is not to manage ordinary pressure fluctuations. It must remain ready to provide full performance during significant fire protection demand.
Avoiding unnecessary starts can help reduce:
- Starting stress
- Mechanical wear
- Battery use in diesel systems
- Fuel consumption during testing or accidental starts
- Unnecessary controller operation
- Pressure disturbances
- Maintenance requirements
This does not mean the main pump should remain untested. Periodic testing is essential to confirm readiness.
What Is the Role of an Additional Fire Pump?
Some installations include more than one fire pump because of hydraulic demand, driver requirements, redundancy strategy, or the approved fire protection design.
An additional unit may provide:
- Extra capacity
- An alternative driver
- Support if another pump is unavailable
- Greater system resilience
However, a second fire pump does not automatically guarantee uninterrupted operation. Water supply, controllers, power or fuel, pipework, valves, and other shared failure points must also be considered.
The required configuration depends on applicable standards and authority approval.
Why Is Reliability Sometimes About Operating Less?
Continuous operation is not automatically evidence of a well-designed system.
Reliability often comes from ensuring that each component operates only for its intended purpose:
- The jockey pump manages minor pressure losses.
- The main fire pump supplies significant fire demand.
- Additional pumps operate according to the approved sequence.
- Controllers monitor and initiate the required actions.
This division of responsibility helps maintain system readiness without using the largest equipment for every small change.
What Happens If the Jockey Pump Runs Frequently?
Frequent jockey pump operation may indicate a problem such as:
- System leakage
- A leaking valve
- A defective non-return valve
- Incorrect pressure settings
- Pressure-sensing problems
- Temperature-related pressure variation
- Damaged pipework
Repeated operation should be investigated because it may reveal a developing system impairment.
How Is the System Kept Ready?
Readiness depends on more than the starting sequence.
The complete installation requires:
- Periodic inspection and testing
- Correctly positioned valves
- Reliable water supply
- Available electrical power or fuel
- Functional controllers
- Suitable pump-room conditions
- Accurate pressure sensing
- Alarm supervision
- Planned maintenance
NFPA 20 addresses the installation of stationary fire pumps, including electric and diesel drives, controllers, and acceptance testing. The applicable edition and project requirements must be confirmed with the authority having jurisdiction.
Conclusion
The main fire pump does not respond to every small pressure loss because not every pressure loss represents a fire demand.
The jockey pump maintains pressure and manages minor system changes. If demand exceeds its limited capacity, pressure continues to fall and the main fire pump starts to provide the required fire protection flow.
This sequence is not based on a lack of power. It is based on a deliberate division of responsibility.
Reliable fire pump systems do not activate every component at once. They ensure that the correct equipment responds at the correct pressure and for the correct purpose.
Frequently Asked Questions
Why does the jockey pump start before the main fire pump?
Its start setpoint is normally higher, allowing it to correct minor pressure losses before the main fire pump is required.
Does the jockey pump supply water during a fire?
It may operate briefly, but it is not designed to provide the required fire flow. Genuine demand should cause the main fire pump to start.
How does the main fire pump know there is a fire?
It does not directly detect fire. Its controller normally responds to a pressure drop through the approved sensing arrangement.
What happens if the jockey pump is too large?
It may satisfy more flow than intended and delay the pressure reduction required to start the main fire pump.
Why does a jockey pump keep starting and stopping?
Possible causes include leakage, faulty valves, incorrect setpoints, pressure-sensing problems, or other system pressure losses.
Does every fire pump station use the same start sequence?
No. The sequence depends on the approved hydraulic design, number of pumps, driver arrangement, applicable standards, and authority requirements.