Jockey pump sizing NFPA 20

Most people approach firefighting systems based on the main fire pump. However, much importance is also attached to a jockey pump. In addition, this pump keeps the system pressurized, minimizes the unwanted running of the main pumps, and maintains the entire network ready at all times. That is why NFPA 20 gives detailed guidelines related to the selection and sizing of jockey pumps.

This article will walk you through exactly what a jockey pump is, why it is needed, and how the engineers correctly size them based on NFPA 20. Simple language is used, allowing the beginner to easily understand.

What Is a Jockey Pump?

The jockey pump is a small pump installed in the firefighting system to maintain pressure in the fire pipeline. Due to small pressure drops during temperature changes or tiny leaks, this jockey pump automatically turns ON to restore the pressure.

Since it deals only with small losses, it generally has a much smaller capacity than the main fire pump. Still, it saves the main pump from cycling on again and again; this protects the pump, saves energy, and prolongs equipment life.

Why Jockey Pumps Are Needed (According to NFPA 20)

NFPA 20 clearly points out that a jockey pump shall be provided in every fire pump installation unless the pressure is maintained by another approved method. That is because:

This keeps the system always pressurized.

It prevents the main pump from unnecessary start–stop cycles.

This ensures faster system response in case of an actual fire.

It compensates for very small pressure drops.

It prevents water hammer by making sure the pressure is stable.

In firefighting networks, pressure stability is very important; hence, the jockey pump enhances the reliability of the whole system.

How to Size a Jockey Pump (NFPA 20 Method)

Sizing a jockey pump is straightforward if the recommendations in NFPA are followed. The idea behind this is to size it so that system pressure is restored smoothly but never allows it to replace the main fire pump.

1. Flow Rate Selection

NFPA 20 recommends the flow rate of a jockey pump should be:

3% to 10% of the main fire pump capacity

For example:
If the main fire pump is 1000 GPM, the jockey pump flow should be between 30 to 100 GPM.

Most engineers usually choose about 3–5% for stability. This ensures the jockey pump only deals with small losses and does not take over a fire event.

2. Pressure Setting

The pressure of the jockey pump must be:

Higher than main fire pump start pressure
but

Less than the pressure rating of the system

Typically:

Jockey pump cut-in: 5 to 10 psi below system pressure

Fire pump cut-in: 10 psi below jockey pump cut-in This sequence ensures that only the jockey pump starts for normal losses, while the main pump starts only during a real fire.

3. Head Selection

Jockey pump head, in general, is:

10 psi higher than the main pump churn pressure

This difference in size ensures that the jockey pump can build the system pressure on its own, but never override or replace the main pump.

4. Pump Type

Most jockey pumps are:

Vertical multistage centrifugal pumps

Horizontal centrifugal pumps

Vertical multistage pumps are preferred because they produce high pressure with a compact size.

5. Motor Requirements

The jockey pump motor shall be:

Sized for continuous duty

Able to deliver the required pressure

Connected to a reliable power source

NFPA 20 requires the jockey pump controller to be automatic so that it switches ON and OFF based on system pressure.

Benefits of a Correctly Sized Jockey Pump

A properly sized jockey pump will provide the following advantages:

Maintains system pressure 24/7

Reduces wear on the fire pump

Improves response time during emergencies

Minimizes pressure fluctuation

Prolongs system life-span

Reduces breakdowns and service issues

This is why jockey pumps are so important in fire protection systems.

Common Mistakes to Avoid

Even though the sizing rules are simple, there are a few mistakes engineers must avoid:

Choosing a jockey pump too large

Matching its pressure too close to the fire pump

Ignoring system leakage patterns

Poor pressure controller quality

Installation of the pump without check valve

An incorrectly sized jockey pump can cause the fire pump to start unintentionally or fail to hold pressure properly.

Although a jockey pump can be very small in size, it can contribute largely to firefighting systems. NFPA 20 affords clear direction on getting the right sizing to avoid the fire pump from running unnecessarily and keeping the system ready for any emergency. Engineers can make the system more reliable and efficient through the proper selection of flow, pressure, motor, and controls.

BIf you are designing or learning firefighting systems, understanding jockey pumps is one of the important steps toward mastering NFPA 20 standards.