Understanding Fire Pump Pressure Switches: How They Work and Why They Matter
Understanding Fire Pump Pressure Switches: How They Work and Why They Matter
Understanding Fire Pump Pressure Switches: How They Work and Why They Matter
Within every automatic fire pump system, there is one relatively small component that plays a critical role in protecting life and property: the pressure switch.
Whether controlling a jockey pump, an electric fire pump, or a diesel fire pump, pressure switches are responsible for detecting changes in system pressure and initiating the appropriate response.
Without a correctly functioning pressure switch, a fire pump may fail to start when required or start unnecessarily, leading to reliability issues and potential non-compliance.
In this article, we'll explain what fire pump pressure switches are, how they work, where they are installed, common faults engineers encounter, and why regular testing is essential.
What Is a Fire Pump Pressure Switch?
A pressure switch is an electromechanical device that monitors water pressure within a sprinkler system.
Its purpose is simple:
To detect a pressure change and activate a set of electrical contacts when a predetermined pressure is reached.
In fire protection systems, pressure switches are commonly used to:
- Start jockey pumps
- Stop jockey pumps
- Start electric fire pumps
- Start diesel fire pumps
- Generate alarm signals
- Monitor system conditions
Although small in size, pressure switches are one of the most important control components within a fire pump installation.
Why Are Pressure Switches Needed?
A fire pump must start automatically when water demand occurs.
The easiest and most reliable way to achieve this is by monitoring sprinkler system pressure.
Under normal conditions, the sprinkler system remains fully pressurised.
When a sprinkler head operates:
- Water begins flowing from the system.
- Pressure starts to fall.
- The pressure switch detects the pressure reduction.
- The switch changes state.
- The fire pump controller receives a start signal.
- The fire pump starts automatically.
This entire process happens within seconds.
Where Are Pressure Switches Installed?
Pressure switches are typically connected to the sprinkler system via a sensing line.
They are commonly found:
On Jockey Pump Systems
To start and stop the jockey pump.
On Electric Fire Pumps
To initiate automatic pump operation.
On Diesel Fire Pumps
To initiate automatic engine starting.
On Alarm Systems
To provide flow or pressure-related alarm signals.
Many installations utilise multiple pressure switches, each performing a specific function.
How Does a Pressure Switch Work?
Inside the pressure switch is a sensing mechanism that responds to changes in pressure.
Depending on the design, this may include:
- A diaphragm
- A piston
- A bellows assembly
As pressure changes, the internal mechanism moves.
When the pressure reaches a predetermined value, electrical contacts either:
Close
Completing an electrical circuit.
or
Open
Breaking an electrical circuit.
This change in contact position is what signals the controller to take action.
Pressure Switches in a Typical Fire Pump System
A typical fire pump installation may contain multiple pressure switches.
For example:
DeviceTypical Start PressureJockey Pump9.5 BarElectric Fire Pump8.5 BarDiesel Fire Pump8.0 Bar
Under normal conditions:
- The jockey pump starts first.
- If pressure continues to fall, the electric fire pump starts.
- If additional redundancy is required, the diesel fire pump starts at a lower pressure setting.
This staggered arrangement ensures the correct response for different operating conditions.
Why Are Pressure Settings So Important?
Pressure settings determine how the system behaves during both normal operation and fire conditions.
Incorrect settings can lead to:
Nuisance Starts
The fire pump starts unnecessarily.
Excessive Jockey Pump Cycling
Increased wear and maintenance.
Delayed Fire Pump Operation
Potential fire protection issues.
Simultaneous Pump Starts
Unnecessary stress on equipment.
Correct pressure settings are therefore a critical part of commissioning and maintenance.
Common Types of Pressure Switch
Several different pressure switch designs are used within fire protection systems.
Mechanical Pressure Switches
The most common type.
Advantages include:
- Proven reliability
- Simple operation
- Easy adjustment
- Long service life
Electronic Pressure Switches
Increasingly common on modern installations.
Advantages include:
- Improved accuracy
- Digital displays
- Advanced diagnostics
- Easier monitoring
Differential Pressure Switches
Used in specialist applications where pressure differences must be monitored.
Common Fire Pump Pressure Switch Faults
Pressure switches are exposed to continuous system pressure and can eventually develop faults.
Incorrect Calibration
One of the most common issues.
Symptoms include:
- Incorrect start pressures
- Pumps starting too early
- Pumps starting too late
Blocked Pressure Sensing Lines
Debris can restrict pressure transmission.
Symptoms include:
- Delayed operation
- Inconsistent readings
- Failure to start
Contact Wear
Electrical contacts wear over time.
Symptoms include:
- Intermittent operation
- Failure to signal controller
- Unreliable starts
Internal Corrosion
Particularly common in older installations.
Symptoms include:
- Erratic operation
- Calibration drift
- Complete failure
Mechanical Fatigue
Years of pressure cycling can wear internal components.
Symptoms include:
- Inconsistent switching
- Unstable settings
- Premature failure
Signs a Pressure Switch May Need Replacing
Engineers should investigate pressure switches if they notice:
- Fire pumps failing to start
- Incorrect start pressures
- Frequent false starts
- Pumps starting unexpectedly
- Inconsistent system pressures
- Repeated controller alarms
Many pressure switch failures develop gradually, making regular testing particularly important.
How Are Pressure Switches Tested?
During routine maintenance, engineers typically:
Verify Start Pressures
Confirm switching occurs at the correct pressure.
Check Stop Pressures
Verify proper operation where applicable.
Inspect Pressure Lines
Ensure sensing lines remain clear.
Test Electrical Contacts
Confirm reliable operation.
Compare Against Previous Records
Identify any developing drift or calibration issues.
Testing helps ensure the pressure switch remains capable of initiating fire pump operation when required.
Why Pressure Switch Reliability Matters
A fire pump controller can only react to the information it receives.
If the pressure switch fails:
- The controller may never receive a start signal.
- The fire pump may not operate.
- Sprinkler performance may be compromised.
For this reason, pressure switches are considered safety-critical components within the fire protection system.
Common Pressure Switch Manufacturers
Many fire pump installations utilise pressure switches from manufacturers such as:
- Mercoid
- Danfoss
- United Electric
- SOR
- Ashcroft
- WIKA
The specific model selected depends on:
- System pressure
- Approval requirements
- Controller design
- LPCB or FM compliance requirements
Selecting Replacement Pressure Switches
When replacing a pressure switch, engineers should ensure:
- Pressure range is correct
- Switching differential is suitable
- Electrical ratings match requirements
- LPCB or FM approvals are maintained where necessary
- Installation instructions are followed
Using an incorrect pressure switch can compromise system operation and compliance.
Final Thoughts
Pressure switches may be relatively small components, but they perform one of the most important functions within a fire pump installation.
By continuously monitoring sprinkler system pressure and initiating automatic pump operation when required, they form a critical link between the sprinkler system and the fire pump controller.
Routine inspection, testing, and maintenance help ensure these vital components remain reliable and ready to perform when needed.
At Fire Pump Spares, we understand the importance of maintaining every component within a fire protection system. Whether you're looking for replacement pressure switches, spare parts, technical information, or engineering support, our goal is to help keep fire pump installations operating safely and reliably.
Because when sprinkler system pressure falls during a fire emergency, the pressure switch is often the first component expected to react.