Wholesale Pneumatic Solenoid Valve And Sensor Units Factory, Manufacturers

Product Overview

What Is a Pneumatic Solenoid Valve and Sensor Unit?

Definition

A pneumatic solenoid valve and sensor unit is an electro-pneumatic module that combines a solenoid-operated air valve with one or more sensors in a single housing or a matched pair. The solenoid turns an electrical signal from a switch or control unit into an air action, such as engaging a differential lock or raising a lift axle, and the sensor reports back the resulting pressure or position so the driver and the vehicle electronics know that the action has taken place.

Most air-operated functions on a modern commercial vehicle are not controlled by air lines running to the driver. They are controlled by a wire. A switch on the dashboard or a message from a control unit energises a solenoid valve near the component, and that valve directs compressed air where it is needed. The same function needs to report back, because a driver who selects differential lock or a lift axle expects to see confirmation that the lock has engaged or the axle has lifted. The solenoid valve does the work, the sensor gives the confirmation, and in this product family both are designed to work as a pair.

From Electrical Signal to Air Action

A solenoid valve contains a coil around a movable steel core, called the armature. When current flows, the coil generates a magnetic field that pulls the armature against a spring and opens or closes an air passage. In a direct-acting valve, the armature moves the seat itself, which suits small flows. In a pilot-operated valve, the armature opens a small pilot passage, and air pressure moves a larger piston or diaphragm that controls the main flow. Pilot operation allows a small coil to switch a large flow with low power.

Valve Functions: 2/2, 3/2 and 5/2

The two numbers describe how many ports and positions the valve has. A 2/2 valve has two ports and two positions and simply opens or shuts one line. A 3/2 valve has supply, working and exhaust ports and either feeds an actuator or vents it, which suits single-acting cylinders such as differential lock or PTO engagement. A 5/2 valve feeds a double-acting cylinder in either direction, and is used for gearbox range and splitter shifting. Each type can be normally closed or normally open, which decides the behaviour when power is lost.

Sensor Functions: Switches, Transducers and Position Sensors

The sensor half of the unit can take several forms. A pressure switch closes or opens a contact at a set pressure, for example to show that a low-pressure warning threshold has been crossed. A pressure transducer gives a continuous electrical output, typically a voltage or current proportional to pressure, and feeds it to a control unit or gauge. A position sensor detects whether a cylinder piston or shift fork has reached the engaged or released end position. The output type must match the input of the vehicle electronics.

Coils, Connectors and Supply Voltage

Trucks and buses commonly run 24V systems, while some vehicles use 12V, and coils are wound for one or the other. A 24V coil on a 12V circuit will not switch reliably, and a 12V coil on 24V will overheat. Connectors vary from industrial rectangular plugs to sealed automotive types, and a good unit is only useful if its connector matches the vehicle harness. Coil power draw is normally a few watts, low enough for direct switching from a control unit output.

Electrical Protection and Environmental Sealing

A solenoid coil generates a voltage spike when it is switched off, and this can damage control units unless the circuit includes a suppression diode or the vehicle electronics are designed to tolerate it. Solenoid valves and sensors are also installed in wheel arches, on chassis rails and near axles, where water, dirt and salt are constant. Seals and housings with a high ingress protection rating are therefore essential to long life.

Matching the Unit to the Wiring and Air Function

Match the valve function and normal position, the supply voltage, the port thread, the sensor type and output, the connector type and the mounting arrangement. A unit with the right air function but the wrong connector or sensor output is a common source of returns, so always check the electrical side as carefully as the pneumatic side.

Fit point: near the air-operated component
Function: converts electrical signals to air actions
Valve types: 2/2, 3/2 and 5/2, NC or NO
Sensor types: pressure switch, transducer, position sensor
Supply voltage: 12V or 24V DC
Service parts: coil, connector, seal kit, sensor

Technical Data

Solenoid Valve and Sensor Unit Model Range

Standard configurations below. Custom coil voltages, port threads, sensor outputs and connectors can be produced to your drawing.

Table 1 — Genuine gzbrake.com Ref NO. and OE cross-reference data for representative European Solenoid Valve & Sensor products.

Ref NO.	Product Name	Application	Technical Specification	OE / Cross-Reference (Sample)	Cross-Ref. Count	Product Line
4721730010	3/2 Way Solenoid Valve for European Series	MERCEDES	3/2 Solenoid Valve	MERCEDES:A0009973312,0009973712	1	European Solenoid Valve & Sensor
4721700800	Enhanced 3/2 Way Solenoid Valve for European Series	MERCEDES	3/2 Solenoid Valve	MERCEDES:A0009973612	1	European Solenoid Valve & Sensor
4721707970	12V Solenoid Command Valve for American Chassis	VOLVO	Port 1 = M6x1,Port 2 = Ø14.5,Port 4 = 1/4 NPTF,Voltage = 12V DC,Socket: Bayonet DIN 725...	VOLVO:S4721707970, FREIGHTLINER, KENWORTH, MACK, MERITOR	1	European Solenoid Valve & Sensor
4721729010	Precision 3/2 Way Solenoid Valve Assembly for European Series	MERCEDES	MERCEDES	MERCEDES:A0009975212, 0009973812	1	European Solenoid Valve & Sensor
4630840310	Pneumatic Pressure Sensor	KRONE	Port 11,12 = 2xM16x1.5,Port 21,22 = 2xM16x1.5, 2xM16x1.5,Port 3.1 = M22x1.5,Voltage = 2...	KRONE:515003124	1	European Solenoid Valve & Sensor
20590252	Normally Closed Solenoid Directional Control Valve	VOLVO	Port 1 = 1/8'NPT,Port 2 = Flange DIA 90,Port 22 = 1/8'NPT Pluged,Port 4 = Quick Connect...	VOLVO:20514657,20366720,3192385,21450362,20514687	1	European Solenoid Valve & Sensor
21031448	Enhanced Pneumatic Differential Pressure Sensor	VOLVO	Port 1,2 = M12x1.5 with special Fitting,Voltage = 24V DC,Socket: Bayonet DIN 72585-A1-2.3	VOLVO:21031448	1	European Solenoid Valve & Sensor
51259020130	High-Temperature Proportional Solenoid Valve	MAN	Port 1,3 = 2x M16x1.5 VOSS232 NG8,Port 4,5 = 2x M10x1 VOSS232 NG6,Voltage = 24V DC,Sock...	MAN:51.25902-0130	1	European Solenoid Valve & Sensor

Ref NO. and cross-reference numbers above are drawn directly from our European Solenoid Valve & Sensor product range on gzbrake.com. Cross-reference lists are sampled for space; contact us with your vehicle's OE number or chassis details for the complete, current cross-reference list and stock availability.

Typical Control Functions

Differential Lock ControlPTO EngagementLift Axle ControlExhaust Brake ControlEngine Brake FeedAir Suspension LiftingTransmission Shift ControlSplitter and Range ControlTail Lift ControlAir Horn SwitchingDoor ActuationBrake Light Pressure SignalLow Pressure WarningParking Brake IndicatorGauge Pressure SenderRetarder ControlFifth Wheel Slide ControlTipper Body Valve

Working Principle

How a Solenoid Valve and Sensor Unit Works

The unit turns a switching signal into an air action and reports the result. Five stages describe a typical cycle.

Signal Sent

The driver operates a switch or a control unit sends a command. Electrical current flows to the solenoid coil through the connector.

Armature Moves

The coil creates a magnetic field that pulls the armature against its spring. In a pilot-operated valve this opens a small pilot passage.

Air Directed

The main valve element changes position, connecting the supply to the working port. Air flows to the cylinder or actuator and the function engages.

Sensor Confirms

The pressure switch, transducer or position sensor detects the change and sends an electrical signal to the dashboard or control unit.

Signal Removed

When current stops, the spring returns the armature. The valve vents the working port, the function disengages and the sensor output returns to its rest state.

What Happens When the Solenoid or Sensor Stops Working

A solenoid that will not switch leaves the function unavailable, for example no differential lock or no lift axle control.
A solenoid stuck in the energised position keeps the function engaged even when it should be released.
A leaking valve seat drains air from the system or holds the actuator partly engaged.
A faulty sensor gives a false warning light or no confirmation, so the driver cannot tell what state the system is in.
Water in a connector causes intermittent faults and corrodes contacts, which is the most common cause of electrical failure.

Product Features

Built for Reliable Switching in a Harsh Environment

The unit works every time a driver selects a function, in rain, dust, cold and heat. Each assembly is designed for endurance.

Choice of Valve Functions

2/2, 3/2 and 5/2 versions, normally closed or normally open, cover single-acting and double-acting applications.

12V and 24V Coils

Coils wound for the vehicle voltage switch reliably at low supply voltage and run cool at full voltage.

Integrated Sensor Options

Pressure switch, transducer and position sensor versions provide feedback in the same unit.

Sealed Connector Systems

Sealed connectors and overmoulded coils resist water and salt to a high ingress protection rating.

Pilot-Operated Flow

Pilot operation lets a small coil control a large air flow with low power consumption and low heat.

Suppression Options

Coils with built-in suppression diodes reduce voltage spikes that can damage control units.

Selection Guide

How to Choose the Right Solenoid Valve and Sensor Unit

Five points decide whether the unit switches the correct air function and communicates correctly with the vehicle electronics.

01
Define the air function
Decide whether the actuator is single-acting or double-acting, and choose a 2/2, 3/2 or 5/2 valve accordingly. Confirm whether the valve should be normally closed or normally open.
02
Match the supply voltage
Confirm 12V or 24V from the vehicle wiring diagram. A wrong voltage will cause either a failure to switch or an overheated coil.
03
Check the sensor type and output
A pressure switch, a transducer and a position sensor each give a different signal. Match the switch type, the pressure setting and the output range to the control unit input.
04
Match the connector
Compare the connector shape, number of pins and orientation with the vehicle harness. Fitting an adapter adds a potential failure point.
05
Verify the port thread and pressure
Check the port thread, flow requirement and working pressure. A valve that is too small slows the actuator, and one that cannot handle the pressure will leak.

Table 2 — Air function and typical valve and sensor combination.

Air Function	Typical Valve and Sensor	Note
Differential lock	3/2 NC solenoid with position switch	Confirm dash indicator signal
Lift axle	3/2 solenoid with pressure switch	Check low-pressure release
Gearbox range or splitter	5/2 double solenoid with sensor	Match to the transmission controller
Exhaust brake	2/2 or 3/2 solenoid	Normally open or closed depending on design
Low-pressure warning	Pressure switch only	Set at the specified warning pressure

Combinations are typical and vary by manufacturer. Always confirm against the vehicle's wiring and air diagrams.

Applications

Where These Solenoid Valve and Sensor Units Are Fitted

Any commercial vehicle with electrically controlled air functions uses solenoid valves and sensors. The functions below account for most of our shipments.

Differential Lock Systems

Tractors and construction trucks use solenoid-controlled cylinders to lock the differential and sensors to confirm lock engagement.

PTO Engagement

Tippers, mixers and refuse trucks use air-operated PTO clutches controlled by a solenoid and monitored by a sensor.

Lift Axle Control

Solenoid valves raise and lower auxiliary axles, with pressure sensors preventing lifting under heavy load.

Exhaust and Engine Brakes

Solenoids switch exhaust flaps and engine brake feeds on and off in response to the driver's control.

Gearbox Actuation

Five-way double solenoids shift range and splitter cylinders under transmission controller command.

Air Suspension Functions

Lifting, lowering and kneeling functions use solenoid valves with pressure feedback.

Buses and Coaches

Doors, kneeling and accessory circuits use solenoid valves and pressure sensors throughout the vehicle.

Fleet Retrofits

Adding a PTO, lift axle or air horn to an older vehicle usually needs a solenoid valve and a warning sensor.

Installation

Installation Notes for Workshops

A solenoid unit fails as often from wiring or connector faults as from the valve. The steps below cover the checks that avoid repeat visits.

Isolate Power and Air

Switch off the ignition, disconnect the battery if required and release air pressure from the circuit before working on the unit.

Check the Voltage

Confirm 12V or 24V at the harness connector with a multimeter. Fit the coil voltage that matches the vehicle.

Inspect the Connector

Check the connector pins, seals and locking tab. Replace any corroded or damaged connector and use dielectric grease if the manufacturer recommends it.

Fit New Seals and Fittings

Use new sealing washers or O-rings on every port. Reused seals on a multi-port valve leak slowly and cause the actuator to drift.

Mount Clear of Water and Heat

Fit the unit with the connector pointing downward or sideways so water cannot pool. Keep it away from exhausts and heat sources.

Test the Function

Charge the system, switch the function on and off and confirm that the actuator moves. Check that the sensor gives the correct signal and that any warning lamp responds.

Maintenance

Electrical and Pneumatic Service Schedule

Electro-pneumatic units are low-maintenance, but connectors and seals age. A simple schedule prevents most faults.

Table 3 — Recommended inspection and replacement schedule for solenoid valve and sensor units.

Item	Interval	What to Check
Connector and wiring	Every 6 months	Check for corrosion, loose pins and chafed wires; clean or replace as needed.
Coil resistance	Every 12 months	Measure resistance and compare with the specification; an open or shorted coil must be replaced.
Valve function test	Every 12 months	Switch the function on and off and confirm that the actuator moves quickly and fully.
Air leakage	Every service	Listen for constant leakage at the exhaust or ports, which suggests a worn seat.
Sensor output	Every 12 months	Check the switch point or output signal against the specification with a test gauge.
Seal kit	Every 3 years or 200,000 km	Replace seals before leakage causes the actuator to drift or fail to hold.
Mounting and housing	Annual inspection	Look for cracks, loose brackets and salt damage, particularly on chassis-mounted units.

We supply coils, connectors, sensors, seal kits and complete replacement units for every model listed on this page.

Diagnostics

Solenoid Valve and Sensor Troubleshooting Guide

Trace the symptom back to its cause before replacing the unit. Many complaints trace back to wiring, connectors or a blocked air line.

Table 4 — Common solenoid valve and sensor symptoms, causes and corrective actions.

Symptom	Likely Cause	Recommended Action
Function does not engage when the switch is operated	No voltage at the coil, failed coil or blocked air supply.	Test the voltage at the connector, measure coil resistance and check the supply.
Function stays engaged after the switch is released	Armature stuck, damaged seat or wiring short holding the coil on.	Check the wiring and clean or replace the valve.
Actuator moves slowly	Restricted supply line, low voltage or valve too small for the flow.	Check the supply and voltage; use a larger valve if needed.
Constant air leakage from the exhaust	Worn seat or a damaged seal.	Replace the seal kit or the unit.
Coil gets very hot	Wrong voltage coil or continuous energising beyond rating.	Confirm coil voltage and duty cycle; replace with the correct coil.
Warning lamp on with no fault	Faulty pressure switch or wiring short.	Test the switch with a gauge and check the wiring.
Intermittent operation	Water or corrosion in the connector.	Clean or replace the connector and seal it properly.
Sensor reads a wrong value	Transducer drift, damaged diaphragm or wiring fault.	Check the supply voltage and replace the sensor.

If the symptom continues after the unit is replaced, the fault is usually in the vehicle wiring, the control unit or the air supply. Send us the wiring diagram and the voltage readings, and our technicians will help you decide whether the fault is electrical or pneumatic.

Terminology

Solenoid Valve and Sensor Glossary

Plain-language definitions of the terms you will see on wiring diagrams, data sheets and part listings.

Solenoid Valve: A valve operated by an electromagnetic coil that moves an armature to open or close an air passage.
Armature: The movable steel core inside the coil that is pulled by the magnetic field.
Direct-Acting Valve: A solenoid valve in which the armature moves the main seat directly.
Pilot-Operated Valve: A solenoid valve in which the armature controls a pilot passage and air pressure moves the main element.
2/2, 3/2 and 5/2: A code for the number of ports and positions of the valve.
Normally Closed (NC): A valve that blocks flow when the coil is not energised.
Normally Open (NO): A valve that passes flow when the coil is not energised.
Pressure Switch: A sensor that opens or closes an electrical contact at a set air pressure.
Pressure Transducer: A sensor that gives a continuous electrical signal proportional to air pressure.
Position Sensor: A sensor that detects whether a cylinder or shift fork is at an end position.
Ingress Protection (IP): A rating that describes how well the housing keeps out dust and water.
Suppression Diode: A component that absorbs the voltage spike created when the coil is switched off.

Questions

Frequently Asked Questions

Twelve questions our distributors, workshops and fleet buyers ask most often about pneumatic solenoid valve and sensor units.

It turns an electrical signal into an air action, such as engaging a differential lock or raising a lift axle, and it reports the pressure or position back to the driver or control unit so the state of the function is known.

A 2/2 valve opens or closes a single line. A 3/2 valve supplies or vents a single-acting cylinder. A 5/2 valve drives a double-acting cylinder in both directions, as used in gearbox range and splitter shifting.

It describes the valve state when no power is applied. A normally closed valve blocks flow when off, while a normally open valve passes flow. Choose the state that gives a safe condition if power is lost.

No. A 24V coil will not switch reliably on 12V, and a 12V coil will overheat on 24V. Always fit the coil voltage that matches the vehicle system.

A pressure switch is enough for a simple warning lamp. A transducer is needed if the control unit needs a continuous pressure value. A position sensor confirms that a cylinder has reached its end position.

Measure the resistance with a multimeter and compare it with the specification. An open circuit or very low resistance means the coil has failed. Also check the voltage at the connector while the function is selected.

The usual causes are water in the connector, a wrong voltage coil, a voltage spike without suppression or contamination in the air supply. Check these before replacing the unit again.

Yes. Send the diagram, the connector type and the supply voltage, together with the air function it controls. We will confirm the valve function, coil and sensor output within two working days.

Yes. Coils, connectors and seal kits are available for the models listed on this page. Give us the unit number and connector type, and we will list the matching coil, connector and seal part numbers.

For units mounted on chassis rails or in wheel arches, IP67 is recommended. For units in a protected cab or gearbox area, IP65 is usually sufficient.

Stocked coils, valves and sensor units can be bought in small quantities for testing and normally ship within 3 to 7 working days. Custom connectors or sensor outputs are built to order, and the delivery date is written on the proforma invoice.

Yes. We can produce units with alternative connectors, sensor outputs and port threads to your drawing, and supply them in neutral cartons or under your own brand.

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