Solenoid Valves, Electrically Switched Valves and Coils

How a Solenoid Valve Works

When current flows through the coil, it creates a magnetic field that pulls a steel plunger or armature. On small valves, the plunger opens or closes the seat directly. On larger valves, it opens a small pilot passage, and line pressure moves the main seal or spool.

Hydraulic solenoid valves usually have a wet pin design. The plunger runs in oil inside a sealed tube and the coil slides over the outside, so you can change the coil without opening the hydraulic circuit.

Coil Voltage: AC or DC?

• 24 V DC: the most common voltage in Australian automation and machine control.
• 12 V DC: common on mobile machines, trucks and battery systems.
• 110 V and 240 V AC: found in older plants and stand alone equipment.

DC coils switch quietly and smoothly, while AC coils pull in hard and can hum. Never fit an AC coil on a DC supply, or the reverse, as it will overheat quickly. Some connectors include a rectifier, which lets a DC coil run on an AC supply.

Connectors

• DIN EN 175301-803 Form A: the large, square plug common on hydraulic valves.
• Form B and Form C: smaller versions. Form C is typical on compact pneumatic valves.
• M12 round connectors: common on modern machines and valve islands.
• Flying leads: loose wires for direct connection.

Connectors with LED indicators show when the coil is powered, and those with surge suppression protect PLC outputs from voltage spikes.

Ratings That Matter

• Duty rating: most industrial coils are rated for 100% duty, so they can stay on all day.
• Insulation class: Class F or H coils tolerate higher temperatures.
• Ingress protection: IP65 is standard, and IP67 suits washdown and outdoor use.
• Hazardous areas: coils for explosive atmospheres need the right certification.

Testing a Coil

1. Check the voltage at the plug with the coil switched on.
2. Measure the coil resistance and compare it with the datasheet. An open circuit means the coil has failed.
3. Hold a screwdriver near the centre of the energised coil. A strong pull means it is creating a field.
4. Never power a coil while it is off the valve, especially an AC coil. Without the plunger tube inside, it overheats and burns out quickly.

Choosing the Right Valve Type

The coil is only half the story. A small direct acting valve works from zero pressure, while a pilot operated valve needs a minimum pressure difference to open, and our 2/2 way valves page explains that choice in detail. For smooth, variable control instead of simple on and off, look at proportional valves, which use a coil whose force varies with the signal.

Solenoid Valves Specifications to Check

• Valve type: ports, positions and function
• Coil voltage, AC or DC, and power in watts
• Connector type, and any LED or suppression
• Duty rating, insulation class and IP rating
• Port size, pressure range and medium
• Any hazardous area certification

Why Buy From TSA Hydraulics Engineering

As a solenoid valves supplier, we match the valve, coil and connector as a set, so it plugs straight in. You get clear prices in AUD, OEM or equivalent options, and help sourcing solenoid valves replacement parts such as coils, connectors and seal kits. We tell you upfront whether a valve or coil is genuine or an equivalent.