In brief
A solenoid valve is a valve actuated by an electric coil that opens, closes or switches the flow of liquids or gases.
Contents
What is Solenoid valve?
In a solenoid valve, a current-carrying coil generates a magnetic field that attracts a movable armature (plunger). The armature opens or closes the valve seat directly or indirectly. Solenoid valves link electrical control with media circuits, for example for water, compressed air, oil, steam or technical gases, and are used in automation, fluid power and building services.
Direct-acting solenoid valves switch the seat by magnetic force alone and also work without a pressure differential, but are limited to smaller nominal sizes. Pilot-operated valves use the media pressure to assist and therefore usually require a minimum pressure differential. By number of ports and switching positions, a distinction is made, for example, between 2/2-way valves for opening and closing and 3/2-way valves for switching or venting. The normal position is normally closed (NC) or normally open (NO).
Also important for operation are coil voltage and type of current, power consumption, duty cycle, degree of protection of the coil and the materials of the body and seal. Common faults are burnt-out coils, worn seals and deposits on the seat.
In practice: maintenance and procurement
For a replacement, the valve function, normal position, nominal size, connection thread, pressure range, medium and temperature as well as coil voltage and type of current should be stated. Often, replacing the coil or a seal kit is sufficient; this requires the exact designation of the existing part.
Synonyms and abbreviations: solenoid-operated valve · electromagnetic valve · solenoid valve NC/NO · directional valve (solenoid-operated)
Frequently asked questions
What is the difference between a direct-acting and a pilot-operated solenoid valve?
In a direct-acting valve, the magnetic force opens the seat directly; it also works without a pressure differential but is limited to smaller nominal sizes or pressures. A pilot-operated valve uses the media pressure to move the main seat via a diaphragm or piston. It switches large flows with a small coil but generally requires a minimum pressure differential.
What do normally closed (NC) and normally open (NO) mean?
Normally closed means that the valve is shut when there is no voltage at the coil and only opens when energised. Normally open means, conversely, that the valve allows flow in its rest state and closes when energised. The choice depends on which state is safe in the event of a power failure.
What does the designation 3/2-way valve mean?
The first number indicates the number of ports, the second the number of switching positions. A 3/2-way valve therefore has three ports, usually pressure, working line and exhaust, and two switching positions. It is used, for example, to pressurise and then vent a single-acting cylinder. A 5/2-way valve, by contrast, typically controls double-acting cylinders.
What information is needed to replace a solenoid valve?
Important are valve function, normal position, nominal size, connection size, permissible pressure range, medium, media and ambient temperature, and seal material. For the coil, voltage, type of current, power, connector type and degree of protection are needed. In potentially explosive atmospheres, the appropriate Ex marking is also required. A photo of the nameplate and coil makes unambiguous identification easier.