Solenoid valves that switch exactly when it matters.

Rule of thumb: low flow or no pressure → direct-acting; high flow with reliable pressure → pilot-operated; high flow without reliable pressure → force-pilot-operated. Direct-acting solenoid valves open the seat directly via the armature and switch from 0 bar, meaning they also work pressureless and under vacuum, but their flow capacity is limited. Pilot-operated (servo- or diaphragm-operated) valves use the media pressure: the armature only opens a small pilot bore, and the pressure differential does the rest – this delivers high flow rates with a small coil, but requires the minimum pressure differential between inlet and outlet stated in the datasheet. Force-pilot-operated valves mechanically couple the armature and diaphragm, so they switch even without a pressure differential while still providing high flow.

A 2/2-way solenoid valve has an inlet and outlet and works as a shut-off valve: open or closed. A 3/2-way valve additionally has a vent or return port and can either pressurize or relieve the actuator. The first number indicates the ports, the second the switching positions. 3/2-way valves are typical for single-acting cylinders, pneumatic rotary actuators and the pilot control of larger process valves.

NC (normally closed) means the spring holds the valve closed when de-energized; only applying voltage opens it. NO (normally open) is the opposite – open when de-energized, closed when energized. The decisive factor is the safe position in case of power failure: if the line must seal on power loss (e.g. water or gas supply), choose NC; if a circuit must stay open (e.g. cooling, pressure relief), choose NO. For valves that are mostly open, the matching function also saves continuous coil heating and energy.

The coil must match the control system: common options are 24 V DC and 230 V AC, plus 12 V DC, 48 V or 110 V among others. Also check the duty cycle – valves that remain energized continuously need a coil rated for 100% duty cycle. The protection class (typically IP65) only applies with a correctly mounted and screwed connector including the seal. Connectors are available with additional circuitry (e.g. LED indicator, surge suppression), which is useful for electronic controls and long cable runs. Coils and connectors are available separately as spare parts – a faulty valve rarely needs to be replaced completely.

Rough guideline: NBR for water, air and mineral oil at moderate temperatures, EPDM for hot water, steam and many aqueous chemicals (not for mineral oil), FKM for oils, fuels and higher temperatures, PTFE for aggressive media. For the body, brass is standard for water and air, while stainless steel is the choice for corrosion, food contact or cleaning media. What matters most is always the medium, concentration, temperature and cleaning procedure – give us these four details and we'll check the resistance based on the manufacturer's datasheet.

Not based on the pipe size, but on the required flow rate and the permissible pressure drop – the decisive factor is the valve's Kv value, not the thread size. An oversized valve costs more and, in pilot-operated designs, may switch imprecisely, while an undersized valve causes pressure loss and heat build-up. Also check the installation position, permissible operating pressure, switching frequency and, for liquids, the flow direction, which is fixed for solenoid valves. If several channels need to be switched, it's worth looking at solenoid valve manifolds and islands.