What Is a Solenoid Valve? Selection Guide and How It Differs from a Pneumatically Actuated Valve

A solenoid valve is an on-off valve that converts electrical energy directly into mechanical movement. When voltage is applied to the coil, the magnetic field pulls an iron plunger and the orifice opens or closes; when the voltage is removed, a spring returns the plunger to its rest position.

There is no intermediate position; the valve is either fully open or fully closed. Response time is tens of milliseconds for direct-acting types and a few hundred milliseconds for pilot-operated ones. Solenoid valves serve two roles: shutting off the process fluid directly, and directing the air supply to a pneumatic actuator. In the second role the solenoid is the control element of an actuated ball valve, and this distinction is the foundation of the selection guide.

A normally closed (NC) solenoid valve is closed when de-energised and opens when power is applied; it is the standard on filling, dosing and safety lines where flow must stop on power loss. A normally open (NO) valve stays open without power and saves coil life only on continuously flowing lines with brief interruptions.

Ports and positions are written as a fraction. A 2/2 valve has two ports (inlet, outlet) and two positions and is the simplest type. A 3/2 valve, with supply, outlet and exhaust ports, drives single-acting (spring-return) pneumatic actuators. A 5/2 valve feeds two air outlets alternately and is standard for double-acting actuators.

Solenoids with a NAMUR interface mount directly on the actuator body without tubing or fittings, shortening installation and reducing leak points.

Coil voltage matches the control system: 24 V DC is common on PLC outputs and offers low-voltage safety; 220–230 V AC is used in simple control panels. Wrong voltage is the most frequent cause of coil burn-out; an AC coil connected to DC is destroyed within minutes.

Coil power is around 8–20 W for direct-acting and 5–10 W for pilot-operated types; continuous energisation needs an ED 100% rated coil. Ingress protection follows the location: IP54 may suffice inside a panel, outdoors IP65 or IP67 coils and connectors are needed, and explosive atmospheres require ATEX certification. A DIN 43650 connector with LED indication makes fault finding easier.

In a direct-acting valve the magnetic force of the coil moves the plunger on its own. The orifice is small (typically 1–8 mm) and the valve works at zero differential pressure, which suits low-flow dosing lines and drawing from unpressurised tanks. Because coil power rises steeply with orifice size, it is impractical above DN25.

In a pilot-operated type the coil opens a small pilot orifice and the main diaphragm is lifted by line pressure differential. A small coil can thus control DN15 to DN50 and larger in the 0.5–16 bar range. The condition is a minimum differential pressure (usually 0.3–0.5 bar); on unpressurised lines it will not open or close.

Flow capacity is expressed as Kv (m³/h at 1 bar pressure drop) and depends on orifice size far more than on connection size. Two solenoids with the same 1/2-inch connection can differ in Kv by a factor of two; selection should start from the required flow and permissible pressure drop.

Brass bodies are the economical standard for water, air and oil; AISI 316 stainless steel is required for chemicals, deionised water and food applications. Seal material sets the limits: NBR from roughly -10 to +90 °C, EPDM for hot water and steam up to +140 °C, FKM up to +150 °C and PTFE for aggressive chemicals and steam up to about +180 °C. Steam solenoids form a separate family with a special piston design and high-temperature coil.

Dirty fluids are the weak point of solenoid valves: the pilot orifice is only 0.1–0.5 mm, so particle build-up leads to failure to close. An upstream Y-strainer with a 100–200 micron mesh prevents most of the faults we see in the field. Standard models are not recommended for viscous fluids above roughly 20 cSt.

A solenoid valve is the right choice for clean fluids from DN8 to DN50 where fast, frequent on-off operation and a compact, economical solution are needed: filling machines, cooling water circuits, compressed air lines and dosing points. Its limits are size, sensitivity to dirty fluids and continuous coil energy consumption.

A pneumatically actuated ball valve takes on the same duty at a larger scale and under harsher conditions. The actuator on an ISO 5211 valve runs on 2–8 bar air; from DN15 to DN250 and PN10 to PN63 it delivers full bore, low pressure loss and reliable closure with dirty fluids. A spring-return actuator guarantees the safe position on air failure.

The decision rule is simple: above DN50, with dirty or viscous fluids, steam and high pressure or a full-bore requirement, choose the actuated ball valve; for small-bore clean fluids and high cycle rates, choose the solenoid valve. Where no air supply exists, an electrically actuated valve is the third option. In Vanera's sets the pilot solenoid is configured together with the actuator; the two technologies complement each other.

Solenoid valve price depends less on connection size than on body material, operating principle and coil options. A brass 2/2 NC 230 V AC water solenoid is the economical reference; a 316 stainless body, steam-rated piston and PTFE seals raise the price step by step. IP67, ATEX, ED 100% and NAMUR manual override options are separate items.

Compared with an actuated ball valve, a solenoid valve is lower in initial cost, but the gap closes quickly from DN40 upward. Once coil energy consumption, strainer requirements and expected cycle life are included, the actuated valve turns out cheaper on some lines. Quantity, stock and lead time affect the unit price of both.

From Umraniye, Istanbul, Vanera supplies pneumatically and electrically actuated ball and butterfly valves, NAMUR pilot solenoids and complete control sets to industrial plants. Our engineers work through the choice between solenoid valve and actuated valve with you based on fluid, pressure, size and cycle frequency.

For a quotation, share the fluid type and temperature, working and minimum pressure, size, supply voltage and required safe position. Send your request through the Quick Quote form on the Actuated Valve page and our team will respond with a technical recommendation and price within the same business day.