Solenoid Valve Types — A Selection Guide
Understand 2/2, 3/2, and 5/2-way solenoid valves, NC vs NO, direct-acting vs pilot-operated, and how to choose the right coil and body for your media.
Solenoid valves convert an electrical signal into automatic on/off control of a fluid. Choosing the right one means matching the port configuration, operating principle, body material, and coil to your media and pressure. This guide explains the main solenoid valve types and how to select them.
Port Configurations
Direct-Acting vs Pilot-Operated
- Direct-acting: the coil directly opens the seat; works from 0 bar (no minimum pressure differential needed) — ideal for low-flow and vacuum service
- Pilot-operated (servo): uses line pressure to help open a diaphragm/piston; needs a minimum differential but handles larger ports and higher flow efficiently
- Semi-lift / forced-lift: a hybrid that opens at zero differential yet handles larger orifices
- NC (normally closed): closed when de-energised — the most common, fail-safe-closed
- NO (normally open): open when de-energised — for fail-safe-open duty
Frequently Asked Questions
What is the difference between 2/2 and 3/2-way solenoid valves?
A 2/2-way valve has two ports and simply turns one flow path on or off. A 3/2-way valve has three ports and two positions, used to pressurise and then exhaust a line (e.g., a single-acting cylinder) or to divert flow.
Direct-acting or pilot-operated — which do I need?
Use direct-acting valves for low flow or where there is little/no pressure differential (including vacuum). Use pilot-operated valves for larger flows where line pressure (above a minimum differential) helps actuate the valve efficiently.
What is the difference between NC and NO solenoid valves?
Normally Closed (NC) valves are shut when the coil is de-energised and open when energised; Normally Open (NO) valves are the reverse. Choose based on the desired fail-safe state on power loss.
How do I select the coil voltage?
Common coil voltages are 24V DC and 110/230V AC (50/60 Hz). Select to match your control system and specify the insulation class and enclosure (IP65, or Ex d for hazardous areas).
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