Operational Mechanism of Pneumatic Solenoid Valves

Nov 29, 2025

A pneumatic solenoid valve is an electromechanical device that controls the flow of compressed air in pneumatic systems. It operates by using an electromagnetic coil to move a plunger, which opens or closes the valve, allowing for precise control of airflow.

Understanding how solenoid valves work is crucial for their proper use and maintenance. I will now primarily introduce the working principle of pneumatic solenoid valves.

What is a Pneumatic Solenoid Valve?

To understand how pneumatic solenoid valves operate, it is necessary to first have a thorough understanding of their structural components.

(1)Solenoid Coil

(2)Armature or Plunger

(3)Valve Body

(4)Valve Seat / Poppet / Spool

(5)Spring (if applicable)

(6)Seals and O-rings

(7)Pilot System

How Does A Pneumatic Solenoid Valve Work?

The operation of a pneumatic solenoid valve is based on electromagnetic principles. Solenoid valves can be categorized into direct-acting and pilot-operated types. Next, we will analyze the two types represent how the actuator is driven.

How Does A Direct-Acting Solenoid Valve Drive A Cylinder?

Direct-acting 3/2 Solenoid Valve Controlling a Single-Acting Cylinder

1. Coil energized → Piston rod extends

The solenoid coil generates magnetic force

directly attracting the small valve core

After the valve core opens, a passage is formed, allowing compressed air to enter the cylinder

Overcoming spring force, friction, and load

The piston rod extends

2. Coil de-energized → Piston rod retracts

The solenoid coil is de-energized

The valve core is pushed back to its original position by the spring, closing the passage

Air inside the cylinder is expelled

The return spring inside the cylinder pushes the piston back.

Direct-acting 4/2 or 5/2 Solenoid Valve Controlling a Small Double-Acting Cylinder

This direct-acting type does not use a spring return; it relies on two chambers to alternately intake and exhaust air.

After the direct-acting solenoid valve actuates, it directly switches the air path internally:

P → A: Left chamber intake line

B → R: Right chamber exhaust line

Air enters the left chamber, pushing the piston to the right → Piston rod extends.

Switching the solenoid valve changes the airflow direction:

P → B: Right chamber intake line

A → R: Left chamber exhaust line

Air enters the right chamber, pushing the piston to the left → piston rod retracts.

How Does A Pilot-Operated Solenoid Valve Drive A Cylinder?

Pilot-operated single-acting cylinder

Electromagnetic coil energized → Pilot valve opens

A small amount of pilot air flows into the main valve chamber → Pushing the main valve spool

The main valve opens the large-diameter air path: P → A (cylinder chamber)

Air enters the cylinder, overcoming the internal cylinder spring → Piston rod extends

Electrode off (return stroke)

Electromagnetic coil de-energized → Pilot valve closes → Pressure in the main valve chamber is released

The main valve spool returns to its original position under the action of the spring

Cavity A connects to R (exhaust port) → Air is expelled from the cylinder

The piston rod retracts due to the cylinder spring

Controlling a double-acting cylinder

Electromagnetic coil energized → Pilot valve opens

A small amount of pilot airflow pushes the main valve spool → Switching the large-diameter air path

P → A: Intake line, B → R: Exhaust line, cylinder extends to the right

Electrode the other coil or de-energize

Electromagnetic coil switching → Pilot valve reverses action

The main valve spool reverses its action

P → B: Intake line, A → R: Exhaust line, cylinder retracts to the left.

Operation Summary Table of Pneumatic Solenoid Valve

Item	Direct-acting Solenoid Valve	Pilot-operated Solenoid Valve
Valve Actuation	Coil directly moves the valve core	Coil actuates a small pilot valve → small pilot airflow controls the main valve core
Flow Capacity	Small bore → low flow	Large bore → high flow, can drive large cylinders
Power Consumption	Direct operation → higher current (overcomes spring)	Pilot operation → low current, only a small pilot airflow needed
Applicable Cylinders	Single-acting (can drive small double-acting cylinders, limited flow)	Single-acting or double-acting

(9016)

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