Solenoid Valves: The Air Switches#
A solenoid valve is an electrically controlled valve that routes working-pressure air to a cylinder. Two types matter, and the difference is crucial for both wiring and behavior.
Single Solenoid (single-acting valve)#
Has one electrical connection. Energize it and air flows one way; remove power and a spring returns it to its default state. Because it returns to default when power is lost, a single solenoid is safe-by-default — when the robot is disabled or powered off, the valve (and its cylinder) returns to the spring position. Use this when a fail-safe resting state matters.
Double Solenoid (double-acting valve)#
Has two electrical connections and holds its last commanded state even with no power — it needs an active signal to switch direction. A double solenoid drives a double-acting cylinder forward or back on command and stays put when disabled. Use this when the mechanism should hold position through a disable.
Valves are limited by rule to a 1/8 inch NPT maximum port size (R804). Many teams use SMC valves; the Pneumatics Manual shows a typical valve with ports 1, 2, and 4 that you plumb to supply and the two cylinder ports.
Cylinders (Pneumatic Actuators)#
A cylinder is a piston in a tube; air pressure on one side pushes the rod out or in.
Single-Acting (spring-return)#
Air extends the rod; an internal spring retracts it (or vice versa). Needs only one air line and pairs with a single solenoid. Simpler plumbing, but the spring eats some force and the retract direction is not powered.
Double-Acting#
Has two air ports; air drives the rod both directions with full force. Pairs with a double solenoid. This is the most common FRC choice because both strokes are powered and strong. Popular options include Bimba and SMC cylinders sold through AndyMark — for example a Bimba double-acting cylinder with a ~1.06 in bore and a 6 in stroke.
Sizing Preview#
Bore (piston diameter) sets force; stroke sets travel distance. A bigger bore = more force but more air per stroke. You will calculate exact force and air usage in the next module. For now, remember: single solenoid + single-acting cylinder for fail-safe binary jobs, double solenoid + double-acting cylinder for powered-both-ways, hold-on-disable jobs.
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Key takeaways
- Single solenoids have one wire and spring back to a default state when unpowered (fail-safe); double solenoids have two wires and hold their last state.
- Single-acting cylinders use a spring return and one air line; double-acting cylinders are powered both directions and use two lines.
- Pair single solenoid with single-acting cylinder, and double solenoid with double-acting cylinder.
- Valve ports are limited to 1/8 in NPT (R804); double-acting Bimba/SMC cylinders are the common FRC default.
Mechanical, Build & PneumaticsThe Components: Controllers, Compressor, Valves, and Cylinderslesson 4 of 4
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Sources and corrections
This lesson is AI-assisted: drafted from primary sources, then reviewed and edited by hand. Errors still get through. When one is reported we fix it and write down what changed, in public, in the corrections log.
sources and further reading
- andymark.comAndyMark - Pneumatic Cylinders
- docs.wpilib.orgWPILib Docs - Operating pneumatic cylinders (Solenoids)
- firstinspires.orgFIRST Pneumatics Manual (Working Pressure Side)
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answer sheet
Lesson quiz
All 3 right completes the lesson. Miss one and only that question comes back, anything you already answered correctly stays banked.
0 of 3 answered
01What happens to a single solenoid valve when power is removed (e.g., the robot is disabled)?
02What is the key behavioral advantage of a double solenoid valve over a single solenoid valve?
03What distinguishes a double-acting cylinder from a single-acting (spring-return) cylinder?
Answer every question to submit.
All 47 lessons in Mechanical, Build & Pneumaticsopenclose
01 / prerequisites
02 / drivetrains
03 / power-transmission
04 / structure-materials-fasteners
05 / mechanisms-fabrication-assembly
06 / pneumatics-fundamentals
07 / pneumatic-components
08 / build-wire-program
09 / safety-rules-testing
10 / worked-examples-mini-projects
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11 / common-mistakes-troubleshooting
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12 / advanced-techniques-case-studies
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