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Mechanical, Build & Pneumatics·Lesson 25 of 47

Solenoid Valves and Cylinders

The output stage: solenoid valves switch air, and cylinders turn it into motion. Learn single vs double solenoids and single vs double-acting cylinders.

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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.

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.

Go deeper

Lesson quiz

Required

Answer all 3 questions correctly to complete this lesson.

1.What happens to a single solenoid valve when power is removed (e.g., the robot is disabled)?

2.What is the key behavioral advantage of a double solenoid valve over a single solenoid valve?

3.What distinguishes a double-acting cylinder from a single-acting (spring-return) cylinder?

Answer every question to submit.