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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Robotics / Mechatronics › Pneumatics and Hydraulics for Mechatronics › Lesson 2
MFG-MECH15-03 · Lesson 2 · 14 clock hours · demo

Pneumatic Components: Identification and Function

Objective. Students will identify a compressor, air dryer, filter-regulator-lubricator (FRL) unit, directional control valves (2/2, 3/2, 5/2, 5/3), flow control valves, and single- and double-acting cylinders by name and function, and read ISO 1219 schematic symbols for each.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Pneumatic Components: Identification and Function

Pneumatic systems use compressed air to create controlled mechanical motion. In manufacturing and marine automation, pneumatics move parts, clamp workpieces, actuate valves, and assist robots. Before you can build, troubleshoot, or maintain a pneumatic circuit, you must recognize every major component by sight, know its function, and read its ISO 1219 schematic symbol.

Safety First

Compressed air carries stored energy that can cause serious injury. Always treat a pneumatic line as energized until you have verified it is not. Follow OSHA 29 CFR 1910.147 (lockout/tagout) when working on machinery: isolate the air supply, depressurize the system, and verify zero energy before opening fittings or removing components. Wear safety glasses at minimum; escaping air can propel debris or cause eye injury. Respect OSHA 1910.212 machine-guarding rules — cylinder rods can extend rapidly and strike a hand. Never direct compressed air at skin or toward another person.

The Compressor

The compressor is the power source of a pneumatic system. It converts mechanical energy (usually from an electric motor) into potential energy stored as pressurized air in a receiver tank. Industrial shops typically supply air at 80–120 psi (approximately 550–825 kPa). The compressor itself is upstream of every other component and is controlled separately. In your schematic, the compressor is shown as a circle with a triangle pointing inward toward the circle, representing the inlet, mounted on a rectangle representing the tank.

Air Dryer

Moisture in compressed air corrodes valves, washes out lubricants, and damages cylinders. A refrigerated or desiccant air dryer removes water vapor downstream of the compressor and receiver. In schematics it is represented by a box with a zigzag or cooling element symbol inside. Many facilities combine drying with filtration.

Filter-Regulator-Lubricator (FRL)

The FRL is a three-stage service unit mounted near the machine, always in the order Filter → Regulator → Lubricator.

In ISO 1219, each section has its own symbol; the three are drawn in series with connecting lines.

Directional Control Valves (DCVs)

DCVs route compressed air to and from actuators. They are named by positions/ports: a 2/2 valve has 2 ports and 2 positions (on/off); a 3/2 valve has 3 ports and 2 positions (used to extend or retract a single-acting cylinder); a 5/2 valve has 5 ports and 2 positions (the standard valve for a double-acting cylinder); a 5/3 valve has 5 ports and 3 positions (center position can be exhaust, pressure, or blocked — you must identify which type).

ISO 1219 DCV symbols use boxes (one box per position), arrows inside showing flow paths, blocked-T shapes for closed ports, and external actuation symbols:

Always read the symbol in its rest (de-energized) position, which is the box nearest the actuation symbol that acts last (spring or pilot return side).

Flow Control Valves

A flow control valve (also called a needle valve with check) meters the air speed by restricting flow in one direction while allowing free flow in the other through an internal check valve. Meter-out restricts exhaust air leaving the cylinder (preferred for most cylinder applications because it provides smooth, controlled motion). Meter-in restricts supply air entering the cylinder. The ISO 1219 symbol shows a variable restrictor (arrow through a circle) in parallel with a check valve (triangle pointing in the free-flow direction).

Actuators: Single-Acting and Double-Acting Cylinders

A single-acting cylinder (SAC) has one port; compressed air extends the rod and a spring returns it. It is used where force is needed in only one direction. The ISO 1219 symbol shows a rectangle (barrel) with a rod, one port arrow, and a spring symbol inside.

A double-acting cylinder (DAC) has two ports — one at each end of the barrel. Compressed air can both extend and retract the rod under power, giving force in both directions. Most industrial cylinders are double-acting. The ISO 1219 symbol shows a rectangle with a rod and two port arrows, no spring.

Cylinder force is calculated as: Force = Pressure × Area (where area = π × bore² ÷ 4). This formula tells you how much push or pull a cylinder can produce at a given supply pressure.

Reading a Complete Circuit

Trace air flow from left to right (supply to actuator): Wall supply → Compressor/receiver → Air dryer → FRL (filter, regulate, lubricate) → DCV → Flow control valves → Cylinder. Each connection is a line; each component is its ISO 1219 symbol. Annotate port labels: P = pressure supply, A and B = cylinder ports, R or EA/EB = exhaust ports.

Key terms8

FRL (Filter-Regulator-Lubricator)A three-stage pneumatic service unit that removes contaminants, sets downstream pressure to a desired level, and adds oil mist to protect downstream components; always installed in that order.
Directional Control Valve (DCV)A valve that controls the path of compressed air to and from an actuator; named by the number of ports and positions (e.g., 5/2 = 5 ports, 2 positions).
ISO 1219The international standard that defines graphical symbols for fluid power systems, including pneumatic and hydraulic components, used on schematic diagrams.
Single-Acting Cylinder (SAC)A pneumatic cylinder with one air port; compressed air moves the rod in one direction and an internal spring returns it; used when powered force is needed in one direction only.
Double-Acting Cylinder (DAC)A pneumatic cylinder with two air ports, one at each end; compressed air provides powered force in both the extend and retract directions.
Flow Control ValveA variable restrictor with a bypass check valve that meters air speed in one direction (typically meter-out on the exhaust side) to control cylinder speed.
Meter-OutA flow control configuration that restricts the exhaust air leaving a cylinder port, providing smooth and controllable motion; the preferred method for most cylinder speed-control applications.
Solenoid ActuationAn electromagnetic coil that shifts a valve spool when energized by an electrical signal; shown in ISO 1219 as a rectangle with diagonal lines adjacent to the valve symbol.

Worked examples4

1. A double-acting cylinder has a bore diameter of 2 inches and is supplied at 80 psi. What is the extend (push) force in pounds?
  1. Calculate the piston area: Area = π × (bore/2)² = π × (2/2)² = π × 1² = 3.1416 in²
  2. Apply the cylinder force formula: Force = Pressure × Area = 80 psi × 3.1416 in²
  3. Force = 251.3 lb
Answer: Approximately 251 lb of extend force at 80 psi.
2. A cylinder must produce at least 400 lb of force. The available supply pressure is 100 psi. What minimum bore diameter is required?
  1. Rearrange the force formula for area: Area = Force ÷ Pressure = 400 ÷ 100 = 4.00 in²
  2. Solve for bore diameter: Area = π × (d/2)², so (d/2)² = 4.00 ÷ π = 1.273 in²
  3. (d/2) = √1.273 = 1.129 in, therefore d = 2 × 1.129 = 2.258 in
  4. Select the next standard bore size at or above 2.258 in (commonly 2.5 in bore).
Answer: A minimum bore of approximately 2.26 inches is required; select a standard 2.5-inch bore cylinder.
3. A 5/2 solenoid valve controls a double-acting cylinder. The valve has ports labeled P, A, B, EA, and EB. Describe which ports are active when the solenoid is energized (valve shifts to position 2) to extend the cylinder rod.
  1. In position 2 (solenoid energized), the valve routes supply air from P to the A port (cap end of cylinder) to extend the rod.
  2. Simultaneously, the B port (rod end of cylinder) is connected to the exhaust port EB, allowing return air to escape.
  3. Port EA is closed (not used in this position).
Answer: P connects to A (cylinder extends); B connects to EB (exhaust); EA is closed.
4. A technician sets the FRL regulator to 70 psi but the downstream gauge reads 90 psi under no-flow conditions. What is the most likely cause, and what should be checked first?
  1. A regulator set to 70 psi should not allow downstream pressure to exceed the set point; a reading of 90 psi suggests the regulator is not functioning correctly.
  2. First, verify the regulator knob is fully engaged and the set-point is locked — some regulators require pulling the knob out before adjustment.
  3. If the gauge still reads high, the regulator poppet or diaphragm may be damaged and not seating properly, allowing upstream pressure to pass through uncontrolled.
  4. Lock out the supply air per OSHA 29 CFR 1910.147, depressurize the system, and inspect or replace the regulator.
Answer: The regulator is likely faulty (damaged seat or diaphragm); isolate per lockout/tagout procedure and replace or service the unit.

The math in this lesson2

Learners compute extend force from bore area and psi for a 2-inch double-acting cylinder.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor-led component tour at the bench: each component is passed around; students complete a component identification card listing port labels, ISO 1219 symbol, and typical operating pressure range for each item. · Symbol drawing exercise: students receive a blank worksheet with 15 ISO 1219 symbols and must label each component name, port count, and actuation method (spring, solenoid, pilot, manual); completed sheets are peer-checked. · Demonstration: instructor traces compressed air from the wall supply through an FRL to a 5/2 solenoid valve to a double-acting cylinder, explaining each component's role; students sketch the circuit from observation and annotate it with the correct ISO 1219 symbols.
Materials: Pneumatic trainer bench, component display set (FRL, DCV assortment, cylinders, flow controls), ISO 1219 symbol chart, blank worksheet, colored pencils
Check: Component identification practical: instructor points to 10 bench-mounted components; student names each and states its function; pass = 9 of 10 correct.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Fluid Power
1. What does the designation '5/2' mean when applied to a directional control valve?
Fluid Power
2. Which component in the FRL unit is responsible for maintaining a constant downstream pressure regardless of upstream fluctuations?
Fluid Power
3. A single-acting cylinder differs from a double-acting cylinder in that a single-acting cylinder:
Fluid Power
4. A technician wants to control the speed of a double-acting cylinder's extend stroke smoothly. The correct approach is to install flow control valves configured to:
Fluid Power
5. According to ISO 1219, the solenoid actuation symbol on a DCV schematic is represented by:
Fluid Power
6. Before loosening a fitting on a pressurized pneumatic line, a technician must first:
Fluid Power
7. A double-acting cylinder has a 3-inch bore and is supplied at 90 psi. What is the approximate extend force? (Use π ≈ 3.1416)
Fluid Power
8. In a pneumatic system schematic, where should the FRL unit be located relative to the compressor and the directional control valve?
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