Pressure Regulator Symbol
Definition: The Pressure Regulator symbol represents a pneumatic or hydraulic device that reduces and maintains a downstream pressure at a set value regardless of upstream supply pressure fluctuations, depicted in fluid-power schematics per ISO 1219-1 as a circle with horizontal lines of varying thickness indicating the regulating spring mechanism.
Also known as: pressure reducing valve, PRV, pressure reducer, FRL regulator, air regulator.
What the Pressure Regulator symbol means
The Pressure Regulator symbol in a pneumatic or hydraulic circuit diagram denotes a component that accepts a variable high-pressure supply at its inlet and delivers a stable, lower regulated pressure at its outlet, set by an internal spring or pilot mechanism.
Pressure regulators are essential in industrial pneumatic systems to protect downstream actuators and valves from pressure spikes, ensure consistent actuator force, and reduce compressed-air consumption. The symbol communicates that the fluid pressure downstream of this point is actively controlled to a defined set point.
How to identify the Pressure Regulator symbol
The pressure regulator symbol is drawn as a circle (approximately 14 mm diameter in standard drawings) with a vertical inlet line entering the top and a vertical outlet line exiting the bottom. Inside the circle, three horizontal lines are drawn: a thin line near the top, a thick (bold) line in the centre representing the regulated output pressure, and a medium line near the bottom. This stacked-line arrangement inside a circle is the ISO 1219-1 convention for pressure regulators and distinguishes it from a pressure relief valve, which uses a differently styled internal marking.
Function in a circuit
A pressure regulator reduces the incoming supply pressure to a preset, stable downstream pressure by balancing a spring force against the downstream pressure acting on an internal diaphragm or piston. When downstream pressure rises above the set point, the diaphragm compresses the spring and partially closes the valve orifice, reducing flow and pressure. When downstream pressure drops, the spring opens the valve further to restore pressure. This self-regulating feedback maintains constant output pressure across varying flow demands.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 covers electrical symbols and does not define pneumatic/hydraulic components. Pressure regulators in fluid-power diagrams are governed by ISO 1219-1:2012 (Fluid power systems and components — Graphical symbols and circuit diagrams). |
|---|---|
| ANSI/IEEE 315 | ANSI/ASME Y32.10 (Graphic Symbols for Fluid Power Diagrams) defines the pressure regulator symbol similarly to ISO 1219-1 as a circle with internal horizontal lines. The ANSI symbol is functionally identical to the ISO symbol. |
| Key difference | ISO 1219-1 and ANSI/ASME Y32.10 symbols are nearly identical; both use a circle with horizontal lines of differing weight. Minor differences exist in line weights and the representation of the adjusting knob (a dashed line or arrow above the circle for adjustable types). |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Inlet (supply) pressure: typically 0.2–1.6 MPa (2–16 bar) for industrial pneumatics. Outlet (regulated) set pressure: typically 0.1–1.0 MPa (1–10 bar). Flow capacity rated in Nl/min or Cv (flow coefficient). Adjustment range marked on the regulator body.
Where the Pressure Regulator symbol is used
- Industrial pneumatic control panels, reducing main-line supply pressure (6–8 bar) to actuator operating pressure (2–5 bar)
- FRL (Filter-Regulator-Lubricator) units at the entry point of pneumatic machinery to condition compressed air
- Hydraulic press circuits maintaining constant cylinder pressure regardless of pump pressure variations
- Spray-painting and coating equipment requiring precise constant air pressure for consistent atomisation
- Medical gas distribution systems delivering oxygen or anaesthetic gases at controlled low pressures
- Laboratory and test rigs supplying calibration gas or hydraulic fluid at defined stable pressures
Example
In a pneumatic pick-and-place assembly cell, the main compressed-air supply at 8 bar enters the In pin of the pressure regulator symbol; the Out pin feeds the gripper cylinder at a regulated 4 bar, ensuring consistent grip force regardless of compressor pressure fluctuations during production.
Key facts
- The pressure regulator symbol in ISO 1219-1 fluid-power diagrams is a circle with three horizontal lines of varying thickness inside, with vertical inlet (In) and outlet (Out) lines.
- A pressure regulator reduces upstream supply pressure to a stable, lower downstream set pressure by balancing an internal spring against the downstream pressure on a diaphragm.
- Pressure is measured in pascals (Pa) or bar; 1 bar = 100 kPa = approximately 14.5 psi. Industrial pneumatic regulators typically set pressures between 0.1 MPa and 1.0 MPa.
- The symbol has two fluid ports: In (supply inlet) and Out (regulated outlet); adjustable types show an adjustment knob or arrow above the circle symbol.
- Pressure regulators differ from pressure relief valves: a regulator reduces and maintains downstream pressure, while a relief valve opens to vent excess upstream pressure above a set limit.
- In FRL (Filter-Regulator-Lubricator) assemblies, the regulator symbol appears as the middle element between the filter and lubricator symbols in pneumatic circuit diagrams.
- The designator used in pneumatic schematics is typically PR or REG, with a reference number (e.g. PR1) for identification.
Frequently asked questions
What does the pressure regulator symbol look like in a pneumatic diagram?
The pressure regulator symbol is a circle with three horizontal lines inside (thin, thick, and medium, from top to bottom), with a vertical line entering at the top (inlet) and exiting at the bottom (outlet). An adjustable regulator adds a dashed adjustment line or arrow above the circle.
What does the pressure regulator symbol mean?
The pressure regulator symbol indicates a component that reduces and stabilises the downstream fluid pressure to a set value. Any component or actuator downstream of this symbol operates at the regulated (lower) pressure, not the full supply pressure.
What standard defines the pressure regulator symbol?
ISO 1219-1:2012 (Fluid Power Systems and Components — Graphical Symbols) defines the pressure regulator symbol for pneumatic and hydraulic diagrams. ANSI/ASME Y32.10 provides the equivalent North American standard, with a nearly identical symbol.
What is the difference between a pressure regulator and a pressure relief valve symbol?
A pressure regulator symbol (circle with internal horizontal lines) represents a device that reduces supply pressure to a set downstream value. A pressure relief valve symbol typically shows a normally-closed valve with a spring, and it vents excess upstream pressure to atmosphere to protect the circuit rather than delivering regulated downstream pressure.
What are the pins on a pressure regulator symbol?
The pressure regulator symbol shows two fluid ports: In (supply inlet, upstream high pressure) and Out (regulated outlet, downstream set pressure). These connect to the supply line and the downstream actuator or valve circuit respectively.
What units are used with a pressure regulator?
Pressure is measured in pascals (Pa), kilopascals (kPa), megapascals (MPa), or bar. Industrial pneumatic regulators are typically rated in bar (1 bar = 100 kPa). Flow capacity is rated in Nl/min (normalised litres per minute) or by Cv coefficient.
What is the designator letter for a pressure regulator in a schematic?
The most common designator for a pressure regulator in pneumatic schematics is PR (Pressure Regulator) or REG, followed by a sequential number such as PR1 or REG1 to identify each regulator uniquely in the circuit.
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