Gas Header Pressure Control Loop
This diagram shows a pressure-control loop on a compressed-gas header. Gas enters the compressor and passes through PV-101 before entering the downstream header. PT-101 measures that header pressure and sends an electric signal to PIC-101. The controller sends a pneumatic signal to the diaphragm-operated control valve, adjusting inlet flow to maintain its pressure setpoint. PSV-101 is shown separately as an independent protection device. If pressure exceeds its set pressure, it relieves to the designated safe vent rather than relying on the normal control valve. The drawing distinguishes control from pressure relief and is useful for a design discussion or loop check. A completed project must confirm gas properties, relief sizing, vent destination, materials, and applicable safety requirements.
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Scenario
A compressed-gas header needs pressure regulation and an independent overpressure safeguard.
Key decisions
- Measurement: PT-101 senses pressure downstream of PV-101.
- Control: PIC-101 modulates the inlet control valve.
- Protection: PSV-101 relieves independently to the safe vent.
- Fail state: PV-101 closes on loss of actuator air.
When to reuse this
Use this pattern for a basic regulated gas header; review relief sizing and setpoints for the actual service.
Frequently asked questions
What does PIC-101 do?
Why is a PSV separate from the control loop?
What does fail closed mean?
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