What to Do if Pressure Rises/Overpressure Occurs? CNG Pressure Regulating Skid "Pressure Rise" Fault Self-Inspection Guide

1. Typical "Symptoms" of Pressure Rise

• Outlet pressure gauge pointer rises continuously and slowly, exceeding the normal set value

• Overpressure shut-off valve closes automatically, interrupting gas supply

• Safety relief valve frequently pops up, with exhaust sound or odor detectable

• "Hissing" internal leakage sound at the pressure regulating valve

• Severe pressure fluctuation or overpressure alarm at downstream gas equipment

2. Root Cause Chain of Pressure Rise

The essence of pressure rise is: the pressure regulating valve fails to close effectively or maintain the set pressure, causing high-pressure gas to continuously "leak" through the valve into the downstream. There are five common fault points:

1. Poor valve port sealing (impurity jamming or sealing surface damage)

2. Pilot/differential pressure pipe blockage or failure

3. Diaphragm rupture or aging of the pressure regulator

4. Spring failure or set value drift

5. Filter blockage leading to insufficient gas supply, causing abnormal opening of the pressure regulating valve (rare)

3. Emergency Response "Three-Step Method"

Before troubleshooting, take emergency measures to prevent accident expansion:

1. 1. Immediately close the upstream air intake valve to cut off the gas source.

2. 2. Open the downstream relief valve to release the pressure in the pipeline to a safe range (pay attention to ventilation, strictly prohibit fireworks).

3. 3. Observe pressure changes: if downstream pressure still rises slowly after closing the upstream valve, it indicates serious internal leakage at the valve port; if pressure is stable, the problem may lie in the pilot or control system.

⚠️ It is strictly forbidden to tighten valve bolts or strike the valve body under pressure!

4. Step-by-Step Self-Inspection Guide (Execute in Order)

Step 1: Check Inlet Filter

• Phenomenon: Filter differential pressure gauge pointer enters red zone or differential pressure increases significantly.

• Cause: Filter element blockage leads to poor gas supply; pressure regulating valve opens abnormally to maintain outlet pressure, which may cause pressure fluctuation but usually does not directly lead to continuous pressure rise. However, impurities may fall off and get stuck at the valve port after blockage.

• Operation: Close valves before and after the filter, disassemble the filter after pressure relief, clean or replace the filter element.

Step 2: Check Pilot and Differential Pressure Pipe

The pilot is the "brain" of the pilot-operated pressure regulating valve. A common cause of pressure rise is blockage of the pressure tapping pipe or the dissipation hole inside the pilot.

• Check differential pressure pipe: Is the pressure tapping pipe from the pressure regulating valve outlet to the pilot bent, frozen, or blocked by impurities? Check for leaks with soapy water or remove and purge with nitrogen.

• Check pilot: Remove the pilot cover, check if the internal diaphragm is intact and the dissipation hole is unobstructed. If there are impurities, rinse with cleaning agent.

• Special reminder: In winter, the differential pressure pipe is prone to ice blockage, causing signal interruption. Thaw with hot water (pay attention to explosion protection).

Step 3: Check Valve Port Sealing Surface

If the first two steps are normal, check the main valve port.

• Operation: Close upstream and downstream valves, remove the upper cover of the pressure regulating valve after venting, and take out the valve core assembly.

• Check valve port and gasket: Are there iron filings, welding slag, or dust stuck on the sealing surface? Does the gasket have obvious pressure marks, scratches, or hardening?

• Treatment: Clean impurities; if the gasket is worn, replace it with the same specification. Do not scratch the sealing surface with hard objects during cleaning.

Step 4: Check Diaphragm

Diaphragm rupture will cause the pressure regulating valve to lose control and the outlet pressure to rise continuously.

• Check position: Disassemble the diaphragm head of the pressure regulating valve and check if the rubber diaphragm has cracks, perforations, or deformation.

• Treatment: Replace the original diaphragm and check the diaphragm seat sealing ring at the same time.

Step 5: Check Spring and Set Value

• Spring fatigue: Take out the pressure regulating spring and check for permanent deformation, rust, or fracture. If any, replace with the same type of spring.

• Set value calibration: Reset the outlet pressure. Method: Slowly open the upstream valve, adjust to the target pressure with the adjusting screw, lock the nut, and observe whether the pressure is stable.

5. Common Fault Troubleshooting Table (Quick Reference)

6. Daily Preventive Measures

• Regular blowdown: Blowdown the pipelines before filters and pressure regulating valves weekly to prevent impurity accumulation.

• Winter insulation: Add tracing or insulation to differential pressure pipes, heat exchangers, and pressure regulating valve bodies to prevent ice blockage.

• Regular replacement of wearing parts: Diaphragms, gaskets, and O-rings are recommended to be replaced annually even if not damaged to eliminate aging hazards.

• Instrument calibration: Pressure gauges, safety valves, and shut-off valves should be sent for inspection every six months to one year.

• Establish inspection records: Record parameters such as outlet pressure, filter differential pressure, and heating temperature during each inspection, and intervene early when abnormal trends are found.

7. When to Contact Professionals?

In the following situations, please stop the machine immediately and contact professional maintenance:

• Pressure rise still occurs repeatedly after replacing gaskets and diaphragms

• Cracks or air leakage in the pressure regulating valve body

• Unrepairable damage to internal parts of the pilot

• Lack of disassembly tools or safety measures

Hebei Tairan Energy Technology has 15 years of experience in CNG pressure regulating skid maintenance, providing remote guidance, on-site emergency repair, and annual maintenance services. If you encounter unsolvable pressure rise problems, please contact us for technical support.

This guide applies to common pilot-operated CNG primary pressure regulating valves. Structures vary slightly by brand; please refer to equipment manuals. Operations involving high-pressure gas must be performed by certified personnel.