CNG Circuit Leak Tester, built for 200 bar three-stage leak detection.

Introduction

The CNG Circuit Leak Tester ensures absolute integrity of the fuel delivery circuits of CNG vehicles. Leaks in a CNG system pose both safety and environmental risks, so this tester pressurizes the entire circuit with dry nitrogen and precisely monitors pressure decay against a pre-charged reference, automating what would otherwise be a labor-intensive manual check. The system is PLC-controlled for remote start/stop, features multi-level safety interlocks, and is housed in a compact, modular frame for ease of integration on production lines or in service workshops.

Three-module architecture

• 1. Nitrogen bank: four 40 L cylinders (up to 150 bar) with automatic change-over logic; each cylinder's pressure is LED-monitored and automatically sequenced for uninterrupted testing.
• 2. Main panel: contains a five-micron–filtered, regulated air drive (4–7 bar, 40–60 CFM) for the Haskel air-driven gas booster, plus PLC, solenoid valves, and air filters/regulators.
• 3. Dispenser section: houses the high-pressure reservoir, three-stage dome-loaded regulators (0–50 bar, 50–100 bar, 100–200 bar), digital pressure readouts (DRO), and differential pressure transmitter.

Industrial-grade components

• Haskel booster: air-driven, area-ratio piston booster generates up to 250 bar from 4–7 bar air input.
• Swagelok & SMC fittings: high-precision filters, valves, regulators, hoses, relief and ball valves.
• WIKA instrumentation: Bourdon gauges and electronic transmitters for visual and PLC feedback.
• EKC sample cylinder & DRO: maintains a 200 bar reference for differential-pressure leak detection.

Automated sequence & safety

• Pre-test venting cycle eliminates residual line pressure.
• Three-stage pressurization with programmable hold times (10 s at 50 bar, 30 s at 100 bar, 60 s at 200 bar).
• Safety interlocks on air and nitrogen inlet pressures, emergency depressurization solenoids, and annunciator LEDs.

Technical specifications

System components & functionality

• Nitrogen bank: four-cylinder manifold with non-return valves and LED-monitored gauges; automatically switches to the next cylinder when pressure falls below 40 bar.
• Haskel air-driven booster: area-ratio piston design — large air-drive piston coupled to a smaller gas piston — boosts nitrogen up to 250 bar. Maintains separation of drive air and gas sections; pilot-valve cycling ensures continuous reciprocation.
• High-pressure reservoir: 500 cc buffer stores boosted gas for smooth stage transitions; pressure transmitter on reservoir feeds the PLC.
• Three-stage dome-loaded regulators: controlled via E/P converters, permit precise, stepwise pressurization.
• Differential pressure transmitter & sample cylinder: pre-charged to 200 bar; the system compares test-circuit pressure against this reference to detect leaks down to user-defined mbar levels.
• PLC & HMI: coordinates venting, stage sequencing, LED annunciators, emergency shutdown, and remote start/stop via touch-screen.

Operation & testing procedure

• 1. Installation: position the unit in a ventilated area (< 40°C); connect industrial air (4–7 bar), nitrogen hoses (4 cylinders), and 230 VAC power; tighten all fittings and verify air/nitrogen LED status ("PRESSURE OK").
• 2. Startup & venting: turn key-lock "SYSTEM ON"; the PLC opens the vent valve for 20 s to clear residual pressure; "OPERATION READY" LED illuminates.
• 3. Test sequence: attach the dispenser nozzle to the vehicle's CNG receptacle and press "START". Stage 1 ramps to 50 bar and holds 10 s; Stage 2 ramps to 100 bar and holds 30 s; Stage 3 ramps to 200 bar and holds 60 s. The DRO displays differential pressure at each hold; any drop above threshold indicates a leak.
• 4. Leak confirmation & rectification: remove the nozzle; apply soap or Swagelok Snoop solution at joints; tighten any leaking connections and repeat the test as needed.
• 5. Depressurization & cylinder change: upon test completion or emergency stop, the high-pressure solenoid vents the circuit automatically. To replace cylinders: isolate, rotate fixture, unlock clamp, swap cylinder, re-clamp and reconnect.

Safety & precautions

• Pressure settings: never adjust relief valves, dome regulators, or electronic regulators.
• Air & power sequencing: always shut off the air supply after electrical power is switched off to avoid idle booster operation.
• Ventilation & access control: keep doors closed during testing; do not touch hoses or live electrical points.
• Routine checks: confirm no inlet fluctuations; inspect filters (air 5 µm, nitrogen 7 µm) and replace seals per maintenance schedule.
• Emergency procedures: familiarize operators with the emergency depressurization valve and lock-out/tag-out protocols.

Conclusion

By integrating industrial-grade boosters, precision regulators, PLC control, and automated safety interlocks, the Neometrix CNG Circuit Leak Tester delivers rapid, repeatable, and highly sensitive leak diagnostics for CNG vehicle fuel systems. Its modular design, ease of operation, and robust safety features make it an indispensable tool for OEMs, cylinder manufacturers, and service providers committed to CNG safety and quality assurance.