Gas and leak detectors

Gas and leak detectors are instruments dedicated to locating leaks of refrigerant gases, combustible gases (methane, LPG), toxic gases and technical gases, as well as loss of tightness in pneumatic and hydraulic systems. Detecting leaks promptly is critical for safety (combustible and toxic gases), for compliance with environmental regulations (F-Gas for refrigerants, emission control), for energy efficiency (compressed air leaks carry high costs over the long term) and for the service life of the plant. Several technologies are used: semiconductor electronic sensors, PID sensors, ultrasonic leak detectors, UV tracers and acoustic techniques.

Electronic sniffers for refrigerants

Electronic sniffers for refrigerant gases use heated diode sensors, NDIR infrared sensors (non-dispersive infrared) or solid-state sensors that selectively detect the presence of halogenated hydrocarbons in the surrounding air. Sensitivity thresholds are of the order of a few grams per year (for refrigerants regulated under F-Gas, a sensitivity of ≤ 5 g/year is required by EU Regulation 517/2014). A flexible probe is moved along pipework, fittings, valves and exchangers, and the instrument’s audible and visual signal intensifies near a leak. They are indispensable for the mandatory periodic checks on F-Gas refrigeration systems.

Ultrasonic leak detectors

Ultrasonic leak detectors exploit the physical phenomenon whereby a leak of gas or compressed air through a small hole generates a high-frequency sound (20–100 kHz, ultrasound inaudible to the human ear). The instrument combines a directional ultrasonic microphone (focused on a small detection cone) and a real-time converter that turns the ultrasonic signal into audio the operator hears through headphones. They are used to locate: compressed air leaks (a very common problem in plants, with significant energy costs); steam trap leaks; electrical arcing in MV/LV substations; mechanical bearing problems. They are universal (they detect any gas that produces ultrasound as it escapes) and require no contact with the gas itself.

Combustible gas detectors

Detectors for combustible gases (methane CH4, propane C3H8, butane C4H10, LPG, hydrogen H2) use catalytic sensors (pellistors – a catalyzed bead in which the combustible gas burns, generating heat detected by a differential resistance thermometer) or infrared sensors (selective for hydrocarbons). Measuring ranges are 0–100% LEL (Lower Explosive Limit, the lower explosive limit of the gas, for example 5% methane), with the option of switching to volume percent for high concentrations. Applications include: maintenance of domestic and commercial gas installations; monitoring of town gas networks and pipelines; safety in confined spaces (manholes, sewers, tunnels).

Tracer gas detectors

For tightness testing of components (radiators, evaporators, condensers, exchangers), the technique used is pressurization with a tracer gas followed by leak detection. The tracer gases used are: hydrogen (5% in nitrogen, a non-flammable and inexpensive mixture) detected with H2 sensors; helium (an inert, light gas that penetrates the smallest holes) detected with mass spectrometers for applications of the very highest sensitivity (10⁻⁹ mbar·L/s); nitrogen with UV dye (a fluorescent dye revealed with a UV lamp) for applications where easy visual diagnosis is wanted. They are used on the production line for component testing and by technical services to locate complex leaks.

F-Gas and environmental applications

The most widespread regulated application is the tightness testing of refrigeration and air conditioning systems containing fluorinated greenhouse gases (F-Gas), under EU Regulation 517/2014. The inspection frequency depends on the CO2-equivalent content of the system (from 12 months down to 3 months). The electronic sniffer must have a sensitivity of ≤ 5 g/year, must be certified to EN 14624 and must be calibrated annually. The technician must hold F-Gas certification (in Italy, a personal and a company certificate). All inspections and leaks found must be recorded in the mandatory equipment logbook.

Selection criteria

The choice of leak detector depends on the type of gas or leak to be located: for F-Gas and refrigerants → electronic sniffers certified to EN 14624; for industrial compressed air → ultrasonic detectors; for combustible gases → catalytic or IR sensors; for precision tightness testing → helium or hydrogen tracer systems; for UV dye systems → UV lamps with protective eyewear. Sensitivity, specificity for the gas of interest, portability, long battery life and compliance with sector standards are the decisive criteria.