Finding air ingress in a vacuum system: inspection route and verification

Slow evacuation does not prove a leak. First separate pump performance from possible air ingress. Process load, a blocked filter, pump condition and gas released by the product can also affect pressure.

The diagram shows 1 a vacuum vessel, 2 pipe joints, 3 atmospheric air entering through a defect, 4 a directional airborne ultrasonic sensor, and 5 the vacuum pump. It illustrates the principle; it is not an installation drawing.

Start with the symptom

Observation	Inspection focus
Vacuum worsened after maintenance	Flange assembly, gaskets, valve positions
Vacuum drops when one branch is connected	Hoses, joints and consumers on that branch
Evacuation is slow with the section isolated	Pump, filter, pressure measurement and gas load
Pressure rises after isolation	Boundary tightness, gas release and evaporation

Record the pressure unit and whether it is absolute pressure or gauge vacuum. Compare results under the same process load.

Inspection route

1. Record pressure, operating mode, connected branches and evacuation time.
2. Isolate a section only under an approved procedure compatible with the process and pump operating limits.
3. Inspect accessible flanges, threaded fittings, flexible hoses, valve stems, filter covers and seals. Mark recent maintenance locations.
4. With a pressure differential present, scan with an airborne ultrasonic sensor. Start with a broad scan and then approach suspect joints; keep settings consistent for comparisons.
5. Check from several directions. Nearby pneumatics and reflections can mislead localization. A signal peak alone is not proof of a defect.
6. Record a point number, photograph, conditions and findings. After repair, repeat the inspection and check vacuum recovery under the same conditions.

Select a method by the required result

Airborne ultrasound can locate accessible turbulent flow under a pressure differential. A directional sensor suits joint-by-joint inspection. An acoustic camera can support a broad survey; distance, background noise and sensitivity requirements determine suitability.

Pressure-rise testing measures change in an isolated volume but does not locate the source. Gas release and temperature changes also affect the result.

Tracer testing may be needed when the required tightness or defect size exceeds acoustic detection capability. Select the tracer, instrument, procedure and acceptance criterion for the installation.

No ultrasonic signal does not prove tightness. Small flow, limited access, background noise and operating conditions can conceal a defect. A contact sensor for bearings does not replace an airborne leak sensor.

Prepare an inspection request

Provide the equipment, medium, pressure and units, access conditions, symptoms, isolation options and required result: localization or verification against a tightness limit. Attach photographs and a diagram. Contact KEG TRK to discuss the method.

Consider LEAKChecker for route inspections or SDT340 with an appropriate airborne sensor for a broader inspection program.

Related reading: leak detection methods, pump suction and dry running, heat exchanger and condenser leaks.

• Vacuum suction cup loses the workpiece: causes and checks.

Sources and scope

SDT airborne sensors and the DOE compressed air sourcebook provide background on acoustic leak detection. The route above is a practical inspection structure, not an acceptance standard or a replacement for the installation procedure.