Flame arrester also in the vacuum truck

A pre-volume deflagration flame arrester or – simplified – a flame arrester prevents flame transmission, through a measuring instrument, into a zone 0 (gas) hazardous area. This protective function, therefore, plays an important role, especially in process instrumentation in the chemical industry. However, it also increases operational safety in the wastewater industry: in mobile wastewater transport.

In densely populated regions, sewer networks convey wastewater to treatment plants. In rural areas, however, there is often a lack of such infrastructure. Wastewater from households flows into septic tanks or cesspools. To empty them, waste management companies use vacuum trucks with tankers. These vehicles then take their load to the nearest sewage treatment plant for processing.

Possible hazard from flammable vapours

The transport to there involves a certain potential hazard. This is because a hydrocarbon layer forms on the surface of the untreated wastewater in the vehicle’s closed collection tank. This can produce flammable vapours. This means that the inside of the tank corresponds to a zone 0 hazard level. According to the definition, an explosive atmosphere prevails there permanently or over a longer period of time.

Flame arrester in the pressure gauge

A sticker marks the zone separation.

As in the application from the article, the flame arrester in the diaphragm seal system shown here is also integrated in a pressure gauge with an output signal. The sticker marks the point where the protected zone begins.

The pressure measuring instruments used for tank monitoring must meet this requirement. For this reason, a manufacturer of vacuum trucks equips its vehicles with a diaphragm seal system from WIKA. Attached to the diaphragm seal with flush diaphragm is an ATEX-approved model PGT23 pressure gauge with an integrated model 910.21 pre-volume deflagration flame arrester.

Both ATEX and also IECEx approval

The flame arrester fulfils the requirements of the harmonised EN ISO 16852:2016 standard. It therefore enables mounting to a zone 0. Furthermore, the model 910.21 is the first flame arrester on the market that has IECEx approval in addition to ATEX approval. The vacuum truck manufacturer is thus increasing the export possibilities for its vehicles.

Pressure information while driving

The model PGT23 pressure gauge, in which the flame arrester is built in, is a hybrid instrument. In addition to the mechanical pressure display, it features an analogue output signal (4 … 20 mA). The signal is transmitted to the cabin of the vacuum tanker so that information about the pressure in the tank is always available, even whilst driving.

Note
In addition to the PGT23, WIKA also combines the flame arrester with other Ex-approved pressure measuring instruments and diaphragm seal systems to form a fixed unit. Technical information on the model 910.21 pre-volume deflagration flame arrester is available on the WIKA website. If you have any questions, your contact will gladly help you.

Also read our articles
Ex pressure sensors for zone 0, zone 1 or zone 2
Ex protection – The most common ignition protection types for sensors in gas hazardous areas



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