The unit, specifically designed to integrate with existing methane shutdown systems, can also operate independently and is already in use in New South Wales and Queensland, with some 100 units sold.

NTC Powertrain sales and marketing manager Martin Gunn told International Longwall News the system is very simple and works with or without a methane sensor – using a methane sensor enables the strangler to be shut off if excess methane is detected.

“The system can work with either air or oil pressure, whichever is more convenient on the vehicle,” he said.

Gunn explained that when working with air, the option taken by most current customers, air is supplied to one end of a piston which overcomes the force of a spring on the other side. The piston is attached to a lever that is connected to the main shaft of the strangler. In the bore of the strangler is an elliptical disc assembly and when air is applied to the piston the disc assembly opens. The disc assembly closes when requested to block the engine intake airflow.

“There are actually two discs in the disk assembly which sandwiches a Viton gasket, so when the discs close, the gasket forms a seal in the bore of the strangler preventing the air/methane mix from reaching the engine.”

The system uses air or oil pressure to actuate a piston to open the strangler valve; if this air/oil supply is shut off, the strangler valve will automatically close via an internal spring force, thereby “strangling” the engine by shutting off the engine intake airflow.

“Our internal seals provide a 100 per cent seal in the engine intake air path so engine shutdown is assured,” Gunn said.

“The air/oil pressure to the strangler can be controlled by any methane shutdown system or by a simple stop valve fitted in the air/oil supply line to the strangler valve.”

Gunn explained that unlike many other systems the NTC valve has a window which allows viewing of the operation and ease of inspection without any need for disassembly during routine maintenance and service checks.

“The NTC strangler is purpose-designed and developed for the rigorous operating conditions of the mining industry, whereas our competitor products have often been modified and patched to suit this application,” he said.

“Through our choice of special alloys and stainless steels, the NTC strangler to date [has] had zero warranty [claims] despite being in the field several years.

“This has obvious benefits for production on-time and minimised downtime.”

The strangler is constructed from industry-accepted aluminium alloys and stainless steel to provide resistance against corrosion and has been approved for underground use by the Queensland Department of Mines and Energy.