Low Air Sentinel

Low Air Pressure Cut-Off Valve for use with Pownall Sentinel EP

Why is this product needed?

Park brake not applied warning devices, often referred to as park brake alarms, are very effective under normal conditions. However, if the vehicles park brake air reservoir is empty and the park brake is off, there is no air present in the vehicles spring brake control line from port 21 of the handbrake control valve. This means that the warning device will not warn the driver if they exit the vehicle without having applied the hand brake.

The warning device operates as if the hand brake was applied because there is no air pressure in the park brake control line just as when the park brake is actually applied under normal vehicle operating conditions. This is a fact and applies to all such warning devices.

Circumstances that can initiate an accident

• Vehicle left standing for a length of time – no air in tanks
• Tractor coupling to trailer with depleted air tank
• Damaged red suzie air line to trailer depleting tractor unit air supply

Typical Scenario

Not realising the vehicles system air is low, the driver drops the hand brake and tries to drive off but finds the brakes do not release. Exiting the cab forgetting to reapply the handbrake, no alert is given due to low system air.

In the meantime, the running engine builds air pressure and the spring park brake actuators release as the hand brake is not applied. The vehicle is now un-braked, free to roll and could cause an accident. Additionally the driver may see the vehicle moving and attempt to get in the vehicle to apply the brakes and sustain injuries during the attempt which could be fatal.

The Sentinel low air cut off valve combined with our Sentinel EP park brake alarm prevents accidents as described above, which are drawn from real life incidents.

The low air cut off valve is mounted in the cab and shuts off the air supply to the handbrake control when the system air pressure drops below a set point and must be manually reset by the driver when air pressure has built up, so the driver will be in the vehicle when the air supply is restored should the park brake not be applied.

Click on the image to the right to download PDF file on the low air cut off valve.

Low Air Sentinel + Sentinel EP