Patent ID: 7665930

Claim:
A mine door installation comprising one or more door frames installed in a mine passageway and one or more door leaves mounted on said one or more door frames for movement between open and closed positions of the respective door leaf, movement of said one or more door leaves between its open and closed positions being powered by a hydraulic system, the hydraulic system comprising: a hydraulic actuator connected to one of said one or more door leaves for driving movement thereof between open and closed positions of the door leaf; a reservoir having a volume for containing a hydraulic fluid used to operate the hydraulic actuator; a fluid circuit providing fluid communication between the at least one hydraulic actuator and the reservoir; a pump operable to pump hydraulic fluid from the reservoir into the fluid circuit; and a fluid circuit flushing system operable to flush hydraulic fluid from the fluid circuit into the reservoir without moving any of the one or more door leaves of the door installation, the fluid circuit flushing system comprising: a bypass valve moveable between at least one working position in which fluid can be pumped into the fluid circuit to operate the hydraulic actuator and a bypass position in which hydraulic fluid pumped into the fluid circuit flushes hydraulic fluid from the fluid circuit without operating the hydraulic actuator; a control system operable to move the bypass valve to its bypass position and activate the pump when the bypass valve is in its bypass position to pump hydraulic fluid from the reservoir into the fluid circuit to flush the hydraulic fluid in the fluid circuit into the reservoir; and a first temperature sensor for measuring either an ambient temperature or a temperature of fluid in the fluid circuit, said control system being responsive to a signal from the first temperature sensor to open the bypass valve when the ambient temperature or the temperature of fluid in the fluid circuit is below a specified temperature.