Patent ID: 7215358

Claim:
In a system for monitoring an inside of a furnace inaccessible to an operator through a hole formed in a wall of the furnace, a motor-less automatic retraction device, comprising: a wall sleeve for cooling and protecting a vision tube by being brought into contact with a flange to prevent compressed air supplied from a control box and discharging the compressed air through a space between the inside of the furnace and the vision tube; a locking device connected to a vision tube bracket by a latch, wherein the bracket is directly fixed to the vision tube at a first part and to a spring at a second part, the latch being fastened to the bracket at the time of being inserted into the furnace so as to prevent the vision tube from being randomly retracted by elasticity of the spring, and to allow automatic retraction by automatically releasing the vision tube from interlocking with the locking device in response to a signal from a control box during an abnormal situation, including at least one of switch manipulation of an operator for automatic retraction, a power failure or pressure reduction of the compressed air; and a shock absorber for buffering impact when the vision tube is inserted into the inside of the furnace with a carriage plate attached to a rail and retracted from the inside of the furnace by the spring.