A fully automated production line in a facility involves metal blocks being placed in a furnace for heat treatment. Two cylinders are employed for this operation - one to open the furnace door and the other to push the metal blocks into the furnace. The order and movement of the two cylinders are as follows:
Stage 1, where the first cylinder retracts to raise the furnace door
Stage 2, where the second cylinder extends to push the metal block into the furnace
Stage 3, where the second cylinder retracts
Stage 4, where the first cylinder extend to close the furnace door
Construct a pneumatic circuit for carrying out this operation and explain the sequence involved.