This type of shield has two sets of legs inclined forward into the canopy and the other two inclined backwards and connected to the goaf shield.
The main features of the 4 leg shield are:
- The front legs connect the base and the canopy and the rear legs connect the base and the top shield member
- The top canopy is hinged to the main rear canopy to allow the canopy to articulate along the line of the face
- The base is connected to the rear shield with a lemniscate linkage
The two legs of the support are connected into the canopy at an inclined angle and the supports are usually operated in Immediate Forward Support (IFS) mode.
The main features of the 2 leg shield are:
- The support density is not uniform throughout the working range
- The lemniscate linkage ensures that the front of the top canopy maintains a constant distance from the coal, between the fully closed state and fully open position
- Full use of the reverse mounted ram
- Side ram shields ensures good flushing protection