On startup both the cylinders A & B are sitting on sensing,valves a1 & b0 respectively. a1 the last sensing valve operated in group II so it receives the main air and select the group I via start stop valve.
If the start valve is operated it will select the group 1 which will operate the power valve A0, cylinder A will retract thus operate the sensing valve a0, which signals to B1 power valve, cylinder B goes + which will select sensing valve b1, which is supplied with the main air and will select group II. This will exhaust the group I output line.
Group II output line is now supplied with air, which will operate the power valve B0, Cylinder B will retract and signals the sensing valve b0 which will operate power valve A1, Cylinder A will go + and signals sensing valve a1 which selects group I and cycle completes.
1. Modify the circuit to provide an emergency stop which will park both cylinders in the extended position (i.e. A + B +). 2. Modify the circuit to provide a fail safe. The fail safe should: (a) act in the event of a reduced pressure at inlet to the group selecting valve (b) park the cylinders in the retracted position.