Mitch Edwards 
PNEUMATICS AND AIR CIRCUITS UNDERSTANDING THE CASCADE VALVE AND PLC UNDERSTANDING 

This ebook has 2 parts, plc and pneumatics. The plc part will take you to where the Diploma of Engineering, Plc module can be studied. The pneumatics side deals with the sequence,  A, B, C, C-, A-, D, D-, B- using 5 ports and 3 port relay valves to a cylinder. It teaches circuit understanding.