Figure 12: Illustrates the functional difference between the basic J.1. locomotive Relay Valve and the J.1.6-16 Step-Up version. It can be seen that for an Independent brake application the J.1.6-16 provides for TWO feeds of control pressure from the #20 pipe, whereas when the control pressure is supplied via the Control Valve (as for an Automatic application) there is only ONE feed to the Relay Valve. Port 16 supplies control pressure to the chamber below the small diaphragm while port 16c supplies control pressure below the large diaphragm. Note that on some rail systems the role of the IBV Cut-out cock is taken by an MU2A valve.