Hawk Industries T-Wrex Jr. Manual Serial Numbers 111 to 118 - Manual (Page 71)

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51886 Control System Elements
The T-WREX controls are face mounted on a remotely located console.
Each lever/button introduces compressed air into different sections of the pneumatic control
system.
A misrouted air line can cause the tool to operate in a manner not intended by the operator.
There are air operated elements in the control system that will route, close off, or vent air signals
to pilot the hydraulic valves.
These elements are located under the control console panel, in the relay box, and up on top of
the extending center pivot -- under a large box-shaped cover (four bolts).
There are two basic logic element types in T-WREX’s control system, with the more
complicated circuits being of varying configurations of logic elements combined.
The ‘OR’ element (PN L15): it has two inputs and one output. Described easily: a three port “Y”
with no crosstalk between the two input ports. Crosstalk is the energizing of an input port from
another input port.
The other element is the air piloted valve (PN A501, or PN A508).
It has one pilot (spring return) or two pilot ports (pilot return), one air supply port, two output
ports, and two venting exhaust ports.
These valves have an internal spool shifted by at least one pilot signal (compressed air).
The input (supply air) is routed by the position of the internal spool to one output port only.
The input port on this valve is located between the two exhaust ports. The two output ports are
on opposite face.
The other pneumatic elements whithin the control system are relays, logical NOT, and
mechanical input valves (rotation and extend limits, set by operator).