Forward control: (Throttle in circuit): If the air to the cylinder is fed via the throttled chamber and the exhaust is effected via the ‘non return value’ or check unit, then it is termed as in feed or throttle in flow control.
Fig. Throttle in circuit
Backward control (Throttle out): If the air to the cylinder is affected via the non return flow control valve and exhaust is fed via throttle chamber then it is termed throttle out circuit.
Fig. Throttle out Circuit