Functionally, the Mk 13 Mod 4 GMLS jettison device is a compact, simple, ready-to-use piece of equipment that is totally independent of the ship's HP air system.
JETTISON REMOTE.- When jettisoning is ordered, the launcher captain activates the REMOTE DUD JETTISON switch on the EP2 panel. Control system circuits automatically cause various guide arm components to set up for jettisoning. The fin opener arm assembly retracts. The forward-motion latch unlocks, and the arming device extends. As the retractable rail retracts, the crossbar between the jettison shafts enters the slot in the crossbar receiver. The guide arm is then mechanically prepared for the jettison operation.
The remote circuits also affect the launcher power drives. Train control is transferred from the fire control system (FCS) computer to synchros in the launching control system. Elevation control is switched to a remote FCS gyrocompass. In response, the launcher automatically moves to a jettison position that aims the missile seaward. Train bearing will be either directly port or starboard. It is controlled by stationary position orders from the digital director in the EP3 panel to the launcher synchros in the train and elevation receiver regulators. Elevation angle will be 36°40' relative to the horizon. As the ship rolls and pitches, gyrocompass signals will maintain the 36°40' elevation angle. This angle ensures the jettisoned missile will clear the ship.
Extend Jettison.- When the launcher synchronizes to a jettison position, the EP2 operator reports ready and awaits the final order. Pushing the DUD
JETTISON- JETTISON push button on the EP2 initiates the extend and jettison cycles.
The extend dud-jettison solenoid is energized. Hydraulic fluid pressure (1,500-1,600 psi) from the launcher guide power unit is applied to the front of the jettison latch. However, at this time the latch cannot be retracted. That is because nitrogen pressure (at 2,400 psi) is constantly applied to the back of the jettison piston. This pressure forces the jettison beam forward (slightly) and places a bind on the latch. Thus normal hydraulic fluid pressure cannot overcome the higher nitrogen pressure. The jettison latch remains extended at this point in the extend sequence.
Hydraulic fluid is, therefore, ported around the latch. The fluid is directed to a pressure intensifier
valve in the pressure intensifier pump. A pumping action takes place as this valve is made to shift rapidly back and forth. The principle behind this action involves the conversion of an applied pressure with
great volume by a large area piston into a greater pressure with less volume by a smaller area piston. Hydraulic fluid pressure is, thus, intensified to more than 8,000 psi and is ported to the front of the jettison piston. Intensified fluid pressure overcomes the nitrogen pressure behind the piston. The jettison piston and beam retract slightly to release the bind on the latch. Normal hydraulic fluid pressure may then retract the jettison latch.
As the latch retracts, the output of the intensifier pump is isolated and stopped. Nitrogen pressure behind the jettison piston causes it to creep forward. Its speed is restricted by an orifice. Movement of the piston cams the two jettison pawls into contact with (behind) the forward missile shoe. The forward-motion latch is displaced, and valves are shifted to remove creep control. The piston accelerates and propels the missile seaward.
At the end of piston travel, a buffering action takes place to slow and stop the piston and beam. Also, an interlock switch is actuated to provide the launcher captain with an EXTENDED lamp indication.
Retract Jettison.- After the extended lamp lights, the launcher captain pushes the DUD JETTISON RETRACT push button. A solenoid energizes to activate the intensifier pump once again. A retract cycle requires a large volume of hydraulic fluid. A special isolation valve provides this large supply by closing and isolating hydraulic fluid from the other components of the guide arm. This action is necessary to prevent these components from reducing the volume of fluid available to the intensifier pump.
Intensified hydraulic fluid is then applied to the front of the extended piston. As the jettison piston and beam retract, nitrogen is forced back into the nitrogen tank. In approximately 15 seconds, the piston reaches its fully retracted position. The latch engages the beam and activates an interlock switch. The control system indicates RETRACTED.
The isolation valve shifts to make hydraulic fluid available to the other guide components. The forward-motion latch locks, and the arming device retracts. The retractable rail reextends; the launcher slews to the load position, ready for future operations.
JETTISON LOCAL.- If the remote elevation order signal is not available from the FCS gyrocompass, the launcher captain switches to LOCAL DUD JETTISON. Fixed position synchros in the EP2 then supply the elevation signal. Ship roll compensation consists of the launcher captain watching a clinometer bubble. The jettison operation is timed to coincide with a down roll. All other operations are the same.
JETTISON EXERCISE.- For maintenance testing, the EP2 operator shifts the system to the STEP-EXERCISE mode. Step push buttons must be activated to extend the arming device and retract the retractable rail.
With the guide arm empty, the rail-loaded indicator plunger and a hydraulic valve are extended. The extended valve ports hydraulic fluid to a throttle valve. This valve restricts the flow of hydraulic fluid to the jettison piston and limits the speed of piston travel. The reduced speed prevents equipment damage that would occur under a no-load condition. Retraction of the jettison piston in the exercise cycle is the same as that in an actual jettison operation.