Pressure Switch No. 2 Mks I and II (Service)

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Description: The switch consists of a housing tube mounted on a rectangular base plate. Inside the housing tube is located a spring-loaded striker, one end of which passes through the head of the housing tube and is secured by a transverse pin recessed into the end of the head. An annular groove in this striker is straddled by the milled-out end of a shearing stud, which is inserted through a hole in the top of the housing tube and engages the striker with a chisel edge. A flat, disc-shaped pressure head is located on top of the shearing stud. A threaded collar is screwed over the open end of the housing tube for attachment of the cap holder.

A safety pin may be inserted through the shearing stud above the housing tube to prevent the shearing stud from being forced downward.

Functioning: Pressure on top of the pressure head will cause the V-shaped cutting edge of the shear stud to break the striker spindle. The striker, driven forward by the spring, fires the percussion cap.

Use: This switch is used under boards, doormats, etc., in booby-trap installations where initiation by pressure is desired. The switch may also be used to initiate demolition charges.

Installing: Remove the pressure cap from the base plate, to which it is attached dur-ing transport. Insert the pressure cap through the hole in the top of the housing tube, and position it to straddle the striker. If properly placed, the pressure cap cannot be ro-tated. Make certain that the safety pin is securely in position. Unscrew the collar and remove the fuse adpater. Place the switch in position. Connect the charge to the fuse adapter with instantaneous fuse. Reattach the collar and the fuse adapter, and gently remove the safety pin. If desired, a Detonator No. 8 can be slipped directly into the fuse adapter, and the connection made to the charge with Cordtex.

Disarming: Insert a safety pin in the safety-pin hole in the pressure cap. Lift the pressure cap out of the housing tube. Cut the length of fuse connecting the switch to the charge. Remove the fuse adapter.

Remarks: The Pressure Switch No. 2 Mk II is almost identical to the Mk I, the princi-pal difference being the fact that the base plate and housing tube are cast in one piece in the Mk II, while in the Mk I they are fastened together with two screws. Also, in the Mk II the hole in the housing tube for the insertion of the pressure cap is surrounding by a raised collar, which contains a rubber washer. The safety pin pierces not only the shearing stud, but the collar and washer is well. The Mk II is issued with the pressure cap in place in the housing tube, rather than secured to the base plate. The alternations incorporated in the Mk II were designed to increase the weather resistance of the switch.

To test the switch prior to re-use, remove the fuse adapter and make certain that the striker is in the cocked position. If the striker spindle has been sheared, the striker will fall out of the housing tube, and the switch cannot be re-used.

A special electric adapter, also used with Pull Switch No. 1 Mk I, is supplied to enable this switch to be used for electric firing, if so desired.