Press-Pull Switch No. 7 Mk I (Obsolete)

Width

Height

Length

Weight

Material

Pull or pressure required

(Depending on setting)

Color

Description: The switch consists of a tin case with a bottom cap and spring to hold either a service Battery, Dry, W, Mk I or a standard 3-cell, flat torch battery. The case is fitted internally with an operating mechanism and internally on the top with two termi-nals for connection to the electric firing cable. The push or pull mechanism on the side of the case consists of a plunger fitted externally with a push or pull plate, and internally with a switch bar which completes the circuit when the plunger is either pushed or pul-led. Two holes are drilled in the push or pull plate for the attachment of a trip wire, and the plate is threaded centrally for the insertion of an extension spindle.

The actuating tension or pressure is determined by the tension of the spring in the ball release catch, which is located on the side of the plunger housing. The tension of the spring is adjusted by the setting stud. The lightest actuating tension is about five lb. and can be increased to any desired amount up to 35 lb. by screwing in the setting stud.

A safety pin with locknut prevents the plunger from being pulled or depressed inadver-tently. The safety pin cannot be withdrawn unless the plunger is in the dead neutral po-sition and held so by the ball release catch.

Functioning: With the safety pin removed, necessary pull or pressure on the plate overcomes the pressure of the ball release catch, and the switch bar completes the cir-cuit, thus firing the electric detonator to which the leads are attached.

Use: This switch is designed for booby-trap installations where initiates by either pull or pressure is desired.

Installing: Place the mechanism either for pressure or for trip-wire use, and adjust the actuating pressure as required. Connect the firing leads to the terminals on the top of the case and withdraw the safety pin.

Disarming: Remove the leads from the battery terminals. Replace the safety pin and remove the switch and charge.

Remarks: To test this switch for re-use, connect to an electric detonator of the type to be used. Withdraw the safety pin, and push or pull the plunger to fire the deto-nator.

In December 1943, the following instructions were issued by the Chief Engineer, Allied Force Headquarters:

"This switch (No. 7) is defective, and if in possession of untils will be destroyed."