Description. The pressure-detectng device (figure 237) consists of three volume tanks, X, Y, and Z, of which only X is variable. Y and Z, although separated by dia-phragm D, are connected through construction C. The over-all unit consists of a machi-ned aluminum casting surmounted by a collapsoble rubber bag. Volume Y servers only as a connecting link between X and the diaphragm. Z is entirely closed except for the con-striction C, which is filled with adjustable, fibrous material (not shown on drawing). This serves as a variable resistance and regulates, within limits, the passage of air through the constriction.

D is backed up, except for a small circular area in the center, by aluminum reinforcing which forms part of the main casting. The surface of the casting is well machined and is bored with five small holes which prevent the diaphragm from sticking due to a possible vacuum seal.

The switch consists of two contacts, one fixed and one movable. The movable con-tact consists of a stirrup, mounted on the center of the diaphragm inside Z. The fixed contact is mounted as indicated in the drawing, and is adjustable. Leads from the two are taken out of the device through a packing gland by a douböe-conductor cable, pas-sed through another packing gland into the main body of the mine case (as in LMB) ot the firing unit (as in BM 1000).

It should be noted that figure 237, the drawing of the pressure detecting device, is schematic in nature and omits some of the refinements present in the actual device.

Figure 237 – Pressure-Detecting Device