Marine Marker Mk I (Obsolescent)

Description: The marker consists of a light metal body and tail, which are separated by a diaphragm. The tail is closed by a metal plate, having a tail cap connected to the main outlet tube. The forward end of the body is closed by a heavy metal plate into which are set two water-inlet valves. A tube passes from the central valve, through the filling and spring-loaded pressure plate, and amost to the diaphrgam. The pilot tube ex-tends aft from the off-center valve to the pressure plate. The pilot outlet tube then continues to a strainer attached to the diaphragm from which the main outlit tube issu-es. The pressure plate retains the main filling in the forward part of the body.

Functioning: When the marker has been prepared for use and dropped into water, the water jacket fills and the scallopped disc in the main valve and the large disc in the pilot valve are forced against the ledges in the valves, thus preventing too great an in-gress of water while it is submerged. Some water, however, enters the main outlet tube, passes through the pressure plate, and reacts with the calcium phosphide. This reaction evolves impure phosphine gas, which ignites spontaneously when the marker surfaces. As it surfaces, the pressure against the valves is relaxed, and the springs return the discs against the circlips, thus permitting the ingress of water through the scallops in the disc to the bottom of the inlet tube and pilot tube. The water entering the main valve passes through the inlet tube into the perforated tube, and after passing through the perforated diaphragm percolates through the flannel sheath and reacts with the main charge to give off pure phosphide, which is not spontaneously inflammable. The cap cover the free end of the perforated tube pervents the water from percolating through the part of the flan-nel sheat above the pressure plate.

The water entering the pilot valve percolates through the flannel disc and dissolves the potassium bisulphate and the sodium nitrite. The chemicals interact and evolve ga-seous oxides of nitrogen which mix with the phosphine in the stariner. The mixed gas are spontaneously inflammable in air, and, passing through the main outlet tube, ignite imme-diately in reaching the air. The flame thus produced continues to burn evenly for approxi-mately two hours, during the whole of which time the gases remain spontaneously in-flammable, to that even if the flame is put out by a wave, it lights up again as soon as contact with air is re-established.

Remarks: The flame is visible in daylight over a distance of at least three miles, and at night over a distance of about 20 miles. White smoke is given off with the flame. In damp atmosphere, after removal of the cover-seals and press-caps, this marker evolves spontaneously inflammable phosphine, and for this reason should be prepared for use only just befor it is to be launched.

Figure 93 - Marine Marker Mk I