Posts by popgun pete

    The much and probably deservedly maligned full-face snorkel dive mask may be getting a new lease on life as it may help in supplying protective breathing gear for hard pressed medical workers by providing a reusable mask that completely shields the face.



    www.scubadivermag.com

    Ocean Reef Launches Adaptor To Change Full-face Snorkel Mask Into COVID-19 Protective Mask | Scuba Diver Mag

    Ocean Reef, which produces full-face diving and snorkelling masks, has created an adaptor which will fit to their snorkelling product and transform it into a COVID-19 protective mask.
    www.scubadivermag.com http://www.scubadivermag.com

    virus masks.jpg

    Here are modified dive masks already in action produced by another group. As the situation worsens there has been a shortage of protective gear, much of it single use, but here only the cartridge needs replacing as the masks are able to be cleaned.

    The main difference, bar being "back to front", is that a pneumatic speargun is totally surrounded by its tank, whereas a "Dreamair" type gun has its tank on either side in two separate "pipes". The two pipes could be joined if the barrel was raised in the gun and the separate pipes were connected at the bottom. However such a shape may be difficult to produce and the rigidity would be different than a fully integrated central pipe top and bottom. The advantage would be only one plug power controller and one-way valve instead of two with the separate side tanks. In some guns, such as the old Scubapro "Magnum" and its "Vintair" successor, the plug and one-way valve are both combined in a system that functions similar to the "Sten" except that high and low power positions are reversed in the power selector gate. Like this version from Salvimar.



    tank with raised barrel.jpg


    The possibility of making a "Dreamair" type of gun with dual power occurred to me while looking at an old diagram of the Mares partitioned reservoir system. In the Mares "Sten" and its many descendants and clones the gun can shoot with all the tank volume (full power) or just a fraction of it from what is often referred to as the pre-chamber (low power). Low power is approximately a half to a third of full power depending on how small the pre-chamber is. The presence of a one-way valve as well as a plug that closes or opens the partition in the gun's bulkhead that separates the tank volumes also allows easy loading in that the gun can be incrementally charged by repeated pushes on the spear during muzzle loading. For a "Dreamair" version this would translate to repeated pulls on the cable wishbone in an analogous process to the muzzle loading of the pneumatic.


    Maybe easier to draw than do, but here the concept is illustrated diagrammatically.

    It is the same idea, but turned back to front as in the "Dreamair" when the gun shoots the piston that hauls the cable flies rearwards inside the gun, not forwards. That means the power selector gate will be in the muzzle, however a remote control position may be installed at the rear handle by either a connecting rod or a hydraulic line to operate the selector switch.

    Up until now most of my diagrams have used estimates based on what the winding drum proportions look like in their profile photos when trying to put numbers on the gearing, but now inventor Andreas has published some numbers of his own. The original is in Greek, so the auto-translator has made a few errors, but you can understand it.


    In the Dreamair aluminum, the piston is 1000mm2 (ie 10Kg armature / atm pressure) with the simple armor having a maximum armature of about 8.5 atm. That is, arming starts at 85kg and ends at 60kg (CVT use). However, since the exterior with the inner winding drum does not start with a 1: 1 transmission ratio, you are arming from 75 kg to 60 kg. The piston at 8,5atm respectively starts charging at 85kg and ends up at about 130kg.

    In the Dreamair Unreal the piston is 500mm2 (that is, 5Kg of armature / atm pressure) with the simple armor having a maximum armature of about 16 atm and the difference between the initial and final power being about the same as the aluminum. In the Dreamair Unreal, the inner drum is not capable of a high call because it anchors within this inner rope of the gun and for this reason you manufacture the Dreamair Unreal with three balloons
    (three air chambers, a central cylindrical one and two flanking chambers as per the patent drawings).
    Dreamair fig 13 & 14.jpg

    The larger the two flanking chamber volumes are then the lower the compression ratio of the gun. In such an arrangement you can use a longer piston travel than you would have in a monotube as in the latter half the tube length travel takes you to a compression ratio of 2.0.


    We have not seen a cross-section of the "Dreamair Unreal" barrel tube, but the closest approximation would be the Sporasub "One Air" tank tube.

    A "Horseshoe Crab" I think that they are called, saw them on a TV show about both them and another living fossil the Chambered Nautilus. From memory a dish was prepared from one which was not particularly appetizing and involved the creature's eggs which are contained in the horseshoe shape around the head. Closest thing to a Trilobite which once was the dominant species in the oceans millions of years ago. Apparently their blue blood is used for testing of biological contamination in laboratories due to some unique properties which have enabled the species to survive the millennia without getting diseased by bacteria and pathogens.

    One thing that I forget to mention is that with power regulated pneumatic guns you need to set them to "full power" and have the gun slightly tilted so that the oil runs down through the now open transfer port before you press on the inlet valve. The tilting places the transfer port to act as a drain hole for the front tank by being the lowest point, otherwise oil sitting inside there will not be blown out. That gun positioning then allows all the oil in the gun to run down into the rear end of the inner barrel which you are intending the air pressure release to blow all the oil out of via the back end of the gun.