Diver Daves Mark-15 Spheres Page 2

OK, enough of the fooling around outside. Here the lid has been removed to expose the two spheres, the center section, and the electronics pod. The Mark-15 is packed full, with little extra volume for anything. You can see how the entire rig was engineered around the spheres, which are one of the main distinguishing factors of this design. The sphere is the most efficient storage vessel available, yet it's cost is prohibitive thus the rarity of designs using it. In the Mark-15, cost was not an object, thus the inclusion of this type of supply. The Mark-15 was a direct spin-off of the General Electric rebreathing system used for lunar EVA activities, and the entire design reflects this heritage.

The standard first stage regulators used by Biomarine are a fairly low performance Sherwood piston design. This may at first appear a strange choice, but it was done as the rig never requires a high flow-rate to be supplied to it and the performance of this regulator is more than adequate. The simple piston design is utterly reliable, and these have given excellent results.

In my rigs, I have replaced the Sherwood diluent regulator with Poseidon 300 first stages. This was done to obtain a second low-pressure port to supply the Air Source inflator on my wings, and also has the advantage of providing a higher performance regulator to supply the air-source in case I ever need to breath from it. Lastly, the Poseidon is a diaphragm first stage, and as such it is adjustable for intermediate pressure without disassembly. The diluent supply pressure of the stock Mark-15 regulator tends to be a little low for diluent makeup from the auto-add valve during fast descents, and the ability to increase the intermediate pressure helps this a lot.

Sphere retention is done with large rubber O-Rings that snap over the brackets shown. The bottle and supply hoses are color coded, and the valves of the bottles are slightly different, making it impossible to fit a diluent sphere to an oxygen regulator. The sphere depicted is made from Inconel, and exotic metal chosen for its non-magnetic characteristics. Carbon steel bottles are also available, and tend to be more durable in service. A late addition to the choices for spheres is the composite sphere, which has become the choice of many Mark-15 divers.

Diluent sphere lifted for removal. Regulator has been detached, and the rubber retention bands have been detached. Note sphere markings. It would be BAD to inadvertently reverse the two in installation. The blue hose has been neatened up since this photograph was taken. It feeds the Air Source on the wings from the on-board diluent sphere. Since the photo was taken a custom length hose has been made to reduce the excess length that is visible here.

With both spheres removed, the components of the rebreather are easier to see. The electronics pod is on the right, and the center section on the left. The red component is the 02 injection solenoid. You can see the color coded recess for the spheres, the green recess indicating placement of the 02 sphere.

	OK, enough of the fooling around outside. Here the lid has been removed to expose the two spheres, the center section, and the electronics pod. The Mark-15 is packed full, with little extra volume for anything. You can see how the entire rig was engineered around the spheres, which are one of the main distinguishing factors of this design. The sphere is the most efficient storage vessel available, yet it's cost is prohibitive thus the rarity of designs using it. In the Mark-15, cost was not an object, thus the inclusion of this type of supply. The Mark-15 was a direct spin-off of the General Electric rebreathing system used for lunar EVA activities, and the entire design reflects this heritage.
	The standard first stage regulators used by Biomarine are a fairly low performance Sherwood piston design. This may at first appear a strange choice, but it was done as the rig never requires a high flow-rate to be supplied to it and the performance of this regulator is more than adequate. The simple piston design is utterly reliable, and these have given excellent results.
	In my rigs, I have replaced the Sherwood diluent regulator with Poseidon 300 first stages. This was done to obtain a second low-pressure port to supply the Air Source inflator on my wings, and also has the advantage of providing a higher performance regulator to supply the air-source in case I ever need to breath from it. Lastly, the Poseidon is a diaphragm first stage, and as such it is adjustable for intermediate pressure without disassembly. The diluent supply pressure of the stock Mark-15 regulator tends to be a little low for diluent makeup from the auto-add valve during fast descents, and the ability to increase the intermediate pressure helps this a lot.
	Sphere retention is done with large rubber O-Rings that snap over the brackets shown. The bottle and supply hoses are color coded, and the valves of the bottles are slightly different, making it impossible to fit a diluent sphere to an oxygen regulator. The sphere depicted is made from Inconel, and exotic metal chosen for its non-magnetic characteristics. Carbon steel bottles are also available, and tend to be more durable in service. A late addition to the choices for spheres is the composite sphere, which has become the choice of many Mark-15 divers.
	Diluent sphere lifted for removal. Regulator has been detached, and the rubber retention bands have been detached. Note sphere markings. It would be BAD to inadvertently reverse the two in installation. The blue hose has been neatened up since this photograph was taken. It feeds the Air Source on the wings from the on-board diluent sphere. Since the photo was taken a custom length hose has been made to reduce the excess length that is visible here.
	With both spheres removed, the components of the rebreather are easier to see. The electronics pod is on the right, and the center section on the left. The red component is the 02 injection solenoid. You can see the color coded recess for the spheres, the green recess indicating placement of the 02 sphere.