Spheres

The two spherical tanks are the second unique feature of the Mk15 rebreather. The one on the right with the green band holds the O2 and the one on the left with the black band holds diluent gas. These particular tanks are carbon fiber wrapped spheres and they are extremely lightweight giving the unit better trim.

Regulator

The original Mk15 used Sherwood piston regulators. These apex replacements supply gas to the unit. The port on the bottom feeds high-pressure gas to the HP gauge to let you know how much gas is in the sphere. The port to the top feeds diluent to the rest of the plumbing.

Plumbing

With the spheres removed, you can see the rest of the plumbing. It looks pretty complicated but the gas flow path is pretty straightforward.

Diluent Plumbing

The onboard diluent supply enters the plumbing system from the regulator through the stainless steel flexible braided tubing indicated by the red 1 arrow. It loops around in the chassis and enters the Whitey valve at the point indicated by the red 2 arrow after making the switch to stainless steel tubing.

Off-Board Diluent Addition

The quick disconnect indicated by the red arrow in this image allows off-board gas to be fed into the system. Any bottle can be equipped with the male QD fitting on a LP hose that plugs into this connector. This allows the diver to carry two or more gasses that can be fed into the system. Usually the bailout bottle is plumbed into this fitting or the diver can carry additional stages. This also allows Mk15 divers equipped with the same system to share gas.

This is not standard equipment on the standard Mk15 but was a brilliant addition by Kevin Juergenson who put this rig together.

Whitey Valve

The off-board gas feeds through the chassis via a stainless steel braided pigtail and feeds into the Whitey Valve at the point indicated by the red arrow. The diver can either select the on-board diluent sphere or the off-board gas to supply the system. The outlet to the Whitey Valve is pointed down in this image and feeds the rest of the system.

Diluent Filter

The gas flows from the Whitey Valve and into the filter at point 1. The 60-micron filter (2) traps any contaminants in the diluent supply and keeps it from clogging any part of the rest of the system. The gas flows from the filter into the "T" fitting immediately below it (3). From the "T" fitting, the diluent gas is fed into the center section and the automatic add valve to the right and into the manual add valve to the bottom.

Diluent Manual Add Valve

The diluent flows from the "T" connector (1) through the stainless steel tubing and into the manual add valve for the diluent (2). By pressing the lever on the outside of the case, the diver can manually add diluent gas into the breathing loop. The outlet to the manual add valve feeds into the distribution manifold and from there, into the center section.

Oxygen Plumbing

The O2 plumbing on the right side of the rig follows a path very similar to the diluent gas. The gas enters the plumbing from the sphere and regulator through the stainless steel braided pigtail (1). It then makes the transition to stainless steel tubing and loops around in the chassis and enters the 60-micron filter (2) for the O2 side. The O2 then loops around and into the "T" fitting right below it (3). From the "T" fitting, the O2 flows out to both the O2 manual add valve to the rear and to the O2 collection tube to the bottom.

O2 Collection Tube

The O2 flows from the "T" fitting in the previous frame and into the O2 collection tube at point 1. The collection tube (2) is a 700 cc reservoir. The O2 flows into the collection tube through a restrictor orifice. This keeps too much O2 from bring delivered to the diver in the event that the solenoid sticks open. It also provides a metered amount of O2 to be delivered to the breathing loop every time the solenoid fires. The O2 flows out of the collection tube at point 3 and travels over to the solenoid.

Solenoid

The red item in the center of this image is the Oxygen Solenoid. If the electronics of the system are the brains, the solenoid is the brawn. When the electronics determine that the partial pressure in the breathing loop is too low, they tell the solenoid to fire. When it fires, the solenoid opens an internal valve. The O2 is delivered from the Collection Tube (the silver cylinder immediately behind the solenoid) through the tubing on the right of the image and out the tubing leaving the solenoid to the left. From there the O2 goes to the distribution manifold immediately below the solenoid in this image and into the center section.

O2 Manual Add Valve

The O2 also flows from the "T" fitting (1) and over to the manual O2 add valve (2). By pressing this valve from the outside of the case, the diver can add a 'squirt' (technical term) of O2 into the loop. The manually added O2 flows out of the add valve at point 3 and flows over to the distribution manifold.

Distribution Manifold

The little silver block (not the big one) in the center of this image is the distribution manifold. It takes gas flowing from either the diluent manual add valve (1), the manual O2 add valve (2) or the O2 from the solenoid (3) and sends it over to the center section where it is added to the breathing loop.

Gas Addition

The gas flowing from the distribution manifold is added to the center section through this port on the right hand side of the unit into the counterlung.

That about wraps things up for the plumbing.