Center Section

This is the Center Section of the Mk15 seen bolted into the chassis. The black band around the middle of the center section seals the two halves together.

Unsealed

With the seal flipped down and the star nut removed, the center section is ready to be opened. The exposed red band provides a visual indication that the seal is not in its proper location. This is important as you are prepping the unit and is used elsewhere in the Mk15. If you can see red, something isn't ready to go.

Lid

The lid to the center section holds one of two absorbent pads used to trap any moisture that has gotten into the breathing loop.

Open

With the lid to the center section removed, you can see the scrubber canister inside. The circular holes in a radial pattern allow gas to flow up through them and return scrubbed gas to the diver. The black circle in the middle covers the O2 sensors.

Diluent Gas Input / Electronics

The top silver connector on the left side of this image is where the diluent gas plumbing passes into the center section. This plumbing feeds the automatic add valve in the counterlung.

The black connector is the Bendix connector where the electrical signal from the sensors passes through the center section and travels to the electronics pod.

The scrubbed gas travels around the outside of the center section and down this space between the scrubber and the outside of the center section.

Sensors

The green sensor bridge holds the three sensors in the gas path as it travels through the loop. The sensors read how much O2 is in the gas immediately after it is scrubbed of CO2.

A portion of the scrubbed gas flows down the center of the scrubber sealed off from the scrubber itself and allows for an accurate reading of the O2 levels in the loop.

Follow this link to more information on the sensors or click on the image to the right.

Scrubber

The scrubber on the Mk15 is massive holding about 10 pounds of scrubber media. The gas flows from the side facing away from you in this image both axially towards you and radially from the center to the outside of the scrubber. The silver plug in the top of the scrubber is where you load the media.

Sensor Bridge

With the scrubber removed, you can clearly see the sensor bridge holding the three sensors. The white material is the second absorbent pad that catches any water that makes its way into the loop before it can get into the scrubber. The hole in the left of the image is where the gas enters the center section.

The "dirty" gas flows into the bottom of this chamber and up through the scrubber. An o-ring seal at the bottom of the sensor bridge insures all of the gas flows through the scrubber.

Top Half

The top half of the center section, which holds the scrubber, is separated from the bottom half of the center section that houses the counterlung by this stainless steel plate. All of the screws that hold this piece in are sealed with o-rings to seal off the "dirty" gas from the "clean" gas.

Counterlung

Here the center section has been removed from the chassis. The bottom half of the center section makes up the counterlung of the Mk15. The black disk in the middle of the counterlung is the over-pressurization valve. As the gas in the counterlung expands, the little nipple in the center presses against the chassis. This opens a valve allowing excess gas to escape.

Bottom Half

With the counterlung removed, you can see the inside of this chamber. Scrubbed gas flows into this chamber around the perimeter before being returned to the diver. The black port to the right in this image is where the hose leading to the DSV is connected.

Diluent Addition/Sensor Wires

This image shows the plumbing for the automatic diluent addition as well as the electrical connector going to the electronics pod from the bottom side pictured earlier.

Horseshoe Board/Automatic Add Valve

This image shows the horseshoe board. The signals from all three sensors are routed to this board. The blue cable going to the left carries the signal over to the electronics pod. The one going up carries the signal over to the secondary display. The entire board is potted with epoxy to seal it from moisture.

The silver nipple in the center is the automatic add valve. When the loop does not have enough gas, the counterlung bottoms out against this valve. This opens the valve and adds diluent flowing from the stainless steel tubing going to the left into the breathing loop.

Secondary Display/Gas Addition Port

The blue cable from the horseshoe board connects to the secondary display cable through the Bendix connector at the top of this image.

The silver port just to its right is where gas is added to the breathing loop. O2 from the solenoid and O2 and diluent from their respective manual add valves are plumbed into this port.

Secondary Display/Gas Addition Port

This image shows Bendix going to the secondary display cable and the gas addition port from the other side of the center section.

Secondary Display/Gas Addition Port

Here is what these connectors look like installed in the unit and connected up.