The moisture condensation is caused by the warm moist gas coming off the Sofnalime hitting the cold surfaces of the lid assembly. Particularly, the metal fittings which conduct the cold water temperature from the top lid creating the lowest temperature point for condensation.

The problem of getting water on the sensors I believe is not directly caused by the condensation of water in the top of the housing area. I think it is caused by condensation of water in the sensor pipe and the hose out of the canister the area above the sensors. The water droplets fall down into the sensors from above is the main problem.

In the attached diagram the following modifications are described.

1. Additional water Trap.

I have put small circle of nylon pan scrubber material with very wide pores placed above the sensors to stop water dropping back from the top hose into the sensor pipe. See the diagram.

This does not effect breathing flow but catches water droplets. After the dive the amount of water trapped in the mesh can be two tablespoon full. Keeping the moisture in the flow path also allows the water to re-evaporate into the flow keeping the breathing gas moist.

2. Additional thermal insulation to loop.

Cutting the end of an old 7mm wet suit sleeve and inserting the hose into it to insulate the sensor pipe plastic from the cold water. The wet suit sleeve fits perfectly and can be held in place by plastic tie wraps. Doubling the sleeving around the plastic providing 14mm of thermal protection is even better. See diagram

By insulating the top of the sensor pipe at the stack top hose fitting stops the cold water above cooling the sensor pipe. The loss of heat up the pipe causes a cold condensation point close to and above the sensors. With no insulation there are lots of large droplets forming on the side of the sensor pipe above the 02 sensors. I suspect that the large drops drop directly onto the sensor face when the unit is moved upside down. With the insulation allowing the sensor pipe to stay warmer than the surrounding area, it is kept completely dry with no droplets forming above the sensors.

3. Results

After dives I open the stack and find the following:

• No water on sensor pipe, completely dry to the touch
• Sensor pipe is 10-15 deg C warmer than the canister plastic
• Very small droplets on the O2 sensor splash guards
• Very small droplets on outside of the 02 sensors
• Two tablespoons full of water, in the additional moisture filter trap above 02 sensors.

It was surprising to find so much water in the additional moisture filter trap positioned above the O2 sensors. I suspect a lot of moisture is dropping down from the stack top hose when handling the unit. The top hose is colder than the stack area so a lot of condensation occurs there.

I believe stopping water dropping from the top hose and stopping condensation above the sensors is critical. These additions are very low cost. I believe will help those people who are having problems with moisture on the sensors. The people who have to live with that beeping, beeping, beeping, "Cell Error" continuously during the dive. CCR should be silent, stealth diving....

Regards, Andy.

 Back