Draeger Dolphin Modifications

Part II

REMEMBER REBREATHERS CAN AND DO KILL!

IF YOU ATTEMPT TO MAKE MODIFICATIONS TO YOUR SYSTEM, YOU DO SO AT YOUR OWN RISK. YOU HAVE BEEN WARNED.

With more than 170 hours and 190 dives on the system, I have encountered a few problems. I have had O2 sensors fail before, during and after dives. My O2 sensor supplier Patrick Duffy of www.oxycheq.com likes rebreather divers. It seems that the normal 2 -3 year life encountered with most O2 analyzers just isn't applicable to rebreathers. One can only expect about 100 hours or so at the higher PO2's encountered in the loop. I have had orifices block, OC bail-out free flow, CO2 hits, collapsed hoses, even a partial flood, kind of all the normal stuff. However, considering the number of dives, I have had fewer aborted dives than my OC buddies, especially in cold water. You just can't put a price on warm, moist air and never a hint of cottonmouth.

I have gone back to the sonic orifice for the O2 feed. Even with the higher risk of blockage a small orifice presents, I feel more comfortable with them than the flow restrictors. I just carry an extra in my spare parts kit. Since installing the hydraulic connectors, I have had no problems with the orifices, but then I do few salt water dives.

In an attempt to further streamline the system, I have made some changes. These changes also allow conversion to semi-closed operation on the fly with the addition of a coupling converter. I followed this route to avoid crossing the O2 and diluent systems.

As with the generation 4, diluent/deco gases can be switched on the fly by the use of the hydraulic connectors. I have had good luck with these connectors. They are holding up well. The main changes concern simplifying all the extraneous stuff. It appears to be about as minimal as it can get and still keep all the attributes I need from a system to accomplish deep and cave diving in a semblance of safety.

I was having trouble with various 1st stages not holding up with elevated IP's. Most regs do not like 16 - 17 bar IP. They tended to leak after a while. I added a IP gauge to the system to monitor the IP and was able to see it happen several times. I even managed to ruin a couple gauges. I have since modified my Draeger Dolphin 1st stage (retapped the holes for 3/8 -24) to accept normal hoses. The Dolphin 1st stage will creep if there is no flow, as will most. But it was designed for the higher IP and has been much more reliable. I therefore added a over-pressure relief valve to the unit to prevent a hose failure. (It is only a problem if the O2 injector is not connected). So far, this has done the job.

Below are some detail photos of the system. The current layout allows for a clean left side for the transport of stage cylinders. The stages serve back-up deco supply as well as ADV use during deco. Again the various stages can be connected to the ADV to change the supply or diluent mix for the different phases of the dive. In all cases, if everything thing works fine, you have enough gas to do a weekend of deep diving and at anytime you can switch to open circuit and still finish the ascent albeit open circuit. It is just as heavy as a set of doubles. The difference is the whole weekend's supply is there with the associated cost savings.

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ADV	Close up of connectors
Overview of O2 injection	Close up of O2 injection manifold
Overview of SCR conversion	Close up of SCR converter
Assembled unit - Notice the ADV moved to side	PO2 sensors in bag
Modification to CL and ADV

I also have discovered that the cage is an excellent platform for cylinder variations. During the warmer months I removed the two 7 l cylinders and replace one with a 4 l cylinder and the other with the 2 l oxygen cylinder. They were held on the cage with a standard cam strap. For open water that was a real nice configuration. With the cylinders filled, I could do five hours of bottom time and still have enough diluent to abort a standard recreational dive of 30 - 40 msw. The beauty is that it weighs no more than a standard OW system and your whole weekends worth of gas is on your back. Kerry McKenzie uses his system in this manner. I don't often have the luxury of diving this way. I am landlocked where the water is always cold below about 7 mfw

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