Experienced rebreather diver and instructor John Adams is in charge of the AP Diving CCR units that are available for BSAC members to use. In the first of a two-part feature, he offers tips for those new to the closed-circuit world.
There are some good tips out there, but they are difficult to identify if you are new on the scene, and you can end up with a lot of bad advice. Looking after the BSAC AP Diving CCRs and making sure that they are ready to go out to different regions and clubs for try dives, courses and expeditions, I see many of the problems encountered by newly qualified CCR divers. My aim is to explore some of the obvious and more common issues that I have encountered, offering, I hope, simple and inexpensive answers coupled with advice that works.
- I have a crack starting on the yellow cover of my CCR – do I need to buy a new one?
That depends on how you feel, you could just do a temporary repair, which will probably last for a number of years. Drill a small hole at the furthest reach of the crack (this will prevent it going any further). Then, drill a series of holes along the line of the crack in pairs, one each side of the crack. Use cable ties to pull it together – sorted.
- When I open up the unit, it takes up too much space on the bench – I find it very awkward
OK, so take the yellow lid off. The plastic clips slide out fairly easily but you could go to any yacht chandlers and buy two ‘P’ clips. Fitting these allows you to strip the back off in seconds, making access much easier.
- One of the buttons on my monochrome vision handset is not reacting properly – it started off being difficult and now it doesn’t work. I have heard that soaking it in warm water or soapy liquid will fix it. I’ve also seen advice to soak it in olive oil…
Sorry – this is complete nonsense and illustrates some of the rubbish you see on internet forums. The buttons on the handsets are not actually buttons. They are hollow caps that do not move at all. No amount of lubricating the top of the button will fix it. Inside the cap is a piezoelectric crystal (similar to those used to pick up vibrations/pressure change on an electric guitar) vibrations/pressures the ‘button’ the piezoelectric crystal converts the vibration or minute pressure change to a small current.
You can tell if this is working because when you operate a button, you should see an underscore line at the bottom of the screen above the relevant button. If it’s not there, then the button was either not touched or the crystal (inside the hollow button) needs to be replaced by the factory.
It has been known for divers with very thick gloves to have difficulty transferring pressure to the button. Thinner gloves rather than a hammer is the correct way forward. Because of the way that the crystals work – they are pre-potted in the hollow cap to make a ‘button assembly’, which is then pressure adjusted – hitting them hard will actually destroy the delicate crystal. The only answer when a button fails is to have the assembly changed at AP.
- I had a spare oxygen cell, but when I needed it, it did not work. It was in a sealed packet. My dive was ruined and it must be someone’s fault. I must have been sold a duff cell.
Hmmm. So what’s happened here, in most cases, is that you bought a cell a year or more ago but didn’t use it, keeping it in its sealed packet. You think it must be new because it is still sealed. Not so. Oxygen cells have a shelf life. All cells from AP Diving, for example, are checked before being sealed in the bag and the serial number and dates are noted.
When they go out and who they go to. Cells from AP are warranted to last one year from the date of despatch from the factory (not the date on the cell), but many last much longer. Often, how long they last depends on the amount of use and how they are stored. In any case, they should no longer be used when the output becomes current limited and the company recommends that you replace them at 18 months to avoid any problems. This is also the recommendation given in the BSAC CCR course.
- So how do I ensure my spare cell will work?
The best way to ensure that your spare cell will work is to use it. If you have a spare cell, use it and move your cells around, in order, every few dives keeping the used ‘spare’ in an airtight container or bag. This way, you always have a tested, working cell that you can rely on when you suddenly need that backup.
AP sells a cell validator which is fairly inexpensive and allows you to check your cells before diving. To see how your cells are doing, try a linearity check on the surface to see if they are becoming current limited. Flush the loop with oxygen and see if the cell readings of the pO2 come up to surface pressure, that is close to 1 bar. Then flush the loop with air and see if they come down to 0.21 bar (the pO2 of air at surface pressure).
Any variation of 0.2 bar or more, while flushing with air – so readings lower than 0.19 bar or higher than 0.23 bar – means that you may have a faulty cell, which needs further investigation. When you fire up your unit, look at the millivolt readings generated while flushing. Make a note of the numbers just before it calibrates. Keep a record of them. As a cell’s readout starts to drop you will get advance warning of a developing problem. Cells that cannot reach 0.7 while calibrating will fail.
New cells may read up to 13mv (1.30) when calibrating and get lower as the cell gets older. Replace it before it gets too low! Another way to check the cell output in a unit with Vision electronics is, once your unit is in dive mode, do a long press on the left-hand button (shows both controllers) followed by another long press – this will show you the output from each cell measured by both controllers.
- I'm getting bubbles of gas emerging around the automatic diluent valve - is this a fault?
This is more likely to be bubbles coming from around the banjo fitting on the ADV and not the ADV itself. Have a good look when the unit is in water. On all the CCR courses I have seen, instructors are very good at showing their students how to grease the O-rings on the breathing-loop hoses.
Very few look at the banjo nut on the ADV. It’s one leak you can sort out for yourself and you should keep the O-rings greased. You will need a 5mm Allen key and you need to be gentle with it. Be wary of any resistance you feel as it is possible to twist the inner shaft in the plastic fitting causing damage.
Undo the nut on the end and slide the banjo fitting off the shaft. Put grease on it. It’s the diluent side so silicon grease is fine, but sometimes using thicker oxygen compatible grease will work better.
There are two O-rings inside the banjo fitting – get a little grease into there, or even grease the shaft and transfer it to those O-rings as you re-assemble it. Be careful when you tighten the nut.
Just ‘nip’ it up. If you go crazy, you can turn the shaft of the ADV and damage it. It’s worth noting that the tightness of the nut does not make the O-rings any more secure – it just needs to be tight enough not to come unscrewed. This is something you should consider doing on a fairly regular basis.
Rebreathers for members’ use
Would you like to give rebreather diving a try? Ask your club or region to run a rebreather Try Dive using rebreathers donated to BSAC from AP Diving.
Author: SCUBA | Posted 09 May 2017
