On a regular basis, I find a portion of the regulators I service for divers have some type of corrosion on the inside of the first stage. This is usually caused by water, mainly salt water, entering the first stage due to diver error. This is a very common mistake. Typically, a diver will go on vacation and have a wonderful time. Throughout the trip divers will forget to cover the first stage well enough, or not at all, either between changing tanks or stowing the gear. At times the diver will allow the Divemaster to handle this. However, some Divemasters will not care too much about the regulator because their job is just to switch tanks or stow the gear.
Dust caps were put on a regulator for a reason. The most common is for the standard Yoke Valve. It is even more important for a DIN valve due to keeping the threads in good shape to be able to have a good secure connection with the tank valve. The dust cap should actually be renamed to ‘Water Prevention Cap’. Dust doesn’t really harm the regulator. Dust can be blown out with a couple of purges from the second stages. It is there to prevent moisture from getting inside. Time and time again I find working on regulators that dust caps are improperly used or not used at all. Divers will forget sometimes to put the cap on PRIOR to any rinsing. Since the average diver only goes on dive vacations less than a couple of times a year, they store the regulator without knowing the water is still inside the first stage. This water can cause corrosion or even mold in some cases. The corrosion can cause the regulator to work improperly. Let’s think about this again… This is your life support underwater. What if this malfunctions? Yes, you may get lucky and just have it free-flow (the regulator releases all the air through the regulator). This may happen most of the time due to the ‘fail-safe’ design of the regulator. Who wants to go through that? Diving is supposed to be enjoyable.
If for any reason you think water may be inside the regulator while out diving simply connect the regulator to the tank. Turn the tank valve on and purge one of the second stages for at least ten seconds. This should blow out any water inside the first stage. Then make sure you bring the regulator into a local dive shop that is authorized to service your regulator. They will let you know if anything further needs to be done.