Wed Oct 23, 2013 7:07 am
Freeflowing at the surface....or in any position that puts the cans lower than the mouthpiece, like swimming on your back....is normal for a DH reg and something a DH diver has to learn to deal with. When you are at the surface and allow the cans to go under water, the pressure of the water tries to fill the cans, it can't because of the regs diaphragm but it can and will apply pressure to the diaphragm causing it to move inward, starting the flow. The design of the reg is such that once flow of a sufficient level has started, the venturi feature of the reg will assist the flow, pulling the diaphragm in even farther increasing the freeflow. If the mouthpiece is lower that the cans, the water pressure is greater there than at the diaphragm and keeps the diaphragm from moving in. The better the reg is tuned for optimal performance, the more prone to freeflow it will be. It is possible to set up a DH to not freeflow at the surface but you will not like how it performs underwater. This is also a problem with single hose regs if you ease one into the water mouthpiece up. Divers are taught to fill the second stage on single hose regs to prevent the freeflow, with equal water pressure on both sides of the diaphragm, the problem does not exist. Clearing a fully flooded single hose second is easy, it is not as simple with a DH reg.
Using a mouthpiece plug will help or simply holding the mouthpiece under water will stop it from free flowing unless you lean back, putting the cans deeper. Try not to lean back at the surface and when in shallow water, avoid getting over chest deep if possible. As much as I hate snorkels, this is one time they can come in handy. For long surface swims, go face down with the snorkel to keep the cans out of the water. Unfortunately, it is a fact of DH life we have to learn to deal with if we want to dive DH regs, a small price to pay IMO.
Herman