Piston first stages use a hollow metal piston in combination with a heavy spring to operate the high-pressure valve that separates tank pressure from intermediate pressure.
The piston consists of a head about 1 inch in diameter and a shaft about ¼ inch in diameter. The end of the piston shaft seals against a hard plastic seat, separating the two chambers in the first stage and sealing tank pressure from intermediate pressure.
When the regulator is not pressurized, the heavy spring keeps the piston shaft separated from the seat. As air flows in from the tank, it flows into the first chamber, through the piston shaft, into the second chamber. As air pressure in the second chamber increases, it pushes against the piston head on the opposite side of the shaft.
When pressure in the chamber reaches intermediate pressure, it forces the piston against the seat and high-pressure air from the tank stops flowing. This process repeats with every breath!
There are advantages to both designs, although balanced piston first stages are considered higher performing and are typically more expensive than unbalanced piston first stages.
The potential for freezing and free-flow: Part of the piston is exposed to surrounding water. In very cold conditions it can freeze open, resulting in a strong free-flow. Those who dive in extremely cold water often prefer diaphragm first stages for this reason. There are ways to seal the piston from water using silicone or PTFE grease, but this adds expense to servicing the regulator.
Diaphragm first stages use a thick rubber diaphragm with a heavy spring to operate the valve between the two chambers in the first stage. This involves a slightly more complex design, as there are more parts used in the valve mechanism than in a piston-style first stage.
There is a pin and secondary spring on the inside of the regulator that operates the high-pressure valve. When the regulator is not pressurized, the heavy spring on the outside of the diaphragm pushes the diaphragm inward, which in turn pushes on the pin that separates a hard plastic seat from a metal orifice.
When connected to a tank and pressurized, air flows into the regulator and pushes the diaphragm outward, which allows the hard plastic seat to seal against the orifice and stop the air flow when the pressure reaches intermediate pressure. This process also repeats with every breath.
One interesting detail of this design is that it is very easy to balance the valve so that the intermediate pressure does not change with tank pressure; in fact, all modern diaphragm first stages are balanced.
YES Sport Diver’s will be moving. Not far, but it will be bigger and better. That said, we are too tired from all the diving we did this summer to move all of our inventory, that we decided to have a big MOVING SALE!!! EVERYTHING in stock is 20-50% off starting this Saturday August 12th. Can’t wait to see y’all!