Back again with some information regarding the first stage scuba diving regulator.
There are two basic first stage regulator designs the piston or diaphragm and then two versions of each design in the balanced or unbalanced.
With the Piston and Diaphragm first stage regulators the differences are:
In a diaphragm first stage, water pressure is transmitted to the valve through a flexible diaphragm. The valve itself is sealed against water intrusion, and the spring chamber can be easily sealed as well. Because water cannot enter the first-stage housing, internal corrosion is minimized. On the other hand, diaphragm first stages have more moving parts and may not lend themselves as well to swivel fittings for low-pressure hoses, because intermediate pressure comes out in the middle of the housing.
In a piston design, water pressure acts directly on the valve, making it simpler, with fewer moving parts. They are easy to adapt to swivel fittings, making low-pressure hose placement more convenient. But because water enters the spring and piston chamber, pistons are more sensitive to corrosion, especially if the owner neglects regular maintenance.
Balanced vs. Unbalanced
Both piston and diaphragm first stages come in balanced and unbalanced versions. A valve is balanced by extending the shaft beyond the pressure chamber so air pushes on both ends equally. A balanced first stage retains ease of breathing all the way down to the last few pounds of tank pressure, because intermediate pressure remains constant. These units are more complex and generally more expensive.
Until a few years ago, unbalanced first stages were severely affected by low tank pressures and would begin to breathe harder below about 700 psi. The reason was a 30- to 40-psi drop in intermediate pressure from full to near-empty tanks. But current models are less sensitive to supply pressure, with a pressure drop of only 20 to 30 psi. Therefore, the performance gap between balanced and unbalanced first stages has tightened. Unbalanced first stages are more economical, have fewer moving parts and are easier to service. But they will usually have fewer ports and lack the convenience of swivel mounting.
A simple description of the regulator first stage would be as follows;
The system operates like this:
1. You inhale, thereby lowering the pressure in the intermediate-pressure chamber to below the ambient water pressure.
2. The water pressure pushes inward, opening the valve or piston.
3. The open valve connects the high-pressure chamber with the intermediate pressure chamber.
4. Air flows from the high-pressure chamber into the intermediate-pressure chamber, thereby increasing the pressure in the intermediate-pressure chamber.
5. When the pressure in the intermediate-pressure chamber equals the ambient water pressure, the valve or piston closes.
6. The process repeats when you inhale again.
Look out for the next more detailed posts on Open Circuit SCUBA equipment Second Stages.
Please feel free to comment on any posts in this blog.
To find out more about SCUBA equipment available from Samui Dive Supply please contact us for more information.
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