Chapter 1- Diving Equipment Diving Equipment 13 depressed by the diaphragm. Pilot-valve tilt-valve assembly Main valve Poppet assembly The main valve of a pilot valve regulator is opened and closed with air pressure, rather than mechanical leverage (figure 1-11). The valve opening pressure is generated by air flow through a diaphragm-activated downstream pilot valve. A simple mechanical linkage is used between the diaphragm mechanism and the pilot valve. Because the pilot valve is tiny, only a small spring tension is required to counterbalance the pressure, and therefore, less force is required to open or close it. The pilot valve opens only slightly and operates the air supply valve by passing a small amount of air into a control chamber. Because there is equal pressure opposite the valve opening that exactly counteracts the opening force pressure, the supply valve is balanced and unaffected by variations in intermediate pressure. The system can be described as a pneumatically amplified second stage, as the small pilot valve pneumatically moves the larger air supply valve. A pilot valve often requires less inhalation effort than is required for other types of second stages. The operation of the second stage is initiated when the diaphragm is depressed. The linkage opens the pilot valve. Air flows through the pilot valve faster than it can flow through the hole in the flexible main valve, so a pressure difference occurs in the chamber, causing the main valve to open. This allows air to flow into the second stage until the pilot valve is closed and a build-up of pressure in the air chamber closes the main valve. The pilot valve also acts as a safety relief valve in the event of a pressure build-up in the first stage. All scuba regulators have factory or dealer specifications to which they are adjusted during servicing. Some second stage regulators have on/off type switches on the housing that are used to control sensitivity, preventing free-flow on the surface, while others may have a diver controlled knob for adjustment of breathing resistance. Regulators that are prepared for use with breathing gases Downstream Second Stage Pilot Valve Mechanism Air to Diver Demand Lever Diaphragm Air from first stage Air to Diver Air to Diver Air from first stage Pilot Chamber Pilot valve orifice Spring Valve seal Main Valve Opening FIGURE 1-8. REGULATOR SECOND STAGE CROSS SECTIONS FIGURE 1-9. INTERGRATED SECOND STAGE Downstream Valve Upstream Tilt Valve FIGURE 1-10. UNBALANCED VALVES
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