Chapter 1- Diving Equipment Diving Equipment 9 FIGURE 1-4. MANIFOLD VALVE WITH ISOLATION MANIFOLD FIGURE 1-5. DIN “H” VALVE predetermined closing pressure, a spring forces a flow check into the air passage and restricts air flow, causing increased breathing resistance. This is gradually followed by total obstruction of air flow unless the spring-loaded check valve is manually overridden by turning the external lever. When the reserve lever is manually depressed, the flow check is mechanically moved away from the air passage and the remaining 20 to 35 bar (300 to 500 psi) becomes available for use with no breathing or flow restrictions. J-valves were popular before the advent of submersible pressure gauges, and are not very commonly used today. All About J-Valves The simpler and less expensive K-valve tends to be more popular than J-valves, since submersible pressure gauges are now considered standard equipment. The following are some additional reasons why: The reserve pressure of a J-valve may be either 20 bar (300 psig) pressure or 20 bar (300 psi) above ambient pressure. If the reserve is not depth-compensated, the air available upon notification is decreased as depth is increased. The J-valve reserve lever must be fully up in order for the reserve mechanism to function. A diver may forget to put the lever up prior to diving, it may be turned down by another diver, or the lever may be accidentally depressed by diving activities. Any of these actions allow the full cylinder of air to be exhausted without warning. The J-valve reserve lever must be depressed when the cylinder is being filled. Failure to do this may damage the reserve mechanism, may prevent a correct fill, and will cause a slower fill. J-valves cost more initially than K-valves and also are more expensive to have serviced. A J-valve mechanism retains reserve air pressure in only one cylinder of a multiple set of cylinders. When the reserve is activated, the reserve air pressure distributes itself equally among all cylinders and the reserve pressure is reduced by a ratio equal to the number of cylinders. The activation pressure can be set to a higher pressure to compensate for multiple cylinders. Galvanic corrosion or electrolysis occurs when dissimilar metals are in contact and moisture is present. This can occur between aluminum cylinders and brass scuba valves. Ions will flow from the aluminum and deposit themselves on the brass, creating a bond that may make the valve unremoveable or damage the cylinder threads upon removal. Fortunately, the chrome plating of brass scuba valves and the scuba cylinder coating, FIGURE 1-6. REGULATOR FIRST STAGE
20047TC
To see the actual publication please follow the link above