Chapter 1- Diving Equipment Diving Equipment 11 There are three basic types of regulators: Two-hose, single-hose, and integrated. The original scuba developed in the 1940’s consisted of a two-hose regulator in which both stages were combined into one mechanical assembly that mounted onto a scuba cylinder valve. A flexible hose led from the regulator body around the right side of the diver’s head to a mouthpiece containing inhalation and exhalation non-return valves. The hose continued over the left shoulder and carried exhaled air back to the regulator assembly on the cylinder where the used air was exhausted into the water. Regulator design evolved to single-hose regulators, which are the standard type in use today because of their reliability, simplicity, and ease of maintenance. Although many hoses may be attached to a single hose regulator, only a single hose is involved in the operation of the regulator itself. With a single-hose regulator, the first pressure reduction stage is attached to the scuba cylinder valve, while the second reduction stage and the exhaust port are included in the mouthpiece portion that is attached to the first stage via a low pressure hose. Integrated regulators are those that are incorporated into other items of equipment such as a buoyancy compensator low pressure inflator or a small contingency scuba unit (figure 1-9). To understand the operational theory of a regulator, you need to be familiar with the types of internal regulating valves used. The fundamental types are downstream and upstream valves. An upstream valve is one which opens against the high-pressure air flow, and a downstream valve is one that opens with high-pressure air flow. In other words, an upstream valve is like a door that opens into the wind; the wind acts to close the door. A downstream valve can be compared to a door that opens with the wind; the wind tends to blow the door open. As cylinder or applied pressure decreases, less force is required to open an upstream valve. The downstream valve is more resistant to operating as cylinder pressure decreases. Because of their tendency to fail in a closed position, upstream valves are rare in modern scuba regulators. A third type of regulator is the balanced valve. In a balanced valve the operation of the regulator is independent of the cylinder or applied pressure. In most balanced valve designs either the valve seat is not exposed to the higher pressure air or equal pressure is applied to both ends of the valve mechanism. First-Stage Valves The internal valves of scuba regulator first stages are available in two basic types, diaphragm and piston. Both are produced in an unbalanced or a balanced configuration. Since a balanced valve in a scuba regulator is one in which cylinder or intermediate air pressure does not affect the force needed to open the valve, the valve operates the same regardless of cylinder pressure. The force required to operate an unbalanced valve is affected by cylinder pressure. In a diaphragm first stage, the valve mechanism is housed behind a rubber diaphragm. A small piston shaped “poppet” closes against the valve opening with the aid of a small spring. A large adjusting spring in the outer chamber pushes against the diaphragm and opposes the internal intermediate pressure. When the diver inhales, this intermediate pressure is reduced. With the pressure lowered, the external spring is able to flex the diaphragm and push open the valve. When the diver stops inhaling, the intermediate pressure rises until it overcomes the adjusting spring tension, and the valve closes. In a piston first stage, a large piston opens and closes the valve (figure 1-7). The valve seat is at the end of the piston’s shaft. Intermediate pressure is on the head of the piston. When the diver inhales, the pressure on the head of the piston is reduced, and the spring in the middle chamber is able to open the piston and allow air to flow. When the diver stops inhaling, the hole in the shaft of the piston allows pressure on the piston head to increase until it is able to move the piston and close the valve. The balanced piston first-stage valve is designed so the piston movement is independent from any directional force of the high pressure in the chamber. When the piston opens, the air flows through the piston shaft and exits in the area of the head. This type of valve is sometimes called a “flow-through” piston first stage. It will often have a swivel where the intermediate-pressure hoses attach. In either type of
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