File Name: scuba regulator maintenance and repair .zip
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The mechanism of diving regulators is the arrangement of components and function of gas pressure regulators used in the systems which supply breathing gases for underwater diving.
Both free-flow and demand regulators use mechanical feedback of the downstream pressure to control the opening of a valve which controls gas flow from the upstream, high-pressure side, to the downstream, low-pressure side of each stage.
Open circuit scuba regulators must also deliver against a variable ambient pressure. They must be robust and reliable, as they are life-support equipment which must function in the relatively hostile seawater environment, and the human interface must be comfortable over periods of several hours. Diving regulators use mechanically operated valves.
Back-pressure regulators are used in gas reclaim systems to conserve expensive helium based breathing gases in surface-supplied diving , and to control the safe exhaust of exhaled gas from built-in breathing systems in hyperbaric chambers.
The parts of a regulator are described here as the major functional groups in downstream order as following the gas flow from the cylinder to its final use.
Details may vary considerably between manufacturers and models. Gas pressure regulators are used for several applications in the supply and handling of breathing gases for diving. Pressure reducing regulators are used to reduce gas pressure for supply to the diver in demand and free-flow open circuit breathing apparatus, in rebreather equipment, and in gas blending procedures. Back-pressure regulators are used in the exhaust systems of the built-in breathing systems of diving chambers , and in the recovery of used helium based breathing gas for recycling.
Some of these regulators must work underwater, others in the more forgiving conditions of the surface support area. All must work consistently and reliably, but some are parts of safety-critical life-support systems , where a single point of failure must not put lives at risk. The first-stage of the scuba regulator may be connected to the cylinder valve by one of two standard types of fittings. The CGA connector, also known as an international connector, which uses a yoke clamp, or a DIN screw fitting to connect it to the valve of the diving cylinder.
There are also European standards for scuba regulator connectors for gases other than air. CGA Yoke connectors sometimes called A-clamps from their shape are the most popular regulator connection in North America and several other countries. They clamp the high pressure inlet opening of the regulator against the outlet opening of the cylinder valve, and are sealed by an O-ring in a groove in the contact face of the cylinder valve.
The user screws the clamp in place finger-tight to hold the metal surfaces of cylinder valve and regulator first stage in contact, compressing the o-ring between the radial faces of valve and regulator.
When the valve is opened, gas pressure presses the O-ring against the outer cylindrical surface of the groove, completing the seal. The diver must take care not to screw the yoke down too tightly, or it may prove impossible to remove without tools.
Conversely, failing to tighten sufficiently can lead to O-ring extrusion under pressure and a major loss of breathing gas. This can be a serious problem if it happens when the diver is at depth. Yoke fittings are rated up to a maximum of bar working pressure. The outlet of the CGA valve is on a flat surface on the valve body, inside a concentric face-sealing O-ring groove, with a conical indentation on the opposite surface of the valve body, co-axial with the O-ring groove.
The yoke clamp fits around the valve body and the sealing face of the regulator inlet seats over the O-ring groove. A conically tipped screw locates in the indentation and when tightened, presses against the valve body and pulls the sealing face of the regulator inlet against the O-ring.
This screw must be tightened sufficiently to maintain metal-to-metal contact between the regulator inlet and the valve body when the valve is opened at full cylinder pressure, and under normal working loads including minor impacts and using the regulator as a handle to lift the set, to prevent failure of the seal by O-ring extrusion and consequent loss of breathing gas.
The screw must also not be over-tightened, as after use it must be removed by hand. The rigidity of the yoke varies depending on design, tightening is by hand and is left to the discretion of the user. Fortunately the mechanism is fairly tolerant of variation in contact force. When the valve is opened, gas pressure on the O-ring presses it against the outer cylindrical surface of the groove and the face of the regulator inlet, squeezing the O-ring towards the contact surfaces of these parts.
The pressure exerts a force to push the regulator away from the valve body, and if pre-load of the screw is insufficient the elasticity of the clamp will allow a gap to form between valve and regulator through which the O-ring may be extruded. When this happens, gas loss is rapid, and the valve must be closed and the clamp loosened, the O-ring inspected and possibly replaced. Recovery from an extruded O-ring underwater is often not possible and bailout to an independent gas supply or an emergency ascent may be necessary.
The DIN fitting is a type of screw-in connection to the cylinder valve. The DIN system is less common worldwide, but has the advantage of withstanding greater pressure, up to bar, allowing use of high-pressure steel cylinders.
They are less susceptible to blowing the O-ring seal if banged against something while in use. DIN fittings are the standard in much of Europe and are available in most countries.
The DIN fitting is considered more secure and therefore safer by many technical divers. DIN valves are produced in bar and bar pressure ratings. The number of threads and the detail configuration of the connections is designed to prevent incompatible combinations of filler attachment or regulator attachment with the cylinder valve. Adapters are available enabling a DIN first-stage to be attached to a cylinder with a yoke fitting valve yoke adapter or A-clamp adapter , and for a yoke first stage to be attached to a DIN cylinder valve plug adapter and block adapter.
Several manufacturers market an otherwise identical first stage varying only in the choice of cylinder valve connection. In these cases it may be possible to buy original components to convert yoke to DIN and vice versa.
The complexity of the conversion may vary, and parts are not usually interchangeable between manufacturers. The conversion of Apeks regulators is particularly simple and only requires an Allen key and a ring spanner. Most scuba cylinder valves are currently of the K-valve type, which is a simple manually operated screw-down on-off valve.
In the mids, J-valves were widespread. J-valves contain a spring-operated valve that restricts or shuts off flow when tank pressure falls to psi, causing breathing resistance and warning the diver that he or she is dangerously low on breathing gas. The reserve gas is released by pulling a reserve lever on the valve. J-valves fell out of favor with the introduction of pressure gauges, which allow divers to keep track of their gas underwater, especially as the valve-type is vulnerable to accidental release of reserve air and increases the cost and servicing of the valve.
J-valves are occasionally still used when work is done in visibility so poor that the pressure gauge cannot be seen, even with a light. Axial spindle valves are also available where the spindle lies on the axis of the thread which connects the valve to the cylinder, with the knob on top, and various configurations with dual outlets or connections for scuba manifolds.
Most contemporary diving regulators are single-hose two-stage demand regulators. They consist of a first-stage regulator, and a second-stage demand valve. A low pressure hose connects these components to transfer breathing gas, and allows relative movement within the constraints of hose length and flexibility.
Other low pressure hoses supply optional additional components. The first stage of the regulator is mounted to the cylinder valve or manifold via one of the standard connectors Yoke or DIN. The breathing gas is then supplied to the second stage through a hose.
A balanced regulator first stage automatically keeps a constant pressure difference between the interstage pressure and the ambient pressure even as the tank pressure drops with consumption. The balanced regulator design allows the first stage orifice to be as large as needed without incurring performance degradation as a result of changing tank pressure. The first stage regulator body generally has several low-pressure outlets ports for second-stage regulators, BCD inflators and other equipment; and one or more high-pressure outlets, which allow a submersible pressure gauge SPG or gas-integrated diving computer to read the cylinder pressure.
The valve may be designed so that one low-pressure port is designated "Reg" for the primary second stage regulator, because that port allows a higher flow rate to give less breathing effort at maximum demand. A small number of manufacturers have produced regulators with a larger than standard hose and port diameter for this primary outlet.
The mechanism inside the first stage can be of the diaphragm type or the piston type. Both types can be balanced or unbalanced. Unbalanced regulators have the cylinder pressure pushing the first stage upstream valve closed, which is opposed by the intermediate stage pressure and a spring. As cylinder pressure falls the closing force is less, so the regulated pressure increases at lower tank pressure. To keep this pressure rise within acceptable limits the high-pressure orifice size is limited, but this decreases the total flow capacity of the regulator.
A balanced regulator keeps about the same ease of breathing at all depths and pressures, by using the cylinder pressure to also indirectly oppose the opening of the first stage valve.
Some components of piston-type first stages are easier to manufacture and have a simpler design than the diaphragm type. They may need more careful maintenance because some internal moving parts may be exposed to water and any contaminants in the water. The piston in the first stage is rigid and acts directly on the seat of the valve. The pressure in the intermediate pressure chamber drops when the diver inhales from the demand valve, this causes the piston to lift off the stationary valve seat as the piston slides into the intermediate pressure chamber.
The now open valve permits high pressure gas to flow into the low pressure chamber until the pressure in the chamber has risen enough to push the piston back into its original position against the seat and thus close the valve. Diaphragm-type first stages are more complex and have more components than the piston type.
Their design makes them particularly suited to cold water diving and to working in saltwater and water containing a high degree of suspended particles, silt, or other contaminating materials, since the only moving parts exposed to the water are the valve opening spring and the diaphragm, all other parts are sealed off from the environment.
In some cases the diaphragm and spring are also sealed from the environment. The diaphragm is a flexible cover to the medium intermediate pressure chamber. When the diver consumes gas from the second stage, the pressure falls in the low pressure chamber and the diaphragm deforms inwards pushing against the valve lifter.
This opens the high pressure valve permitting gas to flow past the valve seat into the low pressure chamber. When the diver stops inhaling, pressure in the low pressure chambers rises and the diaphragm returns to its neutral flat position and no longer presses on the valve lifter shutting off the flow until the next breath is taken.
If a regulator stage has an architecture that compensates for a change of upstream pressure on the moving parts of the valve so that a change in supply pressure does not affect the force required to open the valve, the stage is described as balanced.
Upstream and downstream valves, first and second stages, and diaphragm and piston operation can be balanced or unbalanced, and a full description of a stage will specify which of all of these options apply. For example, a regulator may have a balanced piston first stage with a balanced downstream second stage. Both balanced and unbalanced piston first stages are fairly common, but most diaphragm first stages are balanced. Balancing the first stage has a greater overall effect on the performance of a regulator, as the variation in supply pressure from the cylinder is much greater than the variation in interstage pressure, even with an unbalanced first stage.
However the second stage operates on very a small pressure differential and is more sensitive to variations in supply pressure. Most top range regulators have at least one balanced stage, but it is not clear that balancing both stages makes a noticeable difference to performance.
An intermediate-pressure, medium pressure, or low pressure hose, is used to carry breathing gas typically at between 8 and 10 bar above ambient from the first stage regulator to the second stage, or demand valve, which is held in the mouth by the diver, or attached to the full face mask or diving helmet. Other lengths are also available. There is no possibility of connecting a hose to the wrong pressure port. The second stage, or demand valve reduces the pressure of the interstage air supply to ambient pressure on demand from the diver.
The operation of the valve is triggered by a drop in downstream pressure as the diver breathes in. In an upstream valve, the moving part works against the pressure and opens in the opposite direction to the flow of gas. They are often made as tilt-valves, which are mechanically extremely simple and reliable, but are not amenable to fine tuning.
If the first stage leaks and the inter-stage over-pressurizes, the second stage downstream valve opens automatically resulting in a " freeflow ". With an upstream valve, the result of over-pressurization may be a blocked valve.
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The mechanism of diving regulators is the arrangement of components and function of gas pressure regulators used in the systems which supply breathing gases for underwater diving. Both free-flow and demand regulators use mechanical feedback of the downstream pressure to control the opening of a valve which controls gas flow from the upstream, high-pressure side, to the downstream, low-pressure side of each stage. Open circuit scuba regulators must also deliver against a variable ambient pressure. They must be robust and reliable, as they are life-support equipment which must function in the relatively hostile seawater environment, and the human interface must be comfortable over periods of several hours. Diving regulators use mechanically operated valves. Back-pressure regulators are used in gas reclaim systems to conserve expensive helium based breathing gases in surface-supplied diving , and to control the safe exhaust of exhaled gas from built-in breathing systems in hyperbaric chambers. The parts of a regulator are described here as the major functional groups in downstream order as following the gas flow from the cylinder to its final use.
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