The gases compressed in oxygen and acetylene cylinders are held at pressures too high for oxyacetylene welding.*** Oxygen and acetylene regulators*** reduce pressure and control the flow of gases from the cylinders. The pressure in an oxygen cylinder can be as high as 2200 psi (15,169 kPa), which must be reduced to a working pressure of 1 to 25 psi (6.90 to 172.38 kPa). The pressure of acetylene in an acetylene cylinder can be as high as 250 psi (1724 kPa). A gas pressure regulator will automatically deliver a constant volume of gas to the torch at the adjusted working pressure.


The regulators for oxygen, acetylene, and liquid petroleum fuel gases are of different construction. They must be used only for the gas for which they were designed.

Most regulators in use are either the single stage or the two stage type. Check valves must be installed between the torch hoses and the regulator to prevent flashback through the regulator.

 Single Stage Oxygen Regulators

 Single stage oxygen regulators reduces the cylinder pressure of a gas to a working pressure in one step. The single stage oxygen regulator mechanism (fig. 5-8) has a nozzle through which the high pressure gas passes, a valve seat to close off the nozzle, and balancing springs. Some types have a relief valve and an inlet filter to exclude dust and dirt. Pressure gauges are provided to show the pressure in the cylinder or pipe line and the working pressure.

 Single Stage Oxygen Regulator.


In operation, the working pressure falls as the cylinder pressure falls, which occurs gradually as gas is withdrawn. For this reason, the working pressure must be adjusted at intervals during welding operations when using a single stage oxygen regulator.

Oxygen regulators control and reduces the oxygen pressure from any standard commercial oxygen cylinder containing pressures up to 3000 psi. The high pressure gauge, which is on the inlet side of the regulator, is graduated from 0 to 3000 psi. The low or working pressure gauge, which is on the outlet side of the regulator, is graduated from 0 to 500 psi.

Operation of Single Stage Oxygen Regulators

 The regulator consists of a flexible diaphragm, which controls a needle valve between the high pressure zone and the working zone, a compression spring, and an adjusting screw, which compensates for the pressure of the gas against the diaphragm. The needle valve is on the side of the diaphragm exposed to high gas pressure while the compression spring and adjusting screw are on the opposite side in a zone vented to the atmosphere.

The oxygen enters the regulator through the high pressure inlet connection and passes through a glass wool filter, which removes dust and dirt. The seat, which closes off the nozzle, is not raised until the adjusting screw is turned in. Pressure is applied to the adjusting spring by turning the adjusting screw, which bears down on the rubber diaphragm. The diaphragm presses downward on the stirrup and overcomes the pressure on the compensating spring. When the stirrup is forced downward, the passage through the nozzle is open. Oxygen is then allowed to flow into the low pressure chamber of the regulator. The oxygen then passes through the regulator outlet and the hose to the torch. A certain set pressure must be maintained in the low pressure chamber of the regulator so that oxygen will continue to be forced through the orifices of the torch, even if the torch needle valve is open. This pressure is indicated on the working pressure gage of the regulator, and depends on the position of the regulator adjusting screw. Pressure is increased by turning the adjusting screw to the right and decreased by turning this screw to the left.

Oxygen and acetylene regulators used at stations to which gases are piped from an oxygen manifold, acetylene manifold, or acetylene generator have only one low pressure gauge because the pipe line pressures are usually set at 15 psi (103.4 kPa) for acetylene and approximately 200 psi (1379 kPa) for oxygen. The two stage oxygen regulator (fig. 5–9) is similar in operation to the one stage regulator, but reduces pressure in two steps. On the high pressure side, the pressure is reduced from cylinder pressure to intermediate pressure. On the low pressure side the pressure is reduced from intermediate pressure to work pressure. Because of the two stage pressure control, the working pressure is held constant, and pressure adjustment during welding operations is not required.

Two stage oxygen regulator.

 Acetylene Regulators


Acetylene should never be used at pressures exceeding 15 psi (103.4 kPa).

Acetylene regulators control the acetylene pressure from any standard commercial cylinder containing pressures up to 500 psi (3447.5 kPa). The acetylene regulator design is generally the same as that of the oxygen regulator, but will not withstand such high pressures. The high pressure gauge, on the inlet side of the regulator, is graduated from 0 to 500 psi (3447.5 kPa). The low pressure gauge, on the outlet side of the regulator, is graduated from 0 to 30 psi (207 kPa). Acetylene should not be used at pressures exceeding 15 psi (103.4 kPa).