You can determine the amount of oxygen in a compressed-gas cylinder by reading the volume scale on the high-pressure gauge attached to the regulator.

REGULATORS

You must be able to reduce the high-pressure gas in a cylinder to a working pressure before you can use it. This pressure reduction is done by a regulator or reducing valve. The one basic job of all regulators is to take the high-pressure gas from the cylinder and reduce it to a level that can be safely used. Not only do they control the pressure but they also control the flow (volume of gas per hour).

Regulators come in all sizes and types. Some are designed for high-pressure oxygen cylinders (2,200 psig), while others are designed for low-pressure gases, such as natural gas (5 psig). Some gases like nitrous oxide or carbon dioxide freeze when their pressure is reduced so they require electrically heated regulators.

Most regulators have two gauges: one indicates the cylinder pressure when the valve is opened and the other indicates the pressure of the gas coming out of the regulator. You must open the regulator before you get a reading on the second gauge. This is the delivery pressure of the gas, and you must set the pressure that you need for your particular job.

The pressures that you read on regulator gauges is called gauge pressure. If you are using pounds per square inch, it should be written as

psig (this acronym means pounds per square inch gauge). When the gauge on a cylinder reads zero, this does not mean that the cylinder is empty. In actuality, the cylinder is still full of gas, but the pressure is equal to the surrounding atmospheric pressure. Remember: no gas cylinder is empty unless it has been pumped out by a vacuum pump.

There are two types of regulators that control the flow of gas from a cylinder. These are either single-stage or double-stage regulators.

Single-Stage Regulators

Regulators are used on both high- and low-pressure systems. Figure 4-8 shows two SINGLE-STAGE regulators: one for acetylene and one for oxygen. The regulator mechanism consists of a nozzle through which the gases pass, a valve seat to close off the nozzle, a diaphragm, and balancing springs. These mechanisms are all enclosed in a suitable housing. Fuel-gas regulators and oxygen regulators are basically the same design. The difference being those designed for fuel gases are

Figure 4-8. - Single-stage regulators.

not made to withstand the high pressures that oxygen regulators are subjected to.

In the oxygen regulator, the oxygen enters through the high-pressure inlet connection and passes through a glass wool falter that removes dust and dirt. Turning the adjusting screw

IN (clockwise) allows the oxygen to pass from the high-pressure chamber to the low-pressure chamber of the regulator, through the regulator outlet, and through the hose to the torch. Turning the adjusting screw further clockwise increases the working pressure; turning it counterclockwise decreases the working pressure.

The high-pressure gauge on an oxygen regulator is graduated from 0 to 3,000 psig and from 0 to 220 in cubic feet. This allows readings of the gauge to determine cylinder pressure and cubic content. Gauges are calibrated to read correctly at 70°F. The working pressure gauge may be graduated in "psig" from 0 to 150, 0 to 200, or from 0 to 400, depending upon the type of regulator used. For example, on regulators designed for