Oxy-fuel Apparatus – Part I

Posted by Florida Gas Welding

Oxy-fuel ApparatusTypical oxy-fuel workstations normally include the following items, each designed to perform a specific function:

* Oxygen and fuel supply

* Cutting attachment and tip(s)

* Regulators

* Welding nozzle(s)

* Hose

* Heating nozzle(s)

* Torch Handle

* Operator safety equipment

4.01 Oxygen and fuel Supply

There are two types of workstations, portable and stationary. The portable station is usually supplied by cylinders mounted on a cart. The stationary units are supplied by piping or manifold systems (see Figure 3). The stationary system restricts the operator to the length of hose attached to the torch handle.

CAUTION

Always be aware of the gases in use at the station. Use only the type of apparatus designed for use with those gases.

4.02 Regulators

Oxygen and fuel pressure regulators are attached to the cylinders or piping outlets to reduce high cylinder or supply pressures to suitable lower working pressures for oxy-fuel applications. The basic external features of a regulator are as shown in Figure 3. Figure 3 also shows: CGA inlet connection with filter, pressure adjusting screw, inlet gauge, delivery gauge, outlet connection, and relief valve (where provided).

Regulator Features

Figure 3: Regulator Features

WARNING

Always keep the regulator free of oil, grease and other flammable substances. Never use oil or grease on the regulator, cylinder or manifold connection. Only use the regulator for the gas and pressure for which it was designed. NEVER alter a regulator for use with any other gas.

Inlet Connection

Regulators are attached to the cylinders or piping outlets by their “inlet connections.” Inlet connections must have a clean filter. All inlet connections conform to specifications and standards set by the Compressed Gas Association (CGA) and are marked with an identifying CGA number. CGA numbers identify the cylinder valve and gas service for which that inlet connection is designed. Examples: CGA

510 has been designated for standard fuel gas cylinder connections such as acetylene, propylene/ propylene-based fuel gases, MAPP® and propane. CGA 540 connections are designated for oxygen service only. Fuel gas inlet connections usually have left-hand threads. Those with left-hand threads also have a “V” notch around the inlet nut to further designate the connection for fuel gas service.

All oxygen connections have right-hand threads.

Pressure adjusting Screw

The regulator adjusting screw controls the delivery pressure of the gas to the hose. As previously stated, the regulator’s function is to reduce high supply pressures to a suitable working pressure range. When the adjusting screw is turned clockwise, the regulator allows gases to flow through the regulator to the hoses and to the torch. The threaded adjusting screw applies mechanical force to a spring and diaphragm which controls a pressure valve in the regulator. If the adjusting screw is turned fully counterclockwise, tension on the spring is released and the regulator normally does not allow the gas to flow. The regulator adjusting screw is not intended as a “shut off” mechanism.

Pressure gauges

The inlet pressure gauge indicates the cylinder or supply pressure entering the regulator. The delivery pressure gauge indicates the delivery pressure from the regulator to the hose. All gauges are precision instruments; handle with care.

Outlet Connections

Gas hoses are attached to the regulator outlet connections. Most fuel gas regulators have left-hand threaded outlet connections to mate with the left-hand hose connections and have a “V” notch around the outlet connection to further designate the connection for fuel gas service. Oxygen regulators have right-hand threaded outlet connections to mate with the right-hand hose connections.

Relief Valve (where provided)

Internal or external relief valves are designed to protect the low pressure side of the high pressure regulator from damage due to an inadvertent high pressure surge.

WARNING

DO NOT tamper with the relief valve or remove it from the regulator. Relief valves are not intended to protect downstream equipment from high pressures.

Hose

The gas hose transports low pressure gases (maximum 200 PSIG) from the regulators to the cutting or welding torch. Proper care and maintenance of the hose assists the operator in maintaining a safe, efficient shop or work area.

Hose Construction

Industrial gas hose used in the U.S. is generally color-coded for gas service identification. The oxygen hose is normally green and the fuel hose is red. The colors are subject to change in countries other than the U.S. The hose walls are constructed of continuous layers of rubber or neoprene material over a braided inner section. The hose is marked to indicate its grade. All approved domestically fabricated type VD grade “RM” and “T” hoses are flame retardant and have an oil resistant cover.

Grade “R” hose does not have an oil resistant cover. Grade “T” and “RM” hose will burn, but will not support a flame if the heat source is removed. Grade “T” hose is recommended for all fuel gases.

Grade “R” and “RM” hose is for use with acetylene only.

WARNING

Grade “R” and “RM” hose are for use with acetylene only. These hoses have rubber linings that are degraded by petroleum-based fuel gases. Grade “T” hose is recommended for all fuel gases. It should be used with petroleum-based fuel gases since it has a neoprene inner liner that is compatible with these gases.

Hose Care

Gas hoses are often exposed to severe abuse. They can provide efficient service with proper care.

Hose splices and excessive hose length can restrict and reduce the amount of gas flow within the hose. Molten slag and sparks may come into contact with hoses and burn into the hose exterior. Falling metal during cutting operations might crush or cut into gas hoses. The operator should frequently inspect the hoses and, when necessary, replace them.

Safety Notes

• Falling metal during cutting operations might crush or cut into gas hoses.

• Never allow hoses to become coated with oil, grease, or dirt. Such coatings could conceal damaged areas

• Examine the hoses before attaching them to the gas torch handle or regulators. If cuts, burns, cracks, worn areas, or damaged fittings are found, replace the hose.

• Completely replace the gas hose if it contains multiple splices or when cracks or severe wear is noticed.

Terms you should know

Backfire: The return of the flame into the torch, producing a popping sound. The flame will either extinguish or re-ignite at the tip.

Sustained: The return of the flame into the torch with continued burning within the torch.

Backfire:  This condition may be accompanied by a popping sound followed by a continuous hissing or whistling sound.

Flashback:  The return of the flame through the torch into the hose and even into the regulator.

It may also reach the cylinder. This condition could possibly cause an explosion in the system.

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