Oxy / fuel gas welding
A regulator is a device attached to a gas cylinder that delivers a constant reduced gas pressure at the welding operation even though the pressure at the source may fluctuate. Regulators operate automatically after a setting has been established, and those used in oxyfuel gas welding are known as adjustable pressure reducers.
There are a few differences, but basically the regulators operate on the same principle. If the pressure is reduced in one step, it is known as a single-stage regulator, and if the reduction is in two steps, it is a two-stage unit.
The single -stage regulator exhibits rise or drift, which reflects a rise or drop in the delivery pressure as the cylinder pressure is depleted. This is usually not detrimental unless a high-pressure cylinder is relieved of a large quantity of gas at one time.
The single -stage regulator is designed as a stem type or a nozzle type. With the stem-type design (fig.1)
The outlet pressure of the gas is balanced by forces acting between the thrust of the bonnet spring and any one of the forces created by gas pressure on the underside of the diaphragm, inlet pressure on the valve seat and pressure of the small spring under the valve seat. A decrease in the gas inlet pressure initiates a corresponding decrease of force on the seat. The force of the bonnet spring moves the seat away from the nozzle, allowing gas pressure to build against the diaphragm. A balanced condition is then achieved.
With the nozzle-type design (fig.2), the seat is moved away from the nozzle by inlet pressure, opening the valve. Outlet pressure has a tendency to decrease as inlet pressure decreases. Outlet pressure on the underside of the diaphragm is needed to close the seat against the nozzle.
Two-stage regulators
A two-stage regulator (fig.3) is basically two single-stage regulators combined in a single housing. The combination may be a nozzle and stem type, two nozzle types or two stem types. Regardless, the two-stage regulator offers a precise balance of inlet and outlet pressures. A preset outlet pressure from the first stage delivers a specified inlet pressure from the second stage. As supply pressure decreases, a constant delivery pressure is realised from the outlet of the regulator.
With the two-stage regulator, the outlet pressure variation is usually so slight that it can be disregarded in welding and cutting operations. This type of regulator is recommended for precision welding or cutting conditions that require continuous operation or a very controlled volumetric flow of gas.
Safety must always be followed when using regulators. Major safety factors are as follows:
- the operator must be trained in the use of regulators and competent supervision must be available.
- the manufacturer's operating procedures must be followed.
- the regulator must be clean and in good working condition.
- gas cylinders must be secured to a wall, post or cart to prevent them from falling or tipping.
- examine cylinder valves for damaged threads and the presence of dirt, dust, oil or grease. Remove dust and dirt. Do not attach the regulator if oil, grease or damage is present. Inform the gas supplier of the condition and allow only qualified technicians to perform service.
- crack open, for an instant, the cleaned cylinder valve and then quickly close it. This blows out foreign matter that may be lodged in the valve port.
- attach the regulator to the cylinder valve and tighten securely with a wrench.
- before opening cylinder valve, turn the regulator adjusting screw counter-clockwise until the adjusting spring pressure is released.
- stand to the side of the regulator when opening the cylinder valve. Never stand in front of or behind a regulator. Open the cylinder valve carefully and slowly until the adjusting spring pressure is released.
- never open acetylene cylinder valves more than one complete turn. All other cylinder valves should be opened completely to seal the valve packing.
- turn the regulator adjusting screw clockwise to attain the desired delivery pressure.
- the system should be tested for leaks by methods recommended by the manufacturer.
- keep the cylinder valves closed at all times other than when the cylinder is in use. When finished using the apparatus, close both cylinder valves. To bleed the system, open the fuel gas valve on the torch and allow gas to escape at a safe location. Close the torch fuel valve and turn the regulator pressure adjusting screw counter-clockwise until the screw turns freely. Repeat this operation on the oxygen system. Do not bleed both systems at the same time. A dangerous situation of reverse flow and mixing of gases may occur.