Types, Working Principle, Precautions and Testing and Repairing of Regulators

This is a device used to draw the gas from cylinder at required pressure and control the flow of gases at a constant rate to the torch or blowpipe. For different types of gas, we use different regulators. In oxy-acetylene welding plant we use oxygen and acetylene regulator. There are two types of regulator.

(a) Single stage regulator

(b) Double stage regulator

Single Stage Regulator. This regulator is designed to regulate the pressure in one stage only. Initially, the desired working pressure is set, but as the work proceeds and gas is consumed, pressure drops. This cause a change in the amount of gas delivered and requires constant adjustment to obtain the correct flame. The adjustments are necessary more frequently as the cylinder becomes empty.

Working Principle. When the spindle of the cylinder is opened slowly, the high-pressure gas from the cylinder enters in to the regulator through the valve. The gas then enters the body of the regulator which is controlled by the needle valve. The pressure inside the regulator rises which pushes the diaphragm and the valve to which it is attached, closes the valve and prevents any more gas from entering the regulator.

The outlet side is fitted with a pressure gauge which indicates the working pressure on the blowpipe. Upon the gas being drawn ‘off’ from the outlet side, the pressure inside the regulator body falls, the diaphragm is pushed back by the spring and the valve opens, letting more gas ‘in’ from the cylinder. The pressure in the body, therefore, depends on the pressure of the springs and this can be adjusted by means of a regulator knob.

Double Stage Regulator. In this type, the reduction of pressure is made in two steps. The advantage of this arrangement is that any variation of the first stage pressure is taken care of by the second stage pressure. For heavy duty cutting or welding, it is preferable to have this type of regulator as a constant working pressure is assured.

Working Principle

The two-stage regulator is virtually two regulators in one which operates to reduce the pressure progressively in two stages instead of one. The first stage, which is pre-set, reduces the pressure of the cylinder to an intermediate stage and gas at that pressure passes into the second stage, the gas now emerges at a pressure (working pressure) set by the pressure adjusting control knob attached to the diaphragm. Two-stage regulators have two safety valves, so that if there is any excess pressure there will be no explosion. A major objection to the single stage regulator is the need for frequent torch adjustment, for as the cylinder pressure falls the regulator pressure likewise falls necessitating torch adjustment. In the two-stage regulator, there is automatic compensation for any drop in the cylinder pressure.


Difference Between Oxygen and Acetylene Regulator

Acetylene RegulatorOxygen Regulator
(a) The cylinder and hose connections have left-handed threads on the acetylene regulator.

(b) Acetylene connection nuts have chamfers or grooves cut in them.

(c) Colour band on acetylene regulator in maroon red.

(d) The inlet or high-pressure gauge on the regulator reads upto 8 bar on the acetylene regulator.

(e) The outlet or low-pressure gauge on the regulator reads upto 1 bar on the acetylene regulator.

(a) There is right hand thread in this case.

(b) Nuts are plain, i.e. with no chamfers or grooves.

(c) It is either blue or black on the oxygen regulator.

(d) The inlet or high-pressure gauge on the regulator reads upto 100 bar on the oxygen regulator.

(e) The outlet or low-pressure gauge on the regulator reads upto 4.8 bar on the oxygen regulator.


The various precautions to be observed while handling pressure regulators are as shown below.

(a) Regulators must be handled carefully and must not be damaged. If     damaged, it must be returned to store. The welder must not try to repair it himself.

(b) Under no circumstances, oil or grease to be applied to a regulator.

(c) Before fitting, a regulator must be checked for serviceability.

(d) When fitting to the cylinder, the gland nut must be tightened by hand or may be tapped with a mallet. Hammers must not be used on them.

(e) The only repair permissible to the welder is a leaky joint. No jointing material should be used.

Testing a Regulator

The procedure to be followed for testing a regulator is as given below.

(a) Fix the regulator to the appropriate cylinder.

(b) Open the release valve and trap the gas in the regulator upto its delivery valve.

(c) Close the release valve and watch the gauge. If the needle flickers, the regulator is leaky.

(d) To locate a leak, use soapy water. Never use oil or grease. The regulator may be dipped in a basin of soapy water if necessary.

(e) Before fitting a regulator, the adapter sitting in the cylinder should be cleaned of all dirt and dust by releasing a little gas and blowing away all foreign matter.

Repairing Leak in the Regulator

The leaks in a regulator can be repaired by following methods.

(a) Leak at Joint between Regulator and Cylinder. This may be due to the joint being too loose, or dirt between the nipple and the seating. It can be corrected by tightening the gland nut further. If the leak still persists, the regulator is unserviceable and must be returned to stores.

(b) Leak at the Regulator Outlet Valve. This is due to dust between the needle and the seating. To rectify the leak, trap the gas fully in the regulator and open the outlet cock. If the leak persists, it is due to a deteriorated nipple or seating. In such a case, the regulator is unserviceable and it is to be returned to stores.

(c) Leak at the Safety Valve. This is due to either dirt between the valve and its seating or damage seating. No attempt should be made to repair this. here again, the regulator is unserviceable and must be returned to store.

(d) Leak at the Diaphragm. If there is no other leak i.e. at the valve setting, safety valve, outlet valve, and the pressure is still not maintained, it may be assumed that there is a leak at the diaphragm. No tradesman is permitted to repair this unless he is authorized for repair of regulators.

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