2
Cutting Blowpipes
Proceed with assembly of the equipment exactly as outlined for the
Welding Equipment, but remember the following points. These
instructions apply to nozzle-mix type cutters, since these are of the
most modern design.
1. Fit the correct size cutting-nozzle to the blowpipe.
2. Use the cylinder key to open the cylinder valves and purge both
hoses.
3. Set the working oxygen pressure on the regulator with the
oxygen passing through the cutting valve on the cutter and
hence out through the nozzle.
4. Shut all the valves on the blowpipe.
5. Slowly open the fuel-gas valve and ignite the gas.
6. Slowly open the heating oxygen valve on the cutter and adjust
the flame to neutral.
7. Depress the cutting oxygen lever and again adjust the heating
gas control to give a neutral flame.
8. Depress the cutting oxygen lever and the cutter is ready for use.
Closing-down Procedure
Welding Blowpipe
1. Turn off the fuel-gas by the blowpipe control valve.
2. Turn off the oxygen by the blowpipe control valve.
3. Close the cylinder valves.
4. Open the blowpipe valves one at a time to release the pressure
in the hose, i.e. open the oxygen valve and close it, then open
the fuel gas valve and close it.
5. Unscrew the pressure regulating screws on the oxygen and
acetylene regulators to relieve spring pressures in the
regulators.
Cutting Blowpipe
1. Close the oxygen cutting valve.
2. Close the fuel-gas and heating oxygen valves.
3. Close the cylinder valves.
4. Open and close the cutter, oxygen and fuel gas valves one at a
time to release pressure in the hoses.
5. Unscrew the pressure regulating screws on the oxygen and
acetylene regulators to relieve spring pressures in the
regulators.
Important Information
It is most important to emphasise the earlier instructions that prior to re-
lighting either the welding orcutting blowpipes, the hoses must be
purged to ensure a pure and adequate supply of oxygen and fuel-gas.
Back-fires may occur by one of a combination of circumstances, e.g.
defective equipment, incorrect gas pressure, incorrect lighting-up
procedure or careless handling of the blowpipe in use, such as
permitting the nozzle to touch the work, over-heating the tip of the
nozzle, or working with a loose nozzle.
Usually the back-fire is arrested at the injector in case of low pressure
equipment or the source where the gases are mixed, e.g. the head of
the cutting blowpipe, and if prompt action is taken in turning off first the
oxygen, and then the fuel-gas valve, no damage occurs and the
blowpipe may be re-lit as soon as the cause of the trouble has been
rectified.
In some cases, however, a back-fire may pass beyond the torch and
go back into either the oxygen or the fuel-gas hoses.
This is then termed a ‘flash-back’ and its effect is more serious in that
it may result in immediate damage to hoses and regulators. In extreme
cases there is also a possibility of injury to the operator. The outward
signs of a flash-back may be a squealing or hissing noise; sparks
coming out of the nozzle, heavy black smoke, or the blowpipe handle
may get hot. If the flame burns back far enough it may even burst
through the hose.
Both blow-backs and flash-backs can be avoided by adherence to
recommended procedures for the equipment.
Investigation shows that such occurrences often occur purely through
over-familiarity, leading eventually to neglect of ordinary safeguards.
For example, the blowpipe on lighting, may have incorrect regulator
pressure settings, or a light being applied before the flow of fuel gas is
properly established.
If the flame snaps out when the blowpipe is in use it is because;
a. The regulator pressure and/or gas flow, are incorrect - either too
high or too low.
b. The nozzle has been obstructed.
c. The nozzle is held too close to the work.
d. The nozzle has become over-heated.
When any of the above occur, completely shut both the blowpipe
valves. Check the regulator setting and cylinder pressures. Re-light in
accordance with the correct procedure. In the case of ‘d’, close the
acetylene valve, reduce oxygen flow to a trickle, and plunge the nozzle
and head into cold water.
Hose Check Valves
The hose check valve is a safeguard, which will operate independently
and without attention from the operator. This device is essentially a
non-return valve, the purpose of which is to prevent back feeding or the
reverse flow of gases, it must in all cases be fitted to the inlet
connections of the blowpipe.
Regulator and Pipe-line Flash-back Arrestors
The RS flash-back arrestor is a device to be fitted on the outlet of a
regulator or manifold. It contains:
A non-return Valve (prevents reverse flow of gases).
A flash-back extinguisher.
A fuel gas shut-off device.
The non-return valve prevents gas from flowing in the wrong direction
i.e. from torch to the gas source.
The flash-back extinguisher stops and extinguishes a backfire in the
event of a flash-back.
The fuel gas shut-off device interrupts the supply of fresh gas to the
torch.
V10946
Welding Data
UP TO
S.W.G.
INCHES
Material Thickness M.S.
20
18
14
12
1/
8
5/
32
3/
16
1/
4
5/
16
3/
8
1/
2
3/
4
1
1
Tip Number
1
2
3
5
7
10
13
18
25
35
45
55
70
90
Oxygen Pressure P.S.I.
2
2
2
2
2
3
3
3
4
4
5
5
6
7
Acetylene Pressure P.S.I.
2
2
2
2
2
3
3
3
4
4
5
5
6
7
Consumption of each gas Cu.Ft.Hr
1
2
3
5
7
10
13
18
25
35
45
55
70
90
FLAME CLEANING DATA
Size of Nozzle
2” Flat
3” Flat
4” Flat
6” ’Flat
Round
Oxygen Pressure P.S.I.
8
10
10
12
18
Acetylene Pressure P.S.I
7
8
10
12
12
