Device for ensuring the safety of the gas and oxygen supply to a cutting and welding torch, and a flow-pressure switch for use in said device

A device for ensuring the safety of the oxygen and gas supply to a welding and cutting torch (4). The object of the device is to prevent accidental escape of oxygen and/or gas when the torch is not in use. For this purpose, the device is characterized in that the oxygen supply line and the gas supply line each contain a controlled regulating valve (10, 12), which valves are connected to a common control line (14). The oxygen supply line, downstream of the regulating valve (12), viewed in the direction of flow of the oxygen, contains a starting tank (20), and a flow-pressure switch (21) which operates a regulating slide valve (16) accommodated in the control line, said control line being in communication by way of the regulating slide valve and a line (30) with the part of the oxygen supply line situated upstream of said regulating valve (12). The invention is also embodied in a flow-pressure switch, which is suitable in particular for use in the above device.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for ensuring the safety of the 
gas and oxygen supply to a cutting and welding torch of the type generally 
used in workshops and shipyards. The invention also relates to a 
flow-pressure switch which can be used in such a device. Such a safety 
means is intended in particular for preventing oxygen and/or gas from 
escaping from the torch for one reason or another when said torch is not 
in use. 
A welding or cutting torch generally has a gas cock which is connected to a 
gas supply line, and two oxygen cocks which are connected to a supply line 
for oxygen. One oxygen cock supplies so-called preheating oxygen for the 
welding, and the second oxygen cock supplies cutting oxygen which is not 
mixed with the gas, but is conveyed direct to the torch mouth as 
additional oxygen during the flame cutting. The supply lines are generally 
rubber hoses which run from the torch to a gas distribution block, usually 
situated several tens of metres away. In the case of the known torches 
there is a risk that one of the cocks may be opened accidentally, as a 
result of which gas can escape, with all the consequent risks of such an 
occurrence. In the case of torches operating by vacuum a safety valve is 
generally fitted in the gas supply line and opens only if the oxygen 
flowing out of the torch causes a vacuum in said line. This safety means 
ensures that users of the torch shut off only the oxygen cock and 
generally leave the gas cock open after they have finished their work. 
This can result in dangerous situations if the oxygen cock on the torch is 
opened accidentally, since a combustible mixture will then flow out of the 
torch, which produces the risk of explosions. The safety devices known 
until now are in fact limited to the gas supply, while no means are 
present for preventing the accidental escape of oxygen or for warning the 
user if an oxygen leak has occurred. 
SUMMARY OF THE INVENTION 
A first object of the invention is to provide a device for ensuring the 
safety of the oxygen supply to the welding and cutting torch, in the case 
of which the gas supply line has already been provided with a known safety 
valve. 
A further object is to provide a device for ensuring the safety of the 
oxygen supply to a welding and cutting torch which is reliable and is 
cheap to produce, and where the user putting the torch into operation is 
automatically made aware of the fact that an oxygen leak has occurred. 
These objects are achieved according to the invention by means of a device 
which has the features specified in Claim 1. The fact that the 
flow-pressure switch is set in such a way that the system is put into 
operation only when both oxygen cocks are opened means that a safety means 
is obtained, since there is virtually no chance of such opening occurring 
accidentally. When there is an oxygen leak, only the starting tank 
empties, so that the user is obliged to operate the manual regulating 
slide valve first, before the system can be restarted. 
Another object is to provide a device for ensuring the safety of both the 
oxygen supply and the gas supply to the torch. This object is achieved by 
means of a device with the features described in Claim 2. This device has 
the advantage that no other safety valves are necessary, while this device 
can function efficiently irrespective of whether or not the torch is 
operating with vacuum in the gas supply line. Claim 3 describes an 
advantageous further development of this embodiment, in which a starting 
tank with flow-pressure switch is fitted both in the oxygen supply and in 
the gas supply. 
Claims 4 and 5 describe efficient variants and further developments of the 
present invention. 
The invention is also embodied in a flow-pressure switch which can be used 
advantageously in the safety device according to the invention. Said 
flow-pressure switch must be capable of switching over a regulating slide 
valve depending on the gas flow supplied through said switch, which switch 
for safety reasons must not use electrical current. This last object is 
achieved according to the invention by means of a switch which has the 
features described in Claim 6. 
Claims 7-10 give further details of the flow-pressure switch according to 
the invention. 
The invention is explained in greater detail with reference to the drawing, 
in which:

DETAILED DESCRIPTION OF THE DRAWINGS 
The drawing shows in FIG. 1 by reference number 1 a distribution block, 
from which a gas supply line 2 and an oxygen supply line 3 run to a 
welding cutting torch 4. The torch is of a conventional type, having a gas 
cock 5 and two oxygen cocks 6 and 7. In this case reference number 6 
indicates the preheating oxygen cock, and number 7 the cutting oxygen 
cock. 
A controlled non-return valve 10, which is normally held in the closed 
position by a spring 11, is fitted in the gas line 2. An identical 
controlled non-return valve 12, which is normally held in the closed 
position by a spring 13, is fitted in the oxygen line 3. This means that 
the two non-return valves 10 and 12 are constantly in the closed position 
and are connected to a common control line 14, which is connected by way 
of a line 15 to a regulating slide valve 16. Said regulating slide valve 
16 is a two-position slide valve which is pressed by a spring 17 into the 
position shown, in which position the line 15 is in open communication 
with the environment (i.e. it is pressureless). In the other position of 
the regulating slide valve 16 the line 15 is in communication with an 
oxygen line which is under pressure, and which will be described below. 
The regulating slide valve 16 is operated by a flow-pressure switch 21, 
which will be discussed in detail below with reference to FIG. 2. For a 
good understanding of the device, it is sufficient here to know that the 
flow-pressure switch switches the regulating slide valve from the closed 
position into the open position when a predetermined quantity of oxygen 
flows through the switch, and switches the regulating slide valve back 
again when the quantity of oxygen falls below a predetermined value. 
The oxygen line 3 further has a non-return valve 18, which is normally held 
in the open position by a spring 19. Said non-return valve 18 serves as a 
hose breakage safety means. If the oxygen supply line breaks or is 
accidentally severed downstream of this valve, such a great oxygen flow 
occurs that the ball of the valve is pressed against the pressure of the 
spring 19 and closes the valve. 
A starting tank 20 is accommodated in the oxygen line, between the 
non-return valve 18 and the flow-pressure switch 21, which starting tank 
is normally filled with oxygen, and the function and the operation of 
which will be discussed later. From the starting tank 20 the oxygen line 
runs by way of the flow-pressure switch 21 to the torch 4. 
Between the distribution block 1 and the non-return valve 12 the oxygen 
line has a bypass line 30, which is connected to the regulating slide 
valve 16. Said bypass line 30 in turn has a branch line 31, which is 
connected to the oxygen line 3, to the part thereof which is situated 
between the starting tank 20 and the flow-pressure switch 21. Finally, a 
manually operated switch slide valve 32 is accommodated in the branch line 
31, which valve normally shuts off said branch line 31 and can be opened 
by pressing a control button 33 by hand. 
The operation of the diagram illustrated is as follows: 
Starting from the initial position shown in the drawing, in which both 
valves 10 and 12 are closed, the valve 18 is open, both regulating slide 
valves 16 and 32 are closed, and the starting tank 20 is filled with 
oxygen under pressure. An operative who wishes to start to work with the 
torch 4 first opens the gas cock 5. Nothing happens yet, since the gas 
supply is shut off by the valve 10. The operative then opens both oxygen 
cocks 6 and 7, as a result of which a large volume flow of oxygen flows 
out of the starting tank 20 and through the flow-pressure switch 21 to the 
torch. Said volume flow is sufficiently great to activate the switch 21 in 
such a way that it switches over the regulating slide valve 16 to the open 
position. This allows oxygen to flow by way of the bypass line 30 and the 
regulating slide valve 16 into the control lines 14 and 15. The oxygen 
pressure in the line 14 causes both valves 10 and 12 to be opened 
virtually simultaneously, so that a gas flow to the torch starts, and the 
oxygen stream also flows by way of the valves 12 and 18, the starting tank 
20 and the flow-pressure switch 21 to the torch. The operative can ignite 
the torch and then close the cutting oxygen cock 7 if desired. 
The flow-pressure switch 21 is set in such a way that a greater volume flow 
of oxygen is needed for changing over the regulating slide valve 16 from 
the closed to the open position than for holding it in the open position. 
This means that for putting the torch into operation both oxygen cocks 
must be opened, in order to provide this adequate volume flow. This 
provides additional safety, since accidentally opening one of the two 
oxygen cocks cannot result in the system being switched on. In this case 
the oxygen will only escape from the starting tank 20, without the valves 
10 and 12 being opened. The starting tank 20 has a capacity of 
approximately two litres, so that it cannot endanger the environment if 
its contents run out. 
If the starting tank 20 is empty for some reason or other, the system 
cannot be started by opening the two oxygen cocks. If the operative 
notices that opening of the oxygen cocks produces no result, he or she 
knows that the starting tank 20 is empty and that an oxygen leak has 
therefore occurred. A check can then be made to establish where this leak 
has occurred, and the leak can be repaired. 
For restarting the system after this, it is necessary for the operative to 
hold down the control button 33 of the regulating slide valve 32 with the 
hand for some time, so that the starting tank 20 can fill with oxygen by 
way of the lines 30 and 31. After this, the torch can be put into 
operation again in the manner described above. 
The device shown in FIG. 1 provides a safety means for both the oxygen 
supply and the gas supply. If the gas supply has already been provided 
with a conventional safety valve, the device according to the invention 
can also be fitted on the oxygen supply alone. In this case the control 
line 15 is connected directly to the regulating valve 12, and the 
regulating valve 10 with the control line 14 becomes superfluous. 
The flow-pressure switch 21 from FIG. 1 is shown on a larger scale in FIG. 
2. Said flow-pressure switch is connected to a conventional regulating 
slide valve 16, which is provided with a likewise conventional 
electromagnetic switch 25. The electromagnetic switch consists of a block 
26 which is fitted immovably on the regulating slide valve and has a 
projecting tube 27. A plunger, which is not visible in the drawing, is 
fitted movably in said tube, and the movement of said plunger produces the 
actual switching operation. In the case of the conventional 
electromagnetic switch said plunger is operated by exciting or not 
exciting an electric coil fitted around the tube 27. 
The invention is therefore based on the idea of using this conventional 
electromagnetic switch as a flow-pressure switch. 
As can be seen from FIG. 2, the tube 27 is accommodated in a cylindrical 
housing 35, and the axis of the tube coincides with the axis of said 
housing. The housing consists of a cylindrical wall 36 and two end walls 
37 and 38 which bound a cylindrical interior space of the housing and are 
situated at right angles to the axis of the housing 35. A sliding sleeve 
39, bearing an annular permanent magnet 40, is fitted around the tube 27, 
in such a way that it is freely slidable in the interior space of the 
housing. 
The arrangement is as shown in FIG. 2, i.e. the tube 27 is directed 
vertically and runs from the block 26 down through an opening in the top 
end plate 37 into the interior space of the housing, and lies with the 
free end sealed off by means of an O-ring (not visible) against the bottom 
end wall 38. The outer periphery of the annular permanent magnet 40 lies 
with slight play away from the inner surface 41 of the cylindrical wall 
36, and can therefore move as a freely movable piston vertically along the 
tube 27. The oxygen can enter the interior space of the housing by way of 
an opening 42 in the bottom end wall 38, and leaves the interior space by 
way of an opening 43 made in the top end wall 37. On both parts adjoining 
the end walls, the inner surface 41 of the wall 36 is provided with an 
annular recess 44, 45 respectively, which recesses each form a local 
annular radial widening of the interior space. Said openings 42 and 43, to 
which the oxygen line 3 is connected, are situated in the region of the 
respective end walls adjoining said recesses 44 and 45. 
The regulating slide valve 16 and the switch block 26 with the tube 27 are 
commercially available parts and will not be discussed in any further 
detail here. For a good understanding of the operation of the 
flow-pressure switch according to the invention, it is important to know 
that the tube 27, as already mentioned, contains a plunger (not shown in 
the drawing) which is movable in the axial direction therein. However, the 
movement of this plunger is produced here by moving the permanent magnet 
along the tube 27. Said movement in turn causes the regulating slide valve 
to be switched over, in such a way that if the magnet moves up from the 
rest position shown, the regulating slide valve is switched over from the 
closed position shown to the open position, while in this example the line 
15 enters into communication with the bypass line 30. 
As shown in an exaggerated manner in FIG. 2, the inner surface 41 of the 
wall 36 from the bottom end plate over some distance upwards has a uniform 
diameter, and only a few tenths of millimetres' play is present between 
the permanent magnet and this surface. After this, the inner surface runs 
slightly tapering towards the outside (e.g. from the line 46 onwards), so 
that the play between the magnet and the above mentioned inner surface 
becomes greater as the magnet moves further upwards. The angle at which 
said inner surface widens is approximately 1.degree.-2.degree., and must 
in any case be sufficient, on the one hand, in the highest position of the 
magnet to provide a sufficiently large passage for the maximum volume flow 
of oxygen and, on the other hand, to provide an adequate flow to keep the 
magnet in the up position. 
The operation of the flow-pressure switch is then as follows: 
If oxygen is supplied by way of the line 3 and the opening 42 into the 
interior space of the housing 35, the permanent magnet will initially be 
pressed upwards by the oxygen pressure. The annular recess 45 in this case 
gives a uniform distribution of the oxygen around the periphery of the 
magnet. As a result of this upward movement, the magnet will go beyond the 
switch point at a particular moment, so that the regulating slide valve is 
switched over from the closed position to the working position. This 
switch point can lie, for example, in the region where the internal 
surface widens. The magnet will initially be moved upwards by the pressure 
of the oxygen and will then remain suspended in the oxygen stream in the 
broadened region. It will be clear that at a given weight and surface area 
of the permanent magnet a certain volume flow and pressure are necessary 
to activate the switch. By adapting the weight and surface area of the 
permanent magnet, the volume flow of the oxygen at which the switch goes 
into operation can thus be determined. If said volume flow falls below a 
predetermined value, the magnet will drop by its own weight and switch 
back the switch again. The value of the volume flow for switching on need 
not be the same as for switching back. In order to adapt the weight and 
the surface area of the permanent magnet, a ring 47 made of plastic or 
another suitable material can be fitted around the external periphery 
thereof. According to the invention, this produces a contactless 
flow-pressure switch which, in addition to the application described 
above, can also be applied in many other areas, in particular where the 
use of electrical current is not possible, on account of the risk of 
explosion. 
When it is used in the safety device described with reference to FIG. 1, 
the weight and the surface area of the permanent magnet are such that said 
magnet can move upwards over the switch point only if both the preheating 
oxygen cock 6 and the cutting oxygen cock 7 are open. If after the torch 
has been ignited the cutting oxygen is switched off, the magnet will sink 
slightly by its own weight, but it will in any case remain suspended above 
the switch-off point. Only if the preheating oxygen cock 6 is also turned 
off, will the magnet pass the switch-off point, with the result that the 
regulating slide valve 16 is switched over, the lines 14 and 15 become 
pressureless, and the valves 10 and 12 are closed, following which the 
entire system is switched off. 
Yet another embodiment of the device for ensuring the safety of both the 
gas and the oxygen supply to a torch is shown diagrammatically in FIG. 3. 
In this diagram the same reference numbers as those in FIG. 1 are used as 
far as possible. 
The oxygen is supplied by way of the line 3, while the gas is supplied by 
way of line 2. Regulating valves 10 and 12, which in fact operate in the 
same way as the controlled non-return valves 10 and 12 in FIG. 1, are 
fitted in the lines 2 and 3 respectively. The two valves 10 and 12 are 
normally in the closed position and can be opened jointly by placing the 
control line 14, 15 under pressure. In the oxygen line 3 the starting tank 
20 is again accommodated downstream of the valve 12, while in the gas line 
2 a starting tank 52 is fitted downstream of the valve 10. Each starting 
tank is connected to a flow-pressure switch 21 and 53 respectively, which 
are each again in communication with a regulating slide valve 16 and 54 
respectively, and can switch over the latter from the closed to the open 
position. 
The gas line 2 is provided with a bypass line 55 running around the valve 
10, and in which a manually operated switch slide valve 56 which has a 
control button 57 is accommodated. The oxygen line 3 is again provided 
with a bypass line 30 running around the valve 12 and is connected to the 
regulating slide valve 16. The bypass line 30 has a branch line 31, which 
opens out in the starting tank 20. The manually operated slide valve 32 
with control button 33 is accommodated in this branch line. The bypass 
line 30 continues downstream of the regulating slide valve 16 in the 
control line 15', which is connected by way of the regulating slide valve 
54 to the control line 15. The control line 15 is thus in communication 
with the bypass line 30 by way of the two regulating slide valves 54 and 
16, which are placed in series. This means that the control line 14, 15 
can come under pressure of oxygen and the system can be started only if 
the two regulating slide valves 16 and 54 are in the open position. 
The embodiment described here works as follows: 
The system is at pressure, i.e. both starting tanks 52 and 20 are under 
pressure (are filled). The main valves 10 and 12 are closed, and the 
control lines 14, 15 are pressureless, because both regulating slide 
valves 16 and 54 are closed. The gas cock 5 and the oxygen cock 6 of the 
torch 4 are opened, and a starting pulse is given by opening the cutting 
oxygen cock 7. This means that gas flows out of the starting tank 52 
through the flow-pressure switch 53 to the torch 4, so that the regulating 
slide valve 54 is opened and the control line 15' is connected to the 
control line 15. Opening the cock 7 causes sufficient oxygen for operating 
the regulating slide valve 16 to flow out of the starting tank 20 to the 
torch, so that the control line 15' is connected to the bypass line 30. 
The fact that the two valves 54 and 16 are switched over means that the 
control line 14 is now connected to the oxygen supply 3, and the two 
valves 10 and 12 are opened, so that the oxygen and gas can be supplied to 
the torch by way of the respective starting tanks and flow-pressure 
switches. Therefore, owing to the fact that the two regulating slide 
valves 54 and 16 are placed in series, both the gas cock 5 and the oxygen 
cocks 6 and 7 have to be opened in order to start up the system. If one or 
more of the cocks on the torch is closed, the flow through the respective 
flow-pressure switches will be inadequate, and the regulating slide valves 
54 and/or 16 will make the control line 14 pressureless, with the result 
that the two valves 10 and 12 are closed. If a leak has occurred and one 
or both starting tanks are pressureless, the operative must depress the 
control button 33 and/or 57 to bring the starting tanks under pressure 
again, in order to be able to start up the system. 
It will be clear that the invention is not restricted to the embodiments 
described and illustrated here, but that within the scope of the appended 
claims a large number of modifications can be made, depending on the 
specific use.