Plasma arc torch including means for disabling power source

A plasma arc torch includes a torch body defining a discharge axis, an electrode coaxially aligned on the discharge axis, a nozzle assembly positioned adjacent the discharge end of the electrode, and a heat shield removably secured on the torch body. A power supply delivers electrical current to the electrode to create an electrical arc, and a plasma gas is delivered so as to surround the arc. Also, a pressure sensing system is provided for sensing the pressure of the plasma gas and for disabling the power supply if there is insufficient gas pressure, such as when the heat shield is removed.

FIELD OF THE INVENTION 
The invention relates to a plasma arc torch, and more particularly to a 
plasma arc torch including means for disabling the power source if there 
is insufficient gas pressure to provide the required cooling and plasma 
gas flow through the torch. 
BACKGROUND OF THE INVENTION 
In a plasma arc torch, a high voltage is generated at an electrode to 
create an electrical arc extending from the electrode and through the bore 
of a nozzle assembly. A pressurized flow of gas is supplied between the 
electrode and the bore to form a plasma arc extending through the bore to 
a workpiece positioned beneath the torch. Over time, the electrode and the 
nozzle erode and thereafter do not produce satisfactory cuts. As a result, 
the electrode and the nozzle assembly must be replaced periodically. 
Typically, the electrode is mounted to the torch body and an outer heat 
shield is threaded on the torch body over the nozzle assembly. Thus, the 
operator must remove the heat shield to replace the electrode or the 
nozzle assembly. With the heat shield removed, it is still possible to 
create an electrical arc between the electrode and the workpiece (or any 
object having a lower potential than the electrode) if an electrical 
current is supplied to the electrode. 
A plasma arc torch which includes a mechanism for disabling the power 
source is disclosed in U.S. Pat. No. 5,216,221 issued Jun. 1, 1993 to 
Carkhuff and assigned to the present assignee. The torch includes an outer 
heat shield removably secured on the torch body over the nozzle assembly. 
The heat shield includes an electrically conductive member on its inner 
surface that completes an electrical interlock circuit when the nozzle 
assembly and the heat shield are secured on the torch body. When the heat 
shield or the nozzle assembly is removed, the electrical continuity 
circuit is opened and the power source is disabled. The torch disclosed in 
U.S. Pat. No. 5,216,221 includes a pair of contact members, a pair of 
insulating members, an electrically conductive insert on the outer heat 
shield and a retaining nut configured together to complete the electrical 
circuit. The number and the arrangement of the parts increases the 
complexity of the torch. 
U.S. Pat. No. 4,929,811 issued May 29, 1990 to Blankenship discloses a 
plasma arc torch including a fault detection circuit. A continuity 
interlock circuit indicates a loss of electrical contact when the outer 
heat shield or the nozzle assembly is not in the proper operating 
position. The fault detection circuit prevents the supply of electrical 
current to the electrode in response to an "open" indication from the 
continuity interlock circuit. The disabling mechanism disclosed in the 
patent to Blankenship, however, is also complex. 
U.S. Pat. No. 4,701,590 to Hatch and U.S. Pat. No. 4,580,032 to Carkhuff 
and assigned to the present assignee each disclose a plasma arc torch 
including spring-loaded means for disabling the electrode. In the patent 
to Hatch, the electrode is expelled from the torch body when the outer 
heat shield or the nozzle assembly is removed. In the patent to Carkhuff, 
a spring urges a nonconductive ball against a valve seat to prevent the 
flow of gas through the torch when the outer heat shield is removed. The 
supply of electrical current to the electrode is then prevented by an 
electrical circuit responsive to the flow of gas. 
Although the disabling mechanisms disclosed in the Hatch and Carkhuff 
patents are effective, moving parts are not preferred in a plasma arc 
torch. The moving parts add to the expense of assembling the torch and 
increase its complexity. The complexity of the torch further increases the 
likelihood that the torch will require additional maintenance during its 
service life. 
It is accordingly an object of the present invention to provide a plasma 
arc torch including a relatively non-complex and reliable mechanism for 
disabling the power source if there is insufficient gas pressure to 
provide the required cooling and plasma gas flow through the torch. 
It is another object of the invention to provide a mechanism for disabling 
the flow of electrical current to the torch that does not use moving 
parts. 
It is another, and more particular, objective of the invention to provide a 
mechanism for disabling the flow of electrical current to a plasma arc 
torch when the heat shield is removed and the electrode and other current 
carrying members of the torch are exposed. 
SUMMARY OF THE INVENTION 
The above and other objects and advantages of the present invention are 
achieved by the provision of a plasma arc torch which includes a torch 
body defining a discharge axis, an electrode mounted on the torch body 
along the discharge axis, a nozzle assembly positioned adjacent the 
discharge end of the electrode, and an outer heat shield assembly secured 
on the torch body. The torch also includes a power supply connected to the 
electrode so as to create an electrical arc extending from the electrode, 
and means for supplying a pressurized flow of gas about the electrical arc 
to thereby create a plasma flow. Also, a pressure sensing means is 
provided for sensing the gas pressure in the torch body and for disabling 
the flow of electrical current if the gas pressure falls below a 
predetermined level. 
In a preferred embodiment, the torch body includes a head portion defining 
the discharge axis and a handle portion extending outwardly from the head 
portion. The head portion includes a housing and an electrode holder 
disposed within the housing and extending along the discharge axis. The 
electrode holder defines a cavity coaxially aligned with the discharge 
axis for receiving the electrode. 
The handle portion of the torch body permits an operator to hold the torch 
to accomplish a cutting operation on a workpiece positioned beneath the 
torch. The handle portion includes a housing defining a cavity therein 
accommodating the conduit for supplying the pressurized flow of gas to the 
torch body and the electrical current to the electrode. The cavity further 
accommodates the means for sensing the gas pressure and for disabling the 
flow of electrical current to the torch. A control switch is provided on 
the handle to activate the torch. 
The electrode is mounted to the electrode holder such that the electrode 
may be readily removed for replacement. For example, the electrode may be 
held against the electrode holder by the nozzle assembly when the heat 
shield is secured on the torch body. Preferably, however, the electrode is 
externally threaded opposite its discharge end and engages internal 
threads provided on the electrode holder adjacent the cavity defined by 
the electrode holder. Thus, the electrode is readily removable and is in 
good electrical contact with the electrode holder. 
The nozzle assembly is positioned adjacent the electrode and includes a 
cup-shaped nozzle defining a cavity for receiving the discharge end of the 
electrode. The nozzle has a bore therethrough coaxially aligned with the 
discharge axis. The nozzle assembly may also include a swirl ring 
positioned between a flat on the underside of the electrode and the 
nozzle. 
The outer heat shield assembly includes a large, cup-shaped heat shield 
defining a cavity for receiving the nozzle assembly and the discharge end 
of the electrode. The heat shield is preferably internally threaded and 
engages external threads on the head portion such that the heat shield is 
removably secured on the torch body. A resilient O-ring is positioned 
between the head portion and the heat shield to protect the nozzle 
assembly and the electrode from external contaminants and to seal the gas 
pressure in the torch body when the heat shield is properly secured on the 
torch body. 
The conduit positioned within the handle portion of the torch body defines 
a gas passageway for the pressurized flow of gas. The conduit originates 
at the source of the pressurized gas and terminates in the head portion of 
the torch body at the electrode holder. Thus, the source of pressurized 
gas is in fluid communication with the cavity defined by the electrode 
holder. A power supply cable is centrally positioned within the conduit 
and extends between a source of electrical current and the electrode in 
the handle portion of the torch body. 
The detecting means includes a conduit positioned within the handle portion 
of the torch body and defining a gas passageway. The conduit originates in 
the head portion of the torch body at the electrode holder and terminates 
at a pressure switch. Thus, the cavity defined by the electrode holder is 
in fluid communication with the pressure switch. The pressure switch is 
electrically connected to the power source and is movable between an open 
position and a closed position in response to the gas pressure in the 
torch body. 
In operation, the electrode and the nozzle assembly are positioned on the 
torch body and the heat shield is secured on the torch body. To activate 
the torch and begin cutting, the operator depresses the control switch on 
the handle portion of the torch body. When the control switch is 
depressed, a low voltage circuit in the power source is closed. The 
circuit opens a solenoid valve so that the pressurized gas flows to the 
torch. The detecting means senses the gas pressure in the torch body. If 
the gas pressure is sufficient to provide the required cooling and plasma 
gas flow through the torch, the detecting means closes an electrical 
circuit that permits the power source to supply electrical current to the 
torch. 
In an alternative embodiment, the detecting means is positioned in the 
conduit that supplies the pressurized gas and electrical current to the 
torch. The detecting means of the alternative embodiment includes a 
venturi chamber and a conduit defining a gas passageway. The venturi 
chamber includes a throat having an opening extending radially outwardly 
therefrom and into the gas passageway of the detecting means. 
In operation, the pressurized gas flows through the gas passageway in the 
conduit to the torch body as previously described. If there is sufficient 
gas pressure in the torch body, a back pressure of pressurized gas will 
flow through the opening in the throat of the venturi chamber and into the 
gas passageway of the detecting means. Accordingly, the pressure switch 
will be closed and the power source will supply an electrical current to 
the electrode. 
If there is insufficient gas pressure in the torch body, such as when the 
heat shield is removed, the pressurized gas flows freely to the ambient 
atmosphere. As a result, the venturi chamber creates a vacuum at the 
opening in the throat that suctions any gas in the gas passageway of the 
detecting means into the gas passageway of the conduit. Accordingly, the 
pressure switch will be open and the power source will not supply an 
electrical current to the electrode. 
In another alternative embodiment, the detecting means is positioned within 
the handle portion adjacent the conduit such that the gas passageway of 
the detecting means is in fluid communication with the conduit. If there 
is sufficient gas pressure in the torch body, the pressure switch will be 
closed and the power source will supply an electrical current to the 
electrode. If there is insufficient gas pressure in the torch, such as 
when the heat shield is removed, the pressure switch will be open and the 
power source will not supply electrical current to the electrode. 
In another alternative embodiment, the torch includes circuit means for 
providing a pilot arc between the electrode and the nozzle, and before 
transferring the plasma arc to the workpiece. The gas passageway of the 
sensing means is electrically conductive and is in electrical contact with 
a conducting body secured to the inner surface of the housing of the torch 
body. An insulating body positioned between the electrode holder and the 
conducting body has a slot therein defining a gas passageway such that the 
gas passageway of the detecting means is in fluid communication with the 
cavity defined by the heat shield. If there is insufficient gas pressure 
in the torch body, such as when the heat shield is removed, the pressure 
switch will be open and the power source will not supply electrical 
current to the electrode. 
A particular feature of the invention is that the power source will not 
supply electrical current to the electrode when the heat shield is removed 
even if the head portion of the torch body is inadvertently held firmly 
against the workpiece or a flat surface. When the operator depresses the 
control switch and the pressurized flow of gas is supplied to the torch 
body as previously described, if the head portion is held firmly against 
the workpiece a back pressure of pressurized gas will not flow to the 
pressure switch of the detecting means. Instead, the pressurized gas will 
flow out a radially extending opening in the housing to the ambient 
atmosphere. Thus, the pressure switch will be open and the power source 
will be disabled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the accompanying drawings, FIGS. 1-3 illustrate a preferred 
embodiment of a plasma arc torch, indicated generally at 10, according to 
the invention. The torch 10 comprises a torch body 20, an electrode 40 
mounted within the torch body, a nozzle assembly 50 positioned adjacent 
the electrode and an outer heat shield assembly 60 secured on the torch 
body. The torch 10 further comprises gas supplying means 70 for supplying 
a pressurized flow of gas through the torch body 20 and electrical power 
to the electrode 40, and detecting means 80 for sensing the gas pressure 
in the torch body and for disabling the flow of electrical current to the 
electrode in accordance with the present invention. 
As best shown in FIGS. 2 and 3, the torch body 20 comprises a generally 
cylindrical head portion 21 defining a discharge axis and a handle portion 
31 extending outwardly from the head portion. Torch body 20 is typically 
made of a hard, heat-resistant material such as thermoset plastic or epoxy 
compound which protects the components of the torch from the high heat 
generated during plasma arc cutting. 
Head portion 21 comprises a housing 22 and an electrode holder 23 disposed 
within the housing and extending along the discharge axis. Electrode 
holder 23 defines an internal bore 24 therein which is coaxially aligned 
with the discharge axis. Electrode holder 23 is made of an electrically 
conductive material, preferably copper or copper alloy, such that the 
holder conducts an electrical current to electrode 40. Electrode holder 23 
has at least one radially extending hole 25 therethrough such that the 
bore 24 is in fluid communication with a gas passageway 26 defined by the 
inner surface of the lower portion 27 of housing 22 and the outer surface 
of the lower portion 29 of electrode holder 23. Housing 22 likewise has at 
least one radially extending opening 28 therethrough such that passageway 
26 is in fluid communication with the ambient atmosphere when outer heat 
shield assembly 60 is removed as shown in FIG. 3. 
Handle portion 31 permits an operator to grasp the torch 10 to perform a 
cutting operation. Handle portion 31 is generally cylindrical and 
comprises a hollow housing 32 defining a cavity 34 therein for 
accommodating the gas supplying means 70 and the detecting means 80. 
Handle portion 31 further comprises a control switch 35 for activating the 
torch 10, in the manner further described below. 
Electrode 40 is coaxially aligned with the discharge axis adjacent the 
lower portion 29 of electrode holder 23. Electrode 40 may be mounted to 
electrode holder 23 in any manner that permits the electrode to be readily 
removed for replacement. For example, electrode 40 may be press fit into 
electrode holder 23 or may be held against the lower transverse surface of 
the electrode holder by nozzle assembly 50 when heat shield assembly 60 is 
secured on torch body 20. Preferably, however, electrode 40 comprises an 
externally threaded portion 41 opposite the discharge end 42 thereof, and 
as shown most clearly in FIG. 3. Threaded portion 41 engages internal 
threads provided on the lower portion 29 of electrode holder 23 to 
removably secure the electrode 40 on the torch body 20 and to thereby 
ensure that the electrode is in good electrical contact with the electrode 
holder. 
The discharge end 42 of electrode 40 may comprise an emissive insert (not 
shown) which acts as the cathode terminal for an electrical arc extending 
from the discharge end of the electrode in the direction of the nozzle 
assembly 50. An electrode comprising an emissive insert is disclosed in 
U.S. Pat. No. 5,023,425 to Severance, Jr., and assigned to the assignee of 
the present invention. The emissive insert is composed of a material which 
has a relatively low work function, defined in the art as the potential 
step, measured in electron volts, that permits thermionic emission from 
the surface of a metal at a given temperature. In view of its low work 
function, the insert readily emits electrons in the presence of an 
electrical potential. Commonly used insert materials include hafnium, 
zirconium, tungsten, and alloys thereof. 
Nozzle assembly 50 is positioned adjacent electrode 40 and comprises a 
cup-shaped nozzle 52 defining a cavity 54 between the outer surface of the 
electrode and the inner surface of the nozzle. Nozzle 52 has a bore 55 
therethrough opposite the discharge end 42 of the electrode 40 and 
coaxially aligned with the discharge axis. Nozzle assembly 50 preferably 
further comprises a swirl ring 56 positioned between a transverse annular 
flat 47 (FIG. 3) provided on electrode 40 and a transverse annular flat 57 
(FIG. 2) provided on nozzle 52. Swirl ring 56 is preferably made of an 
electrical and thermal insulating material, such as ceramic, and has at 
least one radially extending hole 58 therethrough such that cavity 54 is 
in fluid communication with gas passageway 26. 
Outer heat shield assembly 60 comprises a large, cup-shaped heat shield 62 
defining a cavity 64 therein. The inner surface of the upper portion 65 of 
heat shield 62 and the outer surface of the lower portion 27 of housing 22 
are threaded such that the heat shield is removably secured on torch body 
20. A resilient O-ring 66 (FIG. 3) is positioned between housing 22 and 
heat shield 62 to protect electrode 40 and nozzle assembly 50 from 
external contaminants and to seal the torch body 20 when the heat shield 
is properly secured on the torch body. Heat shield 62 has an opening 68 
therethrough adjacent nozzle 52 and coaxially aligned with the discharge 
axis. Heat shield 62 engages a shoulder 59 provided on nozzle 52 to hold 
nozzle assembly 50 against flat 47 on electrode 40 when the heat shield is 
secured on torch body 20. Heat shield 62 further has at least one slot 69 
in the periphery of the opening 68 and adjacent the shoulder 59 of the 
nozzle 52, such that the cavity 64 is in fluid communication with the 
ambient atmosphere via the opening 68. 
Gas supplying means 70 comprises a hollow conduit 72 defining a gas 
passageway 74 and positioned within handle portion 31 of torch body 20. 
Conduit 72 originates at the source of pressurized gas (not shown) and 
terminates in head portion 21 of torch body 20 at electrode holder 23 such 
that the source of pressurized gas is in fluid communication with the 
internal bore 24. Gas supplying means 70 further comprises a power supply 
cable 76 centrally positioned within and electrically connected to the 
conduit 72 and the power source (not shown), such that the power source is 
electrically connected to the electrode 40. 
Detecting means 80 comprises a hollow conduit 82 defining a gas passageway 
84 and positioned within handle portion 31 of torch body 20. Conduit 82 
originates in head portion 21 of torch body 20 at electrode holder 23 and 
terminates at a pressure switch 86 such that the pressure switch is in 
fluid communication with the bore 24. Pressure switch 86 is movable 
between an open position and a closed position in response to the gas 
pressure in passageway 84 for a purpose to be described hereafter. 
In operation, outer heat shield assembly 60 is secured on torch body 20 as 
illustrated in FIG. 2. When the operator depresses the control switch 35, 
a low voltage electrical circuit in the power source is closed. The 
electrical circuit opens a solenoid positioned in the power source such 
that means 70 supplies a pressurized flow of gas through passageway 74 in 
conduit 72 to the bore 24 in head portion 21. 
As indicated by the arrows, the pressurized gas flows out of the bore 24 
through hole 25 in electrode holder 23 and into gas passageway 26. From 
passageway 26, the pressurized gas flows into cavity 64 in heat shield 62. 
A portion of the pressurized gas is forced through the hole 58 in the 
swirl ring 56 such that the gas swirls around electrode 40 in cavity 54 
and exits through bore 55 of nozzle 52 in the direction of a workpiece 
(not shown). The balance of the pressurized gas flows out of cavity 64 
through the slot 69 and opening 68 to the ambient atmosphere. 
The pressurized gas may be any gas capable of forming a plasma flow, but 
preferably is air, oxygen, or argon mixed with nitrogen. At its source, 
the pressure of the gas is typically about 65 psi. When heat shield 
assembly 60 is secured on torch body 20, detecting means 80 senses the gas 
pressure in the torch body. With the heat shield assembly 60 secured to 
the torch body 20, the pressure of the gas inside the torch body is 
typically about 25 psi. If means 80 senses sufficient gas pressure in the 
torch body 20 to provide cooling and the required gas flow for a 
predetermined time, typically about five seconds, the detecting means 
closes, or causes to be closed, an electrical circuit to permit the power 
source to supply electrical current to the torch 10. 
As long as there is there is sufficient gas pressure in torch body 20, and 
in particular, as long as heat shield 62 is secured on housing 22, a back 
pressure of pressurized gas will be sensed at pressure switch 86 via 
conduit 82. Thus, pressure switch 86 will be closed as shown in FIG. 2 and 
an electrical control circuit will be established between the pressure 
switch 86 and the power source. Accordingly, the power source will supply 
electrical current to electrode 40. 
If, however, there is insufficient gas pressure in the torch body 20, such 
as when the heat shield 62 is removed, the pressurized gas will flow 
through the torch body in the manner illustrated in FIG. 3. The 
pressurized gas exiting the bore 24 through hole 25 will flow into gas 
passageway 26 as described previously. From passageway 26, however, the 
pressurized gas will flow out opening 28 to the ambient atmosphere. As a 
result, a back pressure of pressurized gas will not be sensed at pressure 
switch 86 via conduit 82. Thus, pressure switch 86 will be open and the 
power source will not supply an electrical current to the electrode 40. 
In an alternative embodiment of the torch illustrated in FIGS. 4-6, 
detecting means 90 is positioned between the source of pressurized gas and 
conduit 72 of supplying means 70. Detecting means 90 comprises a venturi 
chamber 91 and a conduit 92 defining a gas passageway 94. Chamber 91 
comprises a throat 93 having an opening 95 extending outwardly therefrom 
and into conduit 92. Passageway 94 extends between opening 95 of chamber 
91 and a pressure switch 96 such that the pressure switch is in fluid 
communication with throat 93. 
In operation, pressurized gas flows through passageway 74 in conduit 72 as 
previously described. If the heat shield 62 is in place, a restricted flow 
through the body 20 takes place as illustrated schematically in FIG. 5, 
and a back pressure of pressurized gas will be sensed at pressure switch 
96 via passageway 94 and opening 95. Accordingly, pressure switch 96 will 
be closed and the power source will supply an electrical current to the 
electrode 40. 
If, however, there is insufficient gas pressure in torch body 20, such as 
when heat shield 62 is removed, and as illustrated schematically in FIG. 
6, the pressurized gas will flow freely through torch body 20 to the 
ambient atmosphere in the manner previously described and illustrated in 
FIG. 3. As a result, the venturi chamber 91 will suction the gas in 
passageway 94 into passageway 74 in conduit 72. Accordingly, pressure 
switch 96 will not sense sufficient back pressure and will be open. Thus, 
the power source will not supply an electrical current to the electrode 
40. 
In another alternative embodiment of the torch 10, illustrated in FIG. 7, 
detecting means 80 is positioned within handle portion 31 adjacent 
supplying means 70. Thus, gas passageway 84 in conduit 82 is in fluid 
communication with gas passageway 74 in conduit 72. Accordingly, as long 
as there is sufficient gas pressure in torch body 20, pressure switch 86 
will be closed and the power source will supply an electrical current to 
the electrode 40. If heat shield 62 is removed, however, pressure switch 
86 will be open and an electrical current will not be supplied to 
electrode 40. 
In another alternative embodiment of the torch 10, illustrated in FIG. 8, 
the torch includes a pilot arc circuit for creating a pilot arc extending 
outwardly along the discharge axis in the direction of the workpiece. The 
torch 10 is provided with gas supplying means 70 and detecting means 80 as 
previously described. The conduit 82 of the detecting means 80, however, 
is conductive and is in electrical contact with a conducting body 85 
secured to the inner surface of housing 22 of torch body 20. A conducting 
insert 65 secured to the inner surface of the heat shield 62 and in 
electrical contact with the conducting body 85 completes an electrical 
circuit between the conductive conduit 82 and the nozzle 52. 
An insulating body 87 positioned between the electrode holder 23 and the 
conducting body 85 has a slot 88 therein defining a gas passageway 89. 
Thus, the conduit 82 is in fluid communication with the cavity 64 defined 
by the heat shield 62. Accordingly, if there is sufficient gas pressure in 
torch body 20, pressure switch 86 will be closed and the power source will 
supply an electrical current to the electrode 40. If there is insufficient 
gas pressure, such as when heat shield 62 is removed, pressure switch 86 
will be open and an electrical current will not be supplied to the 
electrode 40. 
As illustrated in FIG. 10, a particular feature of the invention prevents 
the power source from supplying electrical current to the electrode 40 
when the heat shield 62 is removed even if the head portion 21 of the 
torch body 20 is inadvertently held firmly against the workpiece or a flat 
surface. When the operator depresses the control switch 35, a pressurized 
flow of gas is supplied to the torch body 20 as previously described. 
Although the housing 22 of head portion 21 is held firmly against the 
workpiece or flat surface, a back pressure of pressurized gas will not 
flow to pressure switch 86 through gas passageway 84. Instead, the 
pressurized gas will flow out the radially extending opening 28 in housing 
22 to the ambient atmosphere. Accordingly, pressure switch 86 will be open 
and the power source will not be supply an electrical current to the 
electrode 40. 
While the embodiments illustrated above show a plasma arc torch that 
utilizes a single gas source, the present invention is equally applicable 
to a plasma arc torch that utilizes more than one gas source. For example, 
and as illustrated in FIG. 9, the invention may be applied to a plasma arc 
torch including a first gas source 70 for supplying the plasma gas to the 
internal bore 24 of the electrode holder and a second gas source, i.e. 
conduit 82, for supplying a shielding and cooling gas to the slot 89 and 
thus the cavity 64, under a regulated pressure. In such an embodiment, the 
torch may include an additional conduit 82a which also communicates with 
the slot 89 for sensing the pressure in the cavity 64 and operating a 
pressure switch in the manner described above. 
From the above disclosure, it will be seen that the present invention is 
able to safely and reliably disable the power source to prevent the flow 
of electrical current to the electrode 40 whenever there is insufficient 
gas pressure in torch body 20, such as when the heat shield 62 is removed. 
Obviously, many alternative embodiments of the invention are within the 
ordinary skill of those skilled in the art. Therefore, it is not intended 
that the invention be limited to the preceding description of illustrative 
preferred embodiments, but rather that all embodiments within the spirit 
and scope of the invention disclosed and claimed herein be included.