U.S. patent number 3,881,375 [Application Number 05/314,285] was granted by the patent office on 1975-05-06 for pipe tong positioning system.
This patent grant is currently assigned to Borg-Warner Corporation. Invention is credited to Robert R. Kelly.
United States Patent |
3,881,375 |
Kelly |
May 6, 1975 |
Pipe tong positioning system
Abstract
The combination of a power driven pipe tong and a backup tong is
supported upon a hoist mechanism to be positioned vertically with
respect to the tool joints of a string of drill pipe. A magnetic
eddy current detector is disposed adjacent to the drill pipe and
produces a command signal to control the hoist mechanism and stop
motion when the tong assembly is in a position at which the tool
joint engaging jaws of the power tong and the backup tong are
properly engageable with the tool joints.
Inventors: |
Kelly; Robert R. (Hoffman
Estates, IL) |
Assignee: |
Borg-Warner Corporation
(Chicago, IL)
|
Family
ID: |
23219348 |
Appl.
No.: |
05/314,285 |
Filed: |
December 12, 1972 |
Current U.S.
Class: |
81/57.35; 166/66;
324/221 |
Current CPC
Class: |
E21B
19/165 (20130101); E21B 3/00 (20130101) |
Current International
Class: |
E21B
19/16 (20060101); E21B 3/00 (20060101); E21B
19/00 (20060101); B25b 013/50 () |
Field of
Search: |
;81/57.15-57.21,57.33-57.35 ;324/37 ;91/361,363R
;166/65R,65M,66,77.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Al Lawrence
Assistant Examiner: Ramsey; K. J.
Attorney, Agent or Firm: Burgess; Aubrey L.
Claims
What is claimed is:
1. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means has a sensing head provided with
spacing means for predetermining the space between said sensing
head and said joint portions.
2. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means has a sensing head provided with
spacing means for predetermining the space between said sensing
head and said joint portions, said spacing means comprising
vertically and laterally spaced joint portion engaging elements
adapted to bridge the anomoly at said joint portions.
3. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means includes a sensing head having a coil
assembly, means supporting said sensing head for movement towards
said joint portions, biasing means for urging said sensing head
towards said joint portions, and means for positioning said coil
assembly in spaced relation to said joint portions.
4. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means includes a sensing head having a coil
assembly, means supporting said sensing head for movement towards
said joint portions, biasing means for urging said sensing head
towards said joint portions, and means for positioning said coil
assembly in spaced relation to said joint portions including spacer
means carried by said sensing head and engageable with said joint
portions.
5. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means includes a sensing head having a coil
assembly, means supporting said sensing head for movement towards
said joint portions, biasing means for urging said sensing head
towards said joint portions, and means for positioning said coil
assembly in spaced relation to said joint portions including spacer
means carried by said sensing head and engageable with said joint
portions at vertically and laterally spaced locations.
6. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means includes a sensing head having a coil
assembly, means supporting said sensing head for movement towards
said joint portions, biasing means for urging said sensing head
towards said joint portions, and means for positioning said coil
assembly in spaced relation to said joint portions including means
adjustably supporting said head on said detector means.
7. In combination, pipe tong means engageable with the threadedly
engaged joint portions of a tool joint of well pipe extending
vertically into a well bore for making up and breaking out said
tool joint portions, power actuated hoist means associated with
said pipe tong means for vertically moving said pipe tong means
along the well pipe between a first inoperative position in which
said pipe tong means is below the tool joint and a second
inoperative position in which said pipe tong means is above the
tool joint, control means associated with said hoist means for
controlling the movements of said pipe tong means between said
positions, said control means including magnetic eddy current
responsive detector means carried by said pipe tong means and
sensitive to the tool joint for operating said control means to
stop said hoist means when said pipe tong means moves into
operative position adjacent to the tool joint in which position
said pipe tong means is engageable with the joint portions, and
wherein said detector means includes a sensing head having a coil
assembly, means supporting said sensing head for movement towards
said joint portions, biasing means for urging said sensing head
towards said joint portions, and means for positioning said coil
assembly in spaced relation to said joint portions including means
adjustably supporting said head on said detector means, and spacer
means carried by said sensing head and engageable with said joint
portions.
8. The combination of claim 1, wherein said hoist means includes
actuator means, means for supplying motive power to said actuator
means, and said control means including manually operable means for
controlling the application of motive power to said actuator
means.
9. The combination of claim 1, wherein said hoist means includes a
fluid pressure operated actuator for raising said tong means, said
control means including valve means shiftable between selected
positions for controlling the application of pressure fluid to and
the exhaust of pressure fluid from said actuator, and means
responsive to said detector means for shifting said valve means to
the position for the application of pressure fluid to said
actuator.
10. The combination of claim 1, wherein said hoist means includes a
fluid pressure operated actuator for raising said tong means, said
control means including valve means shiftable between selected
positions for controlling the application of pressure fluid to and
the exhaust of pressure fluid from said actuator, and means
responsive to said detector means for shifting said valve means to
the position for the application of pressure fluid to said
actuator, and also including means responsive to said detector
means for shifting said valve means to the position for the exhaust
of pressure fluid from said actuator.
11. The combination of claim 1, wherein said hoist means includes a
fluid pressure operated actuator for raising said tong means, said
control means including valve means shiftable between selected
positions for controlling the application of pressure fluid to and
the exhaust of pressure fluid from said actuator, and means
responsive to said detector means for shifting said valve means to
the position for the application of pressure fluid to said
actuator, and also including means responsive to said detector
means for shifting said valve means to the position for and the
exhaust of pressure fluid from said actuator, and manual means for
effecting movement of said valve means to said positions.
12. The combination of claim 1, wherein said hoist means includes a
fluid pressure operated actuator for raising said tong means, said
control means including valve means shiftable between selected
positions for controlling the application of pressure fluid to and
the exhaust of pressure fluid form said actuator, and means
responsive to said detector means for shifting said valve means to
the position for the application of pressure fluid to said
actuator, and also including means responsive to said detector
means for shifting said valve means to the position for and the
exhaust of pressure fluid from said actuator, and manual means for
effecting movement of said valve means to said positions, said
manual means being incorporated in said means responsive to said
detector means.
13. The combination of claim 1, wherein said hoist means includes a
fluid pressure operated actuator for raising said tong means, said
control means including valve means shiftable between selected
positions for controlling the application of pressure fluid to and
the exhaust of pressure fluid from said actuator, and means
responsive to said detector means for shifting said valve means to
the position for the application of pressure fluid to said
actuator, and also including means responsive to said detector
means for shifting said valve means to the position for and the
exhaust of pressure fluid from said actuator, and manual means for
effecting movement of said valve means to said positions, said
manual means including pilot valve means for positioning the first
mentioned valve means.
Description
BACKGROUND OF THE INVENTION
In the drilling of well bores, such as oil and gas wells, into the
earth, and in other operations involving the completion, treatment
or production of wells, a length of pipe is periodically round
tripped. The drill string or string of pipe consists of stands
which are made up of lengths of pipe, and the stands are
successively made up or broken out of the string as the string is
being run into and being removed from the well. During the drilling
of the well, the well drilling pipe string is periodically round
tripped for changing the bit at frequent intervals involving
substantial labor and expense, and in order to facilitate the
making up and breaking out of the so called tool joints between
pipe stands, power tong apparatus has been developed comprising a
power driven pipe gripping tong mechanism which is utilized in
combination with a stationary backup pipe gripping tong mechanism
engageable with the tool joint sections which are relatively
rotatable to make up and break out the joints.
An example of such a combined power driven and backup tong is shown
and described generally in the pending application for letters
patent filed in the name of C. D. Barron, et al, Ser. No. 216,216,
filed Jan. 7, 1962, for Power Tong Positioning Apparatus, now U.S.
Pat. No. 3,780,815, issued Dec. 25, 1973, and assigned to the
parent corporation of the wholly owned subsidiary corporation to
which the present application is assigned, wherein the combined
tong assembly is supported by a hoist mechanism so as to be
positioned with respect to a string of drill pipe or the like, at a
location at which the power operated pipe gripping mechanism and
the backup pipe gripping mechanism are properly engageable with the
tool joint sections.
In the manual control of such pipe tong positioning devices it is
necessary that an operator visually correlate the tool joint with
respect to the tong assembly as the latter is raised or lowered and
be able to precisely position the tong assembly. However, it
frequently occurs that the drilling and other well treating or
producing activities are conducted during the night or during other
periods when visibility is poor. Moreover, in the case of an
automated drilling system it would be necessary that the tong
assembly be properly positioned with respect to the tool joint in a
pipe string in an automatic and accurate manner.
SUMMARY OF THE INVENTION
The present invention involves utilizing sensing means carried by
or adjacent to the combined power driven and backup tongs of a
vertically movable tong assembly, the sensing means being operable
to provide a control signal whereby vertical movement of the tong
combination is arrested at a location at which the power driven
tong and the backup tong are properly positioned for engagement of
the tool joint engaging tong jaws with the tool joint parts of the
pipe joint.
More particularly, the present invention involves the utilization
of a magnetic eddy current responsive sensing unit which is adapted
to provide a control signal whereby the hoist mechanism for a
combined power driven tong and backup tong is controlled to
properly position the tongs with respect to the tool joint
parts.
In a specific sense, in accomplishing the foregoing, a magnetic
eddy current sensing means is carried by the combined power driven
and backup tong assembly and includes a probe supported in close
proximity to the pipe, whereby when the interface between a pair of
tool joint parts is detected due to the discontinuity, a control
signal is supplied to de-energize the hoist operating means so that
the tongs will be properly positioned with respect to the tool
joints.
The joint detector is biased to a position with respect to the pipe
so that the sensing head is adapted to be uniformally closely
positioned relative to the tool joint over a range of tool joint
diameters to compensate for worn, under-sized joints.
The tool joint detecting means may be combined with a set of power
driven and backup tongs which are supported, by way of example, by
the hoist mechanism of the aforementioned application for letters
patent, Ser. No. 216,216, or by other hoist mechanism which is
adapted to be controlled in response to the control signal
transmitted thereto by the sensing means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary view in side elevation with parts of the
tong assembly broken away to disclose a tool joint therein;
FIG. 2 is an enlarged fragmentary detail view illustrating a
typical drill pipe tool joint, portions of the tongs being shown in
broken lines;
FIG. 3 is an enlarged horizontal section between the power tong and
backup tong of FIG. 1, as taken on the plane of the line 3--3 of
FIG. 1 and illustrating the disposition of the sensing means;
FIG. 4 is an enlarged fragmentary view in vertical section, as
taken on the line 4--4 of FIG. 3;
FIG. 5 is an elevation of the end of the sensing means, as taken on
the line 5--5 of FIG. 4;
FIG. 6 is a transverse section as taken on the line 6--6 of FIG. 4
and on a slightly enlarged scale;
FIG. 7 is a fragmentary detailed view in section as taken on the
line 7--7 of FIG. 4 and on an enlarged scale; and
FIG. 8 is a schematic diagram showing the sensing means and the
hoist controlling means.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown hoisting apparatus for
positioning a tong assembly T vertically with respect to a string
of well pipe, such as well drilling pipe P having a joint J which
interconnects the pipe stands. The hoist apparatus includes a
vertically disposed column 10 formed, in the illustrative
embodiment, of an I-beam having a lower or base support 14, and an
upper brace or support 12 is connected to the top of the column 10.
Upper bearing means 16 and lower bearings means 18 provide a
pivotal connection for the beam so that it can be rotated on a
vertical axis and to enable the tong assembly T to be swung to and
from a position aligned with the well bore.
A generally hollow and elongated rectangular support collar 20 is
slideably disposed about the column 10 and is adapted to be moved
upwardly and downwardly on the column 10. The collar 20 is
supported for vertical movement on the column 10 by roller
assemblies 22 incorporated within the collar 20. As shown, a
plurality of flanged rollers 23 are included in each roller
assembly 22 and are engageable with the inner faces of the flanges
of the I-beam column 10 to maintain the collar 20 against cocking
on the column.
A tong supporting yoke structure 24 is mounted on the collar 20 and
projects horizontally therefrom, the yoke structure 24 supporting
the pipe tong assembly T. This tong assembly, as is cutomary,
includes a backup tong 26 and a power driven tong 30 interconnected
together and mounted within a cradle assembly 32. An example of a
power tong assembly T of the type generally disclosed herein is
more particularly shown and described in the application for U.S.
letters patent Ser. No. 134,552, filed Apr. 16, 1972, in the name
of Carl A. Wilms, and assigned to the parent corporation of the
wholly owned subsidiary corporation to which the present
application is assigned. In such an assembly, the backup tong 26 is
adapted to hold one section of a joint J in the pipe P against
rotation while the power driven tong 30 engages the other joint
section and rotates the same in a selected direction depending upon
whether the joint is being made up or broken out.
Disposed adjacent to and extending vertically along side the column
10 is a power source 34 shown in the form of a hydraulic piston and
cylinder actuator unit. The power source 34 is pivotally mounted at
its lower end to the lower support 14 and has at its upper end a
roller or sprocket 38 over which one or more roller chains 36
extend, the chains 36 being anchored at their lower ends to the
lower support 14 and extending upwardly over the sprocket 38 to
provide a downwardly extending run which is connected to the yoke
structure 24. The arrangement of the hoist chain and piston
cylinder unit is such that the movement of the tong assembly T is
twice the movement of the power source so that the tong can be
moved over a large vertical span without necessitating an equally
long actuator.
In the use of the tong hoist when running the pipe string P, the
tong is lowered to a location affording clearance for the pipe
supporting elevator until the pipe in the well bore is supported by
the usual slip mechanism and the elevator is released. A next stand
of pipe is then stabbed into the upper end of the pipe string and
the tong assembly T is elevated to a location at which the
respective tongs are engageable with the tool joints. When
retrieving or pulling the pipe string, the tong assembly T is also
lowered to enable the elevator to be latched on or lowered onto the
pipe string supported in the slips, and when successive joints are
raised the tong assembly T is elevated by its hoist to enable the
tongs to engage the tool joints, as more specifically described
below.
The present invention is addressed to the problem of positioning
the tong assembly T with respect to the pipe P so that the pipe
gripping mechanism or jaws within the respective backup tong and
power tong 26 and 30, as shown in broken lines in FIG. 2 and
designated 26a and 30a, are adapted to engage the respective joint
sections 26b and 30b of the pipe joint J, not only when the pipe
string P is being pulled from the well, but also when the pipe
string is being run back into the well. During the removal of the
pipe string from the well, the tool joints in the pipe string must
be broken out, and during running of the pipe string the joints in
the pipe string must be made up. During the running in and
retrieving of the pipe string from the well, it is, as pointed out
above, hoisted or lowered in an elevator adapted to be hoisted by
the usual drilling rig draw works, and the pipe string in the well
is supported in the usual slip mechanism, while a length or stand
of pipe is being broken out of or being made up in the pipe string.
During the period that the pipe string is not supported in the
slips but is being moved by the elevator, the tong assembly T is
normally lowered to an out-of-the-way location, but when the pipe
string is supported in the slips the tong assembly T must be
elevated to a position at which the pipe gripping jaws 26a and 30a
are adapted to engage the tool joint sections 26b and 30b. Proper
positioning of the tong assembly T with respect to the pipe P is
difficult, at best, but the difficulty is increased when visibility
is poor such as at night or during inclement weather.
Accordingly, the present invention involves the utilization of pipe
joint detecting means M located between the backup tong 26 and
power tong 30 so as to scan the pipe as the tong assembly T is
being elevated and detect a joint so as to cause the hoist
mechanism to be de-energized when the tong assembly T is at its
proper location.
As seen in FIG. 7 the joint detector means M is a magnetic eddy
current detector device, such as the model ED-400 "MAGNATEST"
instrument of Magnaflex Corporation, referred to above,
incorporated in an assembly whereby the device is adapted to
closely follow the pipe joint sections.
More particularly, the instrument M includes an elongated hollow
case 100 suitably mounted on the backup tong assembly 26 as by
releasable clamps or brackets 101, so that the overall disposition
of the case 100 on the tong 26 can be adjusted radially with
respect to the pipe opening 102 through the tong assembly. Other
modes of supporting the case 100 may be employed, including, if
desired, means for retracting the case when the sensor is not in
use and moving the case to an opperative position.
Within the outer case or body 100 of the instrument M is an inner
elongated body 103 having a cylindrical outer surface 104 on which
is longitudinally and slidably disposed a sleeve 105. Interposed
between opposed shoulders 106 and 107 on the inner body 103 and the
sleeve 105, respectively, is a coiled compression spring 108 which
normally biases the sleeve 105 outwardly with respect to the case
100. The sleeve 105 is maintained in a predetermined orientation
within the case 100 by means of a suitable fixed pin 109 and pin
receiving elongated slot 110 in the sleeve 105. Suitably affixed to
the outer end of the sleeve 105 is a sensing head 111, this head
111 rotatably supporting a pair of vertically and laterally spaced
rollers 112 and 113 on axles 114, whereby the proximity of the head
111 to the pipe P and more particularly to the joint sections 26b
and 30b is pre-determined, the spring 106 maintaining a bias on the
sleeve 105 which causes the sleeve to be projected longitudinally
from the case 100 to an extent limited by the length of the slot
110. The length of the slot 110 may be such that the outward
extension of the sleeve 105 with respect to the case 100 is so
limited that the rollers 112 and 113 may not contact the reduced
diameter or mid-section of the pipe P, but in any event the
enlarged diameter coupling portions or tool joints 26b and 30b are
engageably by the rollers 112 and 113, notwithstanding variations
in the diameter of the tool joints which may be caused by wear.
Carried by the head 111 and extending telescopically into a bore
115 within the inner body 103 is a tubular support 116 which is
adjustably threaded at 117 into the head 111 and contains a coil
assembly 118 encapsulated within insulating body 119 and including
coils C1 and C2 connected by conductors 120 and 121 respectively to
the current inducing and detecting system hereinafter to be
described, whereby the anomaly at the upper end shoulder 122a of
the lower tool joint box 122 which is engageable with the anomaly
at the downwardly facing shoulder 124a on the pin end 124 of the
upper pipe section causes a variation in the eddy current in the
tool joint, whereby to establish a signal for interrupting
operation of the hoist power means 34 when the tong assembly T is
in the proper relationship to the tool joint as shown in FIG. 4, at
which position, as seen in FIG. 2, the jaws 26a and 30a of the
backup tong and power tong 26 and 30 respectively are engageable
with the tool joints 26b and 30b.
The coils C1 and C2 are in circuit with the control means, as
typical of the ED-400 "MAGNATEST" instrument referred to above.
Referring to FIG. 8 it will be noted that the coils C1 and C2 are
connected to a bridge circuit 130 containing the usual fixed and
variable balancing resistances and connected to a power source 131.
The output signal from the bridge circuit 130 is supplied to a
tuned pre-amplifier 132, the output of which is supplied to an
amplifier 133 which is adjustable by sensitivity control
potentiometer means 134. The output from the amplifier 133 drives a
demodulator 135 to produce an output signal which is supplied to a
meter 136. In addition, the undemodulated signal from the amplifier
133 is supplied to a threshold switch 137 containing a silicon
rectifier which is adapted to be triggered when the undemodulated
signal is at a pre-determined level as, determined by a threshold
switch adjustor potentiometer 138. When the threshold switch 137 is
triggered, a relay 139 is energized to control operation of the
hoist power source 34, and if is desired, a glow tube 140 may be in
circuit with the relay 139 to indicate that it has been
energized.
As also seen in FIG. 8, the hoist means 34 is adapted to be
elevated by hydraulic fluid pressure supplied to a cylinder 34a
beneath the piston 34b, under the control of a combined manual and
automatically operated valving system. The valving system includes
a pilot operated main valve MV which is, for illustrative purposes,
normally spring loaded to a position at which fluid pressure
supplied from a supply conduit 141 is shut off from the actuator
cylinder 34a and flows to tank at 142. At the same time pilot fluid
pressure is exhausted to tank at 143 through a normally closed
throttle valve TV via the pilot conduits 144 and 145, as shown in
broken lines, and pilot pressure from a source conduit 146 is shut
off at the valve TV.
When it is desired to exhaust pressure fluid from the actuator
cylinder 34a the valve TV is shifted left, as seen in FIG. 8 to
establish communication between the pilot pressure source 146 and
the pilot conduit 144 so as to shift the main valve MV to the left
as viewed in FIG. 8, whereby fluid pressure from the source 141 is
supplied via a conduit 147 to a normally closed pilot valve 148 to
open the latter and allow fluid to exhaust from the actuator
cylinder 34a through the conduit 149 and thence to the tank at 142
through the main valve MV. When it is desired to elevate the tong
assembly T by applying fluid under pressure to the actuator
cylinder 34a, the throttle valve TV is shifted to the right,
thereby applying pilot fluid pressure to the main valve and thereby
shift it to the right to establish communication between the source
conduit 141 and the conduit 149 leading to a back flow preventing
valve 149a by-passing the pilot valve 148, which will effect
elevation of the tong assembly T and hold it in the elevated
position.
The main valve MV is also shiftable between its two positions from
its center position by solenoid actuators under the control of a
switching circuit generally denoted at 150 and including a down
switching mechanism 151 and up switching mechanism 152. The down
switching mechanism includes a down relay 153 which is adapted to
be energized by a manual switch 154 so as to be latched in the
energized condition by a holding switch 153h, so that contacts 155
are maintained to energize the solenoid 155a and move the main
valve MV to the left as seen in FIG. 8. Correspondingly, the up
switching mechanism 152 includes an up relay 156 adapted to be
energized by a manual switch 157 which closes holding contacts 158
to maintain contacts 159 closed and energize the solenoid 159a of
the main valve MV. Each of the down and up switching mechanisms 151
and 152 also includes a manual switch 155b and 159b, respectively
adapted to manually energize the respective solenoids 155a and 159a
in an overriding manner. Interposed in the circuit with the down
and up relays 153 and 156 are respective switches 153a and 156a
which may be suitably actuated to an open position to limit upward
and downward motion of the tong assembly beyond a fixed range when
the system is being controlled by the eddy current detector means
M. Now it will be apparent that energization of the up and down
switching circuitry 151 and 152 requires that the contacts 139a of
the control relay 139 be closed to complete the circuit between a
source conductor 139b and one side of the respective relays 153 and
156. If desired, the detector operated relay 139 or some other
signal responsive means which is energized when the joint J is
properly positioned in the tong assembly T, may be operated to
effect actuation of the tongs 26 and 30.
* * * * *