U.S. patent number 3,770,006 [Application Number 05/277,220] was granted by the patent office on 1973-11-06 for logging-while-drilling tool.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Wilton Gravley, Bobbie J. Patton, James H. Sexton, Vasel R. Slover, Jr..
United States Patent |
3,770,006 |
Sexton , et al. |
November 6, 1973 |
LOGGING-WHILE-DRILLING TOOL
Abstract
A logging-while-drilling tool which is adapted to be positioned
within the drill string of a well drilling apparatus. The tool has
a turbinelike, signal-generating valve which opens and closes at a
defined rate to generate a pressure wave signal in the drilling
fluid which is representative of a measured downhole condition. The
tool includes spring means to normally bias the rotor away from the
stator of the valve. The force constant of the spring means is
greater than the pressure drop across the rotor at low flow rates
but is less than the pressure drop at the flow rate at which the
tool begins operation. This allows the tool to maintain a large gap
between the rotor and stator prior to operation of the tool or
during periods of nonoperation thereby alleviating the problem of
plugging and/or jamming of the valve. During normal operation the
net force holding the rotor down, i.e., the force due to hydraulic
pressure drop minus the spring force, is relatively small so that
the rotor will ride up over and free itself from material which may
become lodged in the gap, thus alleviating jamming of the valve.
Also, structural features of the rotor aid in alleviating plugging
of the valve.
Inventors: |
Sexton; James H. (Duncanville,
TX), Slover, Jr.; Vasel R. (Irving, TX), Patton; Bobbie
J. (Dallas, TX), Gravley; Wilton (Carrollton, TX) |
Assignee: |
Mobil Oil Corporation (New York
City, NY)
|
Family
ID: |
23059904 |
Appl.
No.: |
05/277,220 |
Filed: |
August 2, 1972 |
Current U.S.
Class: |
137/499;
367/83 |
Current CPC
Class: |
E21B
47/20 (20200501); E21B 47/18 (20130101); Y10T
137/7786 (20150401) |
Current International
Class: |
E21B
47/18 (20060101); E21B 47/12 (20060101); G01v
001/40 () |
Field of
Search: |
;137/499,495 ;340/18NC
;73/152 ;181/.5 ;324/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Klinksiek; Henry T.
Assistant Examiner: Miller; Robert J.
Claims
What is claimed is:
1. A logging-while-drilling tool comprising:
a housing adapted to be positioned in a drill string of an earth
drilling apparatus wherein a drilling fluid which is circulated
through the drill string will flow around said housing;
a rotary valve positioned on said housing so that at least a
portion of the drilling fluid flowing through the drill string will
flow through said valve whereby a pressure wave signal will be
generated in the drilling fluid as said valve opens and closes,
said valve comprising:
a rotor having openings therethrough mounted on a drive train
extending from said housing;
a stator on said housing having openings therethrough which when
aligned with said openings in said rotor allow flow through said
valve and when misaligned at least partially block flow through
openings in said rotor; and
means for normally biasing said rotor and said stator relatively
away from each other.
2. The logging-while-drilling tool of claim 1 wherein said biasing
means comprises:
spring means having a force constant which is greater than the
pressure drop across said rotor at flow rates less than the flow
rate at which said tool will operate but which is less than the
pressure drop across said rotor at said operational flow rate
whereby said rotor and said stator will be separated from each
other at a maximum distance during said low flow rates but will
move toward each other to establish a desired gap at said
operational flow rate.
3. The logging-while-drilling tool of claim 1 including:
means to hold said rotor and said stator in a relative position
wherein their respective openings are aligned until said tool
begins operation.
4. The logging-while-drilling tool of claim 1 wherein said drive
train comprises:
a driving shaft and a driven shaft, said rotor being mounted on
said driven shaft; and
said biasing means comprising:
means for coupling said driving shaft to said driven shaft for
rotation therewith while allowing limited, longitudinal, relative
movement therebetween; and
spring means for normally biasing said driven shaft away from said
driving shaft.
5. The logging-while-drilling tool of claim 4 wherein:
said spring means has a force constant which is greater than the
pressure drop across said rotor at flow rates less than the flow
rate at which said tool will operate but which is less than the
pressure drop across said rotor at said operational flow rate
whereby said rotor and said stator will be separated from each
other at a maximum distance during said low flow rates but said
rotor will move toward said stator to establish a desired gap at
said operational flow rate.
6. The logging-while-drilling tool of claim 5 including:
means to hold said rotor and said stator in a relative position
wherein their respective openings are aligned until said tool
begins operation.
7. The logging-while-drilling tool of claim 1 wherein said biasing
means comprises:
means for mounting said rotor on said drive train for rotation
therewith while allowing limited, longitudinal movement of said
rotor on said drive train; and
spring means for normally biasing said rotor on said drive means in
a direction away from said stator.
8. The logging-while-drilling tool of claim 7 wherein:
said spring means has a force constant which is greater than the
pressure drop across said rotor at flow rates less than the flow
rate at which said tool will operate but which is less than the
pressure drop across said rotor at said operational flow rate
whereby said rotor and said stator will be separated from each
other at a maximum distance during said low flow rates but said
rotor will move toward said stator to establish a desired gap at
said operational flow rate.
9. The logging-while-drilling tool of claim 1 wherein said rotor
comprises:
a hub; and
a plurality of lands extending radially outward from said hub, the
space between respective lands defining said openings through said
rotor, said lands extending outward to a point whereby said lands
completely overlap said openings in said stator when said valve is
in a closed position.
10. The logging-while-drilling tool of claim 9 wherein:
the upper surface of each of said lands is peaked so flow will
normally be directed to said openings between said lands.
11. The logging-while-drilling tool of claim 9 wherein:
the leading edge of each of said lands extends radially out from
said hub for a distance greater than the trailing edge of each of
said lands.
12. The logging-while-drilling tool of claim 9 wherein:
the radial surface of each of said lands is relieved inward from
its upper and lower surfaces.
13. A logging-while-drilling tool comprising:
a housing adapted to be positioned in a drill string of an earth
drilling apparatus wherein a drilling fluid which is circulated
through the drill string will flow around said housing;
a rotary valve positioned on said housing so that at least a
portion of the drilling fluid flowing through the drill string will
flow through said valve whereby a pressure wave signal will be
generated in the drilling fluid as said valve opens and closes in
response to a downhole condition measured by said tool, said valve
comprising: a stator on said housing having openings therethrough;
and
a rotor mounted on a drive train extending from said housing, said
rotor comprising:
a hub and a plurality of lands extending radially outward from said
hub, the spaces between respective lands defining openings through
said rotor, said lands extending outward to a point whereby said
lands completely overlap said openings through said stator when
said valve is in a closed position.
14. The logging-while-drilling tool of claim 13 wherein:
the upper surface of each of said lands is peaked so flow will
normally be directed to said openings between said lands.
15. The logging-while-drilling tool of claim 13 wherein:
the leading edge of said lands extends radially out from said hub
for a distance greater than the trailing edge of each of said
lands.
16. The logging-while-drilling tool of claim 13 wherein:
the radial surface of each of said lands is relieved inward from
its upper and lower surfaces.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a logging-while-drilling tool and
more particularly relates to a logging-while-drilling tool which
includes a means for alleviating plugging or jamming of the
signal-generating valve of the tool while the tool is in an
operable position within a well being drilled.
The desirability of a system which is able to measure downhole
drilling parameters and/or formation characteristics and transmit
them to the surface while actual drilling of an earth well is being
carried out has long been recognized. Several such systems have
been proposed and are commonly referred to as
"logging-while-drilling" systems. In logging-while-drilling
systems, one of the major problems exists in finding a means for
telemetering the information from a downhole location to the
surface and having it arrive in a meaningful condition.
In this regard, it has been proposed to telemeter the desired
information by means of a pressure wave signal generated in and
transmitted through the circulating mud system normally associated
with rotary drilling operations. The pressure wave signal which is
representative of a particular piece of desired information is
generated in the mud downhole near the bit by a signal-generating
valve and the wave travels up the hole through the mud to a signal
processor at the surface. Logging-while-drilling systems utilizing
this technique of telemetry are disclosed and fully described in
U.S. Pat. No. 3,309,656 to John K. Godbey, issued Mar. 14, 1967 and
in copending application Ser. No. 213,061, filed Dec. 28, 1971.
In logging-while-drilling systems of the types mentioned above, a
tool having a turbinelike signal-generating valve is positioned in
the circulating mud path near the drill bit. The valve is comprised
of a stator and a rotor, each having openings therethrough which
when aligned allow full flow of drilling mud through the valve.
When the openings are misaligned, the flow therethrough is at least
partially blocked. A motor in the tool is energized in response to
a measured piece of information to open and close the valve at a
rate producing a pressure wave in the mud which is representative
of said measured information.
However, in logging-while-drilling tools of this type, the
signal-generating valve normally develops certain hydraulic torque
characteristics as a function of the flow rate through the valve
which tend to force the valve to its closed position. This creates
problems as drilling mud is pumped down the drill string and
through the valve before the tool begins operation and the motor
begins to power the valve. Due to composition of standard drilling
mud, solid material is normally present therein which tends to
strain out of the mud as it is forced through restricted passages
in the valve which are present when the valve is in its closed
position. This solid material may continue to collect in the valve
and does present a real problem in that it may plug the valve to
such an extent that the valve cannot be opened by the motor when
operation of the tool is commenced.
Furthermore, even when the tool is operating and the valve is being
rotated by the motor, large debris, e.g., wood chips which may be
present in the drilling mud may become wedged between the rotor and
stator as the mud flows through the valve thereby jamming the valve
and making the tool inoperable. If the valve becomes plugged prior
to startup of the tool or becomes jammed during operation of the
tool, the entire drill string has to be removed to free the valve
for rotation before the tool can carry out its function.
SUMMARY OF THE INVENTION
The present invention provides a logging-while-drilling tool of the
type described above which includes means to alleviate plugging
and/or jamming of the tool's signal-generating valve before and
during the operation of the tool.
Structurally, the tool of the present invention is comprised of a
housing which is adapted to be mounted within the central passage
of a drill collar. This drill collar, in turn, is adapted to be
connected into and form a portion of a drill string of an earth
drilling apparatus. The tool housing carries a rotary, turbinelike,
signal-generating valve which is positioned so that at least a
portion of the drilling fluid flowing through the drill string will
pass through the valve. The valve is comprised of a stator which is
affixed to the housing and a rotor which is carried by a rotating
drive train extending from a motor within the housing. Both the
rotor and stator have openings therein which when aligned (i.e.,
open position) allow full flow through the valve and when
misaligned (i.e., closed position) block at least a portion of the
flow therethrough. A turbine, powered by the mud flow, is located
at the lower end of the tool which rotates a generator which, in
turn, furnishes the electrical power for the tool.
When the valve is in a closed position prior to startup of the
tool, mud must flow through restricted passages in the valve in
order to reach the mud turbine to generate the power necessary to
operate the tool. The restricted passages are formed by the bypass
between the outer edges of the rotor lands and the wall of the
drill collar and the gap between the lower surface of the rotor and
the upper surface of the stator. The gap in the tool must be
relatively small during operation of the tool in order for the
signal generated by the valve to have sufficient strength to reach
the surface.
In the present tool, means is provided to allow relative movement
between the rotor and the stator so that a large gap will exist
when the tool is not operating and a small gap will exist at
operating conditions. Structurally, a spring means is included in
the tool which has sufficient force to bias the rotor upwardly away
from the stator when a low rate of flow is passing down the drill
string. As the flow rate increases, the pressure drop across the
rotor also increases. When the pressure drop exceeds the force of
the spring means, the rotor moves downward toward the stator which
establishes the gap necessary for satisfactory operation of the
tool. By allowing the gap to be large during the time the tool is
not operating, the passages available for flow through the valve
during this time are increased and the problem of plugging the
valve is substantially decreased. Further, since the spring means
tends to force the rotor away from the stator when the flow rate is
decreased, if the valve becomes jammed during operation of the tool
by material in the mud, the flow rate can be reduced and the valve
cleared by the relative movement between the rotor and stator. Even
if the flow rate is not reduced during partial jamming, the rotor
can ride up against the bias of the spring over the debris between
the rotor and stator and continue to operate under most
circumstances.
Additional structural features of the rotor of the present
invention further aid in alleviating plugging and/or jamming of the
valve and these will become evident from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
The actual construction, operation, and the apparent advantages of
the invention will be better understood by referring to the
drawings in which like numerals identify like parts and in
which:
FIG. 1 is a schematic elevation of a rotary drilling apparatus
including in vertical section a well containing a drill string in
which the present invention is employed;
FIG. 2 is a schematic elevation, partly in section, of a portion of
the drill string of FIG. 1, having the present
logging-while-drilling tool mounted therein;
FIG. 3 is a detailed sectional view of one modification of the
upper portion of FIG. 2 illustrating the present invention;
FIG. 4 is a sectional view taken along section line 4--4 of FIG.
3;
FIG. 5 is a sectional view taken along section line 5--5 of FIG. 4;
and
FIG. 6 is a detailed view of a second modification of the upper
portion of FIG. 2 illustrating the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to the drawings, FIG. 1 discloses the
present invention as used in a logging-while-drilling system which
is incorporated in a rotary drilling apparatus. A derrick 21 is
disposed over a well 22 being formed in the earth 23 by rotary
drilling. A drill string 24 is suspended within the well and has a
drill bit 27 at its lower end and a kelly 28 at its upper end. A
rotary table 29 cooperates with kelly 28 to rotate string 24 and
bit 27. A swivel 33 is attached to the upper end of kelly 28 which
in turn is supported by hook 32 from a traveling block (not shown).
This arrangement not only supports the drill string 24 in an
operable position within well 22 but also forms a rotary connection
between the source of circulating drilling fluid, such as mud, and
the drill string 24. It should be understood that "mud" as used
throughout this disclosure is intended to cover those fluids
normally used in rotary drilling operations.
The pump 36 transfers drilling mud from a source, such as pit 34,
through desurger 37 into mudline 38. Desurger 37 is adapted to
reduce the pulsating effect of pump 36 as is well known in the art.
The mud flows through mudline 38, flexible hose 39, swivel 33,
drill string 24, and exits through openings (not shown) in drill
bit 27 to pass outward into well 22. The mud then circulates upward
carrying drill cuttings with it through the annulus between the
well and drill string 24 to the surface of the earth 23. At the
surface, well head 41 is secured to casing 40 which is cemented in
the well 22. Pipe 42 is connected to casing 40 for returning the
mud to pit 34.
As schematically illustrated in FIGS. 1 and 2, a
logging-while-drilling tool 46 is located in drill collar 26 which
forms a part of the lower end of drill string 24 near bit 27. Tool
46 has a motor-actuated, rotary signal-generating valve which
periodically interrupts at least a portion of the drilling fluid
flowing through the valve to thereby generate a pressure wave in
the fluid which is representative of a measured downhole condition.
This is the type of logging-while-drilling tool which is disclosed
and described in U.S. Pat. No. 3,309,656. The present invention is
directed to a means for alleviating plugging and/or jamming of the
valve but, in order to fully understand and appreciate the present
invention, a brief description of the entire tool 46 will be
helpful.
A transducer means which is capable of measuring a desired downhole
condition and converting the measurement to an electrical signal is
positioned downhole on or near tool 46. As illustrated, transducer
means 54, e.g., a strain gauge, is positioned on drill collar 26 to
measure the downhole weight on bit 27. The signal from transducer
means 54 is applied to electronic package 53 which is sealed in
compartment 48 of tool housing 46a. For examples of package 58, see
U.S. Pat. No. 3,309,656 or U.S. application Ser. No. 213,061, filed
Dec. 28, 1971. Circuitry in package 53, in response to the signal
from means 54, allows a defined amount of power from electric power
generator 50 in compartment 49 of housing 46a to flow to the
variable speed, electric motor 55 in compartment 47 of housing 46a.
A turbine 52 driven by the mud flow rotates generator 50 to produce
electrical power. Motor 55, in response to the amount of
electricity passing through package 53, will drive rotor 61 of
signal-generating valve 60 through drive train 56 at the rotational
speed necessary to generate a pressure wave signal in the mud which
is representative of the measured condition.
Referring now to the more detailed representation in FIG. 3,
signal-generating valve 60 is comprised of a rotor 61 and a stator
62. Rotor 61 is fixed on driven shaft 63b of drive train 56 by
means of tapered bushing 64 and nut 65. Shaft 63b is journaled in
housing 46a by means of bearings 66. Seal 67 and grease-filled
cavity 67a around shaft 63b seal the interior of housing 46a
against the influx of drill mud. Preferably, both rotor 61 and
stator 62 contain the same number of identical spaced slots, 61a,
62a, respectively, (FIG. 4). Valve 60 is in an "open position" when
the slots are aligned and is in a "closed position" when the slots
are completely misaligned. When valve 60 is in a closed position,
the only flow through the valve is that which passes through gap 70
and bypass 71. Gap 70, as can best be seen in FIG. 3, is that
distance between the bottom surface of rotor 61 and the top surface
of stator 62. Bypass 71 (FIGS. 3 and 4) is that distance between
the outer periphery of rotor 61 and the wall of the conduit
adjacent the rotor. The outer diameter of stator 62 is effectively
the same as the interior diameter of the conduit.
The rate at which valve 60 opens and closes determines the
frequency of the pressure wave signal thus generated in the
drilling mud, but the amplitude or strength of the signal is
directly related to the minimum area defined by gap 70 and bypass
71 which is available for flow when valve 60 is closed. As this
area decreases, signal strength increases. Since a strong signal is
desired, gap 70 should be as small as practical while tool 46 is
operating.
However, when there is flow through valve 60 but before generator
50 develops sufficient power to operate tool 46, the torque
characteristics of valve 60 tend to force it to its closed
position. Therefore, when drill string 24 is lowered into the well
and mud is flowed through tool 46 to rotate turbine 52 at a speed
sufficient to generate the necessary power for the tool, the mud
must flow through the restrictive passages in valve 60 formed by
bypass 71 and gap 70. Since drilling mud normally contains solid
materials which tend to strain out within the restricted passages
of the closed valve, if gap 70 is too small during this time, a
serious problem of plugging exists. If valve 60 becomes plugged to
the extent that it cannot be opened when motor 55 commences
operation, the entire drill string 24 has to be removed to unplug
valve 60 before tool 46 can operate.
The present invention provides a means for tool 46 which alleviates
the problem of plugging valve 60 before tool 46 begins operation.
This means is comprised of structure which permits rotor 61 and
stator 62 to move relative to each other under certain operating
conditions so that gap 70 is large while tool 46 is not operating
but of a desired small value when tool 46 commences operation.
Structurally, in a first modification (FIG. 3) the means comprises
a "telescoping joint" 69 in output shaft 63 of drive train 56.
Driving shaft 63a of output shaft 63 is journaled in housing 46a by
means of bearings 66a and has a cuplike chamber 69a at its outer
end. Driven shaft 63b telescopes into chamber 69a and is slidably
positioned within centralizing bearing 72. Spring means 73, e.g.,
Belleville spring washers, is provided between nut 74 which is
threaded on shaft 63b and shoulder 75 within chamber 69a to
normally bias shaft 63b outward or upward from shaft 63a. Shafts
63a and 63b are coupled together for rotation by interlocking
splines 76 and 77, respectively. Splines 76 are formed
longitudinally on the inner periphery of chamber 69a while splines
77 are formed as part of ring 78 which, in turn, is frictionally
affixed to shaft 63b by tapered bushing 79. Of course, splines 77
could be constructed as an integral part of shaft 63b if desired.
Snap ring 80 is positioned in chamber 69a to limit upward movement
of shaft 63b with respect to shaft 63a. Spacer washers 81 can be
used to adjust the actual length of travel between the two
shafts.
In the tool described, as mud flows through openings in rotor 61,
there is a pressure drop across the rotor which increases with flow
rate. This pressure drop causes a downward force on the rotor. The
force constant of spring means 73 is selected so that the upward
force of spring means 73 is greater at low flow rates than the
downward force on rotor 61. Therefore, at the low flow rates such
as those used prior to commencement of operation of tool 46, spring
means 73 will maintain rotor 61 in an "up" position thereby
providing the maximum gap 70 for tool 46. This increase in gap 70
provides larger passages for flow through valve 60 during
nonoperation of tool 46 and substantially reduces the problem of
plugging. When flow rates are increased to those necessary to drive
turbine 52 at a speed required to generate sufficient power to
operate tool 46, the pressure drop across rotor 61 increases to a
value greater than the force constant of the spring means so that
spring means 73 is overcome and rotor 61 moves downward to its
"down" position. In this position, gap 70 will be a set value which
is necessary for successful operation of tool 46.
To further alleviate plugging of valve 60, a magnetic valve
positioner 83 (FIG. 2) can be included in tool 46 which holds valve
60 in an open position until tool 46 begins operation. The
construction and operation of valve positioner 83 are fully
described in assignee's copending U.S. application Ser. No.
267,851, filed June 30, 1972. Where valve positioner 83 is used in
tool 46, the force constant of spring means 73 is selected such
that rotor 61 will be held in its up position as long as valve 60
is held in its open position by valve positioner 83. When tool 46
begins operation and motor 55 powers valve 60 to its closed
position, the resulting force from the higher pressure drop due to
the valve's closed position will exceed the force constant of
spring means 73 and rotor 61 will move to its down position to
establish the desired gap 70 necessary for generating a
satisfactory signal.
Since normally tool 46 is oil filled and pressure balanced, as
clearly described in assignee's copending U.S. application Ser. No.
145,372, filed May 30, 1971, a bleed port 82 is provided so that
any oil trapped under shaft 63b within bearing 72 can flow
therefrom as rotor 61 moves downward.
When tool 46 is operating and rotor 61 is in a "down" position,
large debris, e.g., wood chips, etc., in the drilling mud may
become lodged between openings in rotor 61 and stator 62 or in gap
70, thereby jamming valve 60 against further rotation. If this
should occur, in accordance with the present invention the flow
rate of the drilling mud is decreased to a valve where the force of
spring means 73 again becomes dominant. This force causes rotor 61
to move toward its "up" position which, in most cases, will clear
whatever material is jamming the valve. After valve 60 has been
cleared, the operating flow rate is resumed and operation of tool
46 is continued.
If the jamming due to a buildup of particles between stator and
rotor is not too severe, tool 46 will continue to operate
satisfactorily without reducing the flow rate. This is due to the
compliance provided by spring means 73 which allows rotor 61 to
ride up over the debris in gap 70 against the bias of the spring
means and to continue to rotate. This continued rotation will, in
many cases, eventually erode the accumulated debris to the point
where the mud flow can carry it on through the valve.
Tool 46 of the present invention includes other structural features
which also aid in alleviating plugging and/or jamming of valve 60.
Lands 61b of rotor 61 extend outward from hub 90 to a point over
openings 62a of stator 62 (FIGS. 4 and 5) so that they overlap
opening 62a when valve 60 is in a closed position. This overlapping
of the stator openings provides higher amplitude and quality of
signal for a given gap 70 by minimizing leakage of valve 60 when
rotor 61 is in a down position and valve 60 is in a closed
position. Thus, a larger gap 70 can be used in generating a signal
of a desired strength than otherwise could be used. Accordingly,
there is less tendency for valve 60 to jam during operation of tool
46.
Jamming tendencies are further reduced and operating performance is
improved by other structural characteristics of rotor 61. First the
longitudinal length 61c (FIG. 5) of rotor lands 61b is reduced to a
minimum value but not below that which is sufficient to maintain
structural rigidity of the rotor lands during operation. The
smaller lands 61b will reduce the turbulence in the area of valve
60 which, in turn, reduces the hydraulic torque loads which are
applied to drive train 56 during operation of tool 46. The upper
surfaces 61d (FIG. 5) are peaked to reduce erosion and to
continuously direct flow toward openings 61a in rotor 61 instead of
toward radial edges 61e (FIG. 4) of lands 61b where plugging is
more likely to occur. Further, radial edges 61e are constructed
with the leading face of each land 61b extending further from the
center of rotor 61 than the trailing edge of said land. This radial
streamlining provides a bypass which is constantly varying between
a small value to a larger value thereby preventing a gradual
buildup of particles in the bypass. Also, radial edges 61e are
relieved as shown in FIG. 3 to further avoid trapping of materials
in bypass 71.
In FIG. 6, a second modification of tool 46 is disclosed which
utilizes a different means for providing relative movement between
rotor 161 and stator 62 of valve 160. The lower portion of tool 46
is the same as before except shaft 163 is continuous without a
telescoping joint therein. Rotor 161 is comprised of mounting
element 182 and land element 183. Mounting element 182 is secured
to shaft 163 for rotation therewith by means of tapered bushing 64
and nut 65. Land element 183 which carries rotor lands 161b is
slidably mounted on mounting element 182. Cooperating splines 184,
185 between elements 182 and 183, respectively, provide a driving
connection between the two elements so that both will be rotated by
shaft 163. Spring means 173 is positioned between a shoulder on
mounting element 182 and splines 185 to normally bias land element
183 upward against a stop provided by tapered bushing 64. Diaphram
seals 186 and 187 provide protection for the interior of rotor
161.
Operation of this modification is basically the same as that of
FIG. 3. The force constant of spring means 173 is selected so that
it will exceed the pressure drop across rotor 161 at flow rate
lower than the operating flow rate. When the operating flow rate is
achieved, land element 183 will move downward on mounting element
182 to establish the gap 70 necessary to generate the desired
signal.
* * * * *