US 3904305 A
A shutoff for a pneumatic tool such as a nut runner is disclosed. The shutoff, effective to terminate air supply to the air motor under stall loading conditions of the tool, employs a centrifugally operated main air valve and a starting bypass valve. In operation of the tool, air is initially supplied to the air motor through the bypass valve. When the motor reaches a predetermined speed level, the centrifugally operated main valve is opened, and the bypass valve is closed thereafter. Under loading, approaching stall, the motor slows to a speed low enough to allow the main valve to close under the influence of a spring. Because the shutoff occurs before the stall condition is attained, stall jerking is substantially eliminated.
Description (OCR text may contain errors)
United States Patent 11 1 Boyd Sept. 9, 1975  SPEED SENSING AIR TOOL SHU'IQFF 3,697,189 10/1972 Tibbott 415/25 3,752,241 8 1973 Be t 415 503  Inventor: Horace Edward Boyd, Euclid, Ohio 3 785 442 1, Arrtsberg et a1. H 41/5/36 73 Assignee: Cooper lndusu-ies, Inc. Houston, 3,791,458 2/1974 Wallace 137/58 Tex.
Primary ExaminerC. J. Husar 1 1 Filed: 19, 1974 Attorney, Agent, or FirmOwen & Owen Co.  Appl. No.: 498,619
 ABSTRACT A shutofi' for a pneumatic tool such as a nut runner is  415/25 fg disclosed. The shutoff, effective to terminate air sup- 2 I ply to the air motor under stall loading conditions of  Int. Cl. F0 5122/00 the tool, employs a centrifugal), Operated main air  f g Z. valve and a starting bypass valve. In operation of the I I l tool, air is initially supplied to the air motor through the bypass valve. When the motor reaches a predeter-  Reierences Clted mined speed level, the centrifugally operated main UNITED STATES PATENTS valve is opened, and the bypass valve is closed thereaf 2,246,910 6/1941 Amtsberg 91/59 ter. Under loading, approaching stall, the motor slows 2,768,546 10/1956 Amtsberg 415/503 to a speed low enough to allow the main valve to close 2925-089 2/1960 Conkli" 415/503 under the influence of a spring. Because the shutoff al f r occurs before the stall condition is attained, stall jerkltc ouse n v 3,384,343 5/1968 Bangcrtcr 415/503 mg subsmm'auy el'mmated 3,608,647 9/1971 Borries 91/59 11 Claims, 9 Drawing Figures 5 r \r w 1 e Z I 42 9 11 f /2 l 2s /9 /3 l q 6/ 2 /6 l 24' L 1 L1 l 7 I 1'- L g I; l 7 l 0 7 3/26 27 I4; 5, L 3 r PATENTED 91975 SHUT 1 OF 3 PATENTEDSEP 9:975 3,904,305
SHEET 2 BF 3 SPEED SENSING AIR TOOL SHUTOFF BACKGROUND OF THE INVENTION The invention relates to pneumatic rotary tools, and more particularly to a pre-stall air shutoff for such tools which is dependent upon a speed responsive device to sense the approaching stall and shut off the tool.
Most prior art rotary tools using a vane-type air motor have used a pressure sensing valve to automatically shut off the tool as the torque resistance encountered caused a build up of back pressure from the air motor to a predetermined value. Examples of such tools are disclosed in U.S. Pat. Nos. 3,373,824 and 3,608,647. This pressure sensitive system, while satisfactory in many applications, has disadvantages in that it is sensitive to line pressure variations. A pressure surge in the line, for example, can prematurely stop the tool. Similarly, sudden opening of the throttle valve can sometimes cause a surge sufficient to activate the shutoff. The most serious effect of pressure sensitivity in such tools, however, occurs when line pressure is too low to activate the shutoff. This condition can occur when there is overdraw on the air line, for example. With a high-torque tool, failure of the shutoff to activate can result in an unexpected and dangerous stall jerk on the operator. Another problem with pressure responsive shutoffs is their sensitivity to air line lubrication and to contaminants carried by the supply air. Hose residue, for example, can interfere with the valving of such tools to the extent that torque output is affected.
Other prior art tools have used mechanical means such as clutches or ratchet-type devices to control the effective output torque upon a fastener or joint; these devices are usually complex and subject to wear and thus continuous maintenance costs. They also will produce a stall jerk if a pressure drop of sufficient magnitude to reduce motor torque below the clutch setting is encountered.
A tool of the type to which this invention relates is shown in Wallace U.S. Pat. No. 3,79l,458. Designed to relieve the stall loading jerk on an operator during tightening of a fastener, the tool employs a speed sensitive air shutoff which terminates air supply to the air motor at a speed just above stall. The tool disclosed in that patent utilizes a slidable spool-type valve which is spring-biased toward its open position. A pressure chamber at the lower end of the slidable valve member receives pressurized air as long as the tools throttle valve is open. However, once the air motor of the tool has built up a degree of speed, an exhaust outlet from the pressure chamber prevents the chamber from fully pressurizing to move the valve to the closed position. A rotatable, centrifugally responsive ball and seat valve is employed to keep the exhaust outlet open during normal operation of the tool but to close it during low speed associated with a stall, allowing the chamber to fully pressurize and close off the air supply to the motor. The primary disadvantages of this tool are construction and maintenance cost. The tool involves rather complex structure including a rotational air coupling which is subject to a great deal of wear, resulting in erratic tool operation.
SUMMARY OF THE INVENTION The present invention provides a speed responsive air tool shutoff which utilizes a centrifugally operated main operating air valve somewhat similar to a conventional governor to control the point of shutoff of the tool. A separate starting or bypass air valve is included, in addition to the usual throttle valve. When the throttle valve is closed, the main valve remains closed under the influence of a compression spring and the bypass valve remains open under the influence of a second compression spring. When the throttle valve is opened, a limited supply of pressurized air is admitted to the motor through the bypass valve, permitting the motor to rapidly build up initial speed during rundown of the nut or bolt. As a predetermined minimum speed is reached, the main operating air valve is opened by centrifugal weights, admitting air to the motor at a much greater flow rate. Shortly after the main valve opens, the bypass valve is closed by the pressurization of an expansible chamber. The pressure chamber is positioned at one end of a slidable member, the position of which determines whether the bypass valve is open or closed. Pressurized air from the throttle valve is gradually admitted to the chamber through an orifice. The size of the orifice in relation to the expansion volume is such that closure of the bypass valve is delayed until after the main valve is opened.
As the joint begins to tighten and the tool encounters increased resistance, the speed of the air motor begins to decrease. At a predetermined low motor speed representative of the desired applied torque, the centrifugal valve opening means is overcome by the main valve compression spring, and the main valve begins to close. The closure of the valve is accelerated when it reaches a certain point at which pressurized air from the throttle valve is admitted to an expansible chamber in the main valve which expands to quickly snap close the main valve, thus shutting off all air to the motor and stopping the tool shortly thereafter so that an accurate torque has been applied to the joint.
As long as the throttle valve is held open, both the main valve and the bypass valve remain closed. Upon closure of the throttle valve, the pressurized condition of the bypass valves expansible chamber is dissipated to the atmosphere through the orifice and the throttle valve, allowing the bypass valve to reopen so that the tool may again be started by opening of the throttle valve.
A second embodiment of the invention employs a different type starting bypass valve which closes in direct response to the opening of the main valve rather than after a time delay depending on an orifice. At one end of a slidable member of the bypass valve is an expansible chamber similar to that of the first embodiment, but the chamber receives pressurized air from a cavity adjacent and downstream of the main valve rather than from a point upstream of the main valve. Bypass air is thus able to reach the chamber initially but does not exert enough pressure in the chamber to close the bypass valve. Only when the main valve opens is there sufficient pressure available to expand the chamber and close the bypass valve. As the bypass valve closes, it seals ofi' a port which supplies its chamber with high pressure air, but simultaneously opens an interlock port which delivers high pressure air directly from the throttle valve. Without this interlock, the bypass valve would reopen, allowing the tool to continue running after the main valve has closed.
The speed sensitive air shutoff of the present invention does not rely upon the sensing of air back pressure for its operation, and thus overcomes the disadvantages of the pressure sensing tools discussed above. In particular, the present shutoff activates at a given low motor speed regardless of variations in line pressure, eliminating danger of injury to the operator. Another advantage of the speed sensing feature is the ability to regulate output torque simply be varying line pressure. The tool is also relatively simple in construction and operation, requiring little maintenance.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a portion of a rotary air tool including an air shutoff according to the present invention;
FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;
FIG. 3 is a view similar to FIG. 1 but with the main valve of the shutoff in the open position;
FIG. 4 is a view similar to FIG. 3 but with the bypass valve of the shutoff in the closed position;
FIG. 5 is another similar view showing both the main and bypass valves in the closed position;
FIG. 6 is a sectional view taken along the line 66 of FIG. 5;
FIG. 7 is a sectional view of another embodiment of the invention;
FIG. 8 is a sectional view similar to FIG. 7 but with the shutoff rnain valve open and the bypass valve closed; and
FIG. 9 is another similar view showing both the main and bypass valves in the closed position.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I of the drawings shows in section a portion of an air tool 10 such as an angle nut runner. The tool 10 includes an air motor 11, a throttle valve 12 behind which is a chamber 13 communicating through a pressure regulator 15 with a source of pressurized air (not shown), and a speed sensing air shutofi' 14 between the throttle valve 12 and the motor 11. The shutofi 14 is adapted to terminate the flow of pressurized air from the throttle valve 12 to the air motor 11 when the motor I l slows to a given speed approaching stall while torquing a fastener, and to keep the air supply shut off until the throttle valve 12 is again closed.
As FIG. 2 indicates, the throttle valve 12 includes a depressing lever 16 on the exterior of the tool, a valve stem 17, a seat 18, a closing member 19, and a compression spring 21 biasing the valve 12 toward its closed position. The structure of the throttle valve 12 is typical of many air tools and is not considered to be a part of this invention.
Downstream of the throttle valve 12, as FIGS. 1 through 5 indicate, the shutoff means 14 includes a main operating valve 22 which is open during torquing of the work and during most of the rundown of the work. The valve 22 includes a valve closing sleeve 23 which is slidable upon a rotor shaft extension 24 driven by the motor 11. The sleeve 23 is not keyed into the shaft extension 24 for rotation therewith; it may rotate with or rotationally slip upon the shaft extension 24. The upstream end of the valve closing sleeve 23 is positioned to come into contact with a flange 26 of a stationary sleeve 27 affixed to the body of the tool 10. In this position of the slidable valve sleeve 23, the space between the upstream end of the rotor shaft extension 24 and the stationary flange 26 is closed, thereby preventing the passage of air therethrough.
A compression spring 28 biases the valve sleeve 23 toward its closed position. In addition, an oblique bore 29 is provided through the upstream end of the rotor shaft extension 24 for accelerating the closure of the valve sleeve 23 once it has progressed beyond a certain point. That point is defined by the uncovering of the downstream end of the bore 29 by the valve closing sleeve 23. This enables pressurized air from the throttle valve 12 to enter an expansible chamber 31 defined between the rotor shaft extension 24 and the surrounding valve closing sleeve 23.
The valve 22 is opened by centrifugal weights 32 pivotally connected to a rotating yoke 33. As shown in FIGS. 1 and 3, the weights 32 are adapted to urge the valve sleeve 23 against the spring bias to open the valve 22 upon the attainment of the predetermined motor speed level. As FIG. 6 indicates, six such weights may be provided on the yoke 33. It should be noted here that, contrary to the usual arrangement of a centrifugal weight governor, the valve 22 here is opened by increased speed and closed by decreased speed.
In order to initially supply pressurized air to the motor 11 before the valve 22 has opened, a bypass assembly 34 is provided. As shown in FIG. I, the valve assembly 34 in the open position provides air communication from the throttle valve to the motor 11 through a duct 36 in a slidable spool 37 which resides within a bore 40. The upstream end of the duct 36 is always open to a chamber 38 communicating with the throttle valve 12, and during the open position of the bypass, the downstream end of the duct 36 communicates through an annular chamber 39 with a bore 41 in the body of the tool 10. As the figures indicate, the bore 41 is always open to the air motor II. The valve spool 37 is biased downwardly toward its open position by a compression spring 42 positioned in a chamber 43 which is open to the atmosphere through a breather port 44 in the body of the tool 10. A low friction O-ring 47 is provided to seal the valve assembly 34 against leakage of pressurized air through the opening 44.
The closing of the valve 34 is accomplished by the pressurization of an expansible chamber 48 defined be tween the lower end of the spool 37 and a threaded plug 53 which forms a boundary of the bore 40. A low friction O-ring 50 seals the chamber 48 from air leakage. To provide the required rate of pressurization, a small orifice 51 through the valve spool 37 admits pressurized air at a measured rate from the chamber 38 into the expansible chamber 48. The size of the orifice 51 is such that the chamber 48 receives sufficient air to pressurize and expand, thus raising the spool 37 and closing the valve 34, after the main operating valve 22 has opened in response to the attainment of the proper motor speed level. The closed position of the bypass valve assembly 34 is shown in FIGS. 4 and S.
In operation of the speed sensitive shutoff 14 of the rotary air tool 10, the line air pressure or flow regulator 15 is first adjusted to a setting corresponding to the desired output torque. Pressurized air is then admitted through the throttle valve 12 by the operator's depression of the lever 16. Air is thus supplied to the motor 11 in limited quantity through the ducts 36 and 4] of the bypass assembly 34. This initial bypass air is sufi'icient to start the motor and quickly bring it to about 5000 rpm or more. At this time, the output spindle (not shown) of the tool is engaged in the running down of a fastener. During this phase, the output spindle torque of the tool, though lower than that of the next phase, is sufficient to run down even a prevailing torque" fastener. The position of the shutoff apparatus 14 during this phase of operation is shown in FIG. 1.
When the motor 11 reaches a predetermined speed which may be in the range of l500-2000 rpm, the pivoted weights 32 on the rotating yoke 33 swing out, urging the valve sleeve 23 in a downstream direction against the bias spring 28 as shown in FIG. 3 and opening the main operating valve 22. The weights 32 preferably swing through an angle of about 36, overcoming the pressure of the spring 28 and any residual air pressure bias in the chamber 31, as well as friction. The bypass valve assembly 34 remains in the open position while the main valve 22 is opening and for a short period thereafter, the length of which is determined by the rate of pressure buildup in the chamber 48, which in turn depends upon the sizing of the small orifice 5].
The next phase of operation of the air tool is shown in FIG. 4. The expansible chamber 48 at the base of the slidable bypass valve spool 37 receives pressurized air through the orifice 51 as long as the throttle valve 12 is open. When the pressure in the chamber 48 is sufficient to overcome friction and the compression spring 42, the chamber 48 expands, sliding the valve spool 37 upward against the pressure of the spring 42 and the friction of the Orings 47 and S0 to shut off the supply of bypass air through the duct 36. At this point, the tool 10 is still engaged in the rundown of the fastener, requiring relatively little torque.
With the main operating valve 22 open and the bypass valve assembly 34 closed as shown in FIG. 4, the tool 10 completes the rundown and begins the torquing of the fastener. The two valves remain in this position until the motor ll, during torquing of the fastener, has slowed to near stall, i.e., in the range of l00l000 rpm. At this speed, representative of the desired final torque on the fastener, the valve sleeve 23 of the main valve assembly 22 begins to slide toward the closed position, the pressure of the return spring 28 being greater than the centrifugal effect of the weights 32.
As the valve sleeve 23 closes the valve 22, air pressure upstream of the valve 22 increases and downstream decreases. When the closure of the valve sleeve 23 has proceeded to such a point that the downstream end of the oblique air passageway 29 is uncovered, the expansible chamber about the spring 28 is immediately pressurized by high pressure air and the sleeve 23 com- I pletes its closure with a snap action. Both the main valve 22 and the bypass valve 34 are now closed, as shown in FIG. 5. The air supply to the motor 11 is thus totally shut off and the motor 11 stops.
Although the operator of the tool 10 may hold the throttle valve 12 open after shutoff of the tool, air flow to the motor 11 will not be resumed. As FIG. 5 indicates, pressurized air from the open throttle valve continues to be available to the chamber 48 through the orifice 51, thereby maintaining the closed position of the bypass valve assembly 34. When the throttle valve 12 is ultimately closed by the operator, high pressure air no longer reaches the chamber 48 and it is quickly depressurized by bleeding of air from the chamber 48 to the atmosphere via the orifice 51, the air chamber 38 and a flat 54 on the valve stem 17 of the closed throttle valve 12. The spring 42 thus returns the valve spool 37 to its original position and the bypass valve is reopened for the next usage of the tool 10.
FIGS. 7, 8 and 9 illustrate another form of the invention. As in the above described embodiment, a rotary air tool 55 of this embodiment includes a throttle valve 56, a main air valve 57 and a bypass valve assembly 58. The main valve 57 is identical in structure and operation to the valve 28 of the first embodiment. The bypass valve assembly 58 is similar to the bypass 34 of the above embodiment in that it includes a slidable valve spool 60 which defines an expansible chamber 59 with a plug member 61 below and it is biased downward toward its open position by a compression spring 62. In the open position, pressurized air from the throttle valve 56 passes through a chamber 38' and a channel 63 appearing behind the valve spool 60, through an annular passage 64 in the spool 60 and through a duct 66 from which it travels to an air motor 67. As is true in the above embodiment, air from the throttle valve 56 can pass with little restriction around the valve spool 60 en route to the main air valve 57 regardless of the position of the valve spool 60.
The difierence between the bypass valve assembly 58 and the above bypass 34 is the manner in which the expansible chamber 59 is pressurized to slide the valve spool 60 upward to its closed position. The chamber 59 receives sufficient pressure to close the bypass valve in direct response to the opening of the main air valve 57. As FIG. 7 indicates, a port 68 provides communication between the downstream side of the main and bypass valve assemblies 57 and 58 and an annular chamber 69 and crossport 70 in the spool 60 leading to the expansible chamber 59. Thus, in the open bypass position of FIG. 7, pressurized air from the throttle valve passing through the bypass assembly 58 is in communication with the expansible chamber 59. However, because of restrictions defined by the channel 63, the annular passage 64 and the duct 66, bypass air reaching the duct 68 for entry into the chamber 59 is under substantially lower pressure than the air immediately downstream of the throttle valve 56. The pressure thus developed in the chamber 59 is not sufficient to move the valve spool 60 against the pressure of the compression spring 62 and a degree of air pressure within a chamber 72 defined above the valve spool 60. Some air pressure develops in the chamber 72 whenever the throttle valve 56 is open by leakage from the annular passage 64 of the valve spool around the upper portion of the valve spool, which is not sealed. An orifice 73 leading from the chamber 72 to the atmosphere limits the pressurization of the chamber 72.
When the main air valve 57 is opened by the necessary motor speed, air passes to the downstream side of the valves 57 and 58 and to the motor 67 at much greater pressure, since few restrictions are encountered. This enables high pressure air to pass through the port 68, the annular chamber 69 and the crossports 70 into the expansible chamber 59, which then expands to move the valve spool 60 upward toward the closed bypass position seen in FIG. 8. As the spool 60 moves upward, the annular chamber 69 is cut off from the port 68. However, before this occurs, the chamber 69 is put in communication with an interlock channel 74, ap pearing behind the valve spool 60, which receives compressed air directly from the throttle valve 56. There is thus a continuity of high pressure air flow into the chamber 59, and the valve spool 60 rises to the closed position of FIG. 8 and is held there by air from the interlock channel 74. The pressure within the air chamber 59 is now greater than the combined effects of the compression spring 62 and the air pressure within the upper chamber 72. The tool 55 operates in the position of FIG. 8 until the shutoff speed is attained as the motor slows during tightening of a fastener.
FIG. 9 indicates the positions of the main and bypass valve assemblies 57 and 58 after the air motor 67 has slowed to a speed low enough to allow the main valve 57 to close. As long as the throttle valve 56 is held open, the expansible chamber 59 continues to receive pressurized air and thus remains in its closed position. When the throttle valve 66 is closed, the pressure in the chamber 59 dissipates through normal leakage. Some air passes through the port 68, seeping out through the motor 67, while some air leaks upward through the channel 63, around the upper portion of the valve spool and out of the orifice 73. The valve spool is thus quickly returned to the open bypass position by the compression spring 62, and the tool is again ready for operation in the position of FIG. 7.
The above described preferred embodiments provide speed responsive air tool shutoffs which are simple and effective in operation, requiring little maintenance. Various other embodiments and alterations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the following claims.
1. A speed sensitive shutoff for a rotary air tool having an air motor operable by a throttle valve with an air passage therebetween,
a main air valve in said air passage between the air motor and the throttle valve including means biasing the valve toward its closed position to close off said air passage,
means for opening said main valve in response to the attainment of a predetermined upper motor speed level and for closing said main valve in response to the attainment of a predetermined lower motor speed level,
a normally open starting valve positioned in parallel relationship with said main air valve and effective to bypass air around said main air valve to said motor, and
means for closing and maintaining closure of said starting valve during operation of the tool after said main valve has opened and until the throttle valve is closed,
whereby, while the throttle valve of the tool is open, the air supply to the air motor continues until the motor speed slows to said predetermined lower motor speed level, then ceases until the throttle valve is closed and reopened.
2. The speed sensitive shutoff of claim 1 wherein said main valve opening means and closing means comprise weights mounted adjacent to the valve for rotation with the air motor, said weights being effective, in response to centrifugal force induced by said predetermined upper motor speed level, to open said main valve against said biasing means, and effective, in response to a lower level of centrifugal force corresponding to said predetermined lower motor speed level, to allow said biasing means to close said main valve,
3. The speed sensitive shutoff of claim 1 wherein said main valve opening means and closing means include centrifugal weights mounted for rotation with the air motor and for outward displacement during operation of the motor above said predetermined lower motor speed level, said main valve being opened in response to outward displacement of said weights.
4. The speed sensitive shutoff of claim 1 wherein said main air valve includes, in addition to said biasing means, means for accelerating the rate of valve closure after it has proceeded beyond a predetermined point.
5. The speed sensitive shutoff of claim 4 wherein said accelerating means comprises a rotating shaft and an axially slidable sleeve mounted circumjacent thereon for rotation therewith, said sleeve and shaft defining an expansible chamber which upon expansion moves the main valve toward closure, and means placing the chamber in communication with pressurized air from the throttle valve after main valve closure has proceeded beyond said predetermined point.
6. The speed sensitive shutofi of claim I wherein said starting valve includes a slidable member within a bore of the tool, said member defining a bypass air passageway closeable in response to sliding movement of the member in one direction, and means urging said member in the opposite direction, and said starting valve closing means comprises an expansible chamber defined by said member and said bore, said expansible chamber including means establishing communication with pressurized air when the throttle valve is open and being effective, in response to an accumulation of pressurized air therein, to move said slidable member in said one direction to close said starting valve.
7. The speed sensitive shutofi' of claim 6 wherein said air communication means comprises an orifice extending from said chamber through said member into the path of airflow from the throttle valve, said orifice being of a predetermined size adapted to permit pressure accumulation in the chamber sufficient for starting valve closure after a time period sufficient to permit said main valve to open.
8. The speed sensitive shutoff of claim 1 wherein said starting valve includes a slidable member within a bore of the tool, said member defining a bypass air passageway closeable in response to sliding movement of the member in one direction, and means urging said member in the opposite direction, and said starting valve closing means comprises an expansible chamber defined by said member and said bore, said expansible chamber including means establishing communication with high pressure air from downstream of the throttle valve in response to the opening of said main air valve and being effective, in response to an accumulation of pressurized air therein, to move said slidable member in said one direction to close said starting valve.
9. The speed sensitive shutoff of claim 8 wherein said air communication means comprises a duct extending from downstream of said main air valve to a position adjacent the slidable member, passageway means in said member connecting said duct with the expansible chamber, said duct being in communication with the chamber while the bypass valve is open and during an initial portion of the travel of the slidable member toward the closed position, and means adjacent and downstream of the throttle valve for establishing communication between the chamber and-high pressure air from the throttle valve during the remainder of the travel of the slidable member.
10. A speed responsive air shutoff for a pneumatic rotary tool having an air motor operable by a throttle valve, comprising a main air valve between the motor and the throttle valve, including means biasing the valve toward closed position and centrifugal means for opening the valve above a predetermined upper motor speed and for allowing the valve to close below a predetermined lower motor speed; and bypass means for initially admitting pressurized air from the throttle valve to the air motor until after said main air valve has been opened.
11. A speed responsive shutoff control for a rotary fluid motor comprising, in combination, a main fluid passage connecting a source of fluid under pressure to said motor, a main shutoff valve upstream of said motor, said main valve including a centrifugal governor device driven by said motor and operably positioned to open said main valve as motor speed increases, said governor device being biased to open said main valve when said motor speed reaches a predetermined minimum, a bypass valve positioned in said fluid passage in parallel relation with said main valve such that said bypass valve, when open, will direct fluid around said closed main valve to said motor, and means for maintaining said bypass valve in its open position for only a predetermined time until said main valve is opened by said governor device when said motor speed reaches said predetermined minimum whereby, after said motor has reached said predetermined speed to open said main valve and said bypass valve has closed, a subsequent drop in motor speed to a low speed below said predetermined minimum will close said main valve, thereby shutting off all fluid supply to said motor.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3 ,904 305 Dated September 9 1975 Inventor(s) Horace Edward Boyd It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Errors due to Patent Office:
Column 1, line ll, "caused" should be -causes.
Column 3, line 7, "be" should be -by-.
Column 6, line 8, "28" should be 22--.
Column 7, line 19, delete "of".
Error due to applicant:
Signed and Scalcd this ninth Day of Decemberl975 [SEAL] Arrest:
RUTH C. MASON C. MARSHALL DANN Arresting Office Commissioner ufParenrs and Trademarks