US2009417A - Governor mechanism - Google Patents

Description

July 30, 1935. A. SCHWENDNER ,90

GOVERNOR MECHANISM Filed June 7, 1934 6 Sheets-Sheet l WITNESSES:

INVENTOR F. SCHWINDNER.

mam

ATTORNEY July 30, 1935. s w fl 2,009,417

GOVERNOR MECHANISM Filed June 7, 1934 6 Sheets-Sheet 2 INVENTOR v nmnmv F.5cnwzuousn.

BY QJIV5'VQ ATTORNEY July 30, 1935.

A. F. SCHWENDN ER GOVERNOR MECHANISM 6 Sheets-Sheet 3 INVENTOR Filed June 7, 1934 WITNESSES:

ANTHONY F. Scnwsuom-zn.

M -QM ATTORNEY y 1935. A. F. SCHWENDNER I 2,009,417

GOVERNOR MECHANISM Filed June 7, 1954 6 Sheets-Sheet 4 WITNESSES: INVENTOR f w /L F16 4 ANTHONY F SCHWENDNER ATTORNEY y 1935- A. F. SCHWENDNER 2,009,417

GOVERNOR MECHANISM Filed June 7, 1934 6 Sheets-Sheet 5 FIa.5.

HIGH PRESSURE OIL FROM GOV- IMPELLER TRRNSF'ORMIO OIL TO VR LVE MECHRNISH INVENTOR ANTHONY F. SCHWENDNEH ATTORNEY Patented July 30, 1935 PATENT OFFICE GOVERNOR MECHANISM Anthony F. Schwendner, Essington, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 7, 1934, Serial No. 729,370

16 Claims.

My invention relates to control apparatus for prime movers, for example, steam turbines, and it has for an object to provide a governing system which is stable and capable of operating with a small percentage of regulation.

A further object of my invention is to provide a governor of the pressure transformer type which utilizes a small range of primary fluid pressure change, the primary fluid pressure being developed as a function of the speed of the prime mover, to secure a large range of secondary or transformed fluid pressure used to actuate the governor or admission valve means.

A further object of my'invention is to provide a prime mover governor of the fluid pressure type wherein fluid pressure developed as a function of the speed of the prime mover is applied to a sealed expansible chamber of transformer governing apparatus, whereby minimum flow of fluid under primary pressure is required.

A further object of my invention is to provide a pressure transformer wherein frictional resistance is minimized.

A further object of my invention is to provide 25 a turbine installation having a governor valve, a throttle valve and an emergency governor, with a transformer governor constructed and arranged so that, in case of overspeeding of the turbine to a predetermined extent, not only is the throttle valve closed, but the transformed or secondary pressure utilized to actuate the governor valve is released, whereby closure of the governing valve is assured.

A further object of my invention is to provide a turbine-installation, having a governor valve, a throttle valve, and an emergency governor with a transformer governor subject, respectively, both to a back pressure regulator and to primary pressure of fluid developed as a function of the speed of the turbine, the transformer governor beingconstructed and arranged so that, in case of over'speeding of the turbine, not only is the throttle valve closed, but also the transformed or secondary pressure is released to permit closure of the governor valve.

These and other objects are effected by my invention, as will be apparent from the following description and claims, taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a diagrammatic view of an embodiment of my improved control system; I

Fig. 2 is a view similar to Fig. 1 but showing a .15 modified form .of the control system;

Fig. 3 is a sectional view of the transformer governor shown in Fig. 1;

,Fig. 4 is a sectional view of a transformer governor employed with the embodiment shown in Fig. 2;

Fig. 5 is a sectional view showing a modified form of pressure transformer;

Fig. 6 is a sectional view of of Fig. 2;

Fig. 7 is a diagrammatic view showing a fur- 10 ther embodiment of my invention: and

Fig. 8 shows an alternative form of accumulator means.

Referring now to the drawings more in detail,

I show a prime mover, for example, a steam tur- 5 bine, at In, including a stator II and a spindle 12. One or more admission valve devices are shown at l3, each device including an admission valve l4 and a servo-motor 15 for opening and closing the valve.

The turbine is provided with primary pressureproducing means, at It, for developing fluid under primary pressure and varying as a function of the turbine speed, the fluid under primary pressure being supplied to a transformer governor, at I1, which, in turn, supplies fluid under transformed or secondary pressure to the servomotors l5 of the admission or governor valves.

The transformer governor, at H, is constructed and arranged to utilize a narrow range of pri- 3o mary pressure change to secure a veryv much I wider range of secondary pressure change so that very small changes in primary pressure are effective to secure response of the steam valve.

The primary fluid pressure producing means, at I6, is constructed and arranged to provide such pressure with very little fluid flow so that power consumption for this purpose is Accordingly, I prefer to use the primary pressure producing means disclosed and claimed in the application of O. N. Bryant, Serial No. 728,257, filed May 31, 1934, and assigned to the Westinghouse Electric & Manufacturing Company and which pressure producing means will now be briefly described. The spindle I2 is provided with an impeller I! of the centrifugal type supplying fluid under pressure to the annular chamber l9 provided in the stator structure, the annular chamber supplying fluid through an orifice 20 to the primary pressure passage 2| communicating with a centrifugal escape device comprised preferably by the annular chamber 22 and the diagonal passage 23 formed in the spindle.

One end of the passage 23 communicates continuously with the annular channel 22' and the the servo-motors other end communuicates with a drain. It will, therefore, be apparent that the pressure existing in the passage 2| and the annular chamber 22 will depend upon the spindle speed, for, the more rapid the rotation of the spindle, the greater will be the centrifugal effect of the oil column in the diagonal passage between the spindle axis and the channel 22; and, in consequence, the pressure in the passage 2| will be modulated to vary substantially as the square of the turbine speed.

The orifice 20 serves as means for supplying fluid under pressure to the passage 2|, but it restricts the rate of flow so that pressure in the passage 2| may be varied as a function of the turbine speed in the manner just referred to. The other end of the passage 2| communicates with the transformer governor, at H.

The transformer governor, at H, includes a housing 25 having an upper chamber 26, an intermediate chamber 21, and a cylinder 28. A sylphon or bellows 29 has its upper end connected to the wall of the chamber 26 and its lower end connected to an abutment 30. A smaller bellows or sylphon 3| is connected, at its upper end, to the abutment 30 and, at its lower end, to the bottom wall of the chamber. Hence, the large and small sylphons 29 and 3|, together with the housing 25, provide a sealed primary pressure chamber 32 with which the primary pressure line 2| communicates, whereby negligible flow of fluid under primary pressure is required so that, not only are impulses quickly transmitted, but the power requirements of the primary pressure producing means are minimized.

As the sylphon 3| is of smaller diameter than the upper sylphon 29, it will be apparent that a lower annular primary piston area 33 is provided by the lower face of the abutment element 30, the primary pressure supplied by the line 2 I being effective against the annular piston area 33 to secure upward movement of the abutment 30 and the lower end of the sylphon 29. This upward movement is resisted by a spring 34 whose compression is varied by a movable spring abutment 35; and means, such as a screw member 36, is provided for moving the abutment upwardly and downwardly, the screw being turned in any suitable manner by a speed changer motor 31.

A spinner piston valve 38 fits the valve cylinder 28 and it has upper and. lower piston valve portions 40 and 4| separated by the annular space 42. (See Figs. 3 and 4.) The lower piston portion 4| normally just laps a pressure supply port 43 connected to the pressure supply passage 44; the intermediate annular space 42 continuously communicates with the secondary pressure supply passage 45; and the upper piston portion 40 laps the exhaust 46. i

It will, therefore, be apparent that, with downward movement of the piston valve, the-high pressure port 43 will be placed in communication, due to the annular space 42, with the secondary pressure supply passage 45 to increase the secondary or transformed pressure; and, with upward movement of the piston valve 38, the secondary or transformed pressure passage 45 will be placed in communication with the exhaust 48 connected to the drain system 41.

The spinner piston valve 38 extends vertically across the intermediate chamber 21 through the wall structure separating the intermediate and upper chambers, and within the small sylphon 3| to contact with the abutment 30, the upper end of the piston valve having a thrust bearing 48 preferably having single point contact with respect to abutment structure 30. The spinner piston 38 is preferably maintained in contact with the abutment structure 30 due to the fact that secondary pressure is applied to the secondary or lower piston area 49 at the lower end of the piston valve 38.

The thrust bearing between the abutment 30 and the spinner piston valve 38 has minimum pressure exerted thereon, with the result that a very efficient thrust bearing, preferably of the point type may be used. The reason for this is that the abutment structure 30 has the opposed primary fluid pressure and springforces applied thereto without such forces being imposed on the thrust bearing, the thrust bearing merely having to carry sufficient load to move the piston valve when the abutment structure moves in a direction toward the spinner piston valve, fluid pressure being utilized to cause the spinner piston valve to follow the motion of the abutment when the latter moves in the opposite direction. Hence, as the thrust bearing is subject to minimum load, minimum resistance to rotation of the spinner valve occurs.

Thus, it will be seen that the piston valve 38 tends to assume an equilibrium position in which the forces of the primary and secondary pressures applied to the primary and secondary piston areas 33 and 49, respectively, are counterbalanced by the force of the spring 34. If there is a change in primary pressure, then the equilibrium of forces is disturbed, and, consequently, the piston valve 38 moves to secure modification of the secondary or transformed pressure, the latter operation continuing until the change in secondary pressure is suflicient to compensate for the change in primary pressure when the piston valve will be restored to neutral or cut-off position.

From the transformer governor structure so far described, it will be apparent that an increase in primary pressure tends to move the abutment 30 upwardly, the spinner piston valve 38 following the abutment, but upward movement of the piston valve bringsabout reduction in secondary pressure, and, consequently, reduction in the pressure applied to the secondary piston face 49, this reduction in secondary pressure continuing until the force of the secondary pressure acting on the secondary face 49 is sufficiently reduced so that the spring 34.acting against the force of the primary pressure applied to the primary piston area 33 may move the piston valve 38 downwardly to its normal or neutral position.

If there is a reduction in primary pressure, the spring causes the abutment 30 to move downwardly, the piston valve 38 being pushed downwardly, and the secondary pressure supply passage being placed in communication with the high pressure port 43, whereupon there will follow an increase in secondary pressure, the secondary pressure increasing until the force thereof acting on the secondary pressure face 49 is sufficient to compensate for the reduction in primary pressure force acting on the primary piston face 33 in order that the spring and the fluid pressure forces may again be in equilibrium, at which time the piston valve 38 will be in neutral cut-off position.

The secondary pressure supply passage 45 is connected to the admission valve servo-motors I5.

To overcome static friction and to make the transformer governor more effective, the pilot valve is provided with turbine means to secure continuous spinning thereof. To this end, the

to move downwardly more than it would if the pilot valve has a rotor 50 against which is impinged motive fluid by the jet 50', the jet 50' being supplied from any suitable source, for example, from the high pressure passage 44.

An important feature of the present invention is to provide a governor'which is highly responsive to load change. To this end, the secondary pressure applied to the secondary piston area 49 of the transformer is modified. The secondary or transformed fluid under pressure is supplied through an orifice 5| to the space or expansible chamber 52 below the secondary piston face or area 49, and an air chamber or bell 53 is in communicatlon with the space 52. Preferably, the orifice area is adjusted by means of the needle valve 54.

For a given load, it will be apparent that there will be primary and secondary pressures which are related as determined by the primary and secondary piston areas, the secondary pressure also existing in the space below the secondary piston area or face and in the air chamber. If there is a gradual change in load, the piston valve 38 follows the motion of the abutment structure so that the secondary pressure changes in accordance with the change in primary pressure without lag; however, with rapid change in load, and consequently with rapid change in primary pressure, flow through the needle valve orifice is not sufficiently rapid to cause the pressure applied to the secondary piston face to change as rapidly as does the primary pressure, with the result that the pressure acting on the secondary piston face or area is effective, with the primary pressure, to produce over-travel of the piston valve and thereby to produce a greater extent of secondary pressure change than would be called for by the change in primary pressure. For example, assume a rapid drop in load, the turbine speed and the' primary pressure rapidly increase and the sylphon moves upwardly in consequence thereof. The piston valve follows the motion of the sylphon causing reduction in secondary pressure; however, due to the needle valve orifice, the pressure below the secondary piston face or area 49 cannot decline so rapidly, with the result that increased effort is applied to the piston valve to move the latter upwardly to reduce the secondary pressure quickly, the reduction in secondary pressure being carried to a greater extent than would be called for by the primary pressure change. The governor valve may, therefore, be closed before the closing speed is reached.

In other words, in this way, the governor is made responsive to the rate of change of speed so as to have an anticipating effect. With drop in load, as the device responds to the rate of change of speed, the governor valve may be operated upon before a change of substantial magnitude is attained. With drop in load, at a sufliciently rapid rate, the steam supply may be entirely out off, thereby preventing further acceleration of the rotor and allowing for the valve to be reset to a position to permit enough steam to be supplied to maintain the speed of the turbine for the load carried.

If there is a sudden increase in load, then the consequent sudden decrease in primary pressure causes the spring 34 to move the piston valve 38 downwardly, causing the secondary pressure to increase more rapidly than the pressure supplied to the secondary piston area or face 49, and, consequently, the piston valve tends secondary pressure built up rapidly below the secondary piston face or area. In other words, there would be a tendency for downward overtravel, and this would quickly bring about a change in secondary pressure to a greater extent than called for by the primary pressure change. The governor valve may, for example, move to wide open position so as to suddenly provide an increased supply of motive steam to the turbine, the governor valve then being reset by the transformer as the primary and secondary pressures are brought into normal relation with the secondary pressure applied to the secondary piston area 48 and the primary pressure attaining a value corresponding to the speed for the load carried.

As soon as permitted by flow through the needle valve orifice, pressurebelow the secondary piston face or area 49 comes into equilibrium with the secondary pressure, and this causes such motion of the piston valve that the secondary'pressure is changed to adjust the governor valve to a position corresponding to its normal speed at the existing load point. In other words, the needle valve orifice and the air chamber cause operation in response to rate of change of speed so that the required operation, depending upon the direction of change, occurs before substantial change in magnitude. the device may respond within a speed difference of a turn or a fractionof a turn of the spindle. On the other hand, if the device depended upon the extent or magnitude of change, the element of anticipation and consequent quick response would be absentthere would be overspeeding with drop in load and too great a speed drop with sudden increase in load. The action in response to rate of speed change causes the governor valve to close before the turbine reaches closing speed and to open wide before the speed drops to a point corresponding to wide open position of the valve.

In addition to the orifice and the air chamber' or accumulator serving as an anticipator, these features introduce a time element in the opera tion of the mechanism preventing hunting and violent fluctuations in the secondary or transformed pressure line. The adjustable orifice 5| restricts the rate of flow of secondary pressure to or from the expansible chamber 52 formed in.

part by the secondary piston face 49. The orifice 5| and the air chamber 53 work together to provide a desired time interval during which pressure change occurs in the secondary expansible chamber 52. When the apparatus is installed, the orifice needle valve 54 is adjusted for best operation and then it is locked in place.

The high pressure passage 44 is supplied from a high pressure line or system 55 supplied by the pump 56. Fluid under high pressure is preferably furnished from the line 55 for actuation of the servo-motor or motors l5.

In addition to the motive steam having to pass For example,

through the admission valve or'valves M, such 5 "by the branch 68 of the orifice line 63. I will be seen that, upon release of the orifice line 63 connected to the high pressure line 55 through an orifice 64.

The passage 63 has a branch 65 going to the trip valve 66 of the autostop or emergency governing mechanism, at 61, and a branch 68 going to the trip valve, at 69, the apparatus operating so that, when the emergency governor is effective, the pressure in the line 63 is suddenly reduced, the orifice 64 preventing rapid replenishment thereof, so that the spring of the throttle valve is effective to secure sudden closure thereof and the trip valve, at 69, is operated as hereinafter pointed out.

The autostop oremergency governor is of the usual type, the turbine spindle I2 being provided with a diametrically extending pin 18 in the diametrically-extending chamber II and the pin is held normally in inactive position by a spring 12. The center of gravity of the pin I8 is arranged sufliciently eccentric and the spring 12 of such force is chosen that, when a predetermined overspeed of the turbine is attained, the pin 18 suddenly flies radially outward, thereby acting on the tripping mechanism, at I3, to release pressure applied to the spring I4 to hold the valve 66 closed, whereupon the latter valve opens, thereby permitting of release of pressure in the orifice line 63 and the branches 65 and 68 for the purposes just stated.

Referring to the trip valve, at 69, this comprises an upper cylinder I6 and a somewhat shorter lower cylinder 11 of larger diameter than the cylinder 16. A piston valve I8 is arranged in the cylinders. The secondary or transformed pressure supply line 45 is provided with a release passage I9, which communicates with the upper portion of the cylinder 16. A drain passage 88 communicates with the cylinder 16 a suitable distance below the point of communication of the release passage I9 so that the piston portion 8| of the piston valve I8 is normally effective to interrupt communication between the passages I9 and 88; however, as hereinafter pointed out, with downward movement of the piston valve I8, the secondary release passage 19 is placed in communication with the drain, whereupon the secondary or transformed pressure in the line 45 is released in order to bring about closure of the servo-motor or motors of the admission valves.

Both the high pressure line- 55 and the high pressure passage 44 communicate with the cylinder I6, the point of communication being preferably at the same level and piston portions 82 and 88, with the annular space 84 therebetween preferably normally affording communication between the high pressure passage 55 and the supply passage 44, but, with downward movement of the piston valve 18, the piston portion 82 interrupts such communication, thereby cutting off the supply of high pressure fluid to the transformer governor. I

The piston valve 18 has connected to the lower end thereof a piston 86 arranged in the lower cylinder 11, a spring 81 preferably acting downwardly on the piston and the piston being forced upwardly by the force of fluid pressure supplied Thus, it

pressure, not only will the throttle valve close, but also the pilot valve 18 of the trip device, at 69, will move downwardly to release the secondary or transformed pressure and to interrupt the supply of high pressure fluid to the transformer governor.

The servo-motors, at l5, may be of any suitable type so long as they are effective to bring about closure of the governor or admission valves upon drop in secondary or transformed pressure. To this end, in Fig. 1, I show the servo-motor l5 comprised by a housing having an operating cylinder 88 with an operating piston 89 therein, a spring 98 being disposed above the piston to exert its force thereon. The piston 89 is moved by fluid pressure applied to its lower face in the manner to be pointed out, increase in fluid pressure causing upward movement of the operating piston 89 until the fluid pressure force is in equilibrium with the force of the spring 98 and reduction in fluid pressure force applied below the piston89 causing downward movement of the piston under influence of the'spring force.

Referring now to the means for applying and modifying fluid pressure applied to the operating piston 89, it will be seen that the secondary pressure supply line 45 communicates with the annular space 9| formed at the lower portion of the servo-motor housing or cylinder, the governor valve stem 92 extending through the annular portion. The valve stem or rod 92 has radial passages 93 communicating with an axial passage 94 to afford communication between the annular space 9| and the interior cylinder 95 of the operating piston structure.

A passage 96 communicates with the space below the operating piston 89 and the interior of the cylinder 95 and a passage 91 communicates with the cylinder 95 at a point below the point of communication therewith of the passag e 96 and it communicates with the annular space 98 formed about the operating piston.

.A pilot valve 99 is arranged in the cylinder 95, a scale spring I88 being disposed in the cylinder and tending normally to move the pilot valve 99 downwardly. The pilot valve 99 is moved upwardly against the force of the spring I88 by secondary pressure applied through the passage 94 and acting against the lower piston portion I8I carried by the pilot valve. The passage 96 is normally lapped by an intermediate piston portion I82 of the pilot valve. With upward movement of the pilot valve in response to an increase in secondary pressure, ensuing as a result of decrease in primary pressure with increase in turbine load and speed thereof, the pilot valve moves upwardly to establish communication between the high pressure space 98 en compassing the operating piston and the passage 96 communicating with the space below the operating piston, whereby the operating piston is raised by the high pressure supplied from the high pressure line 56 until such time as the piston portion I82 interrupts communication between the passages 91 and 96. On the other hand, with a decrease in secondary pressure, the pilot valve moves downwardly to place the passage 96 in communication, through the port I 88, with the space above the piston valve, the latter space being connected with the drain 41; and, thereupon, the operating piston moves downwardly until communication with the space below the operating piston, through the passage 96, is

I again interrupted. With release of the secondary or cut-off position of the latter, it will be apparent that the spring force and, therefore, the secondary pressure, vary from a minimum to a maximum for complete movement in one direction of the operating piston and the connected valve and from maximum to minimum for complete movement in the other direction. Accord ingly, the spring I serves the required function of a scale spring customarily employed in a governing system.

The apparatus shown in Fig. 2 is generally similar to that already described, except that the transformer governor, at I1, in addition to having primary pressure imposed thereon by the primary pressure line 2I, also has tertiary pressure applied thereto and derived from a back pressure regulator, at I06. Furthermore, different types of operating devices or servo-motors for the admission valves are shown at Ia. In addition, the secondary pressure release operative in response to autostop or emergency governor is modified.

Referring first to the back pressure regulator at I06, this may be of any suitable type provided that requisite sensitivity is aiforded. I prefer to use a regulator of the type shown and described in my application, Serial No. 729,372, filed June 7, 1934. Referring to Fig. 2, it will be noted that the regulator includes a housing I01 provided with upper and lower chambers I08 and I09 separated by body structure IIO providing a cylinder III. A piston valve H2 is disposed in the cylinder and it is arranged to place the outlet passage II3 either in communication with the inlet passage II4 supplied from the impeller chamber I9 or with the exhaust passage I I5 communicating with the lower chamber I09, the latter chamber being connected to the drain II6. Hence, with upward movement of the piston valve II2, pressure in the outlet II3 will increase because of communication thereof with the pressure supply passage II4. On the other hand, with downward movement of' the piston valve II2, pressure in the supply line I I3 will decrease because of communication thereof with the exhaust. The pressure line II3 communicates with the upperchamber 26 of the transformer governor so as to act on the upper face of the abutment 30 in the same direction as the spring 34.

From the structure described, it will be apparentthat the transformer governor, at I1, of Fig. 2 operates exactly in the same manner as the transformer governor in Fig. 1, except that an additional fluid pressure is applied thereto, fluid pressure from the back pressure regulator, at I05, being supplied by the passage II3 to the space above the abutment 30. Therefore, not only does the transformer governor serve to control the admission of steam to the turbine in accordance with the load but also controls the admission so as to maintain a predetermined back pressure. It will be obvious that the back pressure regulator may be used in any suitable manner; it may be associated with the line between high and low pressure turbines, with an inter-.

stage bleeder line, or with the back pressure line of a single turbine.

A back pressure steam connection H1 is connected, for example, to the connection II8 between high and low pressure turbine elements, the connection supplying steam to the chamber II9 so that its pressure may be exerted on the' sylphon I20 arranged in the chamber, the sylphon having a piston or abutment face I2I which bears against a stem I 22 carried by the abutment member I24, the latter bearing against the upper end of. the spring I25 as well as against the pointed end I26 of the piston valve II 2.

The lower end of the piston valve I I2 has a point bearing connection I21 with respect to an abutment I28 against which bears a spring I29 arranged in the lower chamber I09. The lower end of the spring I29 is engaged by an adjustable abutment I30, the adjustment mechanismbeing preferably constructed and arranged so as to prevent leakage on account of adjustment. For the latter purpose, the abutment I30 is preferably made cup-shaped as to enclose a bellows or sylphon I3I connected at its upper end to the abutment or follower I33 and at its lower end to the lowermost wall of the lower chamber I09. The sylphon, therefore, provides space to accommodate the adjustment screw or member I32, which may have a connection with respect to the lower wall which is sealed from the interior of the lower chamber I09.

From the back pressure regulator structure so far described, it will be apparent that the piston valve H2 is subject to opposing forces, the force of the spring I29 acting upwardly on the piston valve I I2 and the force of the steam pressure acting downwardly, through the sylphon abutment, on the pilot valve against the force of the spring The pilot valve has an upwardly facing piston face or area I33 to which fluid under outlet pressure is supplied through the passage I34 containing an orifice provided by the needle valve I30, the purpose thereof being to subject the pilot valve to the effect of the outlet pressure. An accumulator, for example, an air bell I31 communicates with the passage I34 at the piston area side of the orifice. Outlet pressure acting on the piston area I33 tends to move thepiston valve II2 downwardly. v

Assuming an increase in back pressure, then the sylphon abutment I2I causes downward movement of the piston valve II2 placing the impeller passage H3 in communication with the exhaust II5, whereupon the pressure applied tov the governing transformer abutment 30 will be decreased and the transformer governor will operate to restrict the supply of steam to the turbine. With a reduction in the outlet pressure brought about in this way, the pressure applied to the piston face I 33 is also reduced, whereby the total of forces tending to cause the piston valve to move downwardly is reduced, this reduction in outlet pressure continuing until the force thereof acting on the piston face I33 is sufficient to counterbalance the back pressure force applied. due to increase in fluid pressure, whereby the piston valve is brought back to a neutral cut-01f position. On the other hand, with a decrease in pressure, the contrary operation takes place, the piston valve moving upwardly because of. the reduced steam pressure acting on the sylphon abutment I2l, thereby placing the impeller passage II4 in communication with the outlet passage II3 to increase the pressure thereof; and the pressure in the passage II3 will increase until such time as the increasing pressure applied to the piston face I33 is sufllcient to compensate for the diminishing steam pressure, whereupon the piston valve will be brought back to neutral or cut-ofi' position.

The piston valve preferably has spinning motion imparted thereto by any suitable means, for

example, a turbine including a rotor I39 carried by the valve.

In Fig. 2, the autostop plunger 10 operates trigger mechanism 13 to permit a valve 66 to open in order to release the pressure in the orifice line 63. the latter having branches going to the throttle valve 51 and to the valve trip device, at I40, the latter preferably consisting of a valve I which normally closes a port I42 of the secondary pressure supply passage 45, the valve I having a piston I43 pressed downwardly by a spring I44 and having the orifice line 63 supplying pressuretherebelow. With opening of the autostop or emergency governor valve 61, the pressure in the orifice line 63 is suddenly released, and the valve I4I moves downwardly under influence of the spring I44 to open the port I42 to drop the secondary or transformed pressure in the line 45.

In Figs. 2 and 6, there are shown servo-motor devices of a different type from that already described. Each serve-motor includes an operating piston I46 connected to a stem I46a, the stem being connected to the governor or admission valve. Each piston I46 is arranged in an operat ing cylinder I41 and the latter has spring means I48 therein and acting on top of the piston I46 so as to exert a biasing eifect thereon tending to move the admission valve in a closing direction.

The piston I46 is moved upwardly and downwardly by means of fluid under pressure supplied to and exhausted through the passages I49 and I50 and controlled by a piston valve II.

The piston valve I 5| is arranged in a valve cylinder I52 having upper and lower high pressure ports I53 and I54, respectively, adjacent to the ports I55 and I56 communicating with the passages I 50 and I49, respectively. Fluid under high pressure is supplied from the high pressure line 55 to the high pressure ports I53 and I 54.

The piston valve I5I is provided with suitablepiston portions I51, I58, I59 and I60 suitably spaced so as to afford communication with the ports, the piston portions I58 and I59 normally lapping the ports I55 and I56. If the piston valve moves upwardly, the upper passage I50 will be placedin communication with the exhaust port I6I and the lower passage I49 will be placed in communication with the high pressure supply port I54, whereupon the operating. piston I46 is caused to move upwardly. On the other hand, if the pilot valve I5I is moved downwardly, pressure will be exhausted from below the piston I46 and applied to the space thereabove.

Secondary pressure from the secondary pressure line 45 is supplied to a chamber I 62 containing at its upper end a sylphon or bellows I63 having an abutment I64. A tension spring I65 is connected to the abtument I64 at one end and the other end of the spring is connected to a threaded screw I66, whereby the spring pull acting in opposition to the secondary pressure may be suitably varied.

The upper end of the piston valve is connected to the lower end of the tension or scale spring I61, the scale of the latter being substantially less than that of the spring I65, the upper end of the spring I 61 being connected to one end of the follow-up lever I16, fulcrumed at an intermediate point I16a, the other end of the latter being pivotally connected to the valve rod I46a.

Assuming that there isv a decrease in load and consequent increase in speed, the primary pressure delivered to the transformer increases and the secondary pressure delivered by the latter through the conduit 45 to the chamber I62 decreases. Therefore, due to this decrease in secondary pressure, the force thereof acting on the piston face I64 becomes less and the consequent preponderating force of the load spring I65 causes the pilot valve to be pulled down against the reduced secondary pressure and the tension of the scale spring I61 with the result that fluid under high pressure is supplied above the operating piston I46 and fluid below the latter is exhausted and the operating piston moves downwardly, such downward movement of the operating piston and movement of the admission valve ina closing direction continuing until such time as the increased tension force of the scale spring is sufficient to overcome the load spring to bring the pilot valve back to neutral or cut-off position.

On the other hand, should the turbine speed decrease due to increase in load, then the secondary pressure supplied to the chamber I62 would increase thereby causing the pilot valve to move upwardly, with increase in the tension force of the load spring I65 and decrease in the tension force of the'scale spring I61; however, such movement of the pilot valve causes motive fluid to be admitted below the operating piston and the latter moves upwardly, and such upward movement of the operating piston will continue, the upward movement being accompanied by decrease in the tension force of the scale spring I61, until such time as the decrease in the tension force of the scale spring is sufiicient to counteract the increase in tension force of the load spring I65, whereupon the pilot valve will be restored to neutral or cutoif position. The scale spring exerts maximiun tension force with the admission valve in closed position and minimum tension force with the valve full open. In this way a scale effect is given to the governing system, there being a range of secondary pressures corresponding to the range of tension forces of the scale spring.

Thus, it will be seen that, under all conditions of operation, a change in secondary pressure is accompanied by movement of the pilot valve, such movement being resisted by the resultant of the tension forces of the load and scale springs and that the consequential movement of the operating piston results in follow-up motion being applied to the scale spring so that the tension force thereof is modified in such manner that the load spring may restore the pilot valve to neutral or cut-off position.

If desired, dash pot apparatus may be associated with the scale spring to avoid hunting effects. To this end, I show the upper end of the scale spring connected to a screw member I69, the latter being held between the head I of the stem I1I, pivotally connected to the upper end of the follow-up lever I16, and a spring I12, the upper end of the spring I12 bearing against the bottom of the inverted cup-piston I15. The stem I1I extends through the bottom portion of the cup piston so that the'spring I12 functions to hold the cup piston upwardly against suitable abutment means at I1Ia. The cup piston i fits within the cylinder I68 so that the space of the latter below the cup piston provides a displacement chamber. The cylindcr has an adjustable orifice at I68a, which restricts to any desired extent the freedom of ingress and egress of fluid into and out of the displacement chamber. The dash pot arrangement prevents jerky or hunting movements of the apparatus. It is to be understood, of course, that the dash pot arrangement is an auxiliary device which may or may not be used, as desired, for the scale spring is fully effective to accomplish its intended purposes, as just pointed out, without having dash pot means associated therewith.

The dash pot comprised by the piston I14 and the cylinder I avoids jerky or hunting movements of the apparatus.

In Fig. 5, I show a further form of transformer governor wherein the impeller pressure is used as the source 01' supply for the transformed or secondary pressure. In this view, I show a housing structure I10 having an upper chamber In, an intermediate chamber I80, and a cylinder having an upper portion I02 01' larger diameter than a lower portion I83.

A sylphon or bellows I is disposed in the upper chamber and has its upper end connected to the wall thereof. The lower end of the sylphon has an abutment I05 engaging the point bearing I" of the spinner piston valve structure I31. A compression spring I" bears at its bottom against the abutment I 05 and has its upper end engaged by a follower I" which is adjusted upwardly and downwardly bythe speed changer motor I".

The piston valve structure III has an impeller or turbine element ISI arranged in the intermediate chamber I80, 9. piston portion I32 disposed in'the cylinder portion I02 of larger diameter and defining a downwardly facing secondary piston face I93 and a piston portion I34.

Oil under primary pressure is supplied from the impeller to the passage I36 for action against the primary pressure face afforded by the sylphon. Also, fluid is supplied from the passage I96 to the jet Ilia to impart spinning motion to the rotor IOI to avoid static friction of the piston valve structure.

With an increase in primary pressure, the

sylphon abutment I85 will be caused to move upwardly; and, as the piston I has a groove Ifla affording communication between the high pressure port and the space below the piston,

primary pressure also acts upwardly on the lowerface I35 of the piston portionJll, the spinner piston structure will thereby be caused to follow the motion of the sylphon, but, immediately upon such-upwardmovement, a groove I31 cut in the piston element I32 afiords communication of the secondary pressure space or passage IS! with the exhaust or drain, whereupon the secondary pressure declines, whereby the upward acting secondary force acting on the piston face I33 is reduced sufliciently so that the spring may overcome the increased primary force to move the piston valve Ill back to neutral or cut-off position. 0n the other hand, with a decrease in impeller pressure, the contrary operation takes place, the piston valve structure I31 moving downwardly under influence of the spring I" due to decrease in impeller pressure, causing the groove IS! in the lower piston valveportion I to place the high pressure supply passage 200 in communication with the secondary passage I90, so as to increase the secondary or transformed pressure, this increase continuing until the increasing secondary pressure force acting on the piston face I93 in an upward direction is 2 sufficient to counteract the diminishing primary orifice 202 and an air bell 203 is arranged between the needle valve and the servo-motor. This arrangement, while giving governor control of the base load machine, avoids response to frequency fluctuations. Where the tubine and its connected generator are used for base load operation, it is desirable to avoid disturbance of the governing system on account of frequency fluctuations, it being customary to have the base load generator connected to a system supplied'by other generators. Frequency disturbances may, therefore, be imposed on the rotary parts of the base load machine and these disturbances would react on the governing system and the admission valve controlled thereby unless the arrangement shown in Fig. '7 were employed. While frequency fluctuations may produce fluctuations in secondary pressure supplied by the passage 45, the secondary pressure fluctuations are substantially damped or absorbed by the cooperation of the orifice 202 and the air chamber 203 arranged at the admission valve side of the orifice, whereby the governor is efiectiveto control the admission valve to secure admission of steam suitable to load requirements 'without the latter being afiected by frequency fluctuations.

With a transformer governor, such as shown in Fig. 1, and the needle valve 20I and the air bell or chamber 203 arranged in the line between adjusting the needle valve 20I to restrict the bers being shown at 53, I31 and 203, it will be apparent that other types of accumulator means may be used. For example, in Fig. 8, I show the expansible chamber for the piston area subject to secondary or outlet pressure formed in part by a bellows 205 whose expansion or distention is resisted by the spring 206, the force of the latter being varied by the follower 201 carried by the threaded stem 208. The bellows form is advantageous in that there is no chance of the accumulator becoming ineffective because of loss of air.

From the foregoing, it will be apparent that as the governing mechanism is of the pressure transformer type, it is highly sensitivev to speed changes. Sensitivity of the transformer governor is increased by having a spinner piston valve and also by having such valve relieved of primary pressure and spring forces so that mini-mum pressure occurs in the thrust bearing between the spinner piston valve and the abutment structure the admission valve means adjusted to admit the proper amount of steam to operate the turbine at the speed required for the load, but it may anticipate rapid changes in load so as to minimize changes in speed or be made to operate more sluggishly depending upon the need. Furthermore, the pressure transformer governor cooperates in peculiar ways with other elements of the power plantinstallation: the governor is adapted to be acted upon by back pressure regulator, the operation being so sensitive that the regulator performs its function of holding the back pressure within a very narrow range of variation; the governor apparatus is peculiarly suitable for primary pressure developing means of low power consumption, this advantage following from the characteristic of the governor of being responsive to pressure change without requiring any flow on account of leakage; and the transformer, due to its particular arrangement of parts and connections, provides for an advantageously cooperative arrangement with pressure controlled parts of the plant such as the admission and throttle valves and the emergency governor, the pressure system or systems therefor being specially arranged to cooperate with features of the transformer governor.

-While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary pressure port; a piston valve movable from an intermediate cut-ofl? position, in one direction, to establish communication of the secondary port with the inlet port, and, in the other direction, to establish communication of the secondary port with the exhaust connection, whereby the secondary or transformed pressure in the supply passage is varied; a movable abutment provided with a piston area; a thrust bearing between one end of the piston valve and the abutment; means providing for the application of fluid under primary pressure to the abutment piston area; biasing means having its force acting on the abutment in opposition to the force of the primary pressure; means providing a secondary piston area on the piston valve; means for supplying fluid under secondary pressure to the secondary piston area; said secondary piston area being so disposed that, with movement of the piston valve in consequence of primary pressure change, the force of the resulting secondary pressure, is effective to restore the I piston valve to neutral or cut-off position; and

means for imparting spinning motion to the piston valve.

. 2. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary port; a piston valve movable from an intermediate cut-off position, in one direction, to establish communication of the secondary port with the inlet port, and, in theother direction, to establish communication of the secondary port with the exhaust connection, whereby secondary or transformed pressure of fluid in the supply passage may be varied; an abutment; a thrust bearing between one end of the piston valve and the abutment; said abutment having a piston area at the thrust bearing side thereof; means providing for the application of fluid un der primary pressure to said piston area; a spring acting on the abutment in opposition to the primary pressure; means providing a secondary piston area on the piston valve; means for supplying fluid under secondary pressure to the secondary piston area; said secondary piston area being so disposed that, with movement of the v piston valve in consequence of primary pressure change, the force of the resulting secondary pressure is effective to restore the piston valve to neutral or cut-off position; and means utilizing fluid under pressure for spinning the piston valve and including a turbine rotor carried directly by the latter.

3. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary pressure port; a piston valve mov able from an intermediate cut-off position, in one direction, to establish communication of the secondary pressure port with the inlet port, and in the other direction, to establish communication of the secondary pressure port with the exhaust connection; an abutment providing a primary piston area; a thrust bearing between one end of the piston valve and the abutment; bellows means cooperating with the abutment to define a fluid-tight compartment whose interior surface is provided in part by the primary piston area; means for supplying fluid under primary.

pressure to said chamber; a spring acting on the abutment in opposition to the primary pressure; means providing a secondary piston area on the piston valve and facing in such a direction that pressure applied thereto causes the .piston valve to follow the motion of the abutment; means providing for the application of fluid under secondary pressure to said secondary piston-area; and means for imparting spinning motion to the piston valve.

4. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary pressure port; a piston valve movable from intermediate cut-off position, in one direction, to establish communication of the secondary port with the inlet port, and in the other direction, to establish communication of the secondary port' with the exhaust connection; an abutment; a thrust bearing between one end of the piston valve and the abutment; said abutment having a piston face at the thrust bearing side thereof; means for applying fluid under primary pressure to the abutment piston area; a spring acting on the abutment in opposition to the primary pressure; means providing a secondary piston area on the piston valve and facing in the same direction as that of the primary piston area; means for supplying'fluid under secondary pressure to the secondary piston area; and means utilizing fluid under pressure for spinning the piston valve and including a turbine rotor carried directly by the latter.

' 5. In combination, means providing fluid under primary pressure; a movable abutment having a primary piston area subject to fluid under primary pressure; spring means acting on the abutment in opposition to the fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust con, nection, and a'secondary pressure port; means providing a supply passage communicating with the secondary pressure port; a piston valve movable with the abutment to place the secondary pressure port in communication either with the inlet port or with the exhaust connection to secure variation of fluid under secondary pressure in the supply passage; means providing a secondary piston area on the piston valve; means providing for the application of fluid under secondary pressure to the piston area; said secondary piston area facing in such a direction that the secondary pressure imposed thereon acts in a direction opposite to said spring means; a thrust bearing between said abutment and the adjacent end of the piston valve; and means for imparting spinning motion to the piston valve.

6. The combination with a prime mover having an admission valve, of means for developing fluid under primary pressure which is a function of the prime mover speed; pressure supply means; a cylinder having an inlet port communicating with the pressure supply means, having an exhaust connection, and having a secondary or transformed pressure supply port; a piston valve for placing the secondary pressure port in communication with the inlet port or with the exhaust connection to vary the secondary pressure; means for moving the piston valve including primary and secondary piston areas subject to primary and secondary pressures, respectively, and biasing means whose force opposes the force of the primary pressure applied to the primary piston area; a servo-motor for adjusting said admission valve and including a pilot valve for controlling the admission and exhaust of motive fluid thereto; a pressure responsive device for moving the servomotor pilot valve; a passage for supplying fluid under secondary pressure from said secondary pressure supply port to the pressure-responsive device; and scale spring means exerting force on the servo-motor pilot valve such that a range of secondary pressures from a lower pressure to a higher pressure is required to move the pilot valve sufliciently to secure full range of movement of the servo-motor in one direction and from the higher pressure to the lower pressure for such movement in the other direction.

7. The combination with a prime mover having an admission valve, of means for developing fluid under primary pressure dependent on the prime mover speed; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary pressure port; apiston valve movable to establish communication of the secondary pressure port either with the inlet port or with the exhaust connection to provide a variable secondary pressure; a movable abutment having a primary piston area subject to primary pressure; a spring exerting its force on the abutment in opposition to that of the fluid under primary pressure; abutment means between one end of the piston valve and the movable abutment and including a thrust bearing; means providing a secondary piston area for the piston valve and so supply passage and responsive to secondary pressure.

8. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure port; means providing a supply passage communicating with the secondary pressure port; a piston valve for placing the secondary pressure port in communication either with the inlet port or with the exhaust connection to secure variation in secondary or transformed fluid pressure; means for actuating the piston valve including primary and secondary piston areas; means for applying fluid under primary pressure to the primary piston area; means including an orifice for supplying fluid from said supply passage to said secondary piston area; and an accumulator in communication with the last-named means at the secondarypiston area side of the orifice.

9. In combination, means providing fluid under primary pressure; a cylinder having an inlet port supplied with fluid under pressure, an exhaust connection, and a secondary pressure supply port; means providing a supply passage communicating with the secondary pressure port; a piston valve movable from an intermediate cut-off position, in one direction, to establish communication of the supply port with the inlet port, and, in the other direction, to establish communication of the secondary port with the exhaust connection; spring means for moving the piston valve in one direction; means responsive to fluid under primary pressure and acting in opposition to the spring means to provide movement of the piston valve in the other direction; means providing a secondary piston area on the piston valve; means for supplying fluid under secondary pressure to the secondary piston area and including an orifice; and an accumulator communicating with the lastnamed means at the secondary piston area side of the orifice; said secondary piston area being so disposed that, with movement of the piston valve in consequence of primary pressure change, the force of the resulting secondary pressure is effective to restore the piston valve to neutral or cutoff position.

10. In combination, means providing fluid under primary pressure, a pressure transformer uti 'zing fluid under primary pressure to provide a secondary or transformed fluid pressure, said transformer including primary and secondary piston areas, means for subjecting the primary piston area to primary pressure, means providing a delivery passage for fluid under secondary or transformed pressure, means providing a branch passage including an orifice for supplying fluid under secondary pressure from the delivery passage for action on the secondary piston area, and an air chamber communicating with the branch passage at the secondary piston area side of the orifice.

11. In a prime mover, admission valve means,

means providing a primary fluid pressure varying as a function of the prime mover speed, means utilizing the primary pressure to provide a transformed or secondary pressure having normal predetermined relation with respect to the primary pressure, means responsive to transformed or secondary pressure to control the admission valve means, and means responsive to'exceeding a predetermined rate of primary pressure change and speed change to cause change of secondary pressure at a greater rate than that corresponding to the rate of primary pressure change to efiect quick adjustment of the valve means for normal speed of the prime mover for the load condition.

12. The combination with a turbine having admission valve means; of means for biasing the admission valve means in a closing direction; pressure responsive means for controlling the admission valve means; means for developing fluid under primary pressure which is a function of the turbine speed; a cylinder having an inlet port, an exhaust connection, and a secondary pressure' port; a passage for supplying fluid under high pressure to the inlet port; a piston valve movable to establish communication of the secondary pressure port either with the inlet port or with the exhaust connection to secure variation in transformed or secondary pressure; means for imparting spinning motion to the piston valve; means providing a primary piston area subject to primary pressure; abutment mean's between the means providing the primary piston area and one end of the piston valve and including a thrust bearing; a spring exerting its force on said abutment means in opposition to the force exerted thereon by-the primary pressure; means providing a piston area on the piston valve; means providing for the application of fluid under pressure to said secondary piston area; an overspeed governor operated by the turbine; and means responsive to operation of the overspeed governor to interrupt said high pressure passage and to release the pressure in the secondary passage, so that said biasing means may close the admission valve means.

13. The combination with a turbine having admission valve means; of means for biasing the admission valve means in a closing direction; pressure responsive means for controlling the admission valve means; means for developing fluid under primary pressure which is a function of the turbine speed; a cylinder having an inlet port, an exhaust connection, and a secondary pressure port; a passage for supplying fluid under high pressure to the inlet port; a piston valve movable to establish communication of the secondary pressure port either with the inlet port or with the exhaust connection to secure variation in transformed or secondary pressure; means for imparting spinning motion to the piston valve; means providing a primary piston area subject to primary pressure; abutment means between the means providing the primary piston area and one end of the piston valve and including a thrust bearing; a spring exerting its force on said abutment means in opposition to the force exerted thereon by the primary pressure; means providing a secondary piston area on the piston valve; means providing for the application of secondary pressure to said secondary piston area; a branch passage supplied with fluid through an orifice from said high pressure passage; a pressure release passage connected to said secondary passage; a valve in the release passage; a valve in said high pressure passage and disposed between the branch connection and said cylinder; a pressure-responsive device connected to said branch passage and efiective normally to maintain the secondary release pasage valve closed and the high pressure passage valve open; an overspeed governor operated by the turbine; and means responsive to operation of the overspeed governor to release pressure. in said branch passage to cause operation of the lastnamed pressure responsive device to secure closure of the high pressure passage valve and opening of the secondary release passage valve so that said biasing means may close the admission valve means.

14. The combination with a prime mover having admission valve means and a throttle valve, of biasing means for closing the admission valve means; pressure responsive means for controlling the admission valve means; means responsive to pressure for holding the throttle valve open against the force of biasing means; means for developing fluid under primary pressure which is a function of the prime mover speed; means including a passage providing a source of fluid under high pressure; a secondary pressure supply passage connected to said admission valve controlling means; a cylinder having high pressure, secondary pressure, and exhaust connections; said high pressure and secondary pressure connections being connected to the high pressure and secondary pressure passages; a piston valve movable in opposite directions in said cylinder to place the secondary pressure connection in communication either with the high pressure connection or with the exhaust connection; means for imparting spinning motion to the piston valve; means providing a primary piston area subject to primary pressure; abutment means between the primary piston area providing means and one end of the piston valve and including a thrust bearing; a spring exerting force on the primary piston area in opposition to the force exerted thereon by the primary pressure; means providing a secondary piston area on the piston valve; means providing for the application of secondary pressure to said secondary piston area; a branch passage supplied with fluid through an orifice from said high pressure passage and connected to the pressure responsive means of the throttle valve; a pressure release passage connected to said secondary passage; a normally closed valve in the release passage; a normally open valve in said high pressure passage between said branch connection and said cylinder; a pressure responsive device connected to said branch passage and effective normally to maintain the release passage valve closed and to maintain the high pressure passage valve open; an overspeed governor operated by the prime mover; and means responsive to operation of the overspeed governor at a predetermined overspeed of the prime mover to release the pressure in said branch passage to bring about closure of the throttle valve, closing of said high pressure passage valve, and opening of said secondary release passage valve so that said biasing means may close the admission valve means.

15. The combination with a prime mover having an admission valve moved by a servo-motor and having means for developing fluid under pressure which varies as a function of the prime mover speed, of means responsive to said fluid pressure to provide transformed fluid pressure bearing predetermined relation with respect thereto, a passage for supplying fluid under transformed pressure to the servo-motor to control the operation of the latter, means providing an orifice in said passage to restrict the flow rate therethrough, and accumulator means in communication with said passage between the orifice and the passage for supplying fluid under secondary pressure to said servo-motor, an exhaust connection, a piston valve for placing the secondary pressure supply passage in communication with said supply means or with the exhaust connection, means for imparting spinning motion to the piston valve, means for actuating the piston valve including primary and secondary piston areas subject to said primary and secondary pressures, respectively, a passage for supplying fluid from the secondary passage to the secondary piston area and provided with an adjustable orifice, an accumulator in communication with said supply passage between the orifice and the secondary piston area, an adjustable orifice in the secondary supply passage, and an accumulator communicating with the secondary supply passage between the lastnamed adjustable orifice and the servo-motor.

ANTHONY F. SCHWENDNER.

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