US2294753A

US2294753A - Elastic fluid turbine arrangment

Info

Publication number: US2294753A
Application number: US367565A
Authority: US
Inventors: Sverker N Hedman
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1940-11-28
Filing date: 1940-11-28
Publication date: 1942-09-01
Anticipated expiration: 1959-09-01

Description

Sept. 1, 1942. s. N. HEDMAN ELASTIC FLUID TURBINE ARRANGEMENT Filed Nov. 28, 1940 2 Sheets-Sheet 1 Invenfipr:

SveYkeF N. Heciman a AMZ A otorrw ey.

ELASTIC FLUID TURBINE ARRANGEMENT Filed Nov. 28, 1940 2 Sheets-Sheet 2 Fig.2.

Inventov: SVGBTKGT" N. Hecirnan,

his A Attpbney Patented Sept. 1, 1942 2,294,753 ELASTIC FLUID TURBINE ARRANGEMENT Sverker N. Hedman, Stoneham, to General Electric Company,

New York Mass, assignor a corporation of Application November 28, 1940, Serial No. 367,565

9 Claims.

The present invention relates to elastic fluid turbine arrangements or power plants in which a stage of an elastic fluid turbine normally is supplied with elastic fluid from. a low pressure source and during abnormal conditions such as upon failure of the low pressure source is connected to a high pressure source. More specifically the invention relates to an improved governing mechanism for controlling the flow of elastic fluid from either of two sources of different pressure to an elastic fluid turbine and for transferring the turbine from operation with low pressure fluid to operation with high pressure fluid upon certain operating conditions.

The general object of my invention is to provide an improved construction and arrangement of the type above specified.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accom- Danying drawings.

In the drawings Fig. 1 illustrates an elastic fluid turbine arrangement embodying my invention, and Fig. 2 shows a modification according to my invention,

The arangement as shown in Fig. 1 comprises an elastic fluid turbine [8 having a stage with an inlet chest and a low pressure inlet conduit for receiving elastic fluid from a source of low pressure. In the present instance the conduit H is connected to a lower stage of a high pressure turbine |2 which latter has an inlet conduit |3 with a valve l4 connected to a source of high pressure fluid such as an elastic fluid generator or boiler IS. The conduit includes governing valve means, in the present example shown as a single throttle valve H; for controlling the flow of elastic fluid to the turbine and a stop valve arranged ahead of the valve l6 as regards the direction of flow of fluid therethrough. The turbine H1 is also directly connected by a conduit l8 to the source of high pressure fluid or boiler IS. The conduit l8 includes governing valve means in the present instance shown as a single throttle valve IQ for controlling the flow of high pressure fluid to the turbine and a stop valve 28 arranged ahead of the valve |9 as regards the direction of the flow of fluid therethrough. During normal operating conditions the valves l9 and 28 are closed and the valves l6, l1 opened as shown in the drawings whereby the turbine I8 is connected to receive low pressure fluid from the intermediate stage of the turbine l2. Upon certain operating conditions, such as upon failure or shut down of the turbine H or in case the fluid received from the turbine I2 is insufficient to carry the load on the turbine ID, the valves l6, H are closed and the valves l9, 28 are opened to connect the turbine l0 directly to the boiler IS. The transfer from low pressure operation of the turbine ID to high pressure operation is efiected automatically by means of a hydraulic governing mechanism in response to a predetermined operating condition.

In the present example the hydraulic governing mechanism includes hydraulic motors 2 22, 23 and 24 for operating the valves I6, l1, l9 and 28 respectively. Fluid under pressure is supplied to the motors by means including a pump 25 having an inlet 26 for connection to a source of fluid, such as oil, not shown, and a discharge conduit 21 connected by a conduit 28 to a multi-way valve, in the present example a 4-way valve 29. The latter serves for conducting fluid under pressure to one of the pairs of motors 2|, 22 and 23, 24 and simultaneously draining fluid from the other pair of motors.

The 4-way valve has a casing 30 with a movable valve member 3| therein forming four connecting grooves or

channels

32, 33, 34 and 35. In

- the drawings the valve member 3| is shown in a lower end position in which the channel 32 connects the supply conduit 28 with a conduit 36 for conducting operating fluid to the motors 2| and 22. In this position the channel 33 connects a drain conduit 31 to a conduit 38 for draining operating fluid from the pair of

motors

23, 24. In normal operating position the valves I9, 28 are closed and the valves |6, open, permitting the supply of fluid from the low pressure source I2 to the turbine I8. If the position of the movable valve member 3| of the 4-way valve 29 is reversed, the supply conduit 28 is connected through the channel 35 to the conduit 38 to supply operating fluid under pressure to the pair of

motors

23, 24 and at the same time the conduit 36 is connected through the channel 34 to the drain conduit 31 to drain fluid from the pair of motors 2|, 22. In this case the valves l6, l1 are closed and the valves I9, 28 are opened, thus connecting the turbine to the source of high pressure elastic fluid of the boiler l5.

The

hydraulic motors

22 and 24 are designed to open with lower oil pressure than the hydraulic motors 2| and 23. Therefore, the stop valves I1 and 28 will in general be either wide open or shut as required. The valves l6 and I9, however, which are governing or throttle valves will be positioned in response to changes of an operating condition of the turbine H), in the present example by means of a speed governing mechanism including a speed governor 39 driven from the turbine ii and connected to control a known type pilot valve 40. The latter has a valve sleeve 4| connected to the governor 39 and a bushing 42 connected by a link 43 to a follow-up mechanism described hereafter. The sleeve 4| and the bushing 42 form a restriction 44 to the flow of operating fluid from the pump 25. This restriction is controlled by movement of the sleeve 4| by the governor 39, and change of the restriction causes oil to flow in or out of the hydraulic'motor on-the governing valve, thus positioningthe governing valve in response to movement ofthe sleeve 4| and the governor 39.

During operation an increase in speed of. the turbine l due to decreasing demand for load causes downward movement of the pilot valve.

sleeve 4| by the governor 39, thus reducing the restriction to flow and'thereby causing operating fluid to be discharged from the hydraulic motor 2|. This results in downward movement of the piston of the motor 2| and closing movement of the valves lfito effect'a reduction in speed of the turbine.

A follow-up mechanism is provided in order to restore the pilot valve sleeve and bushing to their normal relative position in response to? movement of the hydraulic motor. To this end the piston of the motor 2| is connected by a link 45 to an intermediate point ofa follow-up lever 46. The right-hand end of the lever 46 engages a fulcrum 4T andithe left-hand end of the'lever 45 is connected'by a pivot 43 to the aforementioned link 43. With this arrangement, downward movement of the piston of the hydraulic motor 2| effects downward movement of the link 45 andcounterclockwise movement ofthe followup lever 45 aboutthe pivot 41, resulting in downward'movement of the link 43 and the bushing 42, thus restoring the latter to its normal position relative to the sleeve 4|.

A drop inspeed of the turbine Ill causes upward movement of the. pilot valve sleeve 4| whereby the pressure ofthe. operating fluid conducted to the motor 2| is increased to'effectupward movement of its piston and opening of the valve |3. themotor 2| causes clockwise turningmovement of the lever 46 on-the fulcrum 4? whereby. the bushing 42 is moved upward to restore the relative position. between the bushing 42 and the sleeve 4|.

The hydraulic motor 23 is similarly connected.

by a follow-up mechanism to the bushing 43. This mechanism comprises a link 49 connected to an intermediate point of a follow-up lever 50 which has a. right-hand end connected by the aforementioned pivot 48 to the link 43 and a left-hand end arranged in cooperative relation with a fulcrum The fulcrumsfl and 5| are formed on the ends of a lever member 52- which has an intermediate point held on a fulcrum 53. The lever 52 is normally biased towards a stop 54 by the action of a spring 55 so that the fulcrum 4'! engages the follow-up lever 45. Duringoperation of the turbine IS with high pressure elastic fluid the fulcrumed lever member. 52 is turned clockwise about the fulcrum 53 into engagement with another stop 55. In this position the fulcrum 5| engages the left-hand end of thefollow-up lever 50.

In order to change from operation of the'turbine ID with low pressure fluid to operation with Upward movement of. thepiston of.

high pressure fluid it is necessary to turn the fulcrum lever 52 and also to reverse the 1-way valve 29. This is accomplished automatically in response to certain operating conditions, in the present instance such transfer of operation is effected as the pressure in the conduit drops to a predetermined low value. The transfer mechanism comprises a device responsive to a condition of the fluid in the conduit |,.such as a pressure responsive device 5! connected to the conduit near the turbine l0 and carrying a contact-making member 58 for closing a relay circuit 59 for a relay 50. During operation the contact 58 closes the relay circuit 5'! as the pressure in thev conduit drops to a predetermined low value; Energization of the relay 60 causes closing of a relay circuit 5| for energizing two parallel-connected relays, a relay 62 for reversing the 1-way valve 29 and a relay 63 for reversing the position of the fulcrumed lever member 52; Energization of the relay 62-causes upward movement, that is;.reversing of the position of the 4-way valve 3|, and energization of the relay 63 causes clockwise turning movement of the fulcrumed lever member 52. until. the latter-engages the stop 56. Reversing of the 4-way valve and of the fulcrumed lever member transfers operation of the turbine l9 from low pressure to high pressure operation. As stated before, the motors 2|, 22 are connected through the channel 34 to the drain conduit 3'! andthe motors 9, 29 are connected through the channel 35 of the 4-way valve to the supply conduit 28. During high pressure. operationan increase in turbine speed causes downward movement of the pilot valve sleeve by action of the governor 39, thus reducing the pressure of operating fluid in the conduit 28 and eifecting the discharge of fluid from the motorv 23, whereby the lattermovesnormal position relative to the pilot valve sleeve 4|. During drop in turbine speed the. operation is similar, the. different elements moving in a direction opposite to that just described.

The arrangement also includes an. emergency governing mechanism for completely disconnectingltheturbine In from its source offluid during emergency condition. The emergency governing mechanism in the present example includes a valve 64 with a movable valve member 65. The. valve has an inlet connectedby. a conduit fifito thesupply conduit 28, and a. drain conduit 61. The movable valve member 65. is normally held in the position shown in thedrawings-in which it preventsthe. draining. of. fluid from. the conduit 66. by means of alatch BB engaging a catch 59 on the stem of themovable valvemember 65. The latch 68 hasaright-hand portion in. 00- operative relation with anemergency speed governor 10 held on a shaft-1| which may form part of the shaft of the turbine I81 Duringioperation the flyweight of the governor 'lfl is forced out withincreasing speedand ata certain predetermined high speed engages the. latch 68 to effect disengagement-between the latch 68 and of the latter. The operation of the emergency cause closing governing mechanism is the same for both pairs of'motors 2|, 22 and 23, 24.

The arrangement shown in Fig. 2 comprises a turbine or elastic fluid consumer I5 corresponding to the turbine I of Fig. 1 and having a shaft I6. Elastic fluid may be conducted to the turbine I5 from a boiler I! through a conduit I3 including a stop valve 79 and a throttle or governing valve 89 or through a conduit 8I including a stop valve 82 and a throttle or governing valve 83. The conduit 8! is connected to a crossover conduit 89 between a high pressure turbine 85 and a low pressure turbine 86. The high pressure turbine 85 is connected by a conduit 87 including a throttle valve 03 to the boiler 11. The cross-over conduit 84 between the high pressure turbine 85 and the low pressure turbine 83 includes a preheater 89 provided ahead of the connection between the conduits 80 and 8| as regards the direction of flow of fluid through the conduit. The valves [9, 93, B2 and 33 are controlled by a hydraulic governing mechanism including hydraulic motors 90, 9|, 92 and 93 respectively, the motors 9", 9I being connected in parallel and the

motors

92, 93 likewise being connected in parallel. Operating fluid is supplied to the motors by means of a pump 95 ccrresponding to the pump 25 of Fig. 1 and

conduits

95, 98. The conduit 96 may be connected to a conduit 91 for the

motors

92, 93 or to a conduit 98 for the mo-tors 90, 9| by means of a 4-way valve 99 corresponding to the 4-way valve 29 of Fig. 1 and having a movable valve member I00. The pressure of the operating fluid conducted to the hydraulic motors is controlled by a control member or pilot valve IOI with a sleeve I32 connected to a, speed governor I03 driven from the turbine shaft #6 and a bushing 94 connected to a follow-up lever I05. The hydraulic motors 9!, 93 for the governing

valves

80, 83 are designed so that they require a higher oil pressure to position them than the

hydraulic motors

90, 92 for the stop valves I9, 82 respectively. Therefore, at all times when the governing valves are being positioned in terms of oil pressure the

stop valves

78, 82 will be wide open. Only upon dumping of oil pressure from the

hydraulic motors

99, 92 will the stop valves I9, 82 close.

The mechanism so far described and its operation is similar to that described above in connection with Fig. 1 except that the present arrangement has a single follow-up lever I05 corresponding to the two follow-up

levers

46, 50 in Fig. l. The right-hand end of the follow-up lever I95 engages a fulcrum I05 and the lefthand end of the lever I05 is connected by a link I07 to an intermediate point of a followup lever I08 for the motors 9| and 93. The lever I08 is connected to a piston stem I09 of the motor 93 and to a piston stem III! of the motor 9!.

The transfer of the turbine I5 from low pressure to high pressure operation in the present example is efiected automatically by mechanical means in response to a predetermined load condition on the turbine I5. The transfer is accomplished by reversing the position of the 4-way valve 99. To this end the movable valve member I00 has a stem III which forms a catch H2 at its upper end. The catch is normally held by a latch II3 supported on a fulcrum II4. An arm of the latch is in cooperative relation with an extension or end portion '5 of the follow-up lever I08. Upward movement of the end portion II5 causes unlatching of the latch H3 whereby the movable valve member I00 drops downward to its lower end position in which the fluid supply conduit communicates with the conduit 98 for the motors 90, SI, and a drain conduit of the 4-way valve 99 communicates with the conduit 91 for the

motors

92, 93.

The arrangement also includes an emergency governing mechanism comprising a known type emergency flyweight governor IIB associated with the turbine shaft 16 in cooperative relation with a latch III. The latch III normally engages the lower end of a valv stem I I8 holding the latter in an upper end position in which a trip valve II9 in the oil conduit is closed.

During operation the emergency governor II6 at a predetermined speed unlatches the latch III, thereby permitting the valve stem IIB to move downward by the action of a spring I20, causing opening of the valve II9 with a consequentdrop of oil pressure in the system, thereby effecting closing the hydraulic motors and the valves connected thereto. During normal operation with the

valves

92, 83 in open position, as shown in the drawings, low pressure fluid is conducted from the cross-over conduit 34 to the turbine I5. An increase in speed, due to a drop in load on the turbine 15, causes downward movement of the pilot valve sleeve I02, thereby reducing the oil pressure in the conduits 96, 91 and effecting the discharge of oil from the motor 93. This causes closing movement of the latter and of the throttle valve 83. Downward movement of the piston stem I09 of the motor 93 causes downward movement of the follow-up lever I08 about its left-hand end as a fulcrum whereby the link I01 turns the follow-up lever I95 downward, moving the pilot valve bushing I09 intoits original position relative to the sleeve I02. During a decrease in speed the various elements move in the direction opposite to that just described, effecting opening of the

valves

82, 83 and an increased supply of elastic fluid to the turbine I5.

With an increase in load on the turbine I5 the throttle valve 83 is moved until they approach the fully open position. If then the load demand on the turbine I5 increases further, the

piston of the motor 93 is moved further upward until at a predetermined position the right-hand end portion II5 of the follow-up lever I08 unlatches the latch H3 and thus causes reversing of the position of the 4-way valve 99. As the movable valve member I00 is moved to its lower end position, operating fluid is drained from the

motors

92, 93 and simultaneously operating fluid is conducted to the motors 90, 9| for operating the stop valve I9 and the throttle valve 90 re- 'spectively in the high pressure line I8. During high pressure operation the motors 90, 9I are under the control of the speed governing mechanism. Increasing load demand causes opening of the valve 80 and decreasing load demand causes closing thereof. The follow-up action between the motor 9I and the bushing I04 of the pilot valve is effected through the link III], the follow-up lever I03, the link I01 and the follow-up lever I95. During follow-up action the lever I08 in this case turns about its pivotal connection with the piston stem I09 of the motor 93.

The arrangement shown in Fig. 2 operates automatically with regard to the transfer from low pressure operation of the turbine 15 to high pressure operation, but in contrast to the arrangement shown in Fig. 1 the present arrangement has to be reset manually in order to transfer the turbine l5from high pressure to low pressure operation. The manual resetting is accomplished by lifting the'movable valve member I00 of the 4-way valve 99 to engage the catch. H2 with the latch I [3.

Thus, with my invention I have accomplished an improved elastic fluid turbine or prime'mover arrangement in which a turbine or prime mover is normally supplied with elastic fluid from a low pressure source and upon insuflicient supply from such source is supplied with elastic fluidfrom a high pressure source; elastic fluid to a prime mover in accordance with my invention briefly includes a first conduit with a first throttle valve for conducting low pressure elastic fluid to a stage of th prime mover and a second conduit with a second throttle valve for conducting high pressure elastic fluid to said stage. The arrangement for controlling the throttle valves includes a source of controlledv operating fluid and means responsive to an operating condition of said prime mover to vary the pressure of the operating fluid supplied by the source. Each of the throttle valves is positioned by separate hydraulic motor means in accordance with the variation in pressure of the operating fluid from the source. The system in addition includes reversible means for selectively connecting either of the motor means to the source which means is normally positioned to effect supply of operating fluid from the source to the motor means controlling the first throttle valve. The reversible means is actuated by means responsive to a condition indicating insufiiciency of supply of elastic fluid to the prime mover by the low pressure source so that upon such insufliciency, communication is established between the source and the motor means for positioning the second throttle valve.

Having described the method of operation of my invention, together with the apparatus which- I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A system for supplying elastic fluid to a prime mover comprising means including a first conduit with a first throttle valve for conducting low pressure elastic fluid to a stage of the prime mover, a second conduit with a second throttle valve for conducting high pressure elastic fluid to said stage, a source of controlling fluid, means responsive to an operating condition of such prime mover to vary the pressure of the controlling fluid supplied by said source, hydraulic motor means for each throttle valve to position the valves in accordance with the variation in pressure of the controlling fluid from said source, means for selectively connecting either of the motor means to the source being normally positioned to efiect the supply of controlling fluid from the source to the motor means controlling the first throttle valve, and means responsive to a. condition indicating inability of the low pressure supply to meet the demands of the prime mover for actuating said selective means to establish communication between the source and the motor means for positioning. the second throttle valve.

2. Elastic fluid prime mover arrangement comprising a prime mover having a stage, means including a. first conduit with a first throttle valve for conducting low pressure elastic fluid to said A system for supplyingstage, means including a second conduit with a second throttle valve for conducting high pressure elastic fluid to-said stage, separate hydraulic motor means for positioning the throttle valves, a source of controlling fluid for the motors, re-

versible means for connecting the source to either of'the prime mover to vary the pressure of the fluid supplied from said source to the motors.

3. Elastic fluid turbine arrangement comprising an elastic fluid turbine having a stage, means including a first conduit with a first valve for conducting low pressure fluid to said stage, means including a second conduit with a second valve for conducting high pressure fluid to the same stage, and a hydraulic governing mechanism for controlling the valves comprising a first and a.

second hydraulic motor for the first and the second valve respectively, means for controlling the flow of operating fluid comprising a source of fluid pressure, conduit means including a 4-way valve connected betweenthe source and the motors, said 4-way valve in one position conducting fluid to the first motor. and draining fluid from the second motor to open the first valve and to completely close the second valve and in another position draining fluid from the first motor and conducting fluid to the second motor to completely close the first valve and to open the second valve, a speed governor driven from the turbine, a pilot valve operated by the speed governor and connected to said conduit means to control the fluid pressure. in the motors in response to speed changes, and'means responsive to a fluid condition in one of the conduits for automatically reversing the 4-way valve.

4, Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conduct-- ing high pressure fluid to the turbine, and a hydraulic governing mechanism for valves comprising a source of operating fluid under pressure, a first and a second hydraulic motor for the first and the second valve respectively, means for controlling the flow of operating fluid from the source to and from the motors to open and close them respectively-comprising conduits including a 4-Way valve connected between the source and the motors, a speed governor driven from the turbine, a pilot valve connected to the conduits including the 4-Way valve and actuated by the governor to control the fluid pressure in the motors in response to speed changes of the turbine, said 4-way valve in one position conducting fluid to the first motor in accordance with the pilot valve position and draining fluid from the second motor and in another position draining fluid. from the first motor and conducting fluid to the second motor at a pressure dependent.

upon the pilot valve position, and means responsive to a fluid, condition in one of the conduits for automatically reversing the 4-Way valve, said last namedmeans including a pressure responsive device connected to the-low pressure conduit, a relay connected to the 4-way valve and a relay to and from the motors:

controlling thecircuit for the relay actuated by the pressure responsive device.

5. Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conducting high pressure fluid to the turbine, and a hydraulic governing mechanism for controlling the valves comprising a source of operating fluid under pressure, a first hydraulic motor for the first valve, a second hydraulic motor for the second valve, conduit means including a 4-way valve connected between the source and the motors to conduct in one position operating fluid to the first motor and drain fluid from the second motor and in another position to conduct operating fluid to the second motor and drain fluid from the first motor, a pilot valve connected to the conduit means for controlling the fluid pressure in the motors, a governor for actuating the pilot valve in response to changes of an operating condition of the turbine, means including separate followup levers connecting the pilot valve to the motors, a fulcrumed lever member forming in one position a fulcrum for one of the follow-up levers and in another position a fulcrum for the other follow-up lever, and means for transferring the turbine from high pressure operation to low pressure operation and vice-versa upon a predetermined operating condition comprising relays for actuating the lever member and reversing the 4-way valve.

6. Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conducting high pressure fluid to the turbine, and a hydraulic governing mechanism for controlling the valves comprising a source of operating fluid under pressure, a first hydraulic motor for the first valve, a second hydraulic motor for the second valve, means including conduit means and a 4-way valve connected between the source and the motors to conduct in one position operating fluid to the first motor and drain fluid from the second motor and in another position to conduct opreating fluid to the second motor and drain fluid from the first motor, a pilot valve connected to the conduit means for controlling the motors, governor means for actuating the pilot valve in response to changes of an operating condition, means including separate follow-up levers connecting the pilot valve to the first and second motors, a fulcrumed lever member forming in one position a fulcrum for one of the follow-up levers and in another position a fulcrum for the other follow-up lever, and means for transferring the turbine from the high pressure operation to low pressure operation and vice-versa comprising relays for actuating the lever member and reversing the 4-way valve, a relay circuit for the relays and a device responsive to a fluid condition in one of the conduits for actuating the relay circuit.

7. Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conductating the trip valve.

ing high pressure fluid to the turbine, and a hydraulic governing mechanism for controlling the valves comprising a first hydraulic motor for the first valve, a second hydraulic motor for the second Valve, means including a 4-way valve for conducting in one position fluid to the first motor and draining fluid from the second motor and in another position for conducting fluid to the second motor and draining fluid from the first motor, and means cooperatively associated with the first motor and the 4-way valve for automatically reversing the 4-way valve in response to a predetermined position of the first motor in which position the first valve is substantially fully open and the supply of low pressure fluid is insufficient to carry the turbine load.

8. Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conducting high pressure fluid to the turbine, and a hydraulic governing mechanism for controlling the valves comprising a first motor for the first valve and a second motor for the second valve, means for controlling the flow of fluid to and from the motors including a governor driven from the turbine, a pilot valve operated by the governor, a multi-way valve connecting the pilot valve to the motors for conducting in one position fluid to the first motor and draining fluid from the second motor and in another position for conducting fluid to the second motor and draining fluid from the first motor, a follow-up mechanism between the pilot valves and the motors including a lever connected to the first motor, and means for reversing the 4-way valve in a predetermined position of said lever caused by a turbine load demand which cannot be satisfied by the low pressure elastic fluid supply, said means including a latch normally holding the 4-way valve in one position and having an arm in cooperative relation with said lever.

9. Elastic fluid turbine arrangement comprising an elastic fluid turbine, means including a first conduit with a first valve for conducting low pressure fluid to the turbine, means including a second conduit with a second valve for conducting high pressure fluid to the turbine, and a hydraulic governing mechanism for controlling the valves comprising a source of operating fluid under pressure, a first motor for the first valve and. a second motor for the second valve, means responsive to predetermined operating conditions and including a multi-way Valve with a supply conduit and a drain conduit connected to the motors for conducting in one position fluid from the source to the first motor to open the first valve and draining fluid from the second motor and to close the second valve in another position for conducting fluid from the source to the second motor to open the second valve and draining fluid from the first motor to completely close the second valve, and an emergency governing mechanism responsive to an emergency condition of the turbine to effect closing of the valves, said mechanism including a conduit with a trip valve connected to said supply conduit and an emergency governor driven from the turbine for actu- SVERKER N. HEDMAN.