US2982260A

US2982260A - Control device

Info

Publication number: US2982260A
Application number: US599254A
Authority: US
Inventors: David U Hunter
Original assignee: Fairchild Engine and Airplane Corp
Current assignee: Fairchild Engine and Airplane Corp
Priority date: 1956-07-20
Filing date: 1956-07-20
Publication date: 1961-05-02
Anticipated expiration: 1978-05-02

Description

May 2, 1961 D. u. HUNTER CONTROL DEVICE Filed July 20, 1956 INVEN'I'OR.

in E JTTORNEYS m 0 w W a W P w I Q a z w r w J v a T J My 3 m z fiw w m. M w? M wlx A 2 m 4. 0M 2% F I m. A an m w actuator 2,982,260 CONTROLYDEVICE David U. Hunter, Huntington, N.Y., assignor to Fairchild Engine and Airplane Corporation, Bay Shore, N.Y., a corporation of Maryland Filed July 20, 1956, Ser. No. 599,254 6 Claims. c1. 121-46.

This invention relatesto a control device for'an actuator wherein the operation of the actuator is adapted to be controlled by a predetermined'relationship of the pressures exerted by two fluids.

The present invention is particularly applicable for controlling the output flow of a feed pump for a boiler.

In the operation of a boiler, it is ordinarily desirable to I maintain a predetermined differential between the pressure, of the steam in the boiler and the pressure of the feed water delivered to the boiler. In accordance with the present invention, when the pressures of these two fluids reach a predetermined unbalance, an actuator is rendered operable to decrease the speed of operation of the feed pump. If the unbalance is due to a momentary overspeed of the feed pump, the balance will be restored by the decrease in speed of the pump. If the unbalance,

on the other hand, is due to failure of the pump suction or other blockage, the speed of the feed pump will decrease and so will afford an opportunity for the pump to be cleared, the suction restored or the difllculty otherwise remedied.

For a complete understanding of the present invention, reference may be made to the detailed description of the invention which follows and tothe accompanying drawings wherein:

Fig. 1 is a schematic representation of a boiler system embodying the present invention; and i Fig. -2 is an enlarged cross-section view illustrating the control device of the present invention.

Fig.1 of the drawingsillustrates a typical steam generating system including a boiler 10, a feed pump 11 for supplying water to the boiler, and a prime mover 12, such as a steam t'urbine,'for driving the feed pump. The feed pump, driven by the turbine via the drive'shaft 14, is supplied with feed water from the intake conduit 15a and supplies the feed water to the boiler through the conduit 15. The turbine, in turn, is driven by steam admitted via the conduit 13. The speed of the turbine is regulated by a throttle valve 16 in the conduit 13, and the throttle valve is adjusted by a pressure-operated actuator 17 controlled by the control device A of the present invention.

The control device A of the present invention is shown in detail in Fig. 2 of the drawings. It comprises generally a hollow cylinder 20,

inlet ports

21, 22 at opposite ends thereof, an intermediate discharge port 23, and a slide fvalve 24 having interior passages 25 and 26 therein. The

passage 25 communicates with the inlet port 21, and the passage 26 communicates with the inlet port 22. In the cation between the discharge port 23 and one or the'other of the

inlet ports

21 or 22. t a

l The inlet port 21'is connected via a conduit 27 to the conduit 15 through which water is fed to the boiler, and the port 22 is connected via a conduit 28 to the steam in-the .boiler. Preferably,.-.a cooler 29 is interposed in mics v .neutral'position when the pressures exerted by the fluids at opposite ends of the slide valve are in the desired relationship. When, however, the pressures exerted by the fluids at opposite sides of the slide valve are not in the desired relationship, or, stated another way, when the forces at opposite ends of the slide valve 24 are unbalanced, the slide valve will be shifted axially in one direction or the other, establishing communication via one of the passages 25, 26 of the slide valve between one of the

inlet ports

21, 22 and the discharge port 23.

Stops 33 are provided at both ends of the cylinder 20 to limit the movement ofthe slide valve in the cylinder,

The conduit 28 contains

restrictions

34 and 35, and a pressure accumulator 36 is coupled to the conduit between the

restrictions

34 and 35. The exhaust port 23 communicates with the valve actuator via a conduit 38, and the conduit 38 contains a restricted vent 39. The size of the opening in the vent 39 is greater than the size of the opening of the restriction 34, and the size of the opening of the restriction 34 downstream of the accumulator, in turn, is greater than the size of the opening of the restriction 35 upstream of the accumulator.

Turning now to a description of the operation of the present, invention, the slide valve is maintained in a neutral position by the pressures exerted by the fluids in the

conduits

27 and 28 and by the compensating forces exerted by the

springs

30, 31 when the fluids acting on the slide valve are in the proper relationship. In this position of equilibrium, both passages 25 and 26 of the slide valve are closed to the discharge port 23. Furthermore, in this position of the slide valve, the throttle valve 16 is open full, and the speed of the turbine controlled by conventional governing means. a

In the event that the water pressure in the conduit 15 increases without an equal increase in the steam pressure, the slide valve 24 will be shifted to the right, as viewed in Fig. 2, and water will flow through the passage 25 to the conduit 38. When the flow into the conduit 38 is greater than the discharge through the vent 39, the pressure in the conduit 38 will build up, thereby controlling the operation of the actuator to adjust the valve 16 gradually toward a closed position. This throttling action of the valve 16 slows down the turbine and the feed pump, thereby decreasing the pressure of the feed water in the conduit 15. When the pressure has been decreased sufiiciently, the slide valve 24 will be restored to neutral position.

In the event that the water pressure in the conduit 15 drops below a predetermined differential in respect to the pressure in line 28, for any reason, such as for example because of a stoppage in the water supply line 15a or failureof the pump, the steam pressure forces the slide valve 24 to the left, as viewed in Fig. 2, and the steam or condensate will flow through the passage 26 to the conduit 38. With the vent 39 draining, there will be a substantial pressure drop across the restriction 34, and inasmuch as the restriction 35 is smaller than the restriction 34, the accumulator will drain through the restriction 34. The accumulator, therefore, delivers its reserve energy through the restriction 34, and the pressure in the conduit 38 is increased to operate the actuator 17 to slow down the prime mover andthe feed pump during the time that the accumulator pressure is discharging After they discharge of the accumulator, the slide a valve 24 will be restored toward its neutral position'by l atented Mayz, V

the force of the spring 30, speeding up the turbine and the pump. If in the meantime the water pressure in the conduit 15 has been reestablished, equilibrium will be restored. If, on the other hand, the water pressure has not risen, the slide valve 24 will be again forced to the left, as viewed in Fig. 2, as soon as the accumulator pressure has built up again, and the reduced speed cycle repeated as described above. The pressure differential needed to cause reduced speed operation is controlled by the rate of the spring 30 and the length of the dead zone between

ports

26 and 23.

The valve is shown with a very definite underlap or dead space between the passages 25, 26 so that'there is 'a'region of pressure difierential throughout which neither fluid is in communication with the actuator through the conduit 38. While the slide valve is in this intermediate position, the conduit 38 exhausts through the vent 39 and the actuator opens the valve 16 to speed up the turbine and 'the said pump. During normal operation, the slide valve is in the position shown in Figure 2. That is to say, the passage 25 will be in communication with the conduit 38. Thus, when the pump speed decreases and the piston begins to move to the left, the initial effect is to decrease the effective size of the passage 25, thereby speeding up the pump. However, as the slide valve continues to move to the left, the passage 25 closes and the fluid in the accumulator is forced through the restriction 34.

There is a pressure drop across the vent 39 as the fluid from the accumulator is forced through the vent to atmosphere. This pressure drop across the vent 39 will be less than the pressure drop across the restriction 34. In this connection, it should be borne in mind that boilers operate at high pressures, usually above 600 p.s.i. There- 'fore, the pressure drop across the vent 39 will be high enough to provide pressure to allow the actuator to close the valve.

The invention has been shown in preferred form only and by way of example, and obviously many variations and modifications may be made therein without departing from the spirit of the invention. The invention, therefore, is not to be limited to any specified form or embodiment except in so far as such limitations are set forth in the claims.

I claim:

1. A control system comprising an actuator, a housing having a chamber therein, a movable pressure-controlled valve within the chamber, said valve having a closed position and open positions on either side of said closed position, passages communicating with said valve, said passages communicating with fluids which act against said valve in opposite directions, means acting on said valve to -counterbalance the differential pressure of the fluids, thereby maintaining the valve in an intermediate position when the fluids are in the desircd'relationship, a passage connecting the valve with the actuator, passage means controlled by said valve establishing communicationbetween one or the other of said fluids and the actuator when the valve is in either extreme position and cutting oif communication between both fluids and the actuator when the valve is in an intermediate position, and means to relieve the pressure in the passage connecting the valve with the actuator when the actuator is cut from. both fluids.

2. A control system as set forth in claim 1 including a pressure accumulator in at least one of the passages establishing communication between the valve and one of the fluids and characterized in that the passage upstream of said accumulator is more restricted than said passage downstream of said accumulator, permitting the accumulator to discharge into the passage connecting the valve with the actuator when the valve is displaced in the appropriate direction.

3. A control system as set forth in "claim 1 including a 4 pressure accumulator in at least one of the passages establishing communication between the valve and one of the fluids, a restriction in said passage upstream of said accumulator, a restriction in the passage downstream of said accumulator, the opening in the restriction down stream of said accumulator being larger than the opening in the restriction upstream of said accumulator, and a restricted vent in the passage communicating with the valve and the actuator, the opening in the restricted vent being larger than the opening in the restriction downstream of the accumulator, permitting the accumulator to discharge into the passage connecting the valve with the actuator when the valve is displaced in the appropriate direction.

4. A control device comprising an actuator, a chamber therein, a slide valve movable within the chamber, said slide valve having a closed position and open positions on either side of said closed position, an inlet port in said chamber for admitting one fluid on one side of the slide valve, another inlet port in said chamber for admitting another fluid on the opposite side of the slide valve, a discharge port in said chamber in communication with the actuator, means acting on the slide valve to counterbalance the differential pressure exerted by the two fluids on the slide valve, the slide valve being in a closed position with no communication between the inlet ports and the discharge ports when a predetermined relationship is maintained by the pressures of the fluids, but being movable from said closed position when said pressure relationship is not maintained, thereby establishing communication between the discharge port and one of the inlet ports and controlling the operation of the actuator, means to relieve the pressure in the actuator when the valve is restored to closed position, and a pressure accumulator in communication with at least one of said ports whereby the operation of the actuator is controlled for a duration of time until the pressure in the accumulator is exhausted sufliciently to permit the slide valve to return to closed position.

5. A system for controlling the rate of supply of a liquid comprising a pressure responsive actuator operable to decrease the rate of supply of the liquid, a housing having a chamber defined therein, a slide valve movable within the housing chamber, said slide valve having an intermediate closed position and open positions on either side of said intermediate closed position, an inlet port in said housing at one end of said chamber for admitting a control fluid under pressure to said housing chamber on one side of said slide valve, another inlet port in said housing at the other end of said chamber for admitting a control fluid under pressure to said housing chamber on the opposite side of said slide valve, one of said control fluids being a liquid, a discharge port in said housing communicating with said housing chamber intermediate said inlet ports, a pressure transmitting passage connecting said discharge port with said pressure responsive actuator, means to relieve the pressure in the pressure transmitting passage when the valve is restored to intermediate closed position, passage means connecting one of said inlet ports with the liquid, and passage means connecting the other of said inlet ports with the other of the control fluids, whereby the slide valve in its intermediate closed position prevents communication between said discharge port and either of said inlet ports when a predetermined relationship is maintained between the pressures of the two control fluids, but whereby the slide valve is movable from said intermediate closed position to a position to establish communication between said discharge port and one of said inlet ports when said pressure relationship is not maintained.

6. A system for decreasing the rate of supply ofa liquid in the event that the pressure of the liquid increases without a predetermined increase in the pressure of another control fluid, and for decreasing the rate of supply of the liquid for a short interval or for successive short intervals in the event that the pressure of the liquid decreases without a predetermined decrease in the pressure of the said other control fluid, said system comprising a pressure responsive actuator operable to decrease the rate of supply of the liquid, a housing having a chamber defined therein, a slide valve movable within the housing chamber, said slide valve having an inter mediate closed position and open positionson either side of said intermediate closed position, an inlet port in said housing at one end of said chamber for admitting a fluid under pressure to said housing chamber on one side of said slide valve, another inlet port in said housing at the other end of said chamber for admitting a fluid under pressure to said housing chamber on the opposite side of said slide valve, a discharge port in said housing'communicating with said housing chamber intermediate said inlet ports, a pressure transmitting passage connecting said discharge port with said pressure responsive actuator, means to relieve the pressure in the pressure transmitting passage when the valve is in closed position, passage means connecting one of said inlet ports with said one control fluid, passage means connecting the other of said inlet ports with the said other control fluid, and a pressure accumulator in communication with the passage connecting the inlet port with the said other control fluid, said passage upstream of said accumulator being more ,maintained, the movement of said slide valve in one direction operating said pressure responsive actuator to produce a decrease in the rate of supply of the liquid until the predetermined relationship is restored, and the movement of the slide valve in the opposite direction operating said pressure responsive actuator to produce a decrease in the rate of supply of the liquid for a time 1 interval determined by the discharge from the pressure restricted than the passage downstream of said accumuaccumulator.

References Cited in the file of this patent UNITED STATES PATENTS 718,942 Woerner Ian. 20, 1903 868,680 Martin Oct. 22, 1907 1,962,676 Albright June 12, 1934 2,354,791 J Boldt Aug. 1, 1944 2,563,374 Rosenberger Aug. 7, 1951 r 2,774,369 Di Tirro Dec. 18, 1956 2,889,780- Binford June 9, 1959 FOREIGN PATENTS 354,673 Germany Feb. 26, 1920 Great Britain June 18, 1948