US2853058A - Steam plant and controller - Google Patents

Description

P 1953 R. L. HARRIS ETAL STEAM PLANT AND CONTROLLER Filed June 26, 1951 4 Sheets-Sheet 1 PRESSURE INVENTOR5 08597- A. #4205 MP6! Ian/zap Arra /vi) p 1958 R. 1.. HARRIS ETAL 2,853,058

STEAM PLANT AND CONTROLLER Filed June 26, 1951 4 Sheets-Sheet 2 INVENTOR5 f/G. Z Pail-Er A. Mae/5 Mara: tar/leap Sept. 23, 1958 4 Sheets-Sheet 5 Filed June 26, 1951 INVENTORS 4 08527 A Mme/5 M44605 lazy/pa FIG. 3

Sept. 23, 1958 'R. L. HARRIS ETAL 2,853,058

STEAM PLANT AND CONTROLLER I 7 Filed June 26, 1951 4 Sheets-Sheet 4 16.! F/6.5 v F16. 7 4/ 1/ I N V EN TOR5 P0551274 Maw/5 BY Maya/5 [an/Pa? United States Patent O STEAM PLANT AND CONTROLLER Robert L. Harris, Benicia, and Marcus Lothrop, Berkeley,

Calif, assignors, by mesne assignments, to Yuha Consolidated Industries, Inc, San Francisco, Calif., a corporation of Delaware Application June 26, 1951, Serial No. 233,614

2 Claims. (Cl. 122-448) The invention relates to means for the automatic control of steam power plants, particularly of the portable variety. An example of the general environment in which the invention is effective is disclosed in the patent of Harris and Lothrop, 2,596,968, issued May 20, 1952v and entitled Steam Power Plant.

A power plant of the type referred to is characterized by the provision of a steam generator as distinguished from a steam boiler. A boiler is usually considered to be a vessel in which the temperature and pressure of the steam bear a fixed relationship to each other since a large body of water is always present. A. steam generator is sometimes referred to as a forced circulation or series tube generator and is characterized by the fact that the pressure and temperature of the steam do not bear a fixed relationship to each other, the steam being somewhat at random superheated or saturated or even wet. Some control devices, particularly as illustrated in Patent Number 1,898,083 issued to Warren Doble, on February 21, 1933 have been generally effective for providing steam of the desired pressure and temperature under normal conditions in most types of operation. Under some unusual and special types of operation, the control is not as satisfactory as might be desired and particularly when the portable plant is on a vehicle and is subject to a good deal of vibration and motion, the control also tends to become erratic.

It is therefore an object of the invention to provide a steam plant control effective under virtually all conditions to provide steam of the desired temperature and pressure.

Another object of the invention is to provide a controller effective to govern the fire and water input to a steam generator in such a way that the resulting steam will very closely approximate the desired pressure and temperature.

A further object of the invention is, to provide a control system which is effective despite vibration and rough handling.

A still further object of the invention is to provide a control system of a simple nature readily applicable to virtually any steam generator without requiring special construction of the generator.

Another object of the invention is to provide a control system which promptly returns the pressure and tempera.- ture of the steam to the set values if a substantial deviation accidentally occurs.

An additional object of the invention is. to provide a steam plant controller readily set or adjusted to different values of steam pressure and temperature at different times and effective to sustain such set values indefinitely.

A still further object of the invention is in general to improve steam plant controllers.

Other objects, together with the foregoing, are attained in the embodiment of the invention illustrated in the. ac.-

companying drawings and described in the. accompanying description.

In the drawings:

Figure 1 is a schematic diagram of a power plant of the type shown in the copending Harris et a1. application, above identified, but incorporating the general subject matter of the present steam plant controller, various parts being shown according to standard schematic illustration and other parts being shown diagrammatically.

Figure 2 is a front elevation with the cover removed of a control box forming part of the steam plant controller, certain portions being broken away to reduce the size of the figure.

Figure 3 is a side elevation of the structure shown in Figure 2, certain portions being in section and certain portions being broken away.

Figure 4 is a fragmentary view, partially in section on the line 44 of Figure 2 showing one of the controller elements utilized in the control box.

Figure 5 is a schematic view in part and is in part a side elevation of a controller element in one position.

Figure 6 is a view similar to Figure 5 but showing the controller element in an intermediate position.

Figure 7 is a view similar to Figure 5 but showing the controller in a different position.

Figure 8 is an isometric view showing a part of the proportional controller, certain parts being broken away to reduce the size of the figure.

Figure 9 is a cross section similar to Figure 4 of a part of the proportional controller in one position.

Figure 10 is a view similar to Figure 9 but showing a different position ofv the parts.

Figure 11 is a view similar to Figure 9 but showing a still further change in the position of the parts.

Figure 12 is a graph illustrating the general relationship of steam temperature and pressure established by the steam plant controller in one adjusted position.

The complete arrangement of a steam plant to which the controller is especially adapted is shown in the men.- tioned copending application. It includes an internal combustion engine 6 as a source of power for driving the various necessary auxiliaries. The engine has a speed governor 7 for maintaining the speed of the engine at set values despite variations in load upon the engine. The governor is subject, among other things, to control by a. solenoid 8 which places the governor in engine idling speed and another solenoid 9 which places the governor at a medium engine speed especially for starting from cold. By means of a drive shaft 11 the engine is connected to revolve a positive displacement water pump 12, preferably of the reciprocating plunger type, having an inlet pipe 13 extending from a water reservoir 14. The pump inlet valve 16 preferably of. the poppet check type is left alone to operate normally or is held open by a solenoid 17. The pump, although always revolving, can be made ineffective to pump water at all.. When the solenoid 17 is de-energized, the inlet valve is continuously held open by a spring and the water then merely surges back and forth in the pump inlet. When the solenoid 17 is energized, the spring is. overcome, the inlet valve operates normally and the pump then is effective to pump water through an outlet. pipe 18 into a steam generator 19. This is of the series tube or forced circulation; type in which the pressure and temperature do not necessarily bear any fixed relationship to each other.

The generator 19 is heated by means of a burner 21 having a forced draft blower 22 driven from the shaft 11. The burner is supplied with fuel oil through a nozzle. 23. receiving fuel under pressure from a suitably driven pump 24 and derived from a reservoir 26. A bypass pipe 27 leading back to. the reservoir 26 is provided with a valve 28 controlled by av solenoid 29. The arrangement either bypasses fuel from the pump back to the reservoir 26 so that the burner 21 is inoperative or closes; the bypass entirely or partially so that appropriate fuel is released from the nozzle 23 to burn and supply heat to the generator 19.

The pressure and temperature of the steam issuing from the generator steam pipe 30 near a main throttle 31 are utilized as impulses for controlling the operation of the generator controller. For that reason, we provide a pressure line 32 connected to the steam pipe 30 and extending to a control box 33 at a suitable location. A thermostat 34 is disposed alongside the steam pipe 30 to sense the temperature thereof and extends to the control box 33. As especially shown in Figures 2 and 3, the control box conveniently includes a base plate 36 apertured to overlie a thermostat tube 37 enclosing a thermostat rod 38 and extending from the casing of the generator 19. Appropriate jam nuts 39 serve as detachable fastenings for the base plate 36. The operation of the thermostat is such that the rod 38 moves axially within the tube 37, the position and extent of relative motion of the rod depending upon the temperature of the steam in the generator.

The pressure line 32 extends to a mounting block 41 on the base plate 36 from which a Bourdon tube 42 projects. The free end 43 of the Bourdon tube changes its position in direct accordance with the pressure existing within the pipe 30. There is thus provided adjacent the base plate 36 of the control box a movable member 38 indicative of the steam temperature and a movable member 43 indicative of the steam pressure. Upstanding from the base plate 36 are brackets 44 and 46 serving as journals for a shaft 47 freely rotatable therein. The shaft 47 is turned by the thermostat rod 38. A lever 48 secured by a pin to the shaft is urged into contact with the rod 38 by a spring 49, see Figs. 2, 3 e. g.

One of the functions of the control system is to energize the solenoid 9 when the temperature is low in order that the auxiliary engine 6 will operate at its medium speed. The control system is supplied with electricity from a battery 51 having a ground 52 and a master switch 53 in a main conductor 54. An appropriate means completes an electric circuit between the main conductor 54 and a conductor 56 extending to the solenoid 8. The main conductor 54 extends through a pressure responsive switch 57 normally closed at all pressures below a predetermined value and normally connected therefore to a conductor 58 leading to a steam-up switch 59.

All of the switches utilized in the control box are substantially identical and are particularly designed so that they are not disturbed by vibration and pitching and lurching of a vehicle on which they might be installed, yet they are very closely responsive to small changes in operating conditions. The switch 59, see Fig. 3 for example, includes a base 61 secured by fasteners 62 to the base plate 36. Extending from the base 61 is a fulcrum upright 65 on which an armature 63 is pivoted. The armature is urged away from an electromagnet 64 by a coil spring 66 strung between the overhanging end of the armature and a bracket on the upright 65. A keeper 67 on the electromagnet 64 confines the armature 63 to relatively narrow oscillation. A main contact point 68 is located on the other end of the armature 63 in opposition to a main contact point 69 on an upright 71 upstanding from the base 61. The electrical circuits and connections are more apparent from the wiring diagram appearing partially in Figures 5, 6 and 7 and in Figure 1 but the effect of the energization of the electromagnet 64 is to pull the armature 63 downwardly to close the contacts 68 and 69 to complete a circuit between the main terminals of the relay.

As shown particularly in Figure 4 illustrating a similar switch in a different location, the under auxiliary contact 72 for controlling an auxiliary circuit to the electromagnet 64 is carried on an offset duplex frame 73. The frame has twin legs 74 (see Fig. 2) carried by a pivot pin 76 extending between upstanding cars 77 on the armature 63. The motion of the armature is therefore imparted to the offset frame 73. In order that the frame may be adjustably positioned with regard to the base plate 36, it is fabricated with an offset lip 78 carrying an internally threaded boss 79 through which a threaded adjusting screw 81 is disposed. The adjusting screw has a noncircular head held by a detent 82 and when appropriately rotated, lifts or lowers the frame 73 to raise or lower the under auxiliary contact 72. The under contact 72 and the adjusting screw 81 are at slightly different radii from the pin 76 and the resulting difference in motion results in a slight lateral action of the end of the screw with respect to the plate 36. To permit this slight motion yet to keep the frame 73 firmly in position at all times, a relatively strong spring 83 is connected to a hook 84 on the plate 61 and to a book 86 on the frame 73. By appropriately rotating the screw head 81, the under contact 72 is positioned as desired within a relatively wide range and once positioned, is firmly so held.

Cooperating with the under auxiliary contact 72 is an upper auxiliary contact 87 at one end of a bolt 88 (see Figs. 2, 4) passing through and so secured to a contact lever 89 (see Figs. 2, 57). The bolt 88 also acts as a fastening for an auxiliary circuit wire 91 extending to the electromagnet 64. The lever 89 at one end is journalled on the pin 76 independently of the frame legs 74 and is urged into contact closing position by a coil spring 92 (Figs. 2 and 4) at its lower end secured to a hook 93 projecting from the upright 65. A pin 94 spanning a depression 96 in the lever 89 engages the spring either in the looped, upper end thereof, as illustrated in Figure 4, or through the convolutions of the spring in the event the spring is stretched above the lever 89 to afford greater contact pressure.

The end of the contact lever 89 remote from its fulcrum pin 76 lies in the path of a lever 181 (Figs. 2, 3) extending from a hub 102 held by a pin on the shaft 47 and thus moving in response to temperature. The setting is such that at all relatively low temperatures the lever 101 is spaced from and is below the lever 89 but upon the attainment of a predeterrnnied temperature, the lever 101 abuts the lever 89 and moves it about its fulcrum 76 to separate the auxiliary contacts 72 and 87.

Shown especially in Figure 5, in the normal condition of the apparatus, the auxiliary contacts are closed, energizing the electromagnet 64, pulling the armature 63 against the urgency of the spring 66 and closing the main contacts 68 and 69 so that the solenoid 9 (Fig. l) is energized to move the governor 7 to its medium position and the apparatus operates at a medium or steamup speed. When the armature 63 is down, the pin 76 is likewise pulled down with it, as shown in Figure 5.

As the arm 101 rises with increasing temperature (moves counter clockwise in Figures 3 and 5), it eventually comes into abutment with the lever end 89 and begins to lift that end of the lever. The lifting action takes place against the urgency of the spring 92 and is primarily about the rod 76 as a fulcrum. The instant that the auxiliary contacts 72 and 87 are slightly separated or are so lightly in abutment that the current flow through the electromagnet 64 is small, the electromagnet loses all or most of its attractive force. The spring 66 is then solely effective and rocks the armature 63 not only to open the main contacts 68 and 69 and so deenergize the solenoid 9 but likewise lifts the fulcrum pin 76. The lever 89 is then supported on the lever 101 and on the lifted pin 76. This action is shown progressively in Figures 6 and 7.

Figure 6 is an instantaneous position in which the auxiliary contacts have broken to deenergize the electromagnet but the electromagnet has not yet responded. In Figure 7, not only have the auxiliary contacts been opened but the electromagnet has been deenergized and to an exaggerated degree, the armature 63 has lifted under the influence of the spring 66. The armature is then supported only at two points; namely, onits fulcrum support 65 and against the stop 67 (Fig. 3). Furthermore, the lever 89 is supported at only two points, one of them being on the lever 101 and the other being on the fulcrum 76. The spring 92 is then effective to hold the lever against vibration and abnormal dislodgment. The important factor is that a slight separation of the auxiliary contacts not only breaks a circuit atthat point but also causes a bodily displacement of the contact lever 89 because of the resulting motion of the fulcrum pin 76.

Assuming that the temperature. now falls, the lever 101 revolves in the reverse direction (moves clockwise in Figures 3 and 5) and begins to lower the outermost end of the lever 89. Under the influence of the spring 92 and the lowering lever, the auxiliary contact 87 finally abuts the auxiliary contact 72. The position of the lever 101 at which this reabutment takes place is not the same as the position at which the auxiliary contacts were first broken. Due to the intervening change of position of the fulcrum pin 76, the contacts 87 and 72 come together at a lower temperature than the temperature at which they broke. This difference in temperatures is a function of the design of the apparatus and can be established at substantially any interval desired.

As soon as the auxiliary contacts 87 and 72 are again in abutment, current again flows to the electromagnet 64 and the armature. 63 is again attracted. Since the contacts 37 and 72 are already in abutment (even a very light abutment), the movement of the armature 63 toward the electromagnet 64 moves the fulcrum pin 76 downwardly under the urgency of the spring 83 so that the adjusting screw 81 is slightly displaced with respect to the base 36 but more important, the outboard end of the lever 89 is lifted off the actuating lever 101. Again the contacts 87 and 72 are in firm abutment, and the main contacts 68 and 69 are also in firm abutment. The pressure of the spring 83 is effective to hold the auxiliary contacts together while the strengthof the electromagnet is eifective to hold the main contacts 68 and 69 together.

Since the outboard end of the lever 89 is lifted slightly ofi of the actuating lever 101,.the full force of the spring 83 holds the auxiliary contacts closed and any minor vibration and surging movement of the lever 101 or of the mounting is ineffective to cause the auxiliary contacts to chatter. Because the contacts close at a position of the lever 101 diiferent from that at which they open, the contacts remain very firmly pressed together when they are closed, remain completely apart when they are opened and no chattering or hunting of the system occurs.

According to this arrangement therefore, the thermostat is eftective at all temperatures below a predetermined or set temperature as established by the position of the regulating screw 81 (Fig. 3) to cause energization of the solenoid 9 so that the auxiliary engine 6 operates at a medium speed and drives the pump 12 and the blower 22 at a medium speed for steaming up. As soon as a set temperature is reached in the generator 19, the thermostat opens the steam-up switch 59, the solenoid 9 is deenergized and the governor 7 drops the speed of the engine 6 to an idling value.

A similar arrangement is provided to be effective at a maximum set temperature. The shaft 47 carries an arm 121 elfective to operate the lever 122' of a temperature switch 123 identical with the switch 59. The switch 123 is included in a circuit connected to the conductor 58 and extending through a conductor 124 to the solenoid 29 which governs the supply of fuel to the nozzle 23. When the temperature is low, the switch 123 is closed, the solenoid 29 is energized and fuel is not bypassed by the pump 24 but is sent to the nozzle 23 for burning. When the temperature rises in the generator 19 to a. set or predetermined value as established by the adjusting screw of the temperature switch 123, the lever 122 is lifted and by the same-sequence. of operations as previously described, the circuit to the solenoid 29 is interrupted, the valve 28 is opened, the fuel oil bypasses and the burner 21 no longer operates to supply heat to the generator 19.

To make the pressure responsive mechanism 42 effectice, the terminus 43 (Fig. 3) of the responsive device is connected by a link to a lever 126 journalled on or freely mounted on the rod 47. The motion of the rod 47 and of the lever 126 are not dependent upon each other. The lever 126 moves in both directions only in response to the motionof the tube end 43. The lever 126 carries a rod 127 underlying a lever 128 forming part of the pressure switch 57 identical with the switches 59 and 123. Under low pressure conditions, the switch 57, being connected to the main conductor 54 and being normally closed, is effective to complete a circuit through the conductor 58 thereby permitting any of the connected instrumentalities 59, 123, 141 e. g. to be appropriately energized. When the pressure rises to a predetermined value, the end 43 through the link 125 lifts the lever 126 and by means of the rod 127 actuates the lever 128 to open the circuit thereby shutting down all of the electrically controlled apparatus. When the pressure again falls for any reason, the switch 57 is again closed permitting energization of the circuits.

The control system, as so far described apart from the steam-up mechanism, is effective merely to turn off the supply of heat to the generator at a maximum temperature and to interrupt both the supply of heat and the supply of water at a maximum pressure.

In accordance with the invention, means are provided for controlling the supply of Water and heat in an additional fashion so that the temperature and pressure of the steam furnished by the generator not only have fixed or established maximum values, but likewise have related values throughout the entire range of pressure and temperature. As illustrated in Figure 12, there is shown a standard water saturation curve A indicating the relationship of pressureand temperature in a closed vessel containing a large mass of water. The curve indicates that for each particular steam temperature, there is a corresponding steam pressure. The curve is hardly applicable to a series tube generator. Because of the length of the generator tubing and its small diameter and the directional flow, itis quite possible to have water, wet steam, saturated steam and superheated steam all in the same tube. The steam pressure and temperature at the tube outlet do not, therefore, bear any fixed or necessary relationship to each other.

In accordance with the invention, not only is a pressure of say, fifteen hundred pounds per square inch utilized to interrupt the operation of the heat supply and the water supply and not only is a temperature of 900 degrees Fahrenheit, for example used to interrupt the supply of heat, but also a set relationship between temperature and pressure is maintained all the Way up to these terminal values. The choice of values is arbitrary, but for illustration, the point of fifteen hundred pounds per square inch pressure and 900 degrees Fahrenheit tem perature is taken as the terminal point. Likewise arbitrarily chosen is an initial point of 400 degrees temperature and zero pounds per square inch pressure. If a straight line B is then established between such initial point and the terminal point, it is found that corresponding to six hundred pounds per square inch pressure is a temperature of approximately 600 degrees Fahrenheit and that each pressure has a corresponding temperature falling on the straight line. The important factor is that if the intermediate pressures and temperatures are always related as represented by this line, they are always in the proper ratio to their selected terminal values.

Instead of merely responding to pressure and temperature at their terminal values, and when it is too late to correct deviations, the present. control mechanism responds to the pressure and temperature all the way from the low value of zero pounds per square inch pressure and 400 degrees Fahrenheit temperature (for example) approximately along the line B until the terminal point is reached. Truly enough, in actual practice, the relationship of pressure and temperature fluctuates either side of the line B as indicated by the line C but at no time does the pressure and temperature relationship achieve a value below the saturation curve A. Under all circumstances, except possibly at the very lowest starting pressures, the product of the generator 19 is superheated steam very close to the desired characteristics. Since the temperature and pressure relationship is maintained at selected values throughout the entire range, in actual practice the control system described herein prevents the generator from hunting widely over an enormous range as is natural to a series tube generator without a control system.

To accomplish this end, on the base plate 36 of the control box is provided a proportioning switch 141 (see Figs. 2 and 4) identical with the switches 59, 123 and 57 except that instead of being mounted directly upon the base plate 36, it is mounted on a slide plate 142 having a central reenforcement 143. The plate 142 is slidable on the base plate 36 because of the provision of elongated slots 144 and fastenings 146 eifective to clamp the slide plate 142 with its switch 141 and pertinent mechanism in any selected position within wide limits. The switch 141 is included in an electrical circuit extending from the conductor 58 through a conductor 147 to the solenoid 17 regulating the valve 16 at the inlet of the water pump 12. When the proportioning switch 141 is closed, the valve 16 is also able to open and close (in the fashion of a normal pump inlet valve) and the pump 12 can then pump water into the generator. When the switch 141 is open, the operation of the valve 16 is interfered with by the tie-energized solenoid 17 and the pump 12 is ineffective to pump water to the generator 19.

In order to open and close the proportioning switch 141, mechanism is provided which is responsive both to pressure and temperature. The pressure lever 126 not only is provided with a rod 127 on one side but is likewise provided with an extended rod 151 on the other side which underlies a lever 152. (See Figures 8 to 11, inclusive.) Also, the shaft 47 has fastened on it by a pin 153 a bent lever 154 which underlies the other end 156 of the lever 152. The lever 152 therefore rests upon the two levers 154 and 126 and is positioned in accordance with the relationship of those two levers. To permit this, the lever 152 adjacent its center is provided with a fulcrum shaft 157 journalled in a boss 158 carried on an actuating lever 159. This last lever 159 at one end carries a pin 161 journalled in a hub 162 extending from the reinforcing plate 143 of the slider 142. A coil spring 163 urges the actuating lever 159 downwardly so that the lever 152 is pressed normally against the lever 154 and the rod 151.

The direction of motion of the lever 154 under increased temperature is downwardly or toward the base plate whereas the direction of the rod 151 under increased pressure is upwardly. Consequently, if the fulcrum pin 157 is substantially in alignment with the end of the rod 47 and the increase of temperature, as reflected by the downward movement of the lever 154, is substantially in the desired proportion to the increase in pressure as reflected by the upward movement of the rod 151, the net result is merely to rotate the lever 152 on the fulcrum pin 157 without in any wise disturbing the lever 159. A reverse operation of the pressure and temperature levers likewise, if in the proper proportion, produces no efiect upon the lever 159.

However, if the pressure increases much faster than its proper proportion to the temperature, the rod 151 rises out of proportion to the fall of the lever 154 and lifts the end 152 of the proportioning lever more than the end 156 thereof drops. Consequently, the fulcrum pin 157 is lifted somewhat and the lever 159 is then lifted. When it is lifted sufiiciently, the lever 159 engages the lever 166 of the switch 141 and opens the circuit to the water pump solenoid 17 thereby interrupting the operation of the water pump. The supply of water is thus held interrupted until such time as the continuing operation of the burner increases the temperature to a correspondingly greater amount and restores the proper proportion between the pressure and temperature of the steam.

Periodically, when the temperature of the steam seems to exceed its proper value proportionate to the pressure within the generator, the lever 154 permits the end 156 of the lever 152 to drop, lowers the lever 159 and permits the lever 166 to close the switch 141 to energize the solenoid 17 and thus makes the pump 12 effective to supply additional water. The additional water supply continues until the increased pressure is out of proportion with the then existing temperature and the switch is opened and the pump again deactivated. It is thus possible to maintain the temperature and pressure relationship within a close range throughout the entire operation of the generator from low temperature and pressure up to the maximum desired.

While the slope of the line B in Figure 12 indicates a certain relationship of pressure and temperature, it is possible to vary the slope to some other relationship; for example, to start at say, 500 degrees Fahrenheit and at zero pounds per square inch pressure and keep the same terminal values. That is accomplished by loosening the screws 146 (Fig. 2) and moving the slider plate 142 either upwardly or downwardly so that, as shown especially in Figures 9 to 11, inclusive, the effect of the pressure and temperature levers on the proportioning lever 152 is not equal. This is especially illustrated in Figure 11 in which a displacement or movement in an amount indicated by the arrow 171 has been accomplished over the previous setting. In this case, the temperature lever 154 is much closer to the fulcrum 157 than is the pressure lever 151. Changes in temperature, therefore, are far more effective than are changes in pressure. The proportion is therefore established at this new value. Equally, the displacement 171 can be in the opposite direction and in any selected amount within the limits of the apparatus. By the provision of this device, a steam generator is controlled so that the pressure and temperature at all times are very close to their desired relative values.

What is claimed is:

1. A steam plant and controller comprising a steam generator, a heater for supplying heat to said generator, a device for supplying water to said generator, and a mechanism for turning said device on when the steam temperature in said generator is over a set relationship to the steam pressure in said generator and for turning said device ofl? when the steam temperature in said generator is under said set relationship to the steam pressure in said generator.

2. A steam plant and controller comprising a steam generator, a heater for supplying heat to said generator, 8. pump for supplying water to said generator, means for turning said heater and said pump off when the steam pressure in said generator exceeds a set value, means for turning said heater off when the steam temperature in said generator exceeds a set value, and means for turning said pump off when the proportion of steam pressure in said generator to steam temperature in said generator exceeds a set value.

References Cited in the file of this patent UNITED STATES PATENTS 1,827,950 Mulligan Oct. 20, 1931 1,961,395 Schlobohm June 5, 1934 1,975,086 Dickey Oct. 2, 1934 2,088,623 Thompson Aug. 3, 1937 2,342,615 Newton Feb. 22, 1944 (Other references on following page) UNITED STATES PATENTS 10 V Hennessy Feb. 1, 1949 Gebhardt Nov. 1, 1949 Price Dec. 9, 1952 Christiance Nov. 10, 1953 FOREIGN PATENTS France Aug. 21, 1934

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