US2823465A - Moisture control system for paper drying machines - Google Patents

Description

Feb. 18, 1958 A. E. ARMSTRONG ,8

MOISTURE CONTROL SYSTEM FOR PAPER DRYING MACHINES Filed Sept. so, 1955 2 Sheets-Sheet l INVENTOR.

Feb. 18,1958 A. E. ARMSTRONG 2,823,465

MOISTURE! CONTROL SYSTEM FOR PAPER DRYING MACHINES Filed Sept. 50, 1953 2 Sheets-Sheet 2 IN VEN TOR.

v fw? United States Patent 71cc MOISTURE CONTROL SYSTEM FOR PAPER DRYING MACHINES Adam E. Armstrong, Three Rivers, Mich, assignor to Armstrong Machine Works, Three Rivers, Mich.

1 Application September 30, 1953, Serial No. 383,154

16 Claims. (CI. 34-48) This invention relates to improvements in moisture control system for paper drying machines.

- .The principal objects of this invention are: First, to provide a relatively simple control for assurilng the constant moisture content of paper issuing from a ner.

. Second, to provide a moisture regulating control which operates in response to the variation of flow of steam to a constant pressure indicator roll and in which the desired rate of flow corresponding to the desired moisture. con-' stant of the paper is automatically established.

Third, to provide a moisture control apparatus in which the sensitivity of the control to variations in moisture content may be selectively adjusted. a Fourth, to provide amoisture control system that responds quickly to pre-selected degrees of variation in moisture content.

- Fifth, to provide a moisture control system which responds to variations in moisture content in proportion tothe degree of variation from a pre-selected value.

Other objects and advantages of the invention will be apparent from a consideration of the following description and claims. The drawings, of which there are two sheets, illustrate a highly practical form of the invention.

-. Fig. 1 is a diagrammatic view of a paper drier with the control apparatus operatively associated therewith.

Fig. 2 is an enlarged top plan view of the oscillatable contacts employed as part of the control system.

Fig. 3 is a side elevational view of the oscillatable contacts. V

Fig. 4 is a schematic wiring diagram of the electric circuit 'in the control.

Fig. 5 is a plan view of the valve and scale provided in the by-pass pipe. v The control apparatus disclosed and claimed hereinis an improvement on the type of control disclosed and claimed in my Patent No. 2,148,720 issued February. 28, 1939, for Moisture Control System for Paper Making Machines and Method.

- The drier, illustrated conventionally, includes a series of drying rolls 1 around which the web of paper to be dried is trained as at 2 in the usual fashion. One roll of the series indicated at 3 and positioned near the dry end of the drier constitutes an indicator roll. The main series of drier rolls are connected to be supplied with steam from amain supply pipe or header 4. The indicator roll 3 is independently supplied with steam by the pipes 5 and 6. The valve 7 controls the supply of steam to the main header 4.

-As indicated in my above mentioned patent, the indicator roll 3 may be used to reflect the moisture content of the paper passing thereover by noting variations ,in either the pressure in the indicator roll or the supply of steam thereto; that is, if the supply of steam to the indicator roll is kept constant, an increase in the radiation of heat from the roll due to increase in the moisture content r 2,823,465 Patented Feb. 18, 1958 in the web will be reflected by a decrease in pressure in the indicator roll, and vice versa.

The present system maintains a constant pressure in the indicator roll so that increased radiation therefrom due to'increased moisture content in the paper will require an additional amount or flow of steam to the indi cator roll to maintain the pre-selected constant pressure, and vice versa.

In order to maintain a constant pressure in the indicator roll 3 the supply pipe 5 is provided with an accurate, selfactuating pressure regulator valve 8. The valve 8 delivers to a flow measuring chamber'9 having an orifice plate 10 therein. The plate 10 has an orifice 11 of known size therein which delivers to the pipe 6. The pipe 6 is further provided with a second self-actuating pressure regulating valve 12. The condensate from the indicator roll 3 is removed. through a drain 13 which is closed against the passage of steam by a trap 14. The valves 8 and 12 open andclose automatically to maintain the pressure in the r0113 as determined by the settings of the valve.

7 The variations in the amount of steam or flow to the roll 3 are measured by a pair of pressure responsive bellows 15 connected to the flow chamber 9 on opposite sides of the orifice 11 by pipes 16. The pressure responsive r be balanced by a weight 20 adjustably suspended from the beam by the adjusting screw 21. The screw 21 is mechanically connected to be rotated by the shaft 22 and gears 23 from a reversible motor 24 carried on the beam. A switch generally indicated at 25 has a movable center contact 26 carried on a pivoted arm 27 and movable between a pair of spaced contacts 28 and 29. The arm 27 is connected by a link 30 to the beam 17 so as to move in response to movement of the beam.

The amount of moisture in the paper when it reaches the indicator roll 3 depends upon the temperature in the series of drying rolls 1 and therefore depends upon the amount of steam admitted to the series of rolls. The valve 7 which regulates the amount of steam delivered to the header 4 and theseries of drying rolls is mechanically connected by the linkage 31 to a reversible motor 32. The motor 32 is electrically connected to be regulated by a second switch indicated generally at 33. The switch 33 includes a central contact 34 mounted on a pivoted arm 35 and engageable with a second pair of spaced terminals 36 and 37. The switch arm 35 is connected by the link 38 with a second beam 39 pivotally supported at 40. 'A third' pressure responsive bellows 41 is mounted adjacent to the beam 39. and has a pressure member 42 bearing against the beam 39 closely adjacent to the pivot 40. The bellows 41 are subjected to the pressure in the header 4 by means of the pipe 43. Variation in position of the beam 39 due to variations in pressure in the header 4 and bellows 41 shift the switch arm 35 correspondingly to energize the motor 32 and regulate the valve ;7 to restore a relatively constant pressure in the header 4 and a relatively constant balance position of the mounted on the beam 3 9'. The screw 45 is connected by The pair of terminals 28 and 29 on-the flow responsive indicator are connected to a switch 49 for manually selectable alternate connection to the reversible motors 24 and 48. The electrical connections are most clearly shown in Fig. 4 in which the terminals 28 and 29 .are shown connected to the switch blades 50 and 51 for alternative connection with the terminals 52 and 53 or 54 and 55, respectively. A wire 56 forms a common return for all elements of the circuit while the switch blade 57' forms a common supply wire to the movable contacts 26 and 34 in either position of the switch 49.

In order to make the switch 25 more quickly responsive to variations in the flow through chamber 9 while at the same time preventing over-regulation of the steam supply in respect to these variations, the first pair of terminals 28 and 29 are mounted on the end of a bar 58 which is pivotally supported at 59 on the housing of a fourth motor 60. The arm 58 is counterbalanced as at 61 and a spring 62 hearing on the arm at the pivot 59 dampens oscillation of the arm. The motor 60 drives a heartshaped cam 63 on which the arm 58 is supported. The motor 60 and cam 63 are actuated in both positions of the switch 49 through the switch blade 57 and are designed to oscillate the terminals 28 and 29 about twice a minute. The amplitude of the oscillation of the terminals 28 and 29 is such that the terminals approach but do not quite reach the central balanced position of the contact 26.

A very slight variation of flow in the chamber 9 and therefore slight unbalance of the beam 17 and switch armv 27 will bring the contact 26 into engagement with either the terminal 28 or terminal 29 for a short interval twice a minute, resulting in small increments of adjusting motion in the parts connected to the switch 25. Greater variations in the flow through chamber 9 will result in correspondingly longer and even continual contact between the contact 26 and terminals 28 and 29.

In starting the drier the switch 49 is thrown to the right as viewed in Fig. 4 so that the balanced switch arm 27 and contact 26 regulate the motion of the motor 24 and the screw 21. The switch 33 and beam 39 are adjusted manually to cause valve opening operation of the motor 32 of valve 7 to admit steam to the series of drier rolls. The paper is trained around the drier rolls and observed as it leaves the drier until the desired moisture content is achieved in the paper. During this manual adjustment of the beam 39 and the valve 7, the flow through the fiow chamber 9 will vary automatically to maintain the pressure in the indicator roll 3 at the figure determined by the regulator valves 8 and 12. The variation in flow through the chamber 9 will result in certain unbalancing force being applied to the beam 17 and corresponding actuation of the switch arm 27 and movable contact 26. Relatively increased flow will unbalance the beam downwardly on the left and engage the lower terminal 29. This will energize the motor 24 to drive the screw 21 and advance the weight 2% to the right to apply a counterbalancing force. A decrease in flow acts reversely until the switch beam 17 and weight 20 automatically arrive at a balanced position corresponding to normal rate of flow through the flow chamber to supply the indicator roll at the proper rate for the desired moisture content in the paper.

After the desired moisture content in the paper and the corresponding normal flow rate in the chamber 9 have been established, the switch 49 is thrown to an automatic position to the left in Fig. 4. In this position the motor 24. is disconnected and the terminals 28 and 29 are connected through the terminals 54 and 55 to the motor 48. Manual regulation of the beam 39 is then discontinued. Should an increase in the flow rate in chamber 9 indicate the, need for additional drying heat the beam 17 will depress the movable'contact 26 into engagement with the terminal 29 and thus energize the motor 48 to advance 2,823,485 a V I the weight 44 to the right. The resulting unbalance in the beam 39 will raise the switch arm 35 into engagement with the terminal 36 and energize the motor 32 to open valve 7 and increase the pressure in the header 4. The increased pressure in the header and in the bellows 41 increases the drying power of the rolls 1 and thus reduces the demand on indicator roll 3, and at the same time establishes a balance in the beam 39. A reverse adjustment of the control is obvious from the connections described.

Since weight of the paper passing through the drier and the initial moisture content and speed thereof may vary with different batches of paper and, since the response of the control apparatus may cause the drying rolls to regulate or adjust too-- rapidly and too greatly, it is desirable to regulate the sensitivity of the entire control. This is accomplished by providing a bypass pipe 64 or connection around the flow chamber 9 and a manually adjustable valve 65 is provided for regulating flow through the bypass pipe. It is obvious that if the bypass pipe is closed by the valve 65 the entire flow to the indicator roll 3 must pass through the chamber 9 and variations in this flow will result in maximum variations in the pressure in the bellows 15. The control apparatus will therefore respond quickly and to its maximum extent in response to variations in flow. However, if the valve 65 is fully opened to permit part of the fiow to the indicator roll 3 to bypass the flow chamber, pressure differential on opposite sides of the orifice 11 will not be so great and the apparatus will respond in the same time but to a lesser degree than when the valve 65 is closed. Desirably a scale is provided on the-valve 65 cooperative with an indicator 66 so that the valve can be readjusted to predetermined positions.

I have thus described a highly practical form of the control apparatus so that the same can be reproduced and operated by others as desired. I have not attempted to describe possible modifications and variations of the system which may be found desirable and which fall within the scope of the following claims.

Having thus described my invention, what I claim} to be new and desire to secure by Letters Patent is:

1. In combination with a web drier having a series of drying rolls with an indicating roll near the dry :end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series,con-' stant pressure regulators and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the differential of pressure on opposite sides of said orifice and having an adjustable balance weight, a reversible motor connected to adjust said balance weight, a switch contact movable'by said beam between a pair of terminals, a valved bypass conduit connected around the orifice to adjust the sensitivity of the response of said beam to flow to said indicator roll, a second balance beam subject to the pressure inthe pipe to said series of rolls and having an adjustable balance weight, a second reversible motor connected to adjust said second weight, a manual switch electrically connected to alternately connect said pair of terminals to said first and second motors, a valve controlling the flow of said pipe to said series of rolls, a third motor connected to regulate said valve, a switch actuated by said second beam and alternately engageable with a second pair of terminals, said second pair of terminals being connected to reversely energize said third motor, and a fourth motor energized through said manual switch and mechanically connected to oscillate said first pair of terminals in the line of movement of said first switch contact.

-2. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicatorroll and the remainder of the rolls of the series, constant pressure're'gulators and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the differential of pressure on opposite sides of said orifice and having an adjustable balance weight, a reversible motor connected to adjust said balance weight, a switch contact movable by said beam between a pair of terminals, a valved bypass conduit connected around said orifice to adjust the sensitivity of the response of said beam to flow to said indicator roll, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a second reversible motor connected to adjust said second weight, a manual switch electrically connected to alternately connect said pair of terminals to said first and second motors, a valve controlling the flow to said pipe to said series of rolls, a third motor connected to regulate said valve, and a switch actuated by said second beam and alternately engageable with a second pair of terminals, said second pair of terminals being connected to reversely energize said third motor.

3. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series, constant pressure regulators and an orifice member in the pipe to said indicator roll, a flow responsive balance beam subject to the differential of pressure on opposite sides of said orifice and having an adjustable balance weight, a reversible motor connected to adjust said balance weight, a switch contact movable by said beam between a pair of terminals, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a second reversible motor connected to adjust said second weight, a manual switch electrically connected to alternately connect said pair of terminals to said first and second motors, avalve controlling the flow to said pipe to said series of rolls, a third motor connected to regulate said valve, a switch actuated by said second beam and alternately engageable with a second pair of terminals, said second pair of terminals being connected to reversely energize said third motor, and a fourth motor energized through said manual switch and mechanically connected to oscillate said first pair of terminals in the line of movement of said first switch contact.

4. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series, constant pressure regulators and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the dilferential of pressure on opposite sides of said orifice and having an adjustable balance weight, a reversible motor connected to adjust said balance weight, a switch contact movable by said beam between a pair of terminals, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a second reversible motor connected to adjust saidv second weight, a manual switch electrically connected to alternately con.- nect said pair of terminals to said firstand second motors, a valve controlling the flow to said pipe to said series of rolls, a third motor connected to regulate said valve, and a switch actuated by said second beam and alternately engageable with a second pair of terminals, said second pair of terminals being connected to reversely energize said third motor.

5. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series, a preset self controlled constant pressure valve and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the difierential of pressureon opposite sides of said orifice and having an 6 to adjust said balance weight, a control element movabl by said beam, a pair of energy transmitting elements connectable to a source of energy by said control element in oppositely actuated positions thereof, a valved bypass conduit connected around said orifice to adjust the sensitivity of the response of said beam to flow to said indicator roll, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a second reversible motor connected to adjust said second weight, a manual switch element connected to alternately connect said pair of energy transmitting elements to said first and second motors, a valve controlling the flow to said pipe to said series of rolls, a third motor connected to regulate said valve, and a second control element actuated by said second beam and alternately engageable with a. second pair of energy transmitting elements, said second pair of transmitting elements being connected to reversely energize said third motor, and a fourth motor mechanically connected to oscillate said first pair of transmitting elements in the line of movement of said first control element.

6. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series, a preset selfcontrolled constant pressure valve and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the dififerential of pressure on opposite sides of said orifice and having an adjustable balance weight, a reversible motor connected to adjust said balance weight, a control element movable by said beam, a pair of energy transmitting elements connectable to a source of energy by said control element in oppositely actuated positions thereof, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance Weight, a second reversible motor connected to adjust said second weight, a manual switch element connected to alternately connect said pair of energy transmitting elements to said first and second motors, a valve controlling the flow to said pipe to said series of rolls, a third motor connected to regulate said valve, and a second control element actuated by said second beam and alternately engageable with a second pair of energy transmitting elements, said second pair of transmitting elements being connected to reversely energize said third motor.

7. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the, indicator roll and the remainder of the rolls of the series, a self actuated constant pressure regulator and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the differential of pressure on opposite sides of said orifice and having an adjustable balance weight, a control element movable by said beam between a pair of energy transmitting elements, a valved bypass conduit connected around said orifice to adjust the sensitivity of the response of said beam to flow to said indicator roll, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a reversible 'motor connected to adjust said second weight, a source of energy connectable by said control element in 0pposite positions thereof to said pair of transmitting elements, said transmitting elements being connected to reversely rotate said motor, a valve controlling the flow to said pipe to said series of rolls, a second motor connected to regulate said valve, and a second control element actuated by said second beam and alternately engageable with a second pair of transmitting elements, said second pair of transmitting elements being connected to reversely energize said second motor.

adjustable balance weight, a reversible motor connected 8. In combination with a web drier having a series of drying rolls with an indicating roll near the dry end thereof and separate steam supply pipes to the indicator roll and the remainder of the rolls of the series to the exclusion of the indicating roll, a self actuated constant pressure regulator and an orifice forming member in the pipe to said indicator roll, a flow responsive balance beam subject to the differential of pressure on opposite sides of said orifice and having an adjustable balance weight, a control element movable by said beam between a pair of energy transmitting elements, a second balance beam subject to the pressure in the pipe to said series of rolls and having an adjustable balance weight, a reversible motor con nected to adjust said second weight, a source of energy connectable by said control element in opposite positions thereof to said pair of transmitting elements, said transmitting elements being connected to reversely rotate said motor, a valve controlling the flow to said pipe to said series of rolls, a second motor connected to regulate said valve,.and a second control element actuated by said second beam and alternately engageable with a second pair of transmitting elements, said second pair of transmitting elements being connected to reversely energize said second motor.

9. Temperature control apparatus for a series of drier rolls having a common steam supply pipe comprising, an indicator roll positioned in web translating relation near the end of said series of rolls and having a separate steam supply pipe, means for maintaining constant pressure. in said indicator roll, means forming an orifice in said separate pipe and subject to the constant pressure of said indicator roll, a control element movable between two operative positions in response to variation in the pressure differential on opposite sides of said orifice, adjustable means balancing said control element against a selected pressure differential on opposite sides of said orifice, a motor connected to adjust said adjustable means, a second control element movable in response to pressure change in said first pipe, a second adjustable means balancing said second control element against selected pressures in said common pipe, a second motor connected to adjust said second adjustable means, a power source under the. control of said first control element, a manual control for selectively connecting said source to either of said motors to reversibly drive the same, a valve connected to control the pressure in said first pipe, a third motor connected to regulate said valve, and a second power source under the reversible control of said second control element connected to reversibly actuate said last motor.

10. Temperature control apparatus for a series of drier rolls having a common steam supply pipe comprising, an indicator roll positioned in web translating relation near the end of said series of rolls and having a separate steam supply pipe, means for maintainin constant pressure in said indicator roll, means forming an orifice in said separate pipe and subject to the constant pressure of said indicator roll, a control element movable between two operative positions in response variation in the pressure differential on opposite sides of said orifice, means balancing said control element against a selected pressure ditferential on opposite sides of said orifice, a second control element movable in response to pressure change in said first pipe, a second adjustable means balancing said second control element against selected pressures in said first pipe, a motor connected to adjust said second adjustable means, a power source under the control of said first control element, means connecting said source to said motor to reversibly drive the same, a valve connected to control the pressure in said first pipe, a motor connected to regulate said valve, and a second power source under the reversible control of said second control element connected to re versibly actuate said last motor.

1-]. Temperature control apparatus for a series of drier rolls having a common steam supply pipe comprising, an indicator roll positioned in web translating relation near the end of said series of rolls and having a separate steam supply pip'egmeans for maintaining constant Jressure in said indicator roll, means forming an orifice in said separate pipe and subject to constant pressure, a control movable between two operative positions in response variation in the pressure difierential on opposite sides of said orifice, adjustable means balancing said control against a selected pressure differential on opposite sides of said orifice, a motor connected to adjust said adjustable means, a second control movable in response to pressure change in said 4 first pipe, a second adjustable means balancing said second control against selected pressures in said pipe, at second motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, a manual control for selectively connecting said source to either of said motors to reversibly drive the same, a valve connected to control the pressure in said first pipe, a third motor connected to regulate said valve, a second power source under the reversible control of said second control connected to reversibly actuate said last motor, an adjustable by-pass connected around said orifice, and independently driven means connected to said first control to oscillate the same between its two operative positions but to a lesser extent than necessary to render the control operative whereby movements of the control in response to pressure differential and in response to said independent means are integrated.

12. Temperature control apparatus for a series of drier rolls having a common steam supply pipe comprising, an indicator roll positioned in Web translating relation near the end of said series of rolls and having a separate steam supply pipe, means for maintaining constant pressure in said indicator roll, means forming an orifice in said separate pipe and subject to constant pressure, a control movable between two operative positions in response variation in the pressure difierential on opposite sides of said orifice, adjustable means balancing said control against a selected pressure differential on opposite sides of said orifice, a motor connected to adjust said adjustable means, a second control movable in response to pressure change in said first pipe, a second adjustable means balancing said second control against selected pressures in said pipe, a second motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, a manual control for selectively connecting said source to either of said motors to reversibly drive the same, a valve connected to control the pressure in said first pipe, a third motor connected to regulate said valve, a second power source under the reversible control of said second control connected to reversibly actuate said last motor, and independently driven means connected to said first control to oscillate the same between its two operative positions but to a lesser extent than necessary to render the control operative whereby movements of the control in response to pressure differential and in response to said independent means are integrated.

13. A control apparatus for a web drier comprising an advance unit and a succeeding unit, a steam supply pipe for said advance unit, a separate steam supply pipe for said succeeding unit, means for maintaining substantially constant pressure in said succeeding unit, means for forming an orifice in said separate pipe and subject to the pressure of said second unit, a control movable between two operative positions in response to variation in the pressure differential on opposite sides of said orifice, adjustable means balancing said control against a selected pressure differential on opposite sides of said orifice, a motor connected to adjust said adjustable means, a second control element movable in response to pressure change in said first pipe, a second adjustable means balancing said second control against selected pressures in said first pipe, a second motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, a manual control for selectively connecting said source to either of said motors to reversibly drive the same, a valve connected to control the pressure in said first pipe, a third motor connected to regulate said valve, a second power source under the reversible control of said second control element connected to reversibly actuate said last motor, and an adjustable bypass connected around said orifice.

14. A control apparatus for a web drier having an advance drying unit and a succeeding unit, a steam supply pipe for the advance unit, a separate steam supply pipe for the succeeding unit, means for maintaining constant pressure in said suceeding unit, means forming an orifice in said separate pipe and subject to the pressure of said succeeding unit, a control movable between two operative positions in response to variation in the pressure difierential on opposite sides of said orifice, means balancing said control against a selected pressure differential on opposite sides of said orifice, a second control movable in response to pressure change in said first pipe, a second adjustable means balancing said second control against selected pressures in said first pipe, a motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, means connecting said source to said motor to reversibly drive the same, a valve connected to control the pressure in said first pipe, a motor connected to regulate said valve, a second power source under the reversible control of said second control connected to reversibly actuate said last motor, an adjustable bypass connected around said orifice, and independently driven means connected to said first control to oscillate the same between its two operative positions but to a lesser extent than necessary to render the control operative whereby the movements of the control in response to pressure differential and in response to said independent means are integrated.

15. A temperature control apparatus for a drier comprising an advance drying unit and a succeeding unit arranged in series, a steam supply pipe for the advance unit, a separate steam supply pipe for said succeeding unit, means for maintaining approximately constant pressure in said succeeding unit, means forming an orifice in said separate pipe, a control movable between two operative positions in response to variation in the pressure difierential on opposite sides of said orifice, means balancing said control against a selected pressure differential on opposite sides of said orifice, a second control movable in response to pressure change in said first pipe, a second adjustable means balancing said second control against selected pressures in said first pipe, a motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, means connecting said source to said motor to reversibly drive the same, a valve connected to control the pressure in said first pipe, a motor connected to regulate said valve, a second power source under the reversible control of said second control connected to reversibly actuate said last motor, and independently driven means connected to said first'control to oscillate the same between its two operative positions but to a lesser extent than necessary to render the control operative whereby the movements of the control in response to pressure diiferential and in response to said independent means are integrated.

16. A control apparatus for a web drier including an advance drying unit and a succeeding drying unit traversed by the web, a steam supply pipe for said first unit, said succeeding unit having a separate steam supply pipe, means for maintaining constant pressure in said succeeding unit, means forming an orifice in said separate pipe, a control movable between two operative positions in response to variation in the pressure differential on opposite sides of said orifice, means balancing said control against a selected pressure differential on opposite sides of said orifice, a second control movable in response to pressure change in said first pipe, a second adjustable means balancing said second control against selected pressures in said first pipe, a motor connected to adjust said second adjustable means, a power source under the reversible control of said first control, means connecting said source to said motor to reversibly drive the same, a valve connected to control the pressure in said first pipe, a motor connected to regulate said valve, a second power source under the reversible control of said second control connected to reversibly actuate said last motor, and an adjustable bypass connected around said orifice.

References Cited in the file of this patent UNITED STATES PATENTS 1,105,581 Rusby July 28, 1914 2,148,720 Armstrong Feb. 28, 1939 2,208,784 Armstrong July 23, 1940 2,451,835 Johnson Oct. 19, 1948 2,539,430 Jepson et a1 Jan. 30, 1951 2,703,494 Carney Mar. 8, 1955 FOREIGN PATENTS 781,347 France Feb. 25, 1935

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