BACKGROUND OF THE INVENTION

Field of the Invention

The invention pertains to a valve, particularly for use with Fourdrinier dryers of papermaking machines, which controls process vacuum by way of a piston, and includes a break to atmosphere.

Description of the Prior Art

The control of process vacuum on the Fourdrinier dryers of papermaking machines is crucial in ensuring proper sheet formation, prevention of premature fabric wear, and the prevention of wet end breaks.

There are several control valve arrangements that are currently used for wet end vacuum control. These are typically either butterfly valves or some sort of pneumatically controlled floating piston valve such as is disclosed in U.S. Patent No. 4,795,131 entitled "Vacuum Controller" to Robert V. Scarano and Joseph A. Bolton, assigned to Albany Internal Corporation.

Butterfly valves, however, have several inherent control shortcomings. There is no ability for finite adjustment. Moreover, a butterfly valve cannot be used for three-way application in vacuum control, more specifically, the "breaking" of process vacuum to atmosphere. Additionally, the non-linearity of butterfly valves makes the control of very low air flows difficult . Butterfly valves are controlled by an electrical or pneumatic positioner coupled to a digital controller. Process feedback is provided by

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a pressure transducer mounted on a process vacuum piping element. The positioner electronics are mounted at the valve which is in a rather harsh environment for electronic components. This environment will eventually contribute to premature control failures and, in turn, affect overall reliability of the valve.

Similarly, pneumatically controlled "floating" piston valves also exhibit some inherent design shortcomings. These valves usually contain rolling diaphragms which are integral to the vertical movement and control of the valve. These diaphragms tend to stick in certain applications. When diaphragms stick, the control of process vacuum to specific set points is degraded. These valves also have high rates of wear and therefore require more maintenance. The control of this type of valve is typically accomplished with an I/P (current to pneumatic) transducer with a pressure transducer for vacuum feedback. This control valve is an automatic controller, since it floats with a regulated pressure applied and seeks a pressure balance condition to maintain a constant air flow. The controls for this type of valve are simpler and less likely to be affected by the environment.

Other prior art includes U.S. Patent Nos.

5,370,152 5,197,328; 5,158,108; 5,109,692; 4,903,936 4,901,756; 4,794,847; 4,687,179; 4,534,376 4,520,994; 4,460,009; 4,413,644 and 3,793,893.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a valve for control of process vacuum, particularly in the papermaking process, which provides for finite adjustment.

It is therefore a further object of this invention to provide a valve for control of process vacuum, particularly in the papermaking process, which provides for a break to atmosphere. It is therefore a still further object of this invention to provide a valve for control of process vacuum, particularly in the papermaking process, which has a relatively linear response.

It is therefore a final object of this invention to provide a valve for control of process vacuum, particularly in the papermaking process, which is reliable and adapted to the harsh environment of a papermaking machine.

These and other objects are achieved by providing a three-way gate/ported control valve with a sliding piston actuated by a rotary motor. The air motor is coupled to a gear actuator which in turn is attached to the piston to regulate air flow. A controller is coupled to two pneumatic solenoids which allow compressed air to flow to the motor. This controls the rotational and directional movement of the motor shaft and, in turn, the piston. The controller will activate the solenoids to drive the piston up or down depending upon set point vacuum variation and adjust its position based upon changes in air flow. If the process vacuum remains above the set point, a break to atmosphere is provided. The design allows the valve to have high break-away torque, finite piston displacement and variable speed control.

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BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure 1 is a front view of the apparatus of the present invention, partly in cross section, showing the interior of the valve.

Figure 2 is a front plan view of the apparatus of the present invention, showing a typical field installation including the control system and the valve.

Figure 3a is a front plan view, partly in cross section, showing the apparatus of the present invention "breaking" the process vacuum to atmosphere.

Figure 3b is a front plan view, partly in cross section, showing the apparatus of the present invention blocking the flow between the vacuum source and the process vacuum.

Figure 3c is a front plan view, partly in cross section, showing the apparatus of the present invention with full flow between the vacuum source and the process vacuum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in detail wherein like numerals refer to like elements throughout the several views, one sees that Figure 1 is a front plan view, partly in cross section, of the valve apparatus

10 of the present invention.

Valve apparatus 10 includes a generally cylindrical valve body 12 formed from cylindrical wall 13, and further including lower input opening

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14, coaxial with valve body 12, which leads to a process vacuum, such as is required for operation of a Fourdrinier dryer of a papermaking machine (not shown) . Cylindrical valve body 12 further includes lateral opening 16 which leads to the vacuum source (not shown) . The general outer shape of valve apparatus 10 is modeled after valves in use in the industry in order to provide simple compatibility of valve apparatus 10 in existing apparatus. Cylinder chamber 18 is formed by inner cylindrical wall 19 coaxially within cylindrical valve body 12 and outer cylindrical wall 13 and includes an upper open portion 20, an intermediate closed portion 21 and a lower ported spool 22 of somewhat reduced diameter. Upper open portion 20 is in communication with the atmosphere via screened cylindrical wall 23 (also see Figure 2) . Cylinder chamber 18 is in communication with lower input opening 14 (which leads to the process vacuum) and lateral opening 16 (which leads to the vacuum source) . Cylindrical piston 24 travels vertically within cylinder chamber 18. Plug section 26 is coaxially integral with cylindrical piston 24 and formed immediately therebelow. Plug section 26 is of substantially the same reduced diameter as lower ported spool 22 of cylinder chamber 18 so that plug section 26 nests within lower ported spool 22 of cylinder chamber 18 when cylindrical piston 24 is at its lowermost position. Figure 3b shows plug section 26 nested within ported spool 22 so as to block communication between lower input opening 14 and lateral opening 16, while Figure 3c shows plug 26 nested within ported spool 22 above lateral opening 16 thereby allowing full flow between lower input opening 14 and lateral opening 16.

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Inner cylindrical wall 19 of cylinder chamber 18 includes lateral ports 28, 30 which are in communication with lower input opening 14 (and the process vacuum) via passageway 31 formed between outer cylindrical wall 13 and inner cylindrical wall 19. Lateral ports 28, 30 are shown in their open position in Figure 3a wherein cylindrical piston 24 is in its lowermost position thereby blocking lateral opening 16 leading to the vacuum source and unblocking lateral ports 28, 30 thereby providing communication from atmosphere to lower input opening 14 (and the process vacuum) through screen cylindrical wall 23, upper ported end 33 of actuator platform 36, cylinder chamber 18, lateral ports 28, 30, and passageway 31.

Communication between the lower input opening 14 and the lateral opening 16 is regulated by the vertical position of the cylindrical piston 24 and plug section 26. When cylindrical piston 24 is in all but its lowermost position (Figure 3a) , ports 28,

30 of cylinder chamber 18 are sealed by contact with cylindrical piston 24 as shown in Figures 3b and 3c.

A visual indication that the valve 10 is operating is provided by brightly colored flag or emblem 34 (see Figure 2) . This flag or emblem 34 is mounted directly behind the screened cylindrical wall 23 and can be easily seen when viewing the front of the valve apparatus 10.

Cylindrical piston 24 and plug section 26 include aperture 38 through a longitudinal axis thereof. Threaded traversing rod 40 passes through and is contained within aperture 38 and is non- rotationally coupled to plug section 26 at a lower end 32 thereof. Vertical movement of cylindrical piston 24 and plug section 26 is effected by vertical

movement of threaded traversing rod 40. Threaded traversing rod 40 passes through axial aperture 42 of lower stationary beveled pinion gear 44 in lower plate 46 of cylindrical gear housing 48 and is engaged within a complementary threaded aperture 50 within threaded trunion nut 52. Symmetrically opposed beveled idler gears 53, 54 are journaled for rotation on a common bearing journal 56 affixed to threaded trunion nut 52. Common bearing journal 56 is perpendicular to threaded aperture 50 within threaded trunion nut 52.

Symmetrically opposed beveled idler gears 53, 54 meshingly engage lower stationary beveled pinion gear 44 and upper rotating beveled pinion gear 58 which extends through aperture 60 of upper plate 62 of cylindrical gear housing 48. Upper rotating beveled pinion gear 58 includes axial aperture 64 to allow the free passage of threaded traversing rod 40 in its upper positions. Upper rotating beveled pinion gear 58 is rotationally driven by air motor 68 which is positioned on an upper side of upper plate 62 of cylindrical gear housing 48. Air motor 68 is pneumatically driven by pulses of filtered and lubricated compressed air, typically at sixty psi, from an external air supply (not shown) as regulated by I/O control box 70 via an inlet port selected from ports 72 and 74, depending upon the direction of output (i.e., clockwise or counter-clockwise) desired for air motor 68. Air motor 68 further includes manual override knob 75 to allow the user to effect rotational output of air motor 68 manually, thereby rotating upper rotating beveled pinion gear 58.

The rotary motion of upper rotating beveled pinion gear 58 in response to the rotational output

of air motor 68 causes the rotation of symmetrically opposed beveled idler gears 53, 54 about common bearing journal 56. Symmetrically opposed beveled idler gears 53, 54 rotate in opposite directions from one another. As symmetrically opposed beveled idler gears 53, 54 further mesh with lower stationary beveled pinion gear 44, this causes the rotation of threaded trunion nut 52 and common bearing journal 56 about the longitudinal axis of threaded traversing rod 40 at one half the rotational speed of the rotational output speed of air motor 68 thereby causing threaded traversing rod 40 to move vertically upwardly or downwardly, depending upon the direction of rotation of air motor 68, thereby raising or lowering the cylindrical piston 24 and plug section 26 into or out of ported spool 22 thereby controlling the flow of gas between lower input opening 14 and lateral opening 16, thereby controlling the flow of gas between the vacuum source and the process vacuum. Additionally, as shown in Figure 3a, cylindrical piston 24 can be lowered to expose ports 28, 30 on inner cylindrical wall 19 thereby providing communication from the process vacuum to the atmosphere via passageway 31 thereby "breaking" the process vacuum.

I/O control box 70 receives signals from control panel 76 which includes keyboard 78 for the user to enter the desired input setpoints and similar parameters. I/O control box 70 is tuned for the desired incremental movement in response to process air flow changes. A PID controller (not shown) energizes one of two pneumatic solenoids located within I/O control box 70 which allows compressed air to flow to air motor 68, thereby controlling rotational and directional output of air motor 68 and

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upper rotating beveled pinion gear 58. A pressure to current transducer in the I/O control box 70 provides a feedback 4/20 mA process vacuum signal. The PID controller actuates the solenoids to drive piston 24 and plug section 26 up or down depending on the setpoint vacuum variation thereby constantly adjusting valve position to compensate for changes in air flow. The internal design of valve apparatus 10 enables the break of high vacuum to atmosphere if process vacuum remains above the setpoint. The atmospheric break occurs when cylindrical piston 24 is lowered thereby opening ports 28, 30 and providing communication between atmosphere and lower input opening 14 via passageway 31 as shown in Figure 3a. The amount of force available to overcome vacuum and debris buildup is constant regardless of the piston displacement required by the control system. The exhaust port of the pneumatically driven air motor 68 is vented into a plenum with a restricted port to atmosphere. This allows air motor 68 to develop maximum output torque initially from the compressed air pulse delivered by the combination of the solenoid valves and the I/O control box 70. This torque burst duration is regulated by the attenuation of the plenum exhaust port. The torque curve for this drive is the reverse from the typical electrically driven actuator. Due to the plenum charging, the tendency for valve apparatus 10 to "free wheel" is limited. Thus the several aforementioned objects and advantages are most effectively attained. Although a single preferred embodiment of the invention has been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be

determined by that of the appended claims.

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