US3060955A - Float device for controlling stock level in a pressurized headbox - Google Patents

Description

H. C. NELSON Oct. 30, 1962 FLOAT DEVICE FOR CONTROLLING STOCK LEVEL IN A PRESSURIZED HEADBOX Filed April 30, 1957 IVENTOR. Eerbe/f 0 flew/z, BY M @am @ma/ 3,060,955 FLOAT DEVICE FOR CONTROLLHNG ETOCK LEVEL IN A PRESSURIZED IEADBOX Herbert C. Nelson, Neenah, Wis, assignor to Kimberly- Clark Corporation, Neenah, Wis, a corporation of Delaware Filed Apr. 30, 1957, Ser. No. 656,116 3 Claims. (Cl. 137-202) This invention pertains to a device for controlling the liquid level in a pressurized container and in particular for controlling the stock level in a pressurized headbox of a paper making machine.

It has been found desirable in the manufacture of certain types of paper to maintain a velocity of the stock in the headbox of a paper making machine sufiicient to prevent settling of the fibrous material suspended in the stock. One of the ways of maintaining the required velocity is to decrease the level of the stock in the headbox. At the same time, it has been found necessary to maintain a certain head pressure at the headbox outlet. Many times this head will require a stock level much higher than is desirable to maintain a velocity sufiicient to prevent settling of the fibrous material. Therefore, in order to maintain the necessary outlet pressure at a reduced stock level, it is necessary to replace a portion of the total required liquid head with an equivalent air pad pressure.

An air pad refers to the part of the headbox which contains air or a gas generally under a pressure greater than atmospheric. The force of the air pressure displaces a portion of the liquid head in such a manner that the stock level is reduced and the outlet pressure is held constant. The air pressure and the stock level in the headbox are so interrelated that, upon an increase in the air pressure, the stock level will tend to decrease, and conversely upon a decrease in air pressure, the stock level will tend to increase. Therefore, it is possible to control the stock level in a pressurized headbox by varying the air pressure.

On the other hand, it may be desirable in the manufacture of certain other types of paper to maintain an air pad at a pressure less than atmospheric. In that case, if the vacuum increases, the stock level will increase, and conversely, if the vacuum decreases, the stock level will decrease.

In a headbox it is necessary to maintain the stock level substantially constant in order to obtain uniform paper, whether it is pressurized or not. In the prior art there are numerous devices for controlling the stock level in a headbox. One type consists of a series of pneumatic devices. While accurate, they are generally complicated and consequently are expensive, with regard to both initial cost and maintenance. Other types include electrical devices which not only involve the expense of the pneumatic systems but are subject to damage from the moisture present around paper machines.

Therefore, it is an object of the invention to provide a means for accurately controlling the liquid level in a pressurized container by varying the air pressure.

Another object is to provide means for controlling the stock level in a headbox that will instantly and accurately respond to deviations of the stock level from a desired level.

A still further object is to provide means for controlling the stock level in a paper machine headbox that is relatively inexpensive with regard to both initial cost and maintenance.

A still further object is to provide means for controlling the stock level in a paper machine headbox that may readily be adjusted to accommodate any stock level desired within the headbox.

3,%,955 Patented Oct. 30, 1962 A still further object is to provide means for controlling the stock level in a paper machine headbox of such a construction that there is little or no friction between the various elements.

A still further object is to provide means for controlling the stock level in a paper machine headbox that can be located at a remote station from the headbox.

Other objects will be apparent upon further develop ment of the specification with reference to the drawings.

In the drawings:

FIGURE 1 is a side elevation of the control device embodying the invention.

FIGURE 2 is a diagrammatic illustration of one form of the control device in conjunction with a headbox of a paper making machine.

FIGURE 3 is a diagrammatic illustration of a modified form of the control device embodying the invention.

The invention may be described as a system for controlling the liquid level in a pressurized chamber such as the headbox of a paper making machine. Briefly, in the preferred embodiment, it consists of an auxiliary chamber in both hydraulic and pneumatic communication with the controlled chamber, provided with a bleed valve controlled by the liquid level for varying the air pressure.

Referring now to FIGURE l, there is shown a chamber generally denoted by the numeral 10, provided with the cover plates 11 and 12 which are secured by any suitable means such as the bolts 13. The chamber ill is provided with the inlet ports 14 and 15 which pneumatically and hydraulically communicate with the controlled chamber, respectively.

The yoke member 17 is secured to the cover plate 11 at the bottom of chamber 10- by the screws 18. Extending through the yoke 17 and supported thereby is the tube 19 which projects upwardly into the chamber 10. Secured to the tube 19 at the point where it passes through the yoke 17 is the sleeve member 20 which is threadably received by the yoke 17. A turning wheel 21 is affixed to the lower end of the sleeve 20 which aids in the vertical adjustment of the sleeve with respect to the yoke 17.

A fi-oat member, generally denoted by the numeral 22, is positioned within the chamber Ill and is provided with the axial bore 23 which slidably receives the tube 19. A bracket 24 is affixed to the upper end of the float member 22 by some suitable means. Secured at one end to the bracket 24 is the stem 25 which extends downwardly through the tube 1'9. At the other end of the stem are the threads 26 which receive the valve member 27. The valve member 27 may be vertically adjusted on the stem 25 by means of the threads 26. The valve member 27 in this figure is of a tapered construction and of such a size that the end of the tube 19 is adapted to seat on the conical portion 28' of the valve 27 rather than on the cylindrical portion 29. However, normally, the valve member 27 is partially open with respect to the tube 19 so as to provide a metering effect, as will be evident later on.

It may be desirable to provide a third inlet port 30 connected to a suitable supply of fresh water or white water for purging the chamber 10 of foreign material. This is particularly true when a headbox of a paper machine is being controlled.

Referring now to FIGURE 2, there is shown a control device, that is a modification of the one shown in FIG- URE 1, connected to a headbox =31 of a paper making machine. Obviously the embodiment shown in FIGURE 1 may be substituted for the one shown in FIGURE 2. The headbox is of any suitable type, having an air pad for delivering stock 32 onto the web forming region of a paper making machine (not shown). The control device consists of chamber 10 which is connected to the s.) headbox 31 by the ducts 33 14 and 15 respectively. The control device may be located at any remote station desirable from the headbox but in the preferred embodiment is on substantially the same level as shown in FIGURE 2. The duct 33 is positioned below the level of the stock in the headbox 31 so that the stock 32 will flow therefrom into the chamber 10. The air pad which is provided by the distributing ipe 35 communicates through the duct 34 into the chamber 10. Obviously all or a portion of the air may be introduced directly into chamber -10 from which it would pass into the headbox 31. Thus the relationship of air pressure to the stock in the cylinder 10* is substantially the same as that relationship in the headbox 31. If the chamber 11 is on substantially the same level as the headbox 31, then the stock 32 will rise to approximately the same height as the stock level in the headbox 31. Projecting upwardly through the bottom of the chamber 10 is the tube 36, the upper end of which is normally above the level of the stock 32. A pair of float members 37 of a modified form from that shown in FIGURE 1 are disposed within the chamber 10 and are connected together by the bridge 38. Aflixed at one end to the bridge is the stem 39 which extends downwardly through the tube 36. The other end of the stem 39 is provided with the valve member 40 which is adapted to seat on the end of the tube 36 but is normally in a partially open position. It is obvious that the float members must have suflicient buoyancy to support the combined weight of the stem, the valve, and the force of the air flowing from the tubes as will be seen later on. The sensitivity of the controller will depend upon the proper balance of proportions between the valve size, the float size, and the total head at which the headbox and controller will operate. For example, a large valve sized for a machine operating at a relatively high head'will require a large float and a relatively large ratio of water line area to depth of submergence.

The inlet 30 may be provided for purging the chamber 10 with white water or fresh water from any suitable source of supply. The pressure at the inlet should be slightly above the head pressure caused by the stock and the air pad pressure, in order that there may be a positive flow from the chamber 10 to the headbox 31. It has been found that if the purge water pressure is held constant and only slightly above the pressure exerted on it, the chamber 10 will be kept free of the fibrous material or any other foreign material and the accuracy of the control device will be substantially unafiected.

The operation of the device as shown in FIGURE 2 will now be briefly described. The description, while being directed to the modification shown in FIGURE 2., is applicable to the embodiment shown in FIGURE 1. When the stock is at the desired level, the air which is continually introduced into the headbox is continually bled ofl? from the partially opened valve 40. It the stock level should suddenly rise due to an increase in stock input into the headbox, the stock level in the chamber 10 will also rise a corresponding amount. The rise in stock level will cause the floats '37 to rise so that the valve member 40 is partially closed. Then the amount of air being bled off is decreased so that the air pressure in the headbox is increased. As the air pressure in the headbox is increased, the force acting upon the stock 32 is increased, thus forcing it downwardly until the valve 40 is returned to its normally open position. Conversely if the level of the stock should drop, the valve 49 will move toward a fully opened position so that the amount of air being bled ofi is increased. This will result in a decrease in air pressure in both the chamber 10 and the headbox 31 so that less force is exerted upon the stock 32. The stock will then rise until the valve 40 is back in its normal open position. If it should be desired to operate at a different velocity or stock level in the headbox, it may be necessary to adjust the valve either upand 34 through the inlet ports Wardly or downwardly with respect to the stem 25 to achieve the desired level. A was mentioned previously, this may be done by turning the valve 27 relative to the stem 25 by means of the threads 26 as is best shown in FIGURE 1. For example, if it is desired to raise the stock level, the valve 27 should be moved downwardly with respect to the stem 25 so that the distance between the valve and the float is increased, thus allowing the float to be buoyed at greater height and still maintain the valve in its normal partially open position. An alternative means for varying the stock level is to adjust the position of the tube 19 by the turning wheel 21. If it should be desired to raise the stock level, the tube "19 should be raised upwardly, permitting the float member 22 to be buoyed at a higher level before the valve member 27 is closed.

As was mentioned previously, it may be desirable in the manufacture of certain types of paper where a low head is necessary at the outlet, to operate the headbox with an air pad of less than atmospheric pressure. Referring now to FIGURE 3, there is shown a level control device which is adapted to operate where the air pad pressure is less than atmospheric. The chamber 41 is closed to the atmosphere except for the tubular opening 42. The ducts 33 and 34 communicate with a headbox or any other container in which it is desired to control the liquid level. The stock 32 flows through the duct 34 and rises to a level corresponding with that in the headbox. The vacuum or at least partial vacuum is communicated through the duct 33 so that the relationship of the air pad to the stock is the same as that in the headbox. Disposed within the chamber 41 are the floats 43 to which is secured the valve member 45. In this modification the guide rod 44 extends downwardly into the tube 42 and provides guide means for seating the valve member 45 on the upper end of the tube 42. The valve member 45 in this instance is of a spherical configuration of sufiicient diameter so that the tube 42 seats on the spherical surface. The valve member 45 may be adapted if desired to be adjusted vertically with respect to the float member 43 in order to accommodate changes in operating conditions. The chamber 41 is provided with a purgeinlet 30 similar to that shown in FIGURES l and 2.

The operation of this modification will now be briefly described. If the stock level should increase in the headbox above the desired level, the stock in the chamber 41 will rise to a corresponding level. The valve member 45 being normally in a partially open position will be further opened by the rise in the stock level. Since the air pressure in the chamber 41 is less than atmospheric, air will then flow into the chamber 41 so that the pressure therein is increased. The increase in pressure will in turn exert a greater force on the stock 32, causing it to move downwardly until the valve member 45 is returned to its normal partially open position. Conversely, if the level of the stock should decrease, the valve member will move toward the fully closed position so that the vacuum is increased. The level of the stock will then rise until the valve member 45 is returned to its normal position.

In the drawing there are shown valve members of a conical configuration and a spherical configuration. However, it is obvious that other valve configurations may be suitable for this purpose. It has been found that valve members having a tapered surface are particularly adapted for this use. In the preferred embodiment the valve member should be of such a size and shape that it cooperates with the tube to provide a metering eiiect when the valve is in the open or partially open position.

While the control device has been described in conjunction with the headbox of a paper machine, it is to be understood this is merely by way of example and not limitation and that the device may be used in other environments for controlling the level of a liquid.

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It can be seen that the control device as disclosed does not include any mechanical linkages that would be subject to friction. Thus any error that would be induced by friction between the parts has been substantially eliminated.

It has been suggested if an auxiliary chamber is used that it be positioned at substantially the same level as the headbox. However, it is conceivable that the auxiliary chamber may be spaced vertically from the headbox and by varying the relationship between the valve and the float members, eliminate the effect of the difference in level between the headbox and chamber.

From the foregoing description it is apparent that a stock level control device is provided that is simple in construction and will accurately control the level of the stock. The elements of the control device are relatively inexpensive both with regard to initial cost and maintenance. At the same time the construction is such that it requires little if any operator attention.

It is apparent that certain modifications of the invention may be made within the scope of the claims without departing from the spirit of the invention.

I claim:

1. A float type level control for maintaining a liquid at a desired level comprising a closed chamber adapted to be connected to a source of gas under pressure greater than atmospheric and a source of liquid under pressure normally suflicient to partially fill said chamber against the pressure of the gas, a tube means open to atmosphere in said chamber, a float member in said chamber at least partially circumscribing said tube means, a stern connected at one end to said float member and extending through and beyond said tube means, and a valve member connected to the other end of said stem, said valve member cooperating with said tube means to control the flow of gas therethrough, said valve member being intermediate its fully opened and fully closed positions when the liquid is at the desired level, said valve member being moved toward the fully opened position when the liquid level is less than the desired level and toward the fully closed position when the liquid level is greater than the desired level.

2. A float type level control for maintaining a liquid at a desired level comprising a closed chamber adapted to be connected to a source of gas under pressure greater than atmosphere and a source of liquid under pressure normally suflicient to partially fill said chamber against the pressure of the gas, vertical tube means in said chamber open to atmosphere at its lower end, said tube means normally extending above the maximum liquid level within said chamber, a float member in said chamber at least partially circumscribing said tube means and adapted to move freely relative thereto in an axial direction, said float member normally being positioned substantially below the upper end of said tube means, bracket means projecting upwardly from said float member, a stern connected at its upper end to said bracket means and extending through and beyond said tube means, a valve member connected to the other end of said stern, said valve member comprising a portion of a body of revolution having a tapered surface in which the tapered surface cooperates with the end of the tube means to meter the flow of gas therethrough, said valve member being intermediate its fully opened and fully closed positions when the liquid level is at the desired level, said valve member being moved toward the fully opened position when the liquid level is less than the desired level and toward the fully closed position when the liquid level is greater than the desired level, and means for adjusting the distance be tween the upper end of said stem and said valve member whereby the desired level within said chamber may be varied.

3. A float type level control for maintaining a liquid at a desired level comprising a closed chamber adapted to be connected to a source of gas under pressure greater than atmospheric and a source of liquid under pressure normally sufficient to partially fill said chamber against the pressure of the gas, vertical tube means in said chamber open to atmosphere at its lower end, said tube means extending above the maximum liquid level within said chamber, a float member in said chamber at least partially circumscribing said tube means and spaced therefrom so as to move freely relative thereto in an axial direction, said float member normally being positioned stantially below the upper end of said tube means, bracket means projecting upwardly from said float member, a stern connected at its upper end to said bracket means and extending through and beyond said tube means, a valve member connected to the other end of said stem, said valve member comprising a portion of a body of revolution having a tapered surface in which the tapered surface cooperates with the end of the tube means to meter the flow of gas, said valve member being intermediate its fully opened and fully closed positions when the liquid level is at the desired level, said valve member being moved toward the fully opened position when the liquid level is less than the desired level and toward the fully closed position when the liquid level is greater than the desired level, and means for adjusting the height of the tube means within said chamber whereby the desired liquid level in said chamber may be varied.

References Cited in the file of this patent UNITED STATES PATENTS 307,220 Peters 'Oct. 28, 1884 492,597 Way Feb. 28, 1893 1,978,913 Ricci Oct. 30, 1934 2,199,673 Ronning May 7, 1940 2,625,169 Parrish Jan. 13, 1953 2,736,246 Crittenden et al Feb. 28, 1956 2,751,925 Axlander June 26, 1956 2,872,298 Van Loenen Feb. 3, 1959 FOREIGN PATENTS 44,560 Germany of 1888

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