US2347936A

US2347936A - Controlling device for drying apparatus

Info

Publication number: US2347936A
Application number: US389875A
Authority: US
Inventors: George G Crewson
Original assignee: Individual
Current assignee: Individual
Priority date: 1941-04-23
Filing date: 1941-04-23
Publication date: 1944-05-02
Anticipated expiration: 1961-05-02

Description

May 2, 1944. s. G. CREWSON v CONTROLLING DEVICE FOR DRYING APPARATUS Filed April 23, 1941 2 Sheets-Sheet l aw fiiwl y A G. G. CREWSON 2,347,936

CONTROLLING DEVICE FOR DRYING APPARATUS Filed April 25, 1941 2 Sheets-Sheet 2 BYW ATTORNEYS Patented May 2, 1944 OFFICE CONTROLLING DEVICE FOR DRYING APPARATUS George G. Crewson, Bnihlo, N. Y.

Application April 23, 1941, Serial No. 389,875

3 Claims.

This invention relates to a controlling device for use in connection with a drying apparatus in which a heated fluid is employed for drying or baking various articles, such as molding cores, bieadstufis, lumber etc. and while the same is hereinafter described in connection with the use of a fluid such as air and gas as the drying medium it is to be understood that the same is equally applicable to apparatus in which a liquid fluid such as fuel oil, is utilized as the drying or heating medium. a r

In many systems of heating, ventilation, drying, baking, etc., a room or' compartment is heated by a flow 01' hot air or gases supplied from an external source such as a furnace or air heater having fluid fuel furnaces, steam coils,

electric resistors, etc. Any or all of the follow-- ing features may be desirable in these systems:

(1) In order to accelerate the heating or drying action, it may be desirable to circulate very considerable volumes of heated air or gas through the drying chamber in order to provide appreciable surface velocities over the material to be dried or heated.

(2) To maintain essentially the same conditions of temperature, humidity, etc., at allpoints of the drying chamber, hence providing unitormity of heating or drying, it may be desirable to recirculate the heated air or gases in sufilciently large volume that their change of state during one passage through the chamber is small, and the necessary heat increment added to the gases by the heating elements at each cycle in this recirculation.

(3) It may be desirable not only to control the mean temperature, humidity, etc, within the drying chamber, but it may be also desirable to control the maximum temperature, humidity, etc., or the entering gas or air in order that'the material in the chamber be not locally subjected to an improper temperature or other condition in an area adjacent to the inlet of the gas or air.

(4) It may be desirable to waste or discard a proportion of the air or gas in circulation at each cycle in order to carry oil moisture or other products added to this medium by the action taking place within the drying chamber.

(5) When a portion'oi the air or gas is thus discarded. it is usually necessary to substitute for it an equivalent makeup volume of air or other gas in order to maintain the required volume in circulation. g

Heretoiore the flow of the drying medium into and out of the dryingand heating chambers, the supply of i'resh drying medium to the heating chamber, and the discharge of spent or waste drying medium to the outer atmosphere was controlled by a plurality of individual valves arranged in passages communicating with respective parts of the drying system which may it dimcult to properly adjust the fluid flow to suit the requirements or a particular system or apparatus and to maintainthe proper proportion between fluid flow to the' several parts in order to secure the most efilcient and economical operation of the apparatus. I

It is therefore the purpose of this invention to overcome these objections and this is accomplished in accordance with the present invention by employing a single valve or damper controlling device which is located in one place and interconnected with the drying chamber and the heating chamber and also with the fresh air supply and waste or spent air .discharge and provided with a unitary valve for adjusting the area of communication between the drying chamber and the heating chamber and the waste discharge, and also between the fresh air supply I and the heating chamber, thereby simplifying the controlling apparatus and not only reducing the cost of the same but also rendering the operation of adjusting theapparatus more convenient to meet diilerent working conditions.

In the accompanying drawings:

Fig.1 is a diagrammatic view showing a suitable iorm 01 this invention embodied in a drying apparatus in which the heat is derived from an oil or gas burner.

Fig. 2 is a vertical transverse section, on an enlarged scale, taken on line 2-2, Fig. 1 and showing one form of controllingdevice made in accordance with this invention.

Fig. 6 is a. side elevation of the controlling I device shown in Figs. 4 and 5.

In the following description similar reference characters indicate like parts in the several figures of the drawings. Y

Referring toFig. 1 the numeral l0 represents a drying chamber, oven or kiln in which any desired article may be heat treated, dried or deprived of moisture associated with the articles,-

- chamber which burner between the The drying medium such as air or gas at the desired temperature for treating the articles in the drying chamber may be introduced into this chamber by an air delivery pipe, duct or conduit communicating with a fluid inlet i2 on the upper part of the drying chamber and this air together with any gases or vapors which may develop from the action of the air on the articles under treatment may be discharged from this chamber through an outlet pipe, duct or conduit |3 communicating with a fluid outlet It on the lower part of the drying chamber.

The numeral l5 represents a furnace or heating chamber in which the gaseous medium such as air taken from the outer atmosphere or elsewhere for "treating the articles in the drying chamber and any gases resulting from such treatment are heated. Although any source or heat may be employed as an input of heat in this system a fluid burner l6 of any suitable construction is employed in this instance for burning liquid or gaseous fuel in the heating preferably projects into the lower part of this chamber adjacent to the bottom thereof. .The treating fluid such as air or gas or a mixture of the same is introduced by an inlet pipe, duct or conduit H which communicates with a treating fluid inlet la in the heating chamber adjacent to its bottom and preferably opposite the burner lt.

Propelling means are provided for circulating the air and gases though the heating chamber l5 and the drying chamber l9 which are generally in a closed circulation, which means may be of any suitable construction, but as shown in Fig. 1 comprise a fluid propelling fan or blower having the eye of its casing |9 connected by a pipe or duct 20 with the top of the heating chamber while the outlet of this fan case is connected with the duct leading to the top of the drying chamber l9.

The numeral 2| represents a pipe, duct or conduit through which external or makeup air or other fluid medium is supplied to the apparatus to make up or compensate for any occurring during the drying operation or to supply some special fluid which may be required by the articles under treatment.

The numeral 22 represents a vent stack, duct or conduit through which the waste or spent air or gases are discharged from the apparatus to the outer atmosphere or other place adapted to receive them after treatment of the articles in the drying chamber.

That form of device shown in Figs. 1, 2 and 3 for controlling the interconnection of the various ducts or conduits, establishing communication drying and heating chambers, ad- 'mitting fresh air or fluid, and discharging waste or spent air or fluid in accordance with this invention is constructed as follows:

The numeral 23 representsthe cylindrical body of a valve casing which has its opposite ends closed by

heads

24, 25. This body is provided in its-periphery with a plurality of

ports

26, 21, 28, 29 which are arranged in an annular row and in substantially four quarters of this body and which register, respectively, with the drying chamber outlet conduit l3, the inlet conduit l1 of the heating chamber, the fresh air intake or makeup air inlet conduit 2| and the waste or spentair outlet conduit 22 for placing these several conduits in communication with the interlor of the valve casing. The circumferential wastage v widths of the

ports

26, 21, and 29 are equal but the width of the port 23 in this particular organization of the invention is less than any of the

ports

26, 21 and 29 and a neutral or noneffective arc, section or segmental width 30 of the casing body is provided on its cylindrical body between the adjacent sides of the

ports

21, 28. The circumferential extent or width of this neutral casing section 30 and that'of the port 28 are equal to the circumferential extent of any one of the

ports

26, 21 and 29, for a purpose which will be hereinafter explained. The areas of'the

ports

26, 21 and 29 may be equal or if desired thearea of the

ports

21 and 26 may be greater the? that of port 29.

ithin the valve casing is arranged a control valve or damper whereby the flow of fluid through the several ports is controlled and which preferably has the form of a rotatable plate extending diametrically across the casing so as to form two valve wings or members 3|, 32

on opposite sides of the axis about which this valve turns. The valve wing 3| is adapted to move into different positions across the port 26 for diverting the fluid escaping from the drying chamber to the heating chamber or to the waste stack or to divide the same between this chamher and the stack, and the valve wing 32 is adapted to move across the port 28 for controlling the intake of fresh air and also adapted to move along the neutral or n -efiective area 30 of the valve casing. Tuning of the control valve may be accomplished by various means, for example, by an adjusting shaft 33 arranged axially within the body of the casing and extending through

bearing openings

34, 35 in the heads thereof and secured to the central part of the plate forming the diverting and intake valve wings 3|, 32. Rotation of the valve shaft 33 may be efle'cted either by manually operated means or by automatically operated means which are controlled by a thermostatic mechanism responsive to variation of temperature in the drying chamber or other control station. The means shown in Figs. 1 and 2 are satisfactory for manually adjusting the control valve 3|, 32 and holding the same in place after adjustment and as there shown these means comprise an adjusting arm 36 secured to one end of the shaft 33 outside of the valve casing and having a pointer 31 which traverses a scale 38 on the adjacent head of the valve casing, and a thumb screw 39 secured to this arm and passing through a segmental slot in a bracket 4|! on the casing and adapted to fasten the valve arm to the bracket after the control valve has been set in the desired position.

Within the valve casing is arranged a stationary baiile 4| which extends radially inward from the body of the valve casing at a point between the

ports

28 and 29. to the valve shaft 3| relative to one another so that a change in the position of the damper or control valve 3|, 32 will maintain such predetermined. proportion of In case the articles under treatment are of port areas regardless of the changed position of this valve or damper.

Assuming that a load of the desired articles has been placed in thedrying chamber, that a heater is used in the heating chamber which does not require the addition of any air or other fluid, and that the fan Is is working, then the operation of the apparatus would be as follows:

Inasmuch as it may be desirable to first bring all of the air in the apparatus up to a predetermined temperature depending upon the character of the articles or materials which are to be dried or treated an initial circulation of the drying fluidis effected through the heating and drying chambers without admiting any fresh air to the apparatus and at this time no air or gases are discharged as wasted from the apparatus. .To produce this complete circulation of the treating air and gases in the apparatus the

valve

39, 32 is turned into the position within the casing indicated by the dotted lines 3| I, 32! in Fig. 3, in which this valve extends horizontally from the top of the port 23 to the top of the port 27 and connects the full area of these ports and cuts the same completely from the waste outlet port 29 and the air inlet port 28.- In this position of the control valve wings no makeup air is admitted to the apparatus and no waste air or gas is discharged therefrom and the same" treating medium is continuously circulated through the apparatus by the fan i9.

If the means for heating the air are of a character whichrequire the addition of air, such as the oil or gas burner l6 shown in Fig. l to which air must be supplied to support combustion then the control valve is turned in the casing so that its wings 3|, 32 initially occupy the position indicated by the

dotted lines

312 and 322 in Fig. 3, and extend from the bottom of the port 28 to a point below the top of the port 26 a distance equal to the width of the dwell, neutral or ineifective area 30 of the valve casing. When the control valve is thus placed the em; trance of fresh external air to the apparatus is still completely out oh and only a mall part of the gaseous fluid is permitted to escape as waste from the drying chamber through the outlet conduit l3, port 26, valve casing 23, port 29 and waste conduit 22 to the outer atmosphere while the remaining greater part of the gaseous medium is conducted through the lower part of the port 26, valve casing 23, port 21 and conduit I! to the heating chamber whereby the retained aseous medium is heated and again delivered by the fan to the drying chamber for recirculation through the apparatus until the desired temperature has been attained in the drying chamber.

- The extent of the non-eifective movement of the intake wing 32 of the valve from its lowermost position shown at 32| to the position 322 at the bottom of the port 28 is usually calculated to compensate for the amount of air which is supplied tothe fluid burner for combustion purposes so that the volume of fluid in circulation will always remain constant and only such an amount of the treating fluid will be permitted to escape through the waste conduit 22 as can pass through that part of the port 26 between its top and the diverting Wing 3| while the latter is in the position indicated by dotted lines 3l2 in Fig. 3, whereby the addition of air to the fluid burner is balanced by the discharge of waste gas through the stack 22 and the volume of gaseous medium in circulation remains the same.

such character that his necessary to continuouslydischarge or waste some of the gaseous medium in excess of that equivalent to the products of combustion due to laden with moisture from the articles, or for other reasons, the volume of gaseous medium in circulation is maintained constant by admitting an amount of external makeup air to the apparatus equal in amount to that which is wasted or discharged from the apparatus. This is accomplished by turning the controlling valve so that the front or intake wing 32 is raised above the bottom of the fresh air inlet'port 28, as indicated by full lines in Fig. 3, and thus open this port to some extent and the rear or diverting wing 3| is lowered a greater extent from the top of the port 23, as shown by full lines in the same figure, thereby permitting more of the gaseous medium to be discharged from the outlet conduit I3 of the drying chamber to the waste conduit 22 and to the outer atmosphere and less to pass on to the heating chamber I5 for reheating the retained gaseous medium and returning The extent which the intake valve wing 32 opens the makeup or fresh air port 28 and the exteritwhich'the diverting valve wing 3 L "and distributes --the stream*olgaseous niedium'issuing from drying chamber id between the heating chamber and waste outlet is governed by the requirements of the articles in the drying chamber. Regardless however of the position of the controlling valve wings a constant proportion is maintained between the incoming makeup air together with the fluid added thereto by the gases from the heating burner as compared with the volume of fluid discharged from the drying chamber and delivered partly to the heating chamber and partly to the vwaste outlet, so that the volume of fluid in circulation is always the same, notwithstanding that the amount of fresh air admitted and the amount of spent air and gas discharged may be varied to suit the requirements of the particular articles which are being treated.

A position of the control valve similar to the position 3!, 32 shown in Fig. 3 may be desirable when it is necessary to admit fresh air for the purpose of maintaining an oxidizing atmosphere in the oven or drying chamber when the necessity for the admission of such air also requires proportionate wastage to to the stack. v

For the purpose of operating the apparatus without recirculating any of the gaseous medium after the same has been used once in the treatment of the articles in the drying chamber the controlling valve is adjusted so that its front wing 32 is in-line with thetop of the intake or fresh air port 28, as indicated ;by dotted lines 323, in Fig. 3, thereby opening this port to the fullest extent, and the rear or diverting wing 3! of this valve is in line with the bottom of the port 26, as shown by dotted lines 3l3 in this figure, whereby the outlet of the drying'chamber is completely out off from direct communication with the heating chamber and all ofthe gaseous medium escaping from drying chamber is discharged into the waste conduit 22, while the intake port 28 is opened to its fullest extent and the maximum amount of fresh air is permitted to enter the heating chamber.

the same becoming the outlet 22 leading Fig. 3.

4 entering the port 28 or products of combustion from the burner occurs from the port 28 to the port 21 and that complete wastage of the treating medium is eflected through the port 29 after the same has once operated on the articles under combustion are added to the circulation then no wastage shouldoccur to the stack. Under these circumstances the damper or control valve should occupy the position shown at 31 l, 32l in A similar position of the control valve would be required when the burner or heater is turned oil for the purpose of permitting the oven to cool slowly and to induce advantageous uniformity of the cooling effect. 1

Instead of making the wings 3|, 32 of the con-. trolling valve integral, as shown in Fig. 3, so that they are non-adjustable relative to each other and also employing a baflie which always occupies a fixed position, as shown at 4| in the same figure, these valve wings, as shown at 3H! and 320 in Fig. 4, may be made adjustable relative to I each other in a direction circumferentially of the cylindrical body 23 of the valve casing. As there shown the fluid intake valve wing 320 is separate from the fluid diverting valve wing M and adapted to sweep with its outer edge relative to the fluid intake port 28 so as to occupy either a wholly closed position, as indicated by full lines in Fig. 4, or a wholly open position. as indicated by dotted lines 325 in this figure, or a partly open position as indicated by dotted lines 326 in this figure. At its inner edge the fluid intake valve wing 320 is connected with an adjusting shaft 42 which is arranged asially in the valve casing and provided at one of its the maximum desired tion or the diverting valve wing 0 may be adjusted relative to the. intake valve wing and the diverting valve wing relative to-their respective ports may be determined by means of

pointers

46, 41 arranged on the

valve arms

43, 45, respectively, and traversing

segmental scales

48, 49 arranged, respectively, on the arm 45 and on the casing and after these valve wings have been located as desired.

the same may be held in place by a clamping screw 50 passing through an opening in the arm 43, a segmental slot in the arm 45 and a segmental slot'fn a bracket. 5| on the valve casing. The

arms

43 and 45 are arranged, respectively, on the outer and inner sides of the bracket 5|, as shown in Fig. 5 whereby upon tightening ends externally of the casing with an adjusting arm 43, whereby the valve wing 32!! may be moved into the desired position relative to thefluid intake port 28. The fluid diverting valve wing 3) is adapted to sweep with its outer edge relative to the outlet port 26 of the drying chamber into a position in which the outlet of the lat ter is either wholly cut ofi from the waste discharge conduit 22, as shown by full lines in Fig. 4, to effect complete circulation of the treating fluid through the drying chamber or the outlet of the drying chamber may be wholly cut 011 vfromthe heating chamber, as shown by dotted lines 5 in this figure for causing the treating" fluid to pass only once through the drying chamber, or this diverting .valve may be placed in an intermediate position, as indicated by dotted lines M6 in this figure for causing the fluid es-.

caping from the outlet of the dryingchamber to be vdelivered partlyto the heating chamber inlet 11. At its inner edge the diverting valve wingjlll is connected with a tubular or quill shaped shaft 44 arranged around the shaft 42 and journaled at partly to the waste conduit 22 and its opposite ends in the heads of the body of q the valve casing, as shown in Fig. 5. At one of its ends the tubular shaft 44 is provided with an adjusting arm 45 which is arranged-on the ex: terior of the valve casing and whereby the posipart of the movement of the diverting wing 3 lll for connecting the drying chamber outlet lit with the waste vent 22 in a manner resembling that described with reference to Fig 3.

The batiie 4 in the construction shown in Fig. 4 is movable circumferentially within the valve casing about the axis thereof and is connected at its inner edge with the tubular shaft or quill v44 so as to move in unison with the diverting valve wing 3l0 of which it virtually forms an integral part. At its outer edge the miivable bafiie 4| I sweeps idly along a blank area or space 52 on the valve casing between the fluid intake port 28 and the waste fluid port 29, it being immaterial as to what particular part of this blank area is engaged by the baii'ie4ll inasmuch as the same always operates as a partition or wall which prevents direct communication between the intake port 28 and the waste port 29. This idle movement of the battle 4 extends from the position shown by full lines in Fig. 4 to the position indicated by dotted lines 4| 2 in the same figure and corresponds to the extent which the diverting valye wing 3H1 moves frfom the position in which the latter cuts oil the drying chamber completely fromthe vent stack 22, as shown by full lines in Fig. 4, to the position in which the diverting valve wing 3 completely cuts or! the drying chamber from the heating chamber, as shown by dotted lines SIS in Fig. 4'. V

In the construction shown in Fig. 3 the valves 3| and 32 move in unison so' that upon turning the shaft 33 both of these valves are turned at the same time. i v

In the construction shown in Fig. 4 the valves 3M and 320 are adjusted independently of one another within the limits of the slot in the arm 45 but these valves are held in place after adjustment by a single clamping device 50.

It will be noted that in this invention it is possible to efiect complete recirculation of the treating fluid through the apparatus, also to cause the treating fluid to operate but once during each cycle on the articles in the treating the port 28. The positions of,

ways of equal area and therefore do not restrict or throttle the flow of treating fluid when varying the proportions between the makeup air coming in'through the fluid intake and the waste fluid discharged through the vent stack. The foregoing results are obtained by adjusting only one controlling unit inasmuch as the pair of valve wings 3|, 32 move in unison and permit of recirculation or non-recirculation of the treating fluid to be effected at any point between zero and full flow capacity, and compensation for the desired wastage is automatically efiected by the simultaneous admission of a corresponding amount of makeup air or fluid.

This is particularly advantageous in certain installations or applications, such ,as baking cores in the ovens of foundries, in which the heat is supplied by means of combustion in a furnace, the combustion products of which become a part of the circulation gases. These products of combustion therefore add to the volume of treating medium and must be continucusly discharged from the system. In such cases it is necessary that some opening or communication between the port 26 and the port 29 should occur before there is any opening of the port 28. Further, in some drying operations, such as drying foundry cores, the presence of excess oxygen in the combustion or recirculation gases, is of importance for the purpose of oxidizing the binders used in the cores. Also, with an oven under thermostatic bonded together with an oil binder. The sand may, and usually will, contain appreciable moisture as well as the binder. The purpose of the baking is to flrst drive off the moisture and more tempered to a safe entering temperature, either by recirculation, or by admission of excess air. During the initial drying operation, much heat is required but no excess of oxygen. Thus position 3I2, 322 of-valve or damper, as shown in Fig. 3, would be proper, this providing for maximum recirculation without admission of excess air, yet permitting a stack wastage equal to the products of cohnbustion added in the furnace or heating chamber.

control, wherein after reaching or approaching the desired temperature, the combustion may be intermittent, and when it is desired to maintain the oven temperature most economically, there should be neither wastage of circulating gases nor cbld air admitted during the periods when the thermostatic control interrupts further combustion in the furnace.

The construction of the proportioning flow damper or controlling valve mechanism shown in Figs. 2 and 3 is well suited for use in connection with such an oven for drying foundry cores. It is to be noted that in the organization disclosed in Fig. 3 the initial part of the movement of the wing 32 from the position 32! to the po'- sition 322 no openingof the intake 28 occurs but the valve wing 38, due to its moving to the position indicated at m, opens the port 26 partly 5 and permits some wastage of gaseous medium to the vent port 29 before any makeup air enters the system through the intake port 28. The position of the valve wings, as shown by full lines M2, 322 in Fig. 3 therefore establishes just enough communication between the drying chamber outlet port 26 and the waste port 29 to allow escape of gases corresponding to the amount added to the stream of treating fluid by the fuel burner in the heating chamber or furnace, hence no makeup air is required. If further wastage is required then the valve wing 3! is moved to the position shown by full lines in Fig. 3 and thus increase the area of communication between the drying chamber outlet and the waste or vent while at the same time the area of communication. between this outlet and the heating chamber is reduced and suilicient makeup air is added by moving the intake wing to the full line position 32 in F g. 3 in order to compensate for this increased wastage.

As an example of the application of this device, the baking of sand cores as used in foundry practice may be considered.

These cores are frequently made of sand When all the moisture has been driven ed the cores, the temperature which has previously been held down by the heat required for evaporation, rises, and the oxidation period occurs. Then a valve position similar to that indicated at 3|, 32 in Fig. 3 would be proper. When maximum temperature is reached, the thermostatic control, if one is employed, would automatically stop combustion in the furnace. Thus, since no combustion gases are being added, and it being desirable to just maintain temperature, there should be neither wastage to the stack nor admission of air so that position indicated at 3, 32| in Fig. 3 would immediately become desirable.

In practice, a position approximating 3!, 32 can generally be determined by experience as to which is most beneficial, and a setting made accordingly. Automatic control means can then change the dampers to positions 3il-32i, 2-322 and 3l3-323 for the several periods, thus eliminating the uncertainty of manual operation.

-While this device is primarily designed for gas flows in drying and baking work, the same principle is applicable to fluid flows, either liquid or gaseous, and, for any operation in which a continuous circulation of a fluid must be supplemented by discharge of a part of the same and an equivalent makeup supplied from another source. V

For convenience in described this invention it is to be understood that the term air" as occasionally used herein is intended to include any form of gaseous fluid as air, gas or similar medium.

Although the apparatus herein shown and described, sets forth mainly one in which the controlling valve means are adjusted manually it is to be understood that these valve means may be adjusted automatically by a thermostatic shifting mechanism which is responsive to changes in temperature in the drying chamber or other place of which the temperature governs the operation of a system in which this invention forms a part.

I claim as my invention:

1. A controlling device for drying apparatus comprising a casing having a cylindrical wall Both the speed of drying and the provided with a fresh air inlet, an outlet to a heating chamber. an inlet from a drying chamber and a spent air outlet arranged in a cirsaid fresh air inlet being spaced circumferentially by a dwell area from the outlet to the heatin chamber which equals the diflerence in widths between said fresh air inlet and the inlet from the drying chamber, a rotary valve pivoted centrally in said casing to turn about the axis thereof and having a part on one side of its axis movable across said fresh air inlet and dwell area and a part on the opposite side of its axis movable across said inlet from the drying chamber, and a baflle extending from said wall between the fresh air inlet and spent air outlet to the axis of said valve.

2. A controlling device for drying apparatus comprising a casing having a cylindrical wall provided with a fresh air inlet, an outlet to a heating chamber, an inlet from a drying chamber and a spent air outlet arranged in a circumferential row in the order named, said fresh air inlet and the inlet from the drying chamber being of different widths circumferentially, and I said fresh air inlet being spaced circumferentially by a dwell area from the outlet to the heating chamber which equals the difference in widths between said fresh air, inlet and the inlet from the drying chamber, a rotary valve pivoted centrally in said casing to turn about the axis thereof and having a part on one side of its axis movable across said fresh air inlet and dwell area and a part on the opposite side of its axis movable across said inlet from the drying chamber, a baiile extending from saidwall between the fresh air inlet and spent air outlet to the axis of said valve, and means for adjusting said baflie circumferentially between said fresh air inlet and said spe'nt air outlet.

3. A controlling device for drying apparatus comprising a casing having a cylindrical wall provided witha fresh air inlet, an outlet to a heating chamber, an inlet from a drying chamber and a spent air outlet arranged in a circumferential row in the order named, said fresh air inlet and the inlet from the drying chamber being of different widths circumferentially, and saidfresh air inlet being spaced circumferentially by a dwell area from the outlet to the heating chamber which equals the difference in widths between said fresh air inlet and the inlet from the drying chamber, a rotary valve pivoted centrally in said casing to turn about the axis thereof and having a part on one side of its axis movable across said fresh air inlet and dwell area and a part on the opposite-side of its axis movable across said inlet from the drying chamber, a baflie extending from said wall between the fresh air inlet and spent air outlet to the axis of said valve, and means for adjusting said baffle circumferentially between said fresh air inlet and said spent air qutletjncluding concentrio members carrying said valve and baiile, respectively, adjusting arms arranged externally of the casing and connected respectively with said members, a segment which is mounted on said casing and relative to which said arms are moved, and means for securing said arms in position relative to different parts of said segment. v

GEORGE G. CREWSON.