US2511382A - Divided flow blower associated air flow control system - Google Patents

Description

June 13, 1950 E. STONEHOUSE 2,511,332

DIVIDED FLOW BLOWER ASSOCIATED AIR FLOW CONTROL SYSTEM 2' Sheets-Sheet 1 Filed Nov. 9, 1944 June13, 1950 E. STONEHOUSE 2,511,332

' DIVIDED FLOW BLOWER ASSOCIATED AIR FLOW CONTROL SYSTEM Filed Nov. 9, 1944 2 Shets-Sheet 2 Patented June 13, 1950 DIVIDED FLOW BLOWER ASSOCIATED AIR FLOW CONTROL SYSTEM Earl Stonehouse, Larimore, N. Dak.

Application November 9, 1944, Serial No. 562,611

13 Claims.

My invention relates to centrifugal type blowers and to apparatus for handling and controling the air output from such blowers.

An important object of the present invention is the provision of an air blower having relatively high pressure and relatively low pressure outlets capable of operating at one and the same time. A similar but more specific object of the invention is the provision of a blower of the kind above described wherein means is provided for regulating the pressure difference between the high pressure and low pressure outlets of the blower. In the preferred embodiment of the invention, herein illustrated and described in detail, the above objectives are achieved in connection with a centrifugal blower of the type embodying a rotary vane (preferably squirrel-cage type) impeller, and which impeller is enclosed within the usual casing having an eye or axial inlet passage and an outlet that is substantially tangent to a curved peripheral wall of the casing. To accomplish the above noted objectives in connection with a blower of this centrifugal type, I insert a divider element or plate within the outlet passage of the blower in relatively close proximity to the rotary impeller to divide the outlet passage into primary and secondary outlet sections. In the preferred arrangement illustrated, this divider extends transversely across the outlet passage in a plane parallel to the axis of the rotary impeller and the inner end of this divider is positioned relatively close to the outer periphery of the impeller. With this arrangement, air is delivered under considerably greater pressure and velocity into the primary air outlet section than into the secondary air outlet section and the difference in the volume and pressure of air delivered to the two sections may be varied by shifting the inner end of the divider plate toward and from the periphery of the blower. It will be clear, therefore, that a blower thus equipped with high pressure and low pressure outlets can be used to perform double functions normally requiring two independent blowers for the purpose.

Another important object of the instant invention is the provision of an air fiow control system for blowers whereby the blower may be made to automatically deliver an approximately constant volume of air past a variable resistance, such, for example, as a coal fire. While the control system herein illustrated was designed primarily as an air flow control for coal stokers, it will be obvious that the principles involved therein are applicable wherever there is a demand for a substantially constant volume of air to a variable resistance. In coal stokers, eificient burning of the coal requires a substantially uniform volume of air moving through the fire bed and the automatic achievement of this result has been very difiicult due to the fact that the resistance to the flow of air through the fire bed varies over a Wide range under operating conditions and requires that the air be delivered to the fire bed under varying pressure to meet and overcome the varying resistance. There have been many attempts in the prior art to achieve this result, and while some of these have afforded some degree of control, my observations indicate that all such prior art attempts have left much to be desired.

In accordance with the preferred embodiment of the invention herein illustrated, I achieve the last noted important result by dividing the output of a blower into high pressure-high-velocity and low pressure-low velocity columns which are converged prior to delivery to the work. A suitable valve (preferably of the balanced type) is interposed in and controls the high velocity air column from the blower and this Valve or control element is, in turn, controlled by an actuating element subject to and responsive to air velocity variations of the low pressure column, and which velocity variations of the low pressure column are varied as a result of varying restriction of the work, which may be the fire bed of 'a stoker-fired furnace.

A still further important objective of the invention is the provision of an improved air flow control valve which, when interposed in an air conduit or duct, will have substantially no tendency to move as a result of varying air velocities thereagainst or therepast, whereby very delicate apparatus may be used to operate the valve.

The above and other highly important objects, advantages, and features of the invention will be made further apparent from the following specification, claims, and appended drawings.

In the accompanying drawings, like characters indicate like parts throughout the several views.

Referring to the drawings:

Fig. 1 is a view in side elevation, with some parts broken away and some parts shown in axial section, of a Stoker-fired furnace involving a preferred form of the present invention;

Fig. 2 is an enlarged fragmentary view in side elevation, with some parts broken away, of the blowers air delivery conduit and control mechanism;

Fig. 3 is a view similar to Fig. 2, but further including the blower and showing a different position of the air control elements;

Fig. 4 is a view similar to Fig. 2, but showing a still different position of the parts of the control mechanism;

Fig. is a still further enlarged cross sectional view taken on the line 55 of Fig. 2;

Fig. 6 is a similarly enlarged sectional View taken on the line 63 of Fig. 3;

Fig. '7 is a similarly enlarged cross sectional view taken on the line 'l-'i of Fig. 3; and

Fig. 8 is a fragmentary detail view taken on the line i38 of Fig. '7 and on a still further enlarged scale.

In the drawings, I indicates a furnace, 2 indicates the floor of a building, 3 indicates the hopper of a coal stoker, t the auger tube of a stoker, 5 the auger, '3 a windbox receiving air from a blower l through an air duct or conduit 8. Located largely within the windbox 6 is a retort made up of a plurality of rings 9 of progressively larger diameter from bottom to top and having air passages if} therethrough from the windbox. The auger 5 extends into and delivers coal into the bottom portion of the retort and this coal is built up to provide a fire bed 1/ in, above, and radially outwardly of the retort.

The blower l illustrated is of the centrifugal type comprising a rotary vane impeller II and a blower casing ii. The rotary impeller is of the squirrel-cage variety having a circumferentially spaced series of impeller vanes i3 extending parallel to the axis of the impeller. These rotary vanes it are all connected at one end to a mounting disc it carried by a fiange-equipped hub l5 forming power-driven shaft is. The shaft i6 may be assumed to be a projecting end of the stokers electric motor, and which would be located on the opposite side of the blower from that shown, all in accordance with conventional practice. The other ends of the vanes i3 are all connected to a common narrow annular ring I? and said vanes are preferably cur 'ed and pitched forwardly with respect to radius lines from the axis of the imeller; that is, the outer edges of the impeller vanes are shifted in the direction of rotation of the impeller with respect to the inner edges thereof. In this construction, one end of the annular impeller is open, so that the impeller will receive air from the eye or axial air intake passage I8 of the blower casing.

The blower casing i2 is provided with an outlet passage delivering into the air duct 8, the bottom wall of which duct 8 is tangent to the curved outer wall of the casing l2. By reference particularly to Fig. 3, it will be seen that the curved outer wall of the blower casing i2 is of continuously expanding radius from its point of connection to the upper wall of the outlet conduit to its point of mergence and tangency with the bottom of the outlet conduit 8.

In the preferred arrangement illustrated, the receiving end of the blowers outlet duct 8 is divided into primary and secondary outlet conduit sections i9 and 23 respectively by means of an adjustable divider plate 2 i. This divider plate 2| extends transversely across the receiving end of the outlet conduit 8 in a plane parallel to the axis of the impell r and is slidably mounted at its opposite edges in channels 22 of opposite guide elements 23. Fo the purpose of producing edgewise adjustments of the divider plate 2| longitudinally of the conduit ii to vary the spacing therebetween and the impeller i the said divider plate is provided with a gear rack 24 that meshes with a pinion gear 2 5 the pinion gear 25 being mounted on an operating shaft 26 that is journalled to opposite ends in the guide elements 23 and projects through opposite walls of the conduit. At one of its projected ends, the shaft 26 is provided with a knurled operating knob 21. In order to permit limited vertical adjustments 0f the divider plate 2| and its associated guide elements, the opposite sides of the conduit are provided with slots 28 to receive the projecting ends of shaft 25. The front end portions of the guide elements 23 are vertically adjustably supported from the walls of the duct by thumb nut-equipped screws 29 working through duct slots 36. With this construction, the divider plate 2| can effectively be moved to vary the spacing therebetween and the rotary impeller either by longitudinal or vertical adjustments or a combination of both. The important thing is the fact that the divider plate is adjustable with respect to the impeller, and it will be obvious that the desired adjustments can be accomplished in various different ways other than shown without distinguishing from the spirit of the invention.

The element 2| that has heretofore been described as a divider plate is, in the preferred arrangement illustrated, actually only the front section of a compound divider plate comprising also a stationary rear section 210. having at its front edge a channel 3! for slidably receiving the rear end portion of the adjustable forward section 2| of the divider plate. In thi connection, it may be stated that the channel 3| fits with sufficient clearance around the adjustable divider plate section 2| to permit of swinging movements of the section with respect to the fixed. section 2|a.

Section Zia also extends completely across the interior of the outlet duct 3 and may be assumed to be rigidly secured to the sides thereof by welding or the like.

In the preferred embodiment of the invention illustrated, the intermediate portion of the duct 8 is expanded in height to receive the control mechanism presently to be described. This expanding of the duct is not, however, necessary in cases where the over all dimensions of the blower outlet duct are SLlffiClEIlt to accommodate the control apparatus. Before going into a detailed description of the control apparatus, it should, however, be clearly borne in mind that the primary outlet conduit section at the bottom side of the divider plate receives its air from the radially outermost portion of the blower casing Where the air i travelling at maximum velocity, and may, therefore, be pro. erly referred to as a high pressure-high velocity conduit section; Whereas, the secondary conduit section above the divider plate is located in a much less efficient position and, therefore, receives air at lower velocity and pressure, and may properly be referred to as a low pressure-low velocity conduit section.

The valve controlling the flow of air through the primary or high pressure-high velocity conduit section is of a type which is not greatly affected by air movement therepast and, in its preferred form illustrated, comprises a segmental valve plate 32 mounted on a pivotal rod 33 through the medium of rigid spokes 34, and which pivotal rod 33 is journalled in opposite vertical walls of the outlet conduit 3. This segmental valve plate 32 is adapted to be moved pivotally from one extreme position shown in Fig. 2 to its other extreme position shown in Fig. 3 and cooperates with a valve lip 35 with which it has only minimum working clearance. By reference particularly to Fig. 5, it will be seen that the segmental valve plate 32 extends from side to side of the outlet conduit with which it has only minimum working clearance, so that in its upper portion shown in Fig. 3 the high pressure-high velocity conduit section of the outlet conduit will be substantially completely closed to the passage of air. The Weight of the segmental valve 32 is substantially counterbalanced by a counterweight 36 adjustably mounted on a counterbalance arm 31 mounted fast on one projected end of the pivot shaft 33. This type of valve is substantially unaffected by movement of air therepast or pressure of air thereag-ainst and, in this sense, is a balanced valve.

The air flow control valve 32 of the high velocity conduit section is automatically operated by a actuating element subject to the influence of and responsive to pressure variations in the secondary or low pressure-low velocity conduit section above the divider. In the preferred embodiment of the invention herein illustrated, this actuating element is in the nature of an air velocity-operated vane 38 located in and disposed transversely of the said secondary or low .pressure-low velocity conduit section. This actuating element or air vane 38 (see Fig. 5) is of considerably less width than the outlet conduit so as to permit a limited flow of air thereby. Also important to note in connection with this actuating element or vane 38 is the concave shape of its air-receiving face (see particularly Figs. 2, 3, and 4). This actuating element or vane 38 is rigidly connected at its upper edge closely adjacent the top of the conduit to a journalled operating rod or shaft 39 that projects through and is journalled in opposite sides of the outlet duct (see particularly Fig. 5). One projecting end of the shaft ,39 is provided with an adjustable biasing weight-equipped arm 45 that yieldingly biases the element 38 toward an extreme position shown in Fig. 2. The other projecting end of the shaft 39 is operatively connected to the valve 32 through linkage including levers 40, 4|, and 42. One end of the lever 40 is rigidly connected to shaft 39; one end of the lever 4| is pivotally connected to the other end of arm 45; and the other end of lever 4| is pivotally connected to the intermediate portion of lever 42 through slot and pin connections permitting of leverage adjustment. Lever 42 is, in turn, made fast on valve shaft 33. At first glance, it may appear that the weight-equipped arms 31 and 45 were working one in opposition to the other, but in this respect it will be recalled that the sole function of the counterbalance arm 31 is to balance the valve 32 and relieve it from any appreciable tendency to rotate due to an unbalanced condition.

Also rigidly carried by the shaft 39 is an auxiliary actuating element in the nature of an auxiliary or secondary air vane 43 that is attached to said shaft 39 by means of spaced mounting arms 44. This auxiliary vane or actuating element 43 operates in conjunction with the vane 38 to operate the valve 32 but, whereas the vane 38 is operated by variations in air velocity in the ings that the arms 44 are of such length that the auxiliary vane 43 will move below the plane of the divider plate 2|--2|a during part of the normal arcuate or pivotal movement of the prito the periphery of the impeller.

mary actuating element 38. In fact, in the preferred arrangement, the divider plate section 2|a is made of such length that it will serve as a stop or limiting device for the auxiliary vane 43 and its associated mechanism, including the primary vane 38.

Operation Before going into a detailed description of the operation of the blower, divider, control mechanism, and stoker as a cooperative unit, an attempt will be made to further clarify the function of the divider plate, and for this purpose the effects of the divider plate on the blowers output with the blowers output conduit dischar ing directly to atmosphere at a point immediately beyond the divider plate section 2| will first be considered. With the blower in motion, the divider plate section 2| set approximately as illustrated, and the outlet conduit opening to atmosphere beyond said divider plate section, the volume of air through the lower or primary conduit section will be much greater than the volume of air through the secondary conduit section. Now, if we variably restrict the air flow through the primary conduit section, we will, in turn, have a proportionate decrease in the flow of air through the secondary conduit section, and when the flow of air through the primary conduit section has been completely blocked off, we will have a very small quantity of air leaving the secondary conduit section. Conversely, as we begin to release air from the primary conduit section to atmosphere, we will have a proportionate increase in the volume of air flowing through the secondary conduit section, and this increase will be in a pre-determined relation to the increase in the amount of air which is released from the primary conduit section. This fact is very important to keep in mind while considering the operation of the mechanism as an entirety. Also important to bear in mind is that, in the preferred arrangement illustrated, if the inner end of the divider plate section 2| be shifted rearwardly or rearwardly and upwardly to a minimum working clearance with the periphery of the impeller, then the flow of air through the secondary or low pressure-low Velocity conduit section will be reduced substantially to zero when the primary or high pressure-high velocity conduit section below the divider plate is completely broken off to passage of air. In other words, the volume differential between air moving through the primary and secondary duct sections is increased as the divider plate is moved closer to the periphery of the impeller and decreases as the divider plate. is moved away from the impeller. While all of the reasons for the above described results have not yet been fully determined, the effects mentioned have, nevertheless, been definitely observed. Of course, to obtain these results, the inner end of the divider plate section 2| must be located relatively very close In fact, in the arrangement illustrated, it will be seen that the inner end of the divider plate section 2| is spaced from the axis of the impeller a distance less, in fact materially less, than the maximum radius of the blower casing. In a more specific sense, it may be said that, in the preferred arrangement illustrated, the inner end of the divider plate 2| is located within the confines of 2. rectangular space defined at its top by the plane of the top of the secondary conduit section, at its bottom by the plane of the bottom of the primary conduit section, at one side by a verample, in Fig. i,

.7 tical plane intersecting the junction of the top of the secondary conduit section with the blower casing, and at its other side by a vertical plane intersecting the axis of the impeller. It is appreciated that it is not broadly new to place a divider in the outlet of a blower; but, insofar as is known, such dividers have always been located so relatively remote from the blowers outlet that the results above mentioned and attributed to my peculiarly close relationship of blower, impeller, and divider, were completely lost. In this connection, it will be clear that the blower-divider combination described provides a blower with a high pressure outlet and a low pressure outlet wherein varying of the volume through the high pressure outlet will result in a proportionate variation in the same direction of the volume of air moving through the low pressure outlet, and this, it is believed, cannot be said of any of the prior art devices embodying dividers in blower outlets.

. VJith the above clearly in mind, the operation of the blower, together with the divider and the control elements, will now be described in con junction with a Stoker. When the blower is idle, as during inoperative periods oi the stolrer, the control elements will be positioned as in Fig. 3, wherein it will be seen that valve is in its lower completely open position and the is closest to the blower; the parts having been brought to these positions by the yielding action Of gravity acting through the weight-equipped arm :15 and the auxiliary vane New, there be a demand for heat, the stoker and its blower will be set in operation; the stokers auger delivering coal to the retort in the customary manner, and the blower, with the parts thus positioned, delivering air to the Stoker retort through the wide open primary outlet duct section and through the secondary outlet conduit section past the'vane Now, if we assume that the restriction of the ire bed is normal, or someplace between maximum and minimum operating restrictions, the volume of air initially delivered to the fire bed with the valve 32 wide open as in Fig. 3 will be greatly in excess to what is required. However, this excess of air will act almost instantaneously on the pi and secondary vanes and lit respeetiv y and will shift said vanes to intermediate positions approximately as shown in Fig. l, causing a partial closing of valve 32. As a matter of fact, in many instances this initial excess air will cause the control elements to move first to their opposite extreme po tion, shown in Fig. 2, from which they will rapidly settle to their desired intermediate positions, Of course, if, at the time the blower was started in o resistance of the fire bed was the mail to a collection of clinkers or an exceedin ly fine coal condition or otherwise, th n controls will move to and temporarily remain in their extreme valve open positions ol Fig. (in the other hand, if the Work resistance in the bed is at minimum, hen the control elements temporarily re ain in their e" We positions shear l in Fig. 3, l. .rhich conclition the lire bed will receive air only through the secondary conduit section. Now, if, while the control elements are positioned intermedi f their opposite extreme limits, as shown, for the work at the bed increases, this will tend to produce a retardation of air iiowv in both the primary and the secondary duct sections; which, in turn, will permit a returnmovement of the air vane 53 in the direction of the blower, causing the valve 32 to move a little further toward its open position. Now,

as a result of this further opening of valve 32,

the velocity and volume of air moving through 5 the primary duct section will increase to overcome the additional restriction in the fire bed so as to maintain the desired volume of air delivered to the fire bed for the purpose of combustion, and as the volume and velocity of air increases in the primary duct section, a proportionate increase in air volume and velocity takes place in the secondary duct section. This proportionate increase in volume and velocity of air moving in the secondary duct section with respect to the primary duct'section is an important factor in the operation of the present controls, and which tends to hold the controls in a new found intermediate position and to prevent an overriding Of the controls in the direction of the adjustment. In other words, without this proportionate inin air volume moving through the upper secondary duct section with respect to the increase of moving through the lower primary duct section, the controls would tend to move past a desired intermediate position to an extreme valve open position and remain in that extreme position until an approximately minimum resistance condition had been reached in th fire bed. Otherwise, stated, in the absence the above noted proportional increase in air ving through the secondary duct section with respect to moving through the primary duct section, a greater variation in air volume moving through the secondary duct section would be re- 5 ou red to produce any'certain desired movement or the valve. If this proportionate increase in air noving in the secondary duct section with respect to air moving in the primary duct section did not talre place upon opening of valve 32, vane 38 would lose its efficiency due to back pressure on the vane 33 set up by the work resistance upon releasing of a high pressure column of air from the primary conduit section upon opening or partial opening of valve 32.

As work resistance is reduced, the reverse action of the controls takes place. That is to say, that as the work resistance reduces, the flow of air through the primary and secondary duct sections increases, causingvane 3-8 to move in the direction of air ilow imparting closing movement to the valve 32. The partial closing of valve 32 decreases the flow of air from the blowers impeller through both primary and secondary duct sections in a pre-determined relation one to the other, thereby again holding the control vane 38 in a balanced intermediate position.

The auxiliary vane 43 assists the main or priary vane by dropping into the stream of air recharged from the primary duct section at a time whereat the pressure in the common duct beyond the divider plate builds up to a point where it has a tendency to produce a slight back pressure on the vane Under such conditions, this auxiliary vane :33 partly takes up the func- Ihe auxiliary vane 33 also greatly facilitates the reverse of movement of the control mechanism under demands for a re- .feature is again a function of the found unnecessary in other installations (particularly larger commercial installations) and the reason for this is believed to be that the larger the installation the greater are the control tolerances permissible. In other words, it appears that in the small installations the volume of air available for the purpose of control operation is so relatively low as to require a very sensitive control mechanism; whereas, in the larger installations the greater volume of air available for the purpose of control action will satisfactorily operate the vane 38 without the aid of other devices, such as the auxiliary vane.

Weighted arm 45 is for the purpose of setting the control to obtain a minimum requirement of air through the fire bed when the fire bed is at a minimum restriction level or any predetermined level; this pre-determined level of the fire bed resistance requiring a given quantity of air for its maintenance, which air, in turn, should pass entirely through the secondary conduit. This flow of air should then, in turn, hold vane 38 to its approximate outward extreme position. This quantity of air, in turn, is also governed by the position of the inner end of divider plate section 2!. Vane 38 should at this time float at its outward extreme with valve 32 closed or nearly closed. In other words, the air stream striking vane 38 should be so that this vane quivers, ready to drop at the slightest reduction in air flow against its face. Now, the weight which is on arm 45 may be moved up or down to counterbalance the force of the air striking vane 38. This quantity of air will vary, as stated, according to the pre-determined minimum requirement of the fire. Hence, the weight on arm 45 will be adjustably positioned to meet the requirements of any particular installation.

Another important feature of the control system described is that in the event the blower gradually loses efficiency, by accumulation of dust and foreign matter thereon or as a result of reduced motor speed, the control system will automatically compensate for this reduced blower efiiciency at least within the limits of the maximum output of the blower, and this important ratio of the constant relationship of air flowing in the primary and secondary conduit sections.

What I claim is:

1. In an apparatus of the class described, a rotary vane impeller, a blower casing enclosing the impeller, said casing having an inlet passage leading to the axial portion of the impeller and having a peripheral tangent outlet conduit, a divider plate extending transversely across the intermediate portion of the outlet conduit in a direction parallel to the axis of the impeller to thereby divide the inlet end portion of the outlet conduit into high pressure and low pressure sections leading to a common work source of work resistance, the inner end of said divider plate being closely associated with the periphery of the rotary vane impeller, an air velocity-operated actuating element located in the low pressure conduit section and mounted for movements therein responsive to air velocity variations in the low pressure conduit section; and an air flow control valve located to control the flow of air through the high pressure conduit section, and operating connections between the actuating element in the low pressure conduit section and the air flow control valve for the high pressure section.

2. In an apparatus of the class described, a rotary vane impeller, a blower casing enclosing the impeller, said casing having an inlet passage leading to the .axial portion of the impeller and having a peripheral tangent outlet conduit, a divider plate extending transversely across the intermediate portion of the outlet conduit in a direction parallel to the axis of the impeller to thereby divide the inlet end portion of the outlet conduit into high pressure and low pressure sections leading to a common work source of work resistance, the inner end of said divider plate being closely associated with the periphery of the rotary vane impeller, an air velocityoperated actuating element located in the low pressure conduit section and mounted for movements therein responsive to air velocity variations in the low pressure conduit section; an air flow control valve operative to regulate the flow of air through the high pressure conduit section, and an air velocity operated actuating element for the said valve subject to and responsive to air velocity variations in the low pressure conduit section to impart closing movements to said valve under increased air velocity in the low pressure section, and means yieldingly biasing the actuating element and valve toward a valve open position.

3. The structure defined in claim 1 in which the said air velocity operated actuating element is in the nature of an air velocity operated vane mounted for pivotal movements in the low pressure conduit section on an axis extending transversely of the conduit.

4. The structure defined in claim 2, in which the said actuating element is in the nature of an air operated vane mounted for pivotal movements in the low pressure conduit section on an axis extending transversely of the conduit.

5. In an apparatus for delivering an approximately pre-determined Volume of air past a variable resistance, a rotary vane impeller of the centrifugal type, a blower casing enclosing said rotary vane impeller and being of progressively increased radius in a direction of rotation of the impeller, said blower casing having an inlet opening to the axial portion of the impeller and having an outlet passage leading from the maximum radius portion of the casing, an air delivery conduit leading from said outlet passage to a variable work resistance, a divider plate dividing the receiving end portion of the air delivery conduit into high pressure and low pressure sections, the said high pressure conduit section receiving air moving around the peripheral portion of the casing and the said low pressure conduit section receiving air from an area closer to the impeller, an air velocity operated vane movably mounted within the said low pressure conduit section, an air valve located in and controlling the rate of air flow through the high pressure conduit section, and operating connections between said vane and valve whereby the valve will be moved toward closed position when the air velocity through the low pressure conduit section exceeds an approximately pre-determined value resulting from a decrease in work resistance.

6. The structure defined in claim 1 in which the said actuating element and valve are yieldingly biased toward a valve open position.

7. In a coal stoker, a retort, means feeding coal to the retort, a blower having a rotary air impeller and a casing enclosing the impeller and provided with two outlet passages, one of said outlet passages being positioned to receive air from the impeller under higher pressures and velocities than the other of said passages, a common conduit section connecting said outlet passages to the stoker retort, an air flow control valve movable in and controlling the rate of air flow through the outlet passage wherein pressures and velocities are greatest, an air velocity responsive actuating element subject to the influence of varying pressures and velocities in the other conduit section, and operating connections from said actuating element to said Valve said operating connections imparting closing movements to the valve under movements of the actuating element responsive to increased air velocities in its blower outlet passage, and imparting opening movements to the valve under movements of the actuating element responsive to decreasing air velocities in its blower outlet passage.

8. The structure defined in claim 7 in which the said actuating element is in the nature of an air-operated vane located in the low pressurelow velocity outlet passage and mounted for movements therein, and means yieldingly biasing the said actuating element to move toward a valve open position.

9. The structure defined in claim 1 in further combination with an auxiliary valve actuating element movable in the outlet conduit beyond said divider plate to and from a position wherein it is subject to a blast of air from the high pressure conduit section, and being operatively connected to the first said actuating element.

10. The structure defined in claim 1 in which the said air velocity-operated actuating element is in the nature of an air velocity-operated vane mounted for pivotal movements in the low pressure conduit section on an axis extending transversely of the conduit, and in further combination with an arm rigidly connected to the pivoted axial portion of the aforesaid actuating element and projecting therefrom to a point rearwardly of the divider plate, and an auxiliary valve actuating element carried by the projecting end portion of said arm and movable therewith to and from a position where it will be subject to the direct blast of a column of air moving through the high pressure conduit section.

11. In an apparatus for delivering an approximately pie-determined volume of air past a variable resistance, a blower having a rotary air impeller and a casing enclosing the impeller and having two outlet passages, one of said outlet passages being positioned to receive air from the impeller under higher pressure and velocity than the other of said passages, a common conduit section connecting said outlet passages to a variable resistance, an air flow control valve located in and controlling the rate of air flow through the outlet passage wherein pressures and velocities are greatest, an air velocity responsive actuating element subject to the influence of varying air pressures and velocities in the other conduit section, and operating connections from said actuating element to said valve.

12. The structure defined in claim 1, in which the said valve is in the nature of a valve plate having a segmental outer surface disposed transversely across the duct and pivotally mounted therein on an axis substantially concentric to the axis of the segmental valve plate surface.

13. The structure defined in claim 1, in which the said valve is in the nature of a valve plate having a segmental outer surface disposed transversely across the duct and pivotally mounted therein on an axis substantially concentric to the axis of the segmental valve plate surface, and a valve lip spaced from but parallel to a wall of the duct that is substantially parallel to the axis of the valve element and having a valve-acting edge over which the segmental valve works.

EARL STONEHOUSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 21,383 Tifit Aug. 31, 1858 449,743 Landis Apr. 7, 1891 620,358 Reeves et al Feb. 528, 1899 960,815 Carlisle June 7, 1910 1,166,571 Bard Jan. 4, 1916 1,360,285 Gibson Nov. 30, 1920 1,522,877 Gibson Jan. 13, 1925 2,010,694 Jones Aug. 6, 1935 2,059,656 Ring Nov. 3, 1936 2,108,873 Teeple Feb. 22, 1938 2,172,865 Danel Sept. 12, 1939 2,232,981 Swanson Feb. 25, 1941 2,240,779 Hunt et al May 6, 1941 FOREIGN PATENTS Number Country Date 418,544 Germany Sept. 9, 1925

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