US2063453A

US2063453A - Gas mixing apparatus

Info

Publication number: US2063453A
Application number: US668807A
Authority: US
Inventors: Garnet W Mckee
Original assignee: Individual
Current assignee: Individual
Priority date: 1933-05-01
Filing date: 1933-05-01
Publication date: 1936-12-08
Anticipated expiration: 1953-12-08

Description

. 8, 1936. G. w. McKx-:E

GAS MIXING APPARATUS li/Wi.

Filed May 1, 1953 Patented Dec. 8, 1936 UNITED STATES PATENT GFFICE 4 Claims.

The present invention relates generally to apparatus for mixing diiferent kinds or species of gases. More particularly, the invention relates to that type of apparatus which is adapted to 5 mix gases of high calcric value such, for example, as butane or propane, with air in order to dilute the same for combustion purposes.

Industrial furnace equipment of the type now in use is for the most part designed for operation l with artificial gas having a caloric value of approximately 530 B. t. u. per cubic foot or natural gas with approximately a calorific value of 1000 B. t. u. per cubic foot. For various commercial reasons, butane and propane are fast replacing l these gases as an industrial fuel. Butane has a caloriflc value of approximately 3200 B. t. u. per cubic foot and propane has a caloric value of approximately 2500 B. t. u. per cubic foot. In order to burn these two gases economically and without change in existing burner equipment, it is necessary to dilute these gases with air so that the resulting mixture will have approximately the same caloriflc value as the gas replaced.

One object of the invention is to provide a novel apparatus which serves either to dilute With air gases of high caloric value such as butane or propane or to mix combustible gases with the total amount of air required for combustion in furnace or heating equipment. In general, this apparatus comprises a casing which forms a mixing chamber for the gas and air and embodies an inlet for the air, an inlet for the gas and anoutlet for the mixed gas and air. In addition to the casing, the apparatus comprises a compressor, the suction or inlet side of which is connected to the outlet for the casing, and a, zero governor for delivering the gas under zero or atmospheric pressure into the mixing chamber via the gas inlet of the casing. The apparatus further comprises a pair of valves for controlling the gas and air inlets respectively together with means for simultaneously opening and closing the valves in response to the suction produced by the compressor in the mixing chamber.

Another object of the invention is to provide an apparatus of the type and character under consideration in which the valves for controlling the gas and air inlets of the casing are so constructed and arranged with respect to the inlets that the proportion of gas and air mixed in the mixing chamber remains constant throughout substantially the entire capacity range of the apparatus.

Another object of the invention is to provide an apparatus of the last mentioned character in which the valves are mounted on a common shaft and novel means is provided for adjusting one valve relatively to the other so as to insure simultaneous seating of the two valves.

A further object of the invention is to provide an apparatus of the aforementioned character in which the means for conjointly opening and closing the valves in response to the suction created in the mixing chamber by the compressor consists of a. diaphragm which is mounted in a housing on top of the casing.

A still further object of the invention is to provide an apparatus for mixing or diluting gases which is generally of new and improved construction and consists of but a small number of parts.

Other objects of the invention and the various advantages and 'characteristics of the present apparatus will be apparent to those skilled in the art from a consideration of the following detailed description.

The invention consists in the several novel features which are hereinafter set forth and are more particularly dened by claims at the conclusion hereof. y

In the drawing which accompanies and forms a part of this specification or disclosure and in which like numerals of reference denote corresponding parts throughoutthe several views:

Figure 1 is a side view of an apparatus embodying the invention; and

Figure 2 is a vertical longitudinal section showing in detail the construction and arrangement of the valves for controlling the entry or delivery of the gas and air into the mixing chamber of the casing.

'Ihe invention is exemplied in an `apparatus for mixing a combustible gas of high caloric value such, for example, as butane or propane, with air for diluting purposes and for supplying the diluted gas under pressure to a furnace or other point of consumption or use. This apparatus, as shown in Figures l and 2 of the drawing, consists of a device 3 for mixing the gas with the desired proportion of air, a zero governor 4 for supplying the gas under atmospheric pressure to the mixing device 3 and a compressor 5 for drawing the mixture of gas and air, that is, the gas diluted with air, from the mixing device 3 and delivering it under pressure to the furnace or point of consumption.

The mixing device 3 operates in response to the suction of the compressor 5 and comprises a verticallyextending, substantially cylindrical, metal casing 6. The latter embodies a mixing chamber 1 in the lower portion thereof and a sas chamber 8 in its upper portion. The gas chamber is connected to receive gas from the zero governor 4 by way of a pipe 8 and communicates with the mixing chamber via an orifice I3 in a disk-like plate I I. The pipe extends horizontally and is connected by a screw thread I2 to a laterally extending, annular boss I3 at the upper end of the casing 5. Ihis boss, as shown in Figure 2, supports the pipe 9 so that the latter discharges into the gas chamber 8. The oriilce plate II is centrally positioned in the casing 3 and rests on and is supported by an annular flange I4 which projects inwardly from the inner periphery of the casing. Bolts I5 extend through the outer margin of the plate I I and into the ilange I4 and serve removably to connect the plate to the iiange. The orifice I0 is formed in the center of the plate II and is controlled as hereinafter described, by a cone valve I 6. The gas in the chamber 8 is drawn into the mixing chamber 1 via the oriiice III and the flow thereof is controlled by the valve I6. The lower end of the casing 6 of the mixing device 3 is provided with an integral, inwardly extending, annular flange I1. This flange forms a support for a disk-like plate I8 which embodies a circular central orifice I3 and is removably secured to the ange by a pair of studs 23. The latter, as shown in Figure 2 of the drawing, extend upwardly through the outer margins of the plate I8 and into the annular flange I1. By way of the orifice I9, air under atmospheric pressure is admitted into the mixing chamber 1 for admixture with the gas from the chamber 8. The flow of air through the orifice I9 into the mixing chamber is controlled, as hereinafter described, by a cone valve 2|.

'I'he compressor 5 is located at one side of the mixing device 3 and may be either of the centrifugal or reciprocatingtype or any other desired or practical type. 'Ihe one shown in the drawing is of the centrifugal type and comprises a housing 22 and a rotor (not shown) in the housing. It is driven by an electric motor 23 which is located at one side of the housing 22 and has the armature shaft thereof connected to the rotor of the compressor as illustrated in the drawing. The compressor housing 22 embodies an inlet 24 and an outlet 25 and receives the mixture of gas and air from the mixing device 3 by way of a pipe 26. The latter extends horizontally and has one end thereof connected to an annular boss 21 at one side of the casing l of the mixing device 3.- The other end of the pipe is connected to and communicates with the inlet of the compressor housing. The outlet of the compressor housing is connected in any suitable manner to the point of gas consumption. During operation of the electric motor 23, the compressor 5 is driven and operates to draw the mixture of gas and air from the mixing chamber 1 in the casing 5 of the mixing device and to supply it under pressure to the point of use or consumption. The suction created in the mixing chamber 1 by the compressor 5 is proportional to the demand at the outlet 25 of the compressor. In other words, when the requirement for the mixture of gas and air increases, the suction at the inlet and consequently the mixing chamber, increases accordingly. When the demand or requirement for the mixture of gas and air decreases, the suction at the inlet of the compressor and in the mixing chamber 1, decreases correspondingly. The annular boss I3 is formed integrally with the casing 3 andleads to and communicates with the mixing chamber 1.

The zero governor 4 is of standard design and consists of a cast metal valve casing 28. The latter is provided with a horizontally extending gas inlet 25 at one end thereof and a horizontally extending gas outlet 33 at its other end. The inlet 23 is provided with an internal screw thread 3I whereby it is connected to a pipe (not shown) leading to the gas supply. The outlet 33 is longitudinally aligned with the inlet 23 and is connected by a screw thread 32 to the pipe 3. The space in the interior of the valve casing is divided by means of a cross wall 33. The latter embodies a circular aperture 34 whereby the gas is permitted to fiow from the inlet 29 to the outlet 38 for delivery to the gas chamber 8. The flow of gas through the aperture is controlled by means of a vertically movable valve 35. The latter is located in the outlet side of the Valve casing 28 and is provided with a vertically extending stem 35 which projects upwardly through the aperture 34 and is connected to a horizontally extending, flexible diaphragm 31 in a two-piece housing 38 on top of the valve casing. 'Ihis diaphragm operates in response to fluctuation or vacillation thereof to shift the valve to and from the aperture in order to regulate or control the flow of gas through the casing. The housing 38 consists of a circular upper piece 33 and a complemental lower piece 40 and is suitably secured to the top of the governor. The margin of the diaphragm is clamped between the

housing pieces

33 and 43 and the latter are shaped so as to form a compart ment 4I above the diaphragm and a compartment 42 below the diaphragm. The chamber 4I is open to atmosphere by way of a hollow nipple 43 in the upper housing piece 39. The compartment 42 beneath the diaphragm is connected by an equalizing passage or duct 44 to the outlet side of the valve casing 28 so that any pressure in the outlet is transmitted to the under side of the diaphragm and causes the diaphragm to shift the valve to a point wherein zero or atmospheric pressure exists at the outlet 38. An elongated suspension spring 45 isconnected to the central portion of the diaphragm and serves to counter-balance the weight of the diaphragm assembly. This spring is encased in a tube 45 which is connected to and extends upwardly from the central portion of the upper housing piece 33. A flexible diaphragm 41 extends between the diaphragm housing 38 and the valve casing 28 and is arranged to prevent the passage of gas from the inlet to the compression compartment 42 under the diaphragm. The valve 35 is so controlled by the diaphragm 31 that it operates to maintain the gas flowing through the outlet of the casing at atmospheric pressure` Should the pressure at the outlet of the valve casing 28 of the governor increase beyond atmospheric pressure, the diaphragm, due to the accumulation of pressure within the compartment 42. raises and thus tends to close the valve so as to reduce the flow of gas through the valve casing and bring the pressure back to that of the surrounding atmosphere. Should the pressure of the gas flowing through the casing drop below atmospheric pressure, the diaphragm 31 due to the formation of a partial vacuum in the compartment 42, moves downwardly and causes the valve to open and allow an increase of flow of the gas from the inlet to the outlet and thus restores the i aoeaass atmospheric pressure to the gas chamber 8 in the -upper end of the casing 8 of the mixing device 8.

The cone valve I8 for controlling the flow of the gas from the chamber 8 into the mixing chamber 1 ismounted on a vertically extending shaft 48 and is arranged in an inverted position, that is, in a position wherein the apex portion thereof is on the bottom and is disposed in the mixing chamber 1 and the base portion thereof is on .top and is disposed in the gas chamber 8. Preferably, the cone valve I5 is formed separately from the shaft and is secured permanently and flxedly to the latter by welding or brazing it in place. The shaft 48 is vertically movable and the upper end thereof extends through the gas chamber 8 and into a two-piece, cast metal housing 48 on top of the casing 8. The housing 49 surrounds and supports a exible diaphragm 58 and consists of a top section 5I and a bottom section 52. The bottom section, as shown in Figure 2 of the drawing. is secured to and forms a closure for the upper end of the gas chamber 8 and is secured to the casing 8 by means of bolts 53 which extend through an annular, outwardly extending flange 54 at the upper end of the casing 6 and project into the bottom section 52. The marginal or outer portion of the bottom section 52 ofthe housing extends upwardly to form a compartment 55 under the diaphragm 58 and embodies a hori- `zontally and outwardly extending flange 56.

The top section 5I of the casing 48 forms a compartment 51 over the diaphragm 58 and is provided at the margin thereof with a horizontally and outwardly extending ange 58. The margin of the diaphragm 58 is clamped between the

flanges

58 and 58 of the housing sections by means of bolts 59 which extend through these flanges. The top section 5| of the housing is provided at the central portion thereof with a removable cap 68 whereby access may be had to the compartment 51 over the diaphragm 58. The bottom section 52 of the housing embodies a central opening' 6I through which the upper end of the shaft 48 extends and via which the compartment 55 under the diaphragm communicates with the gas compartment 8. The upper end of the shaft 48 extends through and is connected to the central portion of the diaphragm 58 and is connected thereto by means of a pair of nuts 82. These nuts are connected to an external screw thread on the upper end of the shaft 48 and bear respectively against a washer 63 tting against the under face of the diaphragm and a disk 84 bearing against the top face of the diaphragm. The central portion of the diaphragm is clamped between the washer and disk by the nuts and in this manner is connected xedly to the upper end of the shaft with the result that all fluctuations or vacillations thereof are imparted to the shaft 48. The compartment 51 over the diaphragm 58 is air-tight and communicates with the mixing chamber 1 in the casing 8 by way of a longitudinally extending duct 65 in the upper end of the shaft 48. The lower end of this duct terminates directly beneath the lower end of the cone valve I6 and extends laterally as shown in Figure 2 of the drawing so that it opens into the mixing chamber 1 and the suction created in such chamber is transmitted to the compartment 51. During operation of the apparatus, the suction created in the mixing chamber 1 by the compressor 5 is transmitted to the compartment 51 over the diaphragm 58 via the duct 65 and in response to the effect of this suction in the compartment 51 the diaphragm 58 moves upwardly and raises the shaft 48 so as to open or unseat the cone valve I6 and thus results in the flow of gas from the chamber 8 into the mixing chamber 1 for admixture with the air which is introduced into the f the suction in the chamber 1 decreases due to a n decrease or falling off in the demand for the mixture of gas and air at the outlet of the compresser, the diaphragm, because of'a corresponding decrease in the suction within the compartment 51, moves downwardly by gravity and operates to close either partially or fully the cone valve I6. In order to regulate the amount of suction transmitted to the compartment 58 and thus to govern the speed of opening and closing of the cone valve I6, an adjusting Screw 56 is threaded into the upper end of the valve-carrying shaft 48. This screw is associated with the upper end of the duct and is adapted in response to adjustment thereof to regulate the effective size of the duct at the point where it communicates with the chamber 51. When the screw is adjusted so as to open to the fullest extent the upper end of the duct, the suction created by the compressor in the mixing chamber 1 is transmitted directly and without restriction to the compartment 51 with the result that the cone valve I6 opens quickly. When the screw 66 is adjusted so as to restrict the upper end of the duct 65, the suction created in the mixing chamber 1 is transmitted more slowly to the compartment 51 and opening and closing of the valve IE takes place more slowly. Access to the screw 6 8 for adjustment purposes is obtained by removing the cap 68 from the top section of the housing 48.

The diaphragm 58 together with the housing 48 and the duct-equipped shaft 48 exemplify simple means for controlling the valve I6 in response to suction created in the mixing chamber 1 by the compressor 5.

The cone valve 2I for controlling the flow of air into the mixing chamber 1 via the aperture I9 in the plate I8 is mounted on the lower end of the shaft 48 so that it is movable into and out of its open position simultaneously with the cone valve I6. It is mounted on the shaft so as to seat against the aperture plate I8 at the same time the cone valve I6 seats against the aperture plate II and is arranged in an inverted position, that is, in a position wherein the apex portion thereof extends downwardly and is located beneath the aperture plate I8 and its base portion is located above the aperture plate and is disposed in the mixing chamber 1. The cone valves I8 and 2I are what may be termed proportioning cone valves" in that if their sides are extended to the vertices and the bases are considered as at the points of contact with the orifice plates, they have the same height. As a result of this formation, the valves allow the same proportionate flow of gas and air into the mixing chamber regardless of the extent to which they are opened. If, for example, the orifices in the plates II and I8 are of such relative diameter that when fully opened they serve to admit into the mixing chamber 1 one part gas to two parts of air, this ratio or proportion of gas to air will remain constant throughout the entire range of capacity of the mixing device 3 due to the control o f the orifices by the proportioning cone valves, that is,

. cone valves oi' the same height from vertex to effective base. v e

'Ihe cone valve 2| is slidably mounted on the lower end of the shaft 48 and rests upon a split nut il. This nut is threaded to the lower end of the valve-carrying shaft and embodies a cap screw 68 whereby it may be locked against rotation relatively to the shaft. By rotating the nut B1, the cone valve 2| may be adjusted longitudinally of the shaft 48 so as to position it with.

respect to the valve I6 so that it seats at the same time as the latter. The cone valve 2| is urged downwardly against the nut Sl by a compression spring 69 which extends around the intermediate or central portion of the shaft 48 and is arranged so that the lower end thereof abuts against the valve 2| and its upper end against a ring 10 at the lower end of the cone valve I5. The lower end of the shaft 48 is slidablymounted in a tubular guide ll and projects into a dash pot 12. These two parts are supported on a plate 13 which is held beneath and in spaced relation with respect to the orifice plate I8 by the studs 20. The guide 1| extends through an aperture in the central portion of the plate 13 and is provided with a depending, externally threaded stem to which is secured the dash pot 12. The dash pot serves to prevent chattering of the shaft when the cone valves, due to low demand, are in a nearly closed position and the guide 1l serves to hold the shaft in a central position with respect to the orifices in the plates |4 and |8. In view of the fact that the orifice plate |8 is removably connected to the flange Il by the studs 28 and the cone valve 2| may be removed from the lower end of .the shaft 48, a change in the proportion of air to gas may be effected by substituting for the plate |8 a plate with a larger or smaller orifice and substituting a proper valve for the cone valve 2|. The air which is admitted into the mixing chamber 'l via the orifice I9 and the plate I8 flows inwardly around the studs 20 into contact with the lower end of the cone valve 2| and then upwardly through the orifice I9 into the mixing chamber?.

The operation of the apparatus is as follows:

When the compressor 5 is driven by the electric motor 28 suction is created within the mixing chamber 1 of the mixing device 3. This suction, as previously pointed out, is transmitted to the suction compartment 51 over the diaphragm 5I in the housing 49 and causes the diaphragm to move upwardly and thus through the medium of the shaft 48, to unseat the cone valves Ii and 2 Upon opening of these valves, gas and air are drawn into the mixing chamber l via the orifice plates and I8 respectively and pass in a mixed condition and in predetermined proportion from the chamber l to the inlet of the compressor and thence to the compressor outlet in response to the action of the rotor of the compressor. During operation of the apparatus, the zero governor 4 maintains in the gas chamber 8 of the mixing device 3 a supply of gas under atmospheric pressure. When the valves I6 and 2| are unseated, the gas and air enter the mixing chamber under atmospheric pressure. When the demand for the mixture of gas and air increases, the suction at the inlet of the compressor increases correspondingly. This increased suction is transmitted to the suction chamber 51 in the housing 49 and results in the diaphragm 50 moving upwardly and opening the valves I6 and 2| to a greater extent. As the demand for the mixa,oes,4as i ture of gas and air decreases, the suction at the inlet of the compressor and in the mixing chamber T decreases correspondingly and the diaphragm operates to shift the valves toward their respective orifice plates. Due to the fact that the valves I8 and 2| are in the form of proportioning cones, that is, cones of the same height from effective base to vertex, the proportion of the air and gasthat are mixed together in the mixing chamber 1 and are delivered to the point of consumption by the compressor 5 is constant throughout the entire capacity range of the mixing device. If a change in the proportion or ration of the air and gas is desired, it is only necessary to replace the orifice plate I8 with a plate having an orifice of the desired size and to substitute a new cone valve for the valve 2|.

If the cone valve 2| should not seat simultaneously with the cone valve I6, adjustment of the cone valve 2| may be effected by manipulation of the split nut 8l. When it is desired to increase or decrease the speed of opening and closing of the cone valves I6 and 2|, the cap 68 is removed from the top 'section 5| of the housing 49 and the screw 6B is adjusted so as to increase or decrease the cross sectional area of the upper end of the duct 85. The herein described apparatus consists of a small number of parts and hence may be manufactured at a low and reasonable cost. It is exceedingly emcient in operation due to the fact that the proportion or ratio of air to gas remains constant throughout the entire capacity range of the mixing device.

Whereas the apparatus has been described as being adapted for use in connection with the mixing of gas of high caloriflc value with air, itis to be understood that it may be used for other purposessuch, for example, as the mixing of two different gases. When the apparatus is used to mix two different gases, a gas chamber is formed at each end of the casing cf the mixing device and two zero governors are used to supply the two gases to the chamber under atmospheric pressure. The apparatus may also be used instead of as a unit for diluting a gas of high calorific value with air, to mix a combustible gas with-the total amount of air required for combustion.

The invention is not to. be understood as restricted to the details set forth, since these may be modified within the scope of the appended claims, without departing from the spirit and scope of the invention.

Having thus described the invention, what I clatim as new and desire to secure by Letters Paten is:

1. In a gas mixing apparatus of the character described, the combination of a casing having a mixing chamber therein and provided with a pair of circular, inlet orifices for the chamber and a chamber outlet adapted for connection to the suction side of a compressor, means for supplying different kinds of gases under atmospheric pressure to the inlet orifices for passage to the mixing chamber in response to the suction created in the chamber by the compressor, a pair of cone valves for controlling the flow of gases into the chamber fitting in and axially aligned with the orices respectively and having the large ends thereof at one side of the orices and designed to seat in said orifices and having their small ends projecting beyond the other side of the orifices, andl means for conjointly opening and closing the valves comprising an element extending between and connected to the valves and movable back and forth for valve opening or closing purposes to a less extent than the extent to which the small ends of the valves project beyond said other side of the oriiices when the valves are closed, said cone valves being the same in height from vertex to point of orice contact so that the ratio of the areas of the spaces between the orifices and the aligned or coplanar portions of the valves is constant regardless of the extent to which the valves are openediand the same proportionate flow of the gases into the mixing chamber is always maintained.

2. In a gas mixing apparatus of the character described, the combination of a casing having a mixing chamber therein and provided with a pair of axially aligned, circular, inlet orifices for the chamber and a chamber outlet adapted for connection to the suction side of a compressor, means for supplying diierent kinds oi gases under atmospheric pressure to the inlet orices for passage to the mixing chamber in response to thel suction created in the chamber by the compressor, a pair of cone valves for controlling the iiow of gases intol the chamber fitting in and axially aligned with the orifices respectively and having the large ends thereof at one side of the orices and designed to seat in said orifices and having their small ends projecting beyondthe other side of the oriiices, and means for conjointly opening and closing the valves operative in response to the suction in the mixing cham ber and comprising a diaphragm and a shaft extending through the mixing chamber and the orifices and extending through and connected to the valves and connected to and controlled by the diaphragm so that it is movable longitudinally for valve openingl and closing purposes to an extent less than that to which the small ends of the valves project beyond said other side of the orices when the valves are closed, said cone valves being the same in height from the vertex to point of orifice contact so that the ratio oi the areas of the spaces between the orifices and the aligned or copianar portions of the valves is constant regardless of the extent lto which the valves are opened and the same proportionate flow of the gases into the mixing chamber is always. maintained.

3. In a gas mixing apparatus of the character described, the combination of a casing having a mixing chamber therein andprovided with a pair of axially aligned, circular, inlet oriiices for the chamber and a chamber outlet adapted for connection to the suction side of a compressor, means for supplying different kinds of gases under atmospheric pressure to the inlet orifices for passage to the mixing chamber in response to the suction created in the chamber by the compressor, a pair of'cone valves for controlling the flow of gases into the chamber fitting in and axially aligned with the orices respectively and having the large ends thereof at one side oi the orifices and designed to seat in said orinces and having their small ends projecting beyond the other side of the orifices, means for conjointly opening and closing the valves comprising a longitudinally movable shaft extending through the mixing chamber and the inlet orices and extending through the valves and having the latter mounted thereon, and means for adjusting one of the valves axially on the shaft relatively to the other so as to insure proper and conjoint seating oi' the valves when the latter are shifted into their closed position, said cone valves beingthe same in height from vertex to point ci oridce contact so that the ratio or the areas of the spaces between the oriiices and the aligned or coplr portions of the valves is constant regardless oi the extent to which the valves are opened and the same proportionate dow oi the gases into the mixing chamber is alwaysmaintained.

4. In a gas mixing apparatus of the character described, the combination of a casing iiiavlng a mixing chamber therein and provided with a circular inlet orifice of one diameter leading trom atmosphere to the chamber and serving to admit air into the latter, a second circular inlet orifice for the chamber of diierent :1 i" eter than the first mentioned orice, and a chamber outlet adapted for connection to the suction side of a compressor, means for supplying gas other than air and under atmospheric pressure to the second inlet orifice for passage to the mixing chamber in response to the suction created in the chamber by the compressor, a pair of cone valves for controlling the o'w of air and gas into the chamber shaped conformably to and axially aligned with the orices respectively and having the large ends thereof at one side of the orifices and designed to seat in said oriiices and their smaller ends projecting beyond the other side of the orices, and automatic suction controlled means operative conjointly to open the valves when the. suction increases and to close the valves when the suction decreases and comprising an element extending between and i connected to the valves and movable back and forth for valve opening and closing purposes to an extent less than, the extent to whichthe small ends of the valves project beyond said other side of the orinces when the valves are closed, said cone valves being the same in height from vertex to point. of oriiice contact so that the ratio of the areas of the spaces between the orifices and the aligned or coplanar portions oi' the valves is constant regardless of the extent to which the valves are opened and the same proportionate ow of air and gas into the mixing chamber is always maintained.

GARNET W. MCKEE.