US2339150A - Blower control system - Google Patents

Description

Jan. 11, 1944. F, commi-@N "2,339,150

y BLOWER CONTROL SYS TEM Filed Dec. 28,' 1940 Patented Jan. 1l, 1944 BLOWER CONTROL SYSTEM Charles F. Codrington, West Allis, Wis.. assigner to Allis-Chalmers Mannino Company,

Milwaukee, Wis., a corporation of Delaware Application December 28, 1940, Serial No. 372,053

(CL 23o- 114) 3 Claims.

'I'his invention relates to improvements in centrifugal blowers and particularly to centrifugal blowers used for supplying the air Anecessary for combustion of the fuel used in metal melting cupolas.

Metal melting cupolas are chargedpwith both the metal to be melted and fuel sufficient for melting the metal and for bringing the molten metal to the proper casting temperature. The weight of the metal to be melted determines the weight of the fuel required. Only the calculated weight of fuel is supplied to a cupola, for several known reasons, and it is therefore necessary to supply theexactly required quantity of oxygen to secure as nearly perfect combustion of the fuel as possible. Fuel being supplied by weight, the

' amount of oxygen required must also be determined by weight while the pressure at which the oxygen is supplied must be varied to overcome the varying resistance of the cupola charge during the melting operation. Supply of the required weight of oxygen at the desired pressure is obtained by forcing air through the cupola by means of a blower -or compressor and the power consumed by the blower is substantially directly proportional to the weight of air supplied and is constant for a given weight of air regardless of the pressure at which such air is supplied.

During normal operation of the cupola a given weight of air, determined by the cupUla charge, is required at a relatively low discharge pressure and a certain amount of power is therefore required for driving the blower. However, when conditions arise during cupola operation which require an increase in the pressure of the air 'supplied, it is necessary that the blower be capable of supplying the predetermined constant weight of air at an increased pressure. It is therefore necessary that the blower be designed for the maximum pressure output which may be required therefrom under any conditions. Designing of the blower for such maximum pressure conditions, however, requires that the blower be operated normally below the maximum output pressure. Such lower output pressure has been obtained for many years ,by placing a valve, usually of the known butterfly type, in the discharge line of the blower to throttle the dischargt-:f air to the pressure required for normal operation. Such throttling, however, consumes the same power for a. given weight of air even at the throttled lower discharge pressure and the quantity of power consumed may amount to as much as onethird more than would be required for the given weight of air at theI lower discharge pressure with vane control. Such wasteof power continues during the time that the blower is running at normal output which is by far the greater portion of its operating time. If means are provid ed for obtaining the desired normal output, that is, a given weight at a lower pressure, without throttling losses and which will also permit the same given weight to be obtained at a higher pressure when required, the size of both the blower and its drive and the power required for operating the blower over its entire range may be reduced bythe amount of the throttling losses eliminated. Elimination of the valve also reduces the length, of the discharge piping required and avoids the introduction of turbulence in the discharge line which must be smoothed down.

It is,'theref0re, an object of the present invention to"provide a control system for blowers of the centrifugal type in which the quantity of air inspired into the blower is controlled by a characteristic of the air discharged from the blower.

Another object of the invention is to provide a control system for blowers of the centrifugal type in which the quantity of air inspired into the blower is controlled by a characteristic of the air ldischarged from the blower.

Another object of the invention is to provide a control system for centrifugal type blowers in which the quantity of air delivered by the blower `is variable without the losses and turbulence due to throttling the discharge of the blower.

Another object oi' the present invention is to provide a control system for centrifugal blowers in which air inlet control means are controlled by air weight responsive means for controlling the weight of air discharged from the blower A regardless of the discharge pressure.

Objects and advantages other than those above set forth will be apparent from the` following description when read in connection with the accompanying drawing, in which:

Fig. 1 diagrammatically illustrates an air inlet control system according to the present invention as applied to a single stage blower for supplying a constant weight of air at variable pressure to a device involving the combustion of fuel; and

Fig. 2 graphically illustrates the saving in power consumed by the present control system as compared to the power consumed by blowers with the discharge throttling control of the prior art, and I Fig. 3 diagrammatically illustrates the manner in which a pluralityof vanes is mounted in the inlet into the casing'and the manner in which such vanes are mechanically interconnected exteriorly o! the casing inlet to provide for movement or the vanes in the same direction and by the same amounts.

Referring to the drawing by characters o! reference, the reference numeral 3 designates driving nfeans, shown as an electric motor, for a single impeller 1 oi the centrifugal type rotating within a casing 8, the impeller being shown as mounted on an extension of the motor shaft and the casing being shown as mounted directly on the motor stator housing. Air is drawn into the central portion of the' impeller 1 through the casing 8 through an inlet conduit II coaxial with the impeller 1 and is discharged from the periphery of the impeller 1 into the casing 8 and into a conduit I2 which is connected with a known metal melting cupola. generally indicated at I3. The blower inlet conduit II is provided with aplurality of vanes I8 of substantially sector shape arranged in an annular series coaxial with and spaced from said impeller and mounted on axles I1 journaled in the wall of the inlet conduit and extending outwardly therefrom and the outer ends of the axles l1 are severally equipped with bevel gears I8 mechanically interconnected. The vanes and the axles extend radially into the inlet conduit for rotation to shut on any desired amount oi the area of the conduit andthe gears on the vane axles vexternally of the conduit mesh with each other around the entire periphery of the inlet conduit.

The-meshing circle of gears I8 mesh with an operating gear I8 which is eccentrically connected with a rod 28 leading to a servomotor shown as being oi' the ilexible diaphragm type suitably mounted adjacent the inlet vanes I6. Such servomotor comprises a casing 22 divided into two chambers by `a iiexible diaphragm 23 connected with the vane'operating rod 28 which extends externally o! the casing 22 into a chamber in which a compression spring 24 acts between the casing 22 and the end of the rod 20 to bias the rodl 2li and the diaphragm 23 upwardly. 'I'he lower chamber of the servomotor casing 22 is vented to and hence under atmospheric pressure while the upper chamber thereof is connected to a pipe 25 leading to a suitable source oi' high pressure iluid. The admission of iiuid under pressure to the upper chamber of the servomotor causes ilexing of the diaphragm 23 to move the rod 2 0 downwardly against the compression of spring 24. Such downward movement oi' the rod 20 rotates the gear I8 and gears I8 to rotate the vanes I8 toward position -the vanes I8 toward the position for opening the inlet conduit II to its fullest extent.

Flow of pressure through the high pressure l pipe 25 is controlled bya mechanism for translating pressure changes in the discharge conduit I2 into movement I'or the operation of an indicating and recording means and for the operation of a control valve for the pressure ilow. An oriiice plate 21 is mounted in the discharge conduit I24 between the blower and the cupola to produce a pressure diiIerence on the two sides oi' the plate. A pipe 28 is connected with the discharge conduit I2 on the one side of the plate 21 and a pipe 28 is connected with the discharge conduit on the other side of the plate 21. Pipe 2lil is connected with the bottom o! a housing 38 havins a nexible support 3| extending across the housing at approximately the central portion thereof and the pipe 28 is connected with the upper portion oi the housing 30. A bell 32 floats in mercury in the lower portion o! the housing 38, the mercury forming a seal against the escape of air supplied beneath the bell by the pipe 28. The bell 32 is connected by way of a rack 33 with the flexible support 3| and is under the pressure of a compression spring 34 acting between the flexible support and an adjustable connection with the top of the housing 38. The bell 32 is therefore responsive to air pressure differences across the plate 21 and such differences exaggerate the variations in pressure due to cupola operation. Movement of the rack 33 is transmitted to a pinion segment 35 which acts through a system of levers 39 on the indicating and recording pointer 4I of an instrument generally indicated at 42 for indicating and recording variations in the weight of the air flowing through the discharge conduit I2.

The casing of the instrument 42 is connected by way of pipes 43 and 44 to the discharge conduit I2 on the two sides of the orice plate 21 to transmit the variations of pressure into the instrument case where such variations act on known temperatureand barometric responsive means not shown, to operate Va. pilot valve including a valve housing 48 and a valve body 41. The pilot valve 41 is double seated and controls the ilow of pressure through the pipe 25 to the servomotor 22, 23 and also ,controls the admission of pressure to diaphragms 48 which actuate the valve 41. For a detailed description of the instrument 42 and its several parts and the manner in which the several parts cooperate to control the pilot valve 41, reference is made to United States Letters Patent 1,582,868, AQM. Dixon, April 27, 1926, which discloses an instrument which may be employed in the present system.`

In operation, the pressure in the discharge l the acti '55 for opening or closing the inlet conduit II. Releasing of the pressure from above the diaphragm of the charge in the cupola I3 occur and such varying pressure acts on the instrument 42 to cause operation of the pilot valve 41. Assuming that the charge resistance in cupola I3 to the passage of air therethrough has'decreased, thus causing decrease in pressure in the conduit I2, of the instrument 42 is such as to cause movement of pilot valve 41 toward the left to allow fluid under pressure to iiow through the pipe 25 from the high pressure source. vSuch pressure forces the diaphragm 23 downwardly and rotates-the operating gear I8 and the vane gears I 8 to rotate the vanes I6 in the conduit closing direction. Closing movement of the vanes I8 continues as long as the valve 41 allows the pressure on the diaphragm 23 to increase. However, when the pressure in the conduit I2 and hence in the instrument 42 reaches its predetermined value, the pilot valve 41 moves toward the right to interrupt further pressure ilow into the vane servomotor V22, 23 and the vanes remain in their4 then position until a further change in cupola and conduit pressure occurs.

When the resistance of the charge in the cupola increases, valve 41 is moved toward the right, thus allowing air under pressure to esr cape from the upperchamber orservomotor 22 and allowing spring 24 to ilex' the diaphragm upwardly. The driving gear. I8 and vane gears I8 then rotate vanes I6 ina direction to open the discharge pipe'ito the maximum free open ing. Opening movement of vanes I continues as long as valve l1 is in position to allow escape of air from servomotor 22 through the valve.

Consideration of the curves shown in Fig. 2 which are test results on a system according to the present invention now in operation, shows that the power consumed for given atmospheric conditions is less at all points of operation, ex

cepting maximum output, than when throttling control is used for the same blower. The saving in power varies from 30 kw. to 45 kw. at various points of operation when the power consumption by the vane controlled lblower varies from 50 kw. to 80 kw. In addition to the saving in operating power, elimination of the throttling losses allows the blower to be designed for more nearly the actual pressure employed in normal operation, thus resulting in a smaller blower and motor for any given operating condition. Elimination of the usual throttling blast gate in the blower discharge eliminates the turbulence in the discharge which is unavoidable when such gate is used and eliminates the losses due to increased friction resulting Irom such turbulence. The gate losses amount to 2 to 3 ounces of pressure even when the gate is in its farthest open position because the gate must even then be set at about 35 w the pipe axis to secure suillciently accurate control thereof. apparent that the present invention provides a control system for blowers which' are provided with means shown as vanes operated by a servomotor which may also be an electric motor operated by a contactor in place o1 valve 41, for varying the quantity of air ilowing into the blower before such air is compressed, rather than varying the pressure of the air after the energy required for compression has been expended thereon, and provides means for operating the air quantity varying means. The means for operating the vane servomotor are responsive to the air weight as a result of the combination of pressure responsive means with compensation for variation of barometric conditions. Such pressure responsive means include the spring pressed bell 32 in the housing l0 and the connections of the several portions of the housing with opposite sides oi' the oriilce plate in the discharge line and the compensation for changing barometric conditions, which compensating means are already knownto the art.

Although but one embodiment o! the present It will therefore be invention has been illustrated and described, it

will be apparent to those skilled in the art that various changes and modications may be made therein without departing from the spirit of the invention or from the scope oi' the appended claims.

I claim:

` 1. In a control system for blowers delivering l of and adjacent said impeller and adjustable on their axes to vary the quantity of air and to impart a whirl to the entering air inspired into said impeller, and means responsive to the weight of air discharged by the blower to adjust said vanes.

2. In a control system for blowers delivering a constant weight of air, a centrifugal blower comprising a casing and an impeller Within Said casing, said casing having an inlet aperture for inspiration of air into said blower, a plurality of adjustable guide vanes mounted in the inlet in said casing and extending radially of the axis of and adjacent said impeller for adjustment on their axes to vary the quantity of air and to impart a whirl to the entering air inspired into said impeller, a servomotor for adjusting said vanes to vary the quantity of air inspired into said casing, and means responsive to the weight of air discharged by the blower to control operation of said servomotor.

3. In a control system for blowers delivering a constant weight of air, a centrifugal blower comprising a casing and an impeller within said casing, said casing having an inlet aperture for inspiration of air into said blower, a plurality 4oi adjustable guide vanes mounted in the inlet' in said casing and extending radially of the axis of and adjacent said impeller and adjustable on their axes to vary the quantity of air and to impart a whirl to the entering air inspired into said impeller, a. fluid pressure operated servomotor for adjusting said vanes, a pilot valve controlling the supply of fluid pressure to said servomotor, and means responsive to the weight of air discharged by the blower to operate said pilot valve.

CHARLES F. CODRINGTON.

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