US2914076A - Flapper-nozzle couple with perforated flapper - Google Patents

Description

Nov. 24, 1959 F. H. ZlMMERLl 2,914,076

FLAPPER-NOZZLE COUPLE WITH PERFORATED FLAPPER Filed May 29. 1953 2 Sheets-Sheet 1 INVENTOR. FREDERICK H.Z|MMERLI ATTORNEY.

Nov. 24, 1959 F, H. ZIMMERLI 2,914,076

' FLAPPER-NOZZLE COUPLE WITH PERFORATED FLAPPER Filed May 29. 1953 2 Sheets-Sheet 2 NOZZLE FORCE OUTPUT PRESSURE INVENTOR. FREDERICK H. ZIMMERLI ATTORNEY.

United States Patent ice FLAPPER-NOZZLE COUPLE WITH PERFORATED FLAPPER Frederick H. Zimmerli, Fort Washington, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minue apolis, Minn., a corporation of Delaware 7 Application May 29, 1953, Serial No. 358,224

2 Claims. (Cl. 137-82) The general object of the present invention is to provide a novel and effective transducer characterized. by its mechanical simplicity, its relatively small weight and bulk and its relatively low inherent cost of production. My invention is particularly adapted for use in converting an electric signalinto a proportional pressure. It is further adapted to produce linear pressure changes in ac- I 2,914,076 Patented Nov. 24, 1959 and area, a smaller difference in pressure is required at the high output pressure for an equal difference in input pressure. This pressure characteristic is the main source of non-linearity, in the operation of embodiments of the lnvention, and the use of a sharp edge nozzle reduces the non-linearity over the operating span of the apparatus. I have also found it possible to reduce the non-linearity by slightly tapering the discharged nozzle bore, and also by replacing the usual flat flapper valve by a flapper valve which may have a flat surface facing the nozzle and having a tapered projection which extends axially into the nozzle bore.

The operative span of the apparatus depends upon its design, but ordinarily it may correspond to a variation in the nozzle pressure from 3 to 15 pounds per square inch as is customary in conventional air controllers.

Another object of the present invention is the provision of a force to pressure transducer which is characterized by its ability to produce linear changes in pressure with linear changes of input force.

A further object of the invention is to provide a force to pressure transducer which is compensated for changes in the air supply pressure to the transducer.

Still another object is to provide a pressure transducer having a nozzle flapper having a predetermined formation of the flapper relative to the nozzle which results in shown in said .Moore' patent comprises a bleed nozzle and flapper valve unit, and opposed bellows elements for adjusting the flapper valve relative to the bleed nozzle on a change in acontrolling condition and cooperating with said unit to control a pilot valve operating as a relay or servornotor to' effect appropriate control actions.

A specific object of the present invention is to provide pneumatic means substantially simpler and less bulky and less expensive to construct and maintain than conventional air. controllers, but which is adapted to cooperate with a conventional pneumatic valve to produce control effects heretofore normally produced by the com.- bination of a conventional air controller and pilot valve.

.Theinvention maybe used with advantage initransmitting a pneumatic signal to controlor. other responsive apparatus at a distance from the apparatus including the nozzle and flapper. I v I My invention is characterized by its use ofthe principle that when. air ,is supplied'through a restricted inlet to a receiving space'havi'ng .a nozzle discharging a jet stream against a movable barrier, such as a flapper valve, to which is appliedf-a suitableforce which tends to move the barrier 'towa rdthe nozzle, the pressure in the receiving space will stabilize at a value dependent on the magnitude of the force applied to the barrier. In the use of the inventionl have found that by suitable relative shaping of the nozzle and the barrier it is possible to obtain a close approach to a linear relation of the receiver pressure to the bias or barrier balancing force, and that the departure from linearity maybe made very small by the use of simple and effective compensating provisions.

In the form of the invention which I now consider preferable for most of its uses, the nozzle tip is formed of a hard metal such as tool steel, has a cylindrical bore, and is externally tapered to form a conical outer surface terminating in a sharp edge at the nozzle tip. The angle of the external conical surface elements 'to the axis of said surface may well vary between-30 and 60. At high output pressure .(which occurs when the space betweenthe flapper and nozzle is small) the effective area of the flapper is; larger. thanat low output pressure.

Since the force on the flapper is theproduct of. pressure the "pressure within the nozzle varying substantially linearly with the movement of the flapper.

' The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its advantages, and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of the invention.

Of the drawings:

Fig. 1' is a schematic representation of a force to pressure transducer;

Fig.2 schematically illustrates a simple pressure to force transducer:

Fig. 3 illustrates a pneumatic transducer in which the nozzle discharge is opposed by a flapper valve carried by the movable coil of a galvanometer;

Fig. 3A shows a special form of flapper-nozzle configuration;

Fig. 4 is a chart showing curves illustrating linearity variations occurring with different operating conditions;

Fig. 5 illustrates an electrical compensating circuit; and

Fig. 6 illustrates a transducer comprising a baffle type barrier carried by a pivoted galvanometer coil and having a compensating nozzle acting on the galvanometer coil.

In Fig. 1, I have schematically illustrated, by way of example, a simple embodiment of the present invention which comprises a conduit or chambered body A with a receiving chamber or space a. The. latter receives air under pressure through a restricted passage b, and discharges air through a lateral nozzle c at a pressure varying with the adjustment of a movable barrier d which faces the nozzle. The barrier d may well be and is assumed to be a flapper valve. The displacement of the flapper valve d from the nozzle 0 varies the pressure in the space a.

As shown, the flapper d is biased for movement toward the nozzle 0 by a spring e acting between the flapper d and an adjustable abutment f. The displacement from the nozzle 0 of the abutment f can be varied by rotating a threaded adjusting member g mounted for threaded engagement with a stationary support h. The member g may be rotated about its axis manually or automatically in accordance with the conditions of operation. The

rotation of the member g in one direction or the other will increase or decrease the tension of the bias spring e and thereby increase or decrease the pneumatic pressure in the space a.

As shown in Fig. 1, by way of example, the space a is in communication through a pipe a with a pressure responsive element in the form of a bellows i which controls an electric circuit j. The latter has a movable end wall in and a stationary end wall zb attached to a stationary housing structure or support I. The pipe a opens into the bellows chamber through an opening formed in the end wall ib. Attached to the movable wall ia is a wiper contact k in engagement with and movable along a slide wire I. The latter is included in the circuit j. As shown diagrammatically, the circuit j includes a source of current m connected in series with the resistor I between the circuit terminal conductors n, and the wiper contact k is connected to one end of the resistor l by a conductor 0, so that as the pressure in the receiver space a increases and decreases, the bellows i expands and contracts. As the bellows expands and contracts, the wiper contact k moves along the slide wire I and thereby short circuits more or less of the slide wire I. As the amount of the resistor l effectively included in series with the source of current m diminishes, the current flow through the circuit j increases.

The air stream discharged by the nozzle c exerts a force on the member d which increases and decreases as the pressure in the space a increases and decreases. The force produced by the air jet discharged by the nozzle and impinging on the flapper valve d constitutes a feed back force regulating the pressure in the space a, and the transducer A thus operates as a force to pressure transducer.

The free end of the nozzle c is shaped to form a conical surface on which terminates at the discharge end of the nozzle in a sharp edge. As is hereinafter explained, the conical or bevelled surface ca is an important characteristic of the invention.

In Fig. 2 I have illustrated a transducer AB comprising a receiving space a, as in Fig. 1. However, the transducer has no outlet or pressure transmitting connection other than the passage through its bleed nozzle c. The nozzle 0 of Fig. 2. discharges an air jet against a barrier d. The latter may be similar in form to the flapper valved of Fig. 1, and may be similarly biased toward the nozzle 0. With the arrangement shown in Fig. 2 the positions assumed by the flapper valve d as the pressure in the space a varies provide a measure of the jet force impinging against the bafl le d, and the Fig. 2 apparatus thus con stitutes a pressure to force transducer.

In Fig. 3 I have illustrated a transducer AC for converting electrical energy into a proportional air pressure. The transducer AC comprises apparatus which may be structurally similar to that shown in Fig. 1, except that the flapper valve aid of Fig. 3 is moved toward and away from the associated nozzle 0 by means responsive to variationin the strength of an electric current. That current may be quite small such, for example, as a thermocouple current. As shown, the flapper a'a is secured to and may extend radially away from the axis of the coil p of a galvanometer P of the DArsonval type. As diagrammatically shown, the coil p has its terminals p connected to a source of a small D.C. current which is shown as a thermocouple q. As shown, the thermocouple q is connected across the terminals p of the coil p. In some cases, and as shown in Fig. 3, the galvanometer P has its U-shaped permanent steel magnet R formed with pure iron pole pieces r, and the coil 2 surrounds the usual cylinder s of soft iron. The movable coil p and the flapper da attached thereto are so proportioned and arranged that a small angular movementof the coil p'in response to changes in the temperature of the thermocouple q may give to the flapper valve da a variable force which tends to cause the valve a'a to move toward the ,4 discharge end of the nozzle c. As previously explained,

full span operation may involve a nozzle pressure range of from 3 pounds to 15 pounds per square inch and the output pressure in this range is dependent upon the force from the coil p.

In Fig. 3, T represents a conventional non-bleed type pilot valve for regulating a control pressure. As shown, air at a regulated pressure which may be 20 pounds per square inch, is supplied by a pipe U to the inlet of the transducer AC which includes the receiving space a. The pipe U also supplies air to the main air inlet of the pilot valve T. The control inlet of the pilot valve T is connected to the receiving space a of the element AC. The control air outlet of the pilot valve T is connected by a conduit t to the pressure chamber of a diaphragm valve W. The latter may be employed to control the flow of fuel through a pipe w to the furnace or heater to control the temperature of which the thermocouple is responsive. While the pilot valve T is shown, such is not essential in many applications of the invention because of the large air handling capacity of the transducer AC and the linear character of the transducer.

In each of the forms shown in Figs. 1, 2 and 3, the flapper nozzle system acts in a dual role, first as a detector and then as a force generator. The two roles are inseparable since the force is proportional to the output pressure, and the output pressure is proportional to the flapper nozzle spacing. In order that the flapper system may be in equilibrium, the nozzle jet force must be equal and opposite to the external force. Therefore, the output pressure is proportional to the external force. The latter is directly due in Fig. 1, to the spring action of the compression spring E, and in Fig. 3 is the result of the torque impressed on the flapper da as a result of the current flow through the coil p located in the magnetic field created by the magnet of the galvanometer P.

The curve 2 in the Fig. 4 chart is a theoretically computed curve showing the ideal nozzle force-output pressure characteristic indicated by the following equation: The value F of the jet force in pounds per square inch is given by the following Equation 1:

Numerous experimentally derived curves made in testing a wide variety of nozzle and flapper configurations, made in an endeavor to obtain optimum practical results, were each found to be of the same type but with the curves being mirror images of the theoretically computed curve 2. All of the curves mentioned show some small output air pressure variation from a linear range as said pressure is varied through a substantial range. I found experimentally, that with a hardened polished tool steel nozzle of the type shown in Fig. 1, and a flat flapper blade, the non-linearity is of the order of -0.6% of full span. The non-linearity characteristic obtained by the last mentioned nozzle is shown by curve 1 of the Fig. 4 chart. With a nozzle having a flat annular surface surrounding and coaxial with the nozzle outlet, the non-linearity is appreciably greater. With a standard commercial nozzle of well known type having a flat annular surface surrounding the nozzle outlet and of appreciable radial extent, the non-linearity was found to be i2.5% of span. That non-linearity characteristic is shown by curve 3 of the Fig. 4 chart.

Air is a gas and consequently has weight. Therefore, it will have momentum if it is forced through a nozzle. If the direction of the flow is changed, a force will be applied to the deflecting member, i.e. the flapper, by the change in momentum. The non-linearity produced by a nozzle with a flat area transverse to and surrounding the discharge end of the nozzle discharge orifice, is caused by the change in pressure gradient between the nozzle hole edge and the outside edge of the flat area as the nozzle flapper spacing changes. With a-highoutlet pres- .sure, i.e., with a relatively smalltflapper' spacihg, the effective area of the flapper is larger than-f at low" pressures. Since force is the productofpressure. and area, for an equal difierence in input pressure, a smaller difference in output pressure is required when thefoutput pressure is relatively high than when it is relatively low. That condition is the main source of non-linearity. Sharp edge nozzles develop a pressure gradient only 'over an infinitesimal distance, and in consequence, the elfective flapper area remains practically constant over the operating span. It is thought that the small remaining non-linearity may be caused by a change inthe velocity coefficient as the spacing is changed, or byvariations'in the change in momentum as the flapper nozzle spacing changes.

When the flapper valve da 'i's"formed'with a small hole da' of the order of .005" in register with the nozzle axis, as shown in Fig. 3, a slight linearity improvement is attained, and the supply pressure effect is also improved.

Fig. 3a illustrates a specially shaped flapper valve db with which it is possible to obtain a non-linearity of i0.6%, when the associated nozzle cb is surrounded by a flat transverse space cc. The specially shaped flapper giving minimum non-linearity with a flat nozzle area, is formed with a lateral projection dc generally conical in cross section but increasing in diameter at an increasing rate as the distance from the projection tip increases, said projection being rounded at its tip and of such size as to enter the nozzle orifice and act as an obturator therein. The use of such a flapper increases the position change .required for full span operation because the exhaust area changes less than it does with the flat flapper. Contrasting the flat flappers d shown in Figs. 1 and 2 with the especially shaped flapper db shown in Fig. 3A, it will be seen that, if the flapper db is moved toward or away from the nozzle cd, the projection dc will cause the ring-shaped opening between the nozzle cb and the flapper db to remain constant in size over a longer path of travel of the flapper than do the openings between the flat flappers d of Figs. 1 and 2 and the cooperating nozzles. The use of such specially shaped flappers while suitable for many purposes, is open to the objection that the proper alignment of the flapper projection with the bore of the nozzle is diflicult to obtain in practice.

I have found that eflective and desirable compensation for non-linearity of the character indicated in curves 2 and 3 may be obtained with apparatus of the general character shown in Fig. 3, by connecting a selenium rectifier or other non-linear element in parallel with the galvanometer coil 12 as indicated in Fig. 5. In Fig. 5, X designates the selenium rectifier and Xa designates a source of direct current such as a thermocouple. The selenium rectifier circuit shown in Fig. 5 is arranged to decrease the rate at which the current through the coil p increases as the temperature of the thermocouple q increases. Thus, the

selenium rectifier X modifies the bias force exerted by the galvanometer coil p in response to the current flow through the galvanometer coil p caused by the varying voltage of the thermocouple Xa as modified by the selenium rectifier X.

As those skilled in the art will understand, the average rate at which air is discharged through the nozzles c and cb of the apparatus shown herein, is substantially higher than the average rate at which air is discharged through the bleed nozzles of conventional air controllers which later rate has become standardized. It is practically essential therefore, that the bore diameter of each of the nozzles c and ab should be appreciably greater than the bore diameter of the conventional air controller bleed nozzle.

Variations in the pressure at which air is supplied to the restricted inlet b to a transducer receiving space produce changes in the pressure of the air discharged from said space. In practice I have found that a change of twopounds per square inch in the supply pressure results in a variation in the pressureof the air discharged from the receiving space through its nozzle outlet of the order of 1.5%. I have not found it feasible to eliminate supply pressure variation effects by nozzle or flapper changes. It is possible, however, toeliminate or substantially reduce such supply pressure effects by the use of a suitable regulator. A regulator arr ange ment which I have devised to compensate for supply pressure variations is shownsomewhat diagrammaticallyin Fig. 6.

In Fig. 6 a galvanometer coil pa is arrangedto' turn about a pivot axis pb on changes inits energizing current, as in the arrangement shown in Fig. 3. In Fig. 6 an angular movement given to the coil pa by a change in the output voltage of the associatedsource qa of the coil energizing current, adjusts the coil and thereby'the flapper valve da carried by the coil, as in Fig. 3. The coil pa, also carries a second flapper valve dd which is moved by the coil pa toward or away from a nozzle ed as the flapper dd is moved toward or away from the nozzle cd. As shown in Fig. 6, the nozzle cd is connected to the air supply pipe at the inlet side of the restriction b through which the supply pipe passes air to the nozzle cd.

In operation the air discharged by the nozzle cd against the flapper dd opposes and reduces the tendency of the coil pa to move the flapper da toward the nozzle c. The apparatus is so designed that with the normal supply pressure, the operation of the apparatus shown in Fig. 6 will be like the normal operation of the apparatus shown in Fig. 3. On an increase in the supply pressure, however, the coil deflecting effect of the air discharged by the nozzle cd on the flapper valve dd will increase relative to the coil deflecting efiect of the jet discharged by the nozzle c on the flapper da. In consequence, the eflect of an increase in the supply pressure may be suitably compensated for by the nozzle cd on the flapper valve dd. In other words, with an increase in the supply pressure, the force produced by the nozzle ed on flapper dd tends to decrease the coil force opposing the jet force from nozzle 0 so that the tendency for the nozzle back pressure in chamber a to increase is compensated by the force from nozzle cd. Conversely, on a decrease in the supply pressure below its normal value, the decrease in the deflecting force of the jet discharged by the nozzle cd against the flapper dd compensates for the tendency of the supply pressure reduction to reduce the deflection of the coil pa.

While in accordance with the provisions of the statutes, I have illustrated and described the best forms of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the forms of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a force to pressure transducer, the combination comprising, an air space having a restricted air inlet and a nozzle outlet, said nozzle outlet disposed to have the air issuing therefrom in a jet, a flapper disposed transversely of said jet and having a hole therein in alignment with said jet so that the air from said jet will produce a force on said flapper in the area adjacent said hole, and a further force producing means acting on said flapper in the direction of said air jet and moving said flapper until the forces of said jet and said force producing means balance on said flapper.

2. An electro-pneumatic transducer comprising an enclosed air space having a restricted inlet for the flow of air under pressure into said space and having a nozzle for the outflow of an air jet from said space, a flapper valve extending across the air jet flow path and having a hole therein which hole is in alignment with the air jet from-said nozzle, an electricalsignal-to-force-producing device including :an electrically ,displaceable coil having an-output force proportional to the input electrical signal, said-coil being disposed to apply a force to said References Cited in the file of this patent UNITED STATES PATENTS 2,535,202 :Gregory-et al. Dec. 26, 1950 2,571,458 -Lawrenceetal Oct. 16, I951 15 8. zCatheron Nov. 18, 1952 Moog Jan. 13, 1953 Bowditch; Sept.'15, 1953 Lerousseau Sept. 13, 1955 vSidea. Apr. 24, 1956 Freeman Feb. 5, 1957 Swartwout July 30, 1957 Side .'..2 July 30, 1957 FOREIGN PATENTS France June 2, 1930 France June 18, 1934 Germany Mar. 23, 1931 Great Britain July 11, 1944

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