US2707487A - Orifices - Google Patents

Description

y 3, 1955 H. L. SQNAVELY 2,707,487

ORIFICES Original Filed Sept. 14, 1948 fiaz'oga l 5222 32 United States Patent ORIFICES Harold L. Snavely, Oak Lawn, IlL, assignor to Atmorol Corporation, Chicago, Ill., a corporation of Illinois Original application September 14, 1948, Serial No. 49,221, now Patent No. 2,670,625, dated March 2, 1954. Divided and this application May 16, 1952, Serial No. 288,112

9 Claims. (Cl. 138-43) This invention relates generally to orifices and more particularly to an improved orifice for continuously indicating gas analyzers of the specific gravity or compo sition of a gas mixture.

This application is a division of my application for Continuous Reading Specific Gravity Indicator invention filed September 14, 1948, Serial No. 49,221, now Patent 2,670,625, March 2, 1954, reference and incorporation of which is hereby made.

Due to the recent developments in the art of heat treating metals wherein controlled gas atmospheres are employed in heat treating furnaces the need has increased for an indicator which can be readily adjusted to zero position or any other standard and once adjusted will give an accurate continuous indication of the specific gravity or composition of gas mixtures used for atmospheres.

One of the objects of the invention therefore is to provide an improved apparatus orifice for determining differences in the specific gravity of gas mixtures as a continuous or instantaneous process.

Another object of the invention is to provide an improved orifice responsive to the amount of hydrogen or carbon dioxide in a furnace atmosphere which is foolproof and readily adjusted for calibration or standardization against a gas as plentiful as air or any other known gases, if desired.

Another object of the invention is to provide an improved orifice responsive continuously to the specific gravity content of a gas atmosphere with only the use of a small stream of gas from the atmosphere being withdrawn.

A further object is to provide an orifice across which a pressure drop can be established to give an indication of the specific gravity or composition of the gas passing through the orifice.

A further object is to provide a novel flow restrictor element having an adjustable orifice which is selfcleaning and which may be readily adjusted to vary the size of the opening thereto.

Another object is to provide an adjustable fluid flow restrictor having a flexible member provided with an opening therethrough, mechanical force being applied to said member to vary the size of the opening before, during or after it is in operation.

A further object is to provide a restrictor element in which a flexible diaphragm having an opening therethrough is stretched to enlarge the size of the opening and relaxed to reduce it.

. Another object of the invention is to provide an orifice which is continuously open and operative at all times to prevent overloading of any other elements in the associated parts of a specific gravity meter.

Other and additional objects and advantages .of this invention will present themselves to those familiar with the art upon the reading of the following specification in conjunction with the drawing and the appended claims.

2,707,487 Patented May 3, 1955 In the drawings:

Fig. 1 is a schematic view showing various elements of an indicator incorporating a device embodying the invention and the manner in which the cooperating elements are connected.

Fig. 2 is a vertical section taken through the restrictor device showing the preferred construction of the restrictor.

Fig. 3 is a horizontal section taken through the pump shown in Fig. 1 on a plane perpendicular to the axis of rotation of the pump.

The fundamental idea of this invention is to withdraw a continuous stream of gas from a body, conduct the stream through an orifice, and measure the pressure drop of the stream over the orifice. This pressure drop has been found to be substantially a linear function of the specific gravity of the gas, which specific gravity, insofar as the usual furnace atmospheres are concerned, has been found to depend directly on the composition of the gas, providing measurements are made under substantially the same conditions of temperature and pressure.

Although the apparatus of this invention may be used for many different mixtures of gases, it functions particularly well for furnace atmospheres containing hydrogen or carbon dioxide because of the wide difference between the molecular weights, and hence specific gravities of these two substances and the other common constituents of furnace atmospheres.

The various elements of the indicator system 10 of this invention are shown schematically in Fig. l as connected to a body of gas to be analyzed indicated at 11. Actually, this body 11 may be a furnace, an atmosphere generator, a gas mixer, a conduit, etc.

In practice, it is preferred to mount the various elements in a metal box having an access door on one side provided with a window or opening through which the gauge 12 is visible. However, for the purpose of description, the various elements are shown to be spread out along a line. Actually, it makes little diflerence how the various elements are mounted or spaced from each other except that it is preferred to keep them close together in order to reduce the response time of the indicator.

The indicator system 10 comprises a sample withdrawal conduit 13, a filter 14, a pressure regulator 15, a flow restrictor 16, and a pump 17 in addition to the pressure gauge 12 mentioned above. The withdrawal conduit 13 extends from the gas body 11 to a throwover valve 18. The other inlet to this valve is open to the atmosphere through an air conduit 20. The outlet of the valve 18 is connected by a conduit 21 through the filter 14 and regulator 15 to the variable restrictor 16. Thus, a filtered sample of gas or air is supplied to the restrictor 16 at a constant pressure.

The regulator 15 is preferably of the negative pressure type and is set to deliver gas at a pressure slightly below atmospheric, preferably in the neighborhood of 5 inches of water. The purpose of this regulator is to eliminate the effects of changes in the furnace pressure of .the gas body or the pressure drop through the filter 14 and to equalize any differential between air and gas pressure. When the body of gas 11 is under high pressure, it is preferred to provide an additional regulator (not shown) in the conduit 13 to lower the pressure to a value near atmospheric.

The variable restrictor 16 (Fig. 2) comprises a two piece hollow cylindrical body 22, a circular flexible elastomer diaphragm supported between the two halves of the body 22, and means for exerting varying mechanical pressure on one side of the diaphragm 23 to cause it to be deformed. A circular opening or orifice 24 for the passage of gas is provided'in the center of the diaphragm 3 23. The lower half of the body 22 is provided with an opening in which the end of the conduit 21 is received and the upper half 22 is provided with an opening in which a conduit 25 is received. Another opening in the top of the body 22 (as shown in Fig. 2) is preferably pro vided for connection of the gauge 12.

The upper half of the body 22 has a boss 26 thereon which is drilled and threaded to receive a washer 27, packing 2S, and a packing gland 30. At the bottom of the boss 26, a threaded opening 31 into the cavity 32 is provided. A threaded stem 33 is received in the opening 31 and extends into the cavity 32. It is preferred to provide left hand threads on the stem 33 and in the opening 31. This is done so that the gauge pointer will move in the same direction as the stem 33 when the stem 33 is rotated, conventional gauges moving in the clockwise direction.

The end of the stem 33 is rotatably connected to a cup shaped member 34, the stem 33 projecting through the member 34 and being peened over. The other end of the stem is provided with a knurled handwheel 35. Thus, by rotating the handwheel 35, the stem 33 is moved in or out carrying the member 34 with it.

The cup shaped member 34 is provided with a plurality of radial holes 36 which serve as gas passageways and the lower end is rounded so as not to injure the diaphragm 23. When the stem 33 is screwed into the body 22, more pressure is exerted on the diaphragm 23 causing it to stretch and enlarge the orifice 24. When the stem 33 is screwed out, the diaphragm 23 relaxes and the orifice 24 becomes smaller. It is preferred to pass the gas through the restrictor 16 from the bottom to the top as shown in Fig. 4, for any solid particles which pass through the orifice 24 and are deposited in the restrictor 16 tend to accumulate in the top of the hollow cup shaped member 34 and may be loosened by moving the member in and out. Actually, however, the restrictor 16 will function regardless of the direction of gas flow.

The pump 17 is preferably constructed so as to induce a pulsating vacuum, the pulsations occurring at a relatively high frequency. To accomplish this, it is preferred to use a vane type pump having three vanes rotating at a speed of approximately 1800 R. P. M. Thus, ninety pulsations per second occur.

The pulsating vacuum causes the diaphragm 23 to vibrate with each pulsation. This vibration prevents the orifice 24 from becoming clogged. It has been found that if the frequency of the pulsations is too low, the pointer of the gauge 12 also vibrates and readings are more diflicult to obtain. On the other hand, if the fre quency of pulsation is too high, the diaphragm 23 will not vibrate satisfactorily. In this connection it is also desirable to keep the length of the conduit 25 as short as possible to prevent the pulsations being damped to too low an amplitude.

In the event, however, that the orifice should become clogged due to a defect in the filter 14- or some other cause, all that need be done is to screw the stem 33 in and out a few times to flex the diaphragm 23 to clean it.

The gauge 12 is a conventional vacuum gauge preferably having a range of approximately 0 to 60 inches of water if the indicator is to be used primarily to measure specific gravities less than unity. When specific gravities above unity are to be measured, a gauge which reads from 40 to -75 inches is preferred, or one whose hand moves quite slowly until a vacuum of 45 inches is reached and then which moves rapidly as the vacuum is increased to 75 inches.

The values cited above are illustrative only, for they will depend on the capacity of the pump with which the gauge 12 is used and the unstretched size of the orifice 24.

The gauge 12 may be calibrated in either specific gravity units or in units of composition, as set out more fully in my earlier filed application, depending on the use to which the indicator is to be put. In most instances,

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however, it has proved desirable to employ specific gravity units, for the conversion to composition is quite simple and can be done with a graph or table or by formula.

The pump 17, as shown in Fig. 3, is a rotary vane pump comprising a three piece casing 40, a rotary impeller 41, and a plurality of vanes 42 carried by the impeller 41. The pump shaft 43 is fixed to the impeller 41 and is journalled in bearings which are eccentric with respect to the casing 44). The vanes 42 are slidably received in radial slots 46 milled into the impeller 41 and are thrown outwardly by centrifugal force to ride against the wall of the casing 44} when the impeller 41 is rotated.

Gas is drawn into the pump 17 through the conduit 25 which connects to the inlet port 47 and is carried by the rotating vanes 42 to the outlet port 48 which opens into a short conduit. The upper end of the conduit projects into a pump supported slightly above the top of the casing 49. An exhaust conduit 52 opens into the top of the pump and provides an exit therefrom. The two conduits 25 and 52 are spaced apart, one being at each end of the pump so that gas must circulate through the pump before entering the conduit 52.

A plurality of radial cooling fins 60 are attached to the outside shell and serve to dissipate heat from the oil and the pump casing 40. The pump shaft 43 is connected by a flexible coupling (not shown) to the shaft of a driving motor (not shown). The motor is a constant speed motor and is preferably synchronous, having a speed of 1800 R. P. M.

The indicator 10 operates as follows: The throwover valve 18 is first turned so as to be open to the air inlet conduit 20. The pump 17 is then placed in operation by energizing the motor. This causes air to be drawn through the filter 14 and the regulator 15 to the conduit 21 and through the restrictor 16.

The handwheel 35 on the variable restrictor 16 is then rotated until the gauge indicates a specific gravity of unity. The throwover valve 18 is then turned so as to withdraw gas from the body of gas, and after a few seconds, the unknown specific gravity of the gas may be read on the gauge 12.

It has been found that once it has been zeroed, as set forth above, the indicator 10 will remain accurate for long periods of time due largely to the self-cleaning feature of the variable restrictor 16. However, when precise readings are desired, it is a simple matter to turn the throwover valve 18 and rezero the instrument.

Various changes and modifications such as will present themselves to those familiar with the art may be made without departing from the spirit of this invention whose scope is defined by the following claims.

What is claimed is:

l. A variable fluid flow restrictor device comprising a body having a hollow cavity therein, a flexible relatively thin diaphragm mounted in said cavity in sealed relationship with the wall of said cavity to divide said cavity into two chambers, means disposed in one of said chambers and marginally engaging a restricted area of said diaphragm, and means for moving the first means in a direction substantially perpendicular to a face of said diaphragm to displace said restricted area from its normal plane and place the remainder of the diaphragm under a stretch tension, said restricted area having an orifice therein which is enlarged by the strain exerted upon the restricted area by the tension upon the remainder of the diaphragm to provide a variable sized orifice opening and said first means having an opening therethroug'n placing said orifice in communication with said one of said chambers.

2. A variable fluid flow restrictor device comprising a body having a hollow cavity therein, a flexible relatively thin diaphragm mounted in said cavity with its circumference in sealed relationship with the wall of said cavity whereby said cavity is divided into two chambers, and

r means including an element disposed in one of the chambers for engaging said diaphragm at points intermediate its circumference and its center for displacing same from its normal plane, said diaphragm having a centrally located normally open orifice therethrough which is enlarged as said diaphragm is forced out of its normal plane to provide a variable size of the orifice said element having an opening therethrough placing the orifice in communication with said one of the chambers.

3. In a device of the class described, the combination of a housing defining a cavity, a member movable in said cavity having predetermined extremities defining a continuous marginal edge and having an opening placing one side of the marginal edge in communication with the other side through said member, a fiat eiastic element resting against said marginal edge and having an orifice therethrough located within the boundaries of said marginal edge, and means interconnecting said element and the walls of said housing including a sealing member disposed under tension to draw said elastic element taut against and over said marginal edge, said sealing member and elastic element dividing said cavity into two chambers in communication with each other through said orifice and said opening.

4. A variable orifice comprising a housing, an elastic diaphragm supported in sealed relationship adjacent its edges in the housing and having an opening therethrough, an element within the housing located on one side of the diaphragm engaging the diaphragm around said opening and bounding a fiat central portion of the diaphragm which is free adjacent to said opening, said element having a passageway therethrough in open communication with said opening and the portion of said housing on said one side of said diaphragm, means supporting said element for stretching said central portion of said diaphragm and causing said opening to be enlarged, and inlet and outlet means in said housing on opposite sides of the diaphragm.

5. A variable self cleaning fluid flow restrictor comprising a hollow body, an elastic diaphragm dividing the hollow in said body into two cavities, said diaphragm having an opening therethrough, means disposed in one of the cavities for stretching said diaphragm to cause said opening to be enlarged with that portion of the diaphragm surrounding the opening under a stretch tension and free to vibrate in a direction transverse to its surface, said means including a member mounted for movement transversely to the diaphragm with respect to the housing and engaging the diaphragm around said opening, said member having an opening therethrough placing said cavities in communication with each other through said orifice, and inlet and outlet means in said hollow body on opposite sides of the diaphragm.

6. A variable fluid flow restrictor device for controlling the flow of gas comprising a body having a cavity therein, a resilient relatively thin diaphragm mounted in said cavity in sealed relationship at its edges with the wall of said cavity to divide said cavity into two chambers, a conduit connected in communication with one chamber and a second conduit connected in communication wili the other chamber, said diaphragm being capable of being kept in constant transverse agitation, said diaphragm having an opening therethrough at the point of approximately greatest agitation of the diaphragm, and means disposed in one of the chambers engaging said diaphragm around said opening and movable to displace said diaphragm laterally to place the portion thereof around said opening under tension to vary the effective size of said orifice said means having an opening therethrough placing said chambers in communication with each other through the first mentioned opening.

7. A variable fluid flow restrictor comprising a body having a cavity therein, a flexible relatively thin coplanar diaphragm mounted in said cavity in sealed relationship at its edges with the wall of said cavity to divide said cavity into two chambers, a conduit connected in communication with one chamber and a second conduit c0nnected in communication with the other chamber, said diaphragm being capable of being kept in constant agitation in a direction transverse to the plane thereof, said diaphragm having an opening therethrough at the point of approximately greatest agitation of the diaphragm which is enlarged as said diaphragm is forced out of its normal plane to provide a variable orifice, and means disposed in one of the chambers engaging said diaphragm around said opening and movable to displace said diaphragm laterally to place the portion thereof around said opening under tension to vary the effective size of said orifice said means having an opening therethrough placing said orifice in communication with said one of the chambers.

8. A variable fluid flow restrictor device controlling the flow of gas and comprising a body having a cavity therein, an elastic relatively thin diaphragm mounted in said cavity in sealed relationship at its edges with the wall of said cavity to divide said cavity into two chambers, a conduit connected in communication with one chamber and a second conduit connected in communication with the other chamber, said diaphragm being capable of being kept in continuous vibration, said diaphragm having an opening therethrough at the point of approximately greatest vibration of the diaphragm, and means engaging said diaphragm around said opening and movable to displace said diaphragm laterally to place the portion thereof around said opening under stretch tension during vibration to vary the effective size of said orifice and resist distortion of said orifice during vibration of the diaphragm said means having an opening therethrough placing said chambers in communication with each other through said orifice.

9. In a device of the class described, a housing defining a cavity, a diaphragm comprising an elastic sheet member marginally supported on said housing to divide said cavity into two chambers, said diaphragm having a centrally located normally open orifice therein under resting conditions, and means supported on said housing including an element engaging said diaphragm at points spaced from and around said orifice, and a member for displacing said element to force said diaphragm in a direction perpendicular to its surface to stretch said diaphragm around said orifice to enlarge said orifice and to References Cited in the file of this patent UNITED STATES PATENTS Hersey July 13, 1943 Babson Mar. 22, 1949

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