US2516333A

US2516333A - Pneumatic control apparatus

Info

Publication number: US2516333A
Authority: US
Inventors: Coleman B Moore
Original assignee: Moore Products Co
Current assignee: Moore Products Co
Priority date: 1946-04-02
Filing date: 1946-04-02
Publication date: 1950-07-25
Anticipated expiration: 1967-07-25

Description

July 25, 1950 c. B. MOORE PNEUMATIC CONTROL APPARATUS Filed April 2, 1946 9 an x 6 a 3 M x M (a 7 a W 4 4 9. 2 m P 3332 5% u 0 u u u R 0 M w M 5 WM m z N P 4 o B 2 m Mo 2 M lw rwY U B .m M M 5 0 mQbhwwi Qwtg wkx I M m 3 m I. D I /2 6 m w; 3 7 4% 7 6 3 I Y I...- 3 7 4 02 M 6 6 6 h 4 .3 a m a I 6 x w Patented 25, 1950 rmaum'nc con'rnor. Arman-rue Coleman B. Moore, Carroll Park, Pa., assignor to Moore Products 00., Philadelphia. Pa., a copartnership Application April 2, 1948, Serial No. 858,897 9 Claims. (CL 137-153) This invention relates to pneumatic control apparatus and more particularly to improvements transmitted pressure. In certain types of transmitting systems, also, upon an increase in the transmitted pressure a decrease in flow occurs across a restriction employed therein. These conditions cause a departure from the optimum of linearity and stability desired.

In the pneumatic transmission system shown in my prior Letters Patent No. 2,359,236, a constant differential is maintained between the pressure on the upstream side of the detector nozzle and the transmitted pressure. For particular different values of transmitted pressure the clearance of the control surface with respect to the nozzle will also be difierent because of the decrease in flow across the fixed restriction and the compressibility of the transmitted air. These factors tend to be non-linear with respect to the transmitted pressure.

It is possible to eliminate the eilect of change of flow across the restriction by substitution for the fixed restriction of a flow controller of the character shown in my prior application for Let ters Patent, filed August 18, 1945, Serial No. 611,321, but this still does not obviate the effect of the compressibility of the transmitted air.

In accordance with the present invention pneumatic control apparatus is provided including an automatic restriction, which compensates both for the compressibility of the transmitted fluid by an increase in flow governed by the same physical laws and for the decrease in pressure drop across the supply restriction.

In accordance with the present invention also, a pneumatic control unit is provided having a restriction, in which the flow is proportional to the square root of the absolute pressure of the delivered fluid.

In accordance with the present invention also, a pneumatic control unit is provided which is particularly useful in transmission systems for providing linearity and stability.

In accordance with the present invention, also, a pneumatic control unit is provided which is free from likelihood of clogging of any restrictions therein and which, when employed with systems having a control nozzle, may have one to one transmission characteristics, and substantially reduces the necessity oi squareness or the nozzle with respect to the cooperating control surface.

Other advantageous features will be apparent from the specification and claims.

The nature and characteristic features of the invention will be more readily understood from the following description, taken in connection with the accompanying drawings forming part hereof. in which:

Figure 1 is a diagrammatic view of one form of the pneumatic control unit in accordance with the present invention;

Fig. 2 is a diagrammatic view of another form of pneumatic control unit in accordance with the present invention;

Fig. 3 is a diagrammatic view of a. pneumatic circuit with the control unit of the present invention employed therewith;

Fig. 4 is a diagrammatic view of a booster pilot valve with a pneumatic control unit in accordance with the present invention embodied therein; and

Fig. 5 is a graph illustrating the characteristics obtained with the use of a pneumatic control unit in accordance with the present invention.

It should, of course, be understood that the de" scription and drawings herein are illustrative merely, and that various modifications and changes may be made in the structure disclosed :Ivithout departing from the spirit ofthe invenion.

Referring more particularly to the drawings, the pneumatic control or automatic restriction unit 9, illustrated in Fig. 1, preferably includes a casing which is provided with a body portion Ill and a cover portion ll secured to the body In in fluid-tight relationship. The casing has mounted therein, preferably within the cover H and secured to the body portion III, in fluid-tight relationship, a flexible member which preferably comprises a flexible metallic bellows l2, closed, at the end remote from the body portion In, by a closure plate l3. A fluid pressure chamber I4 is thus provided within the cover II and outside the bellows l2 and another fluid pressure chamber I5 is provided within the bellows I2.

The bellows I2 is shown partially expanded in its operating position. If the bellows l2 were in its free condition the same would be considerably horter than as illustrated. By suitable selection of free length and spring rate of the bellows II, the characteristics of the unit may be varied as desired.

The closure plate I! has a stem l6 secured chamber 20 has a fluid supply connection 2| connected thereto. V The fluid supply connection 2| is adapted to b connected to a suitable source --of fluid under pressure, the pressure being regulated or not as' desired, and the fluid may be air or other desired gaseous fluid. I

A passageway 22 is provided, in communication with the chamber in the interior of the bellows l2, and is connected through a flxed restriction 23 to a fluid delivery connection 24 for the delivery of pressure fluid as hereinafter explained. The size of opening or oriflce in the fixed restriction 23 may be varied in order to change the flow characteristics. A passageway 25 is provided, connecting the fluid delivery connection 24 to the chamber M.

In the form oi the invention illustrated in Fig. 2, the body portion I0 01' the pneumatic control or automatic restriction unit 3 is provided with a cover H, as before. A flexible metallic bellows 35 is-provided, connected at one end to the body portion ID, in fluid-tight relationship, and similarly connected at its other end to a bellows closure plate 36. Within the interior of the bellows 35, a smaller flexible metallic bellows 31 is pro- If the bellows 35 and 31 were in their free condition the same would be considerably longer than illustrated. Bysuitable selection of free length and spring rate of the bellows 35 and 31 the characteristics of the unit may be varied as desired.

The bellows closure plate 36 is provided with openings or passageways 39 for free access of fluid from a chamber 40, 'within the interior of the bellows 31, to a chamber 4|, in the interior of the casing and outside the bellows 35 and the closure plate 36.

A nozzle member 42 is provided, having a restriction or discharge opening of predetermined size therein, and is mounted in the chamber 40. A control surface 43 is provided, preferably formed as a face of a flat disc 34 mounted on the closure plate 36, for controlling the discharge of fluid through the nozzle 42 in accordance with the positioning of the control surface 43 with respect to the nozzle terminal as hereinafter explained.

. the fluid delivery connection 24, and a passageauaasa 1 the chamber 4| is provided with a restriction 23, for purposes to be explained.

In Fig. 3 there is shown a pneumatic circuit in which the control unit in accordance with the present invention is applied in a pneumatic transmission system. a

A detector pilot 50 is provided having a connection 5| for making a variable condition, which may be a variable fluid pressure, available in a chamber 52 and against a closure plate 53 of a bellows 54, A chamber, within the bellows 54, is connected by a, conduit 56 to a fluid delivery connection 51. The bellows plate 53 is provided with a disc 46 having a flat control surface 49. which surface by its positioning by the plate 53 controls the flow through a nozzle 58, into the chamber 55. The nozzle 53 is connected by a pipe 53 to a chamber 6| of a booster pilot to. The chamber 6| also has the fluid delivery connection 24 of the pneumatic control or automatic restriction unit 9 connected thereto.

The booster pilot 60 has a chamber 62 connected by a fluid connection 63 to the fluid delivery connection 51. The chambers Si and 62 are separated by a diaphragm 64, which may be of the character shown in my prior application for Letters Patent flled December 22, 1945, Se-- rial No. 637,057. The diaphragm 64 controls a valve member 65, movable with respect to a seat 66, in a valve chamber 61 for controlling the delivery of fluid from the chamber 61 to the chamber 62. A spring 68 may be provided, effective on the lower side of the diaphragm 64, for determining the difierential across the nozzle 56.

The stem 69 on which the valve member 65 is carried may also be provided with a valve portion III for engagement with a valve seat 12 carried by the diaphragm 64 controlling the bleed through the diaphragm 64, although any other suitable bleed control could be employed if desired.

The chamber 61 is connected by a fluid supply connection II to a suitable source of fluid under pressure, the supply connection 2| also being connected to the connection 1| In the form of the invention illustrated in Fig. 4, a booster pilot 60a is shown having the automatic restriction unit combined therewith. The booster pilot 60a has a chamber 6| and has a chamber 62 connected to a fluid delivery connection 63. The chambers 6| and 62 are separated by a diaphragm 64 of the character previously described. The diaphragm 64 controls a valve member 65 movable with respect to a seat 66 in a valve chamber 51' for controlling the delivery of fluid from the chamber 61 to the chamber 62. A spring 68 is provided, eflective on the lower side of th diaphragm 64, for determining'the difierential across a detector nozzle (not shown). The stem 69, on which the valve member 65 is carried, is also provided with a valve portion III for engagement with a valve seat 12 carried by the diaphragm 64 for controlling the bleed through the diaphragm 54, although any other suitable bleed control could be employed if desired. The chamber 67 is connected by a fluid supply connection II to a suitable source of fluid under pressure.

The booster pilot 66a has body portions Illa and lllb secured in assembled relationship by screws 15 and the body portions Illa and Nb have a diaphragm 35a interposed therebetween which corresponds in function to the bellows 35.

way-45 extending between the passageway 44 and A chamber 4| is thus provided in the body portion Illa, above the diaphragm 35a, and a chamber 38 is provided below the diaphragm 35a and in the body portion ID. A flexible metallic bellows 31 is provided, is connected in fluid-tight relationship at its lower end in the body portion Nb and is closed at the other end by a closure plate 360. which corresponds to the closure plate 36. A chamber 40 is thus provided, as before, in the interior of the bellows 31 and is in free communication with the chamber 4|, through a passageway 39a. The plate 36a carries thereon a control surface 43 for controlling the nozzle 42, the nozzle 42 being connected to a supply connection 2| which is connected to the supply connection II. The chamber 38 is connected by a passageway 24 with the chamber 6|. The chamber 38 is also in communication with the pipe' 59, in this instance through the passageway 24. A fixed restriction 23 is mounted within the body portion lb and is in communication with the chamber 38 through a passageway 44 on the downstream side.

Referring now to Fig. 1, fluid under pressure.

from the fluid supply connection 2| passes from the valve chamber 28 through the valve seat I8. to the chamber l5, then' through the conduit 22, and the restriction 23 to the fluid delivery connection 24. The pressure of the fluid in the fluid delivery connection 24 is effective, through the fluid connection 25, in the chamber I4. The pressure drop across the restriction 23 produces a pressure difierential on the bellows closure plate l3 urging the same upwardly, and tending to close the valve ll. 4

An equilibrium condition is reached when this differential in an upward direction is Just sufficient to balance the spring action or the bellows l2 at a point at which the valve I1 is nearly,

but not quite, closed.

The flow may tend to increase, due to an in crease in the supply pressure effective at the fluid supply connection 2| or due to a decrease of the delivered pressure at the fluid delivery connection 24. If the flow tends to increase, this results in increasing the differential across the restriction 23, and an increase in the differential effective on the closure plate l3 moves the bellows l2- and the closure plate l3 thereof upwardly, further restricting the valve l1 and throttling the fluid from the fluid supply connection 2|.

Similarly, if the flow tends to decrease, due

to a decrease of supply pressure or an increase of the delivered pressure, this results in a, decreased differential on the bellows plate l3 tends to move the bellows plate I3 downwardly, opening the valve l1 and decreasing the throttling of the fluid from the fluid supply connection 2|.

Referring now to Fig. 2, the action is substantially the same as that described with respect to Fig. 1. Pressure fluid from the fluid delivery connection 2| passes through the nozzle 42 into the chamber 48, then into the chamber 4| through the openings 38, then through the conduit '45 and the restriction 23 to the delivery connection 24. The pressure of the fluid in the delivery connection 24 is effective, through the fluid connection 44 in the chamber 38. By reason of the openings 33, no differential will be effective between the chambers 40 and 4| but the differential is, however, effective between the chambers 38 and 4| on the closure plate 36. This differential forces the plate 36 downwardly from the free position, to a position with the nozzle 42 nearly but not quite closed by the control surface 43.

Any tendency of the flow to increase, effects an increase in the differential between the chambers 4|v and 38 and this forces the bellows 35 and the bellows closure plate 36 downwardly so that the control surface 43 throttles the incoming fluid from the nozzle 42.

The flow of gaseous fluid across an orifice is proportional to the square root of th differential pressure across the orifice and is also proportional to the square root of the absolute pressure at the orifice. Since the differential across the restriction 23 is maintained substantially constant by the bellows I2 and the valve ll, or by the bellows 35 and 31 and the control surface 43, the flow will be proportional only to the square root of the absolute pressure at the restriction 23. The pressure at the restriction 23 is essentially the delivered pressure from this unit at the fluid delivery connection 24.

Referrin now more particularly to Figs. 3 and 4, fluid from the fluid supply connection 1| passes through the supply connection 2| to and through the automatic restriction unit 3 in the manner heretofore explained, through the delivery connection 24 to the chamber 3|, on the upper side of the diaphragm 64, and to the nozzle 58 in the transmitting unit 56. The fluid from the nozzle 58 flows into the chamber and passes through the fluid connection 56 to the fluid delivery connection 51. and then to the instrumentality (not shown) to be controlled.

Fluid from the fluid supply connection 'II also flows into the valve chamber 61, from which it is admitted as required, by the valve 65, tothe chamber 62 against the under side of the diaphragm 54, and passes through the fluid connection 63 and the fluid delivery connection 5 to the instrumentality to be controlled.

At any condition of equilibrium, the pressure in the chamber 52, the pressure in the chamber 65, and the spring effect of the bellows 54 will be balanced, and the control surface 53 will be .very nearly but not quite'in contact with the nozzle 58. The pressure in the chamber 6| will be sufflciently higher than that prevailing in the chamber 62 to compress the spring 68, so that valve is seated and valve Ill exhausts the pressure fluid supplied through the connection 24 from the automatic restriction unit 9.

Any increase in pressure in the chamber 52 will momentarily depress the control surface 49 carried by the bellows plate 53 against the nozzle 53, and the flow of fluid through the delivery connection 24 will cause a building up of pressure in the chamber 6|. This causes the diaphragm 64 to move the seat 12 to closed position with respect to the valve 13 and open the valve 65, allowing supply fluid from the fluid supply connection II to flow from the chamber 61, past the valve 65 and pass into the chamber 55 by way of the

fluid connections

63 and 56 until the pressure in the chamber 55 is again in balance with the pressure in the chamber 52.

A decrease in pressure in the chamber 52 will move the bellows closure plate 53 and the control surface 48 carried thereby away from the nozzle 58, permitting the pressure in the chamber 6| to decrease, thus closing the valve 65 and opening the valve 10. Pressure fluid will then escape from the chamber 55 by way of the

fluid connections

56 and 53, the valve 10 and through the diaphragm 64 to the atmosphere.

In transmission systems of the type herein referred to the pressure in the chamber 55 and the transmitted pressure effective at the delivery conatlases no change in the spring force exerted by the bellows 54. This condition cannot be obtained if the bellows 55 moves to a different position with respect to the nozzle 58 for each balanced pressure unless the bellows has a zero spring rate. No practical bellows of this character can be obtained, but the same result can be obtained if the motion of the bellows l is reduced to zero.

with a pilot nozzle system. in which fluid is supplied through a flxed restriction to a rebalancing chamber having a control surface therein with the discharge to atmosphere from the chamber through a nozzle controlled by the DO- sitionlng of the surface with respect thereto, to rebalance at a different pressure a relative motion between the control surface and the nozzle will be required, because of changes in the differential pressure across the nozzle, because of decrease in the rate of flow through the nozzle upon increase in the rebalancing pressure, and because of changes in the compressibility of the fluid at the nozzle.

In the pneumatic circuit shown in Fig. 3, the first of these factors is eliminated by the use of a constant differential between the chambers SI and 62 which is brought about by the constant spring force of the spring 68.. Even if the flow through the nozzle 58 were maintained constant, relative nozzle motion would stillresult due to the compressibility of the fluid. It is therefore necessary to increase the flow through the nozzle 58, for higher transmitted pressures, in such manner as to exactly compensate for the compressibility of the fluid. The amount ofcompensation required is proportional to the square root of the absolute pressure at the nozzle; It has been previously pointed out that the fluid supplied by the automatic restriction unit 9, through the delivery connection 24, varies in this manner provided the absolute pressures prevailing at the nozzle 58 and at the restriction 23 were identical. slight diiferences between these pressures is neg ligible. From the foregoing it will be seen that by reason of the compensating efiect of the automatic restriction unit 9 only a negligible relative motion of the control surface 49 and the nozzle 58 will be required to efiect a rebalance for different pressures applied in the chamber 52. Since there is only negligible relative motion of the control surface 49 with respect to the nozzle 58 the transmission is one to One or linear.

The significance of this can be seen in Fig. 5 in which values of relative nozzle motion are shown as abscissas and values of transmitted pressure are shown as ordinates. The curve at a is for the system just described. The curve b is for a pilot nozzle system exhausting to atmosphere. The curve at d shows the characteristics obtained with a transmission system shown in my prior Patent No. 2,359,236, in which a fixed restriction is employed in place of the automatic restriction 5 of the present invention.

It will be noted that in curve 11, within the normal operating range of the system which may be assumed as values of transmitted pressure from three to eighteen units, there is a comparatively small relative motion of the control surface 49 and the nozzle 53, and that this relative nozzle motion is substantially linear.

It will be noted that curve b, within the operating range shows a considerable relative nozzle motion, which motion is very non-linear.

It will be noted that curve d, within the operating range shows a considerable relative nozzle motion, and that the motion is also non-linear. The effect of such relative nozzle motion is to reduce the change in the pressure in the chamber 55 for a corresponding change in the pressure in the chamber 52 and this reduction is not uniform throughout the operating range and is accordingly non-linear.

The curve shown at c is also taken with a I system in accordance with the present invention For practical purposesthe effect of but with the automatic restriction unit 9 set for a higher flow rate. It will be noted that the control surface 49 operate with greater clearance but maintains substantially the same small relative motion throughout the operating range.

The characteristic-shown by curve 0 is of particular advantage in pneumatic transmission systems because of the relatively large nozzle clearance thereby made possible. With an increased nozzle clearance the parallelism between the nozzle and its cooperating control surface is rendered less significant.

In transmission systems as herein disclosed the variable pressure applied in the chamber 52 produces a relative motion between a control element, such as the control surface 49, and a nozzle, such as the nozzle 58, to bring about a change in the transmitted pressure and to rebalance or restore the control element and nozzle to their initial relative position- The stability of such a transmitting system is improved when the ratio of nozzle opening to nozzle diameter is increased. This is made possible, without detrimental effects, with the present invention as will be seen from curve 0 of Fig. 5. If the ratio of nozzle opening to nozzle diameter were increased to the same extent in the systems whose nozzle characteristics are shown by curve 1: or d (Fig. 5) the non-linearity and relative nozzle motion would be very greatly increased.

It will be noted that it is permissible to use a considerably larger restriction 23 by virtue of the small differential maintained thereacross as compared to the diiierential across a fixed restriction as shown in the transmission system of my prior Letters Patent No. 2,359,236. The major restrictive efiect occurs at the valve I1 and seat I! or at the nozzle 42 and control surface 43. .These are both automatic in their action and open or close, as required, to maintain the difierential across the restriction 23. This reduces the tendency to clogging.

I claim:

1. In pneumatic control apparatus, means responsive to changes in a condition including a member movable in response to changes in the condition, a pressure control member having an orifice controlled by the positioning of said movable member for controlling the discharge of fluid therefrom, a supply connection in communication with a source of pressure fluid, means for supplyingpressure fluid to said control member through a restriction across which a substantially constant difierential is maintained, and pressure transmitting means responsive to the pressure conditions on opposite sides of said orifice for controlling the pressure transmitted from said supply connection and for rebalancing said movable member substantially at its intial position.

2. In pneumatic control apparatus, a source of pressure fluid, detector pilot means having a portion movable in response to changes in a variable condition, booster pilot means controlled by said detector pilot means for transmitting fluid under 9 pressure from said source, and means for modifying the action of said booster pilot comprising means for compensating for the compressibility of the fluid supplied to said detector pilot means,

3. In pneumatic control apparatus, a source of pressure fluid, detector pilot means having a portion movable in response to changes in a variable condition, booster pilot means controlled by said detector pilot means for transmitting fluid under pressure from said source, and means for moditying the action of said booster pilot comprising means for supplying fluid to said detector pilot means proportional to the square root of the absolute pressure of the transmitted fluid.

4. In pneumatic control apparatus, a detector pilot comprising a control member and a pressure fluid supply nozzle mounted for relative motion in response to a variable condition, and compensated supply means for supplying pressure fluid to said nozzle for reducing the change of spacing of said control member with respect to said nozzle upon a change of said variable.

5. In pneumatic control apparatus, a detector pilot comprising a resilient member responsive to a change in a condition and a pressure fluid supply nozzle, compressibility compensated supply means for supplying pressure fluid to said nozzle, said nozzle having a discharge port controlled by the spacing of said resilient member with respect to said port.

6. In pneumatic control apparatus, a detector pilot comprising a member movable in response to a change in a variable condition and a. pressure fluid supply nozzle controlled by said movable member, and fluid supply means for said nozzle for maintaining substantially constant spacing between said movable member and said nozzle.

'7. In pneumatic control apparatus, a detector pilot comprising a bellows having a flxed closure wall and a movable end closure wall and a fixedly mounted pressure fluid supply nozzle extendin through said fixed closure wall, compressibility compensated supply means for supplying pressure fluid to said nozzle, said nozzle having a discharge port controlled by the spacing of said movable wall with respect to said nozzle.

8. In pneumatic control apparatus, a supply connection in communication with a source of pressure fluid, a fluid delivery connection, a fluid discharge connection, compressibility compensated means for supplying pressure fluid to said discharge connection, a valve member interposed between the supply connection and the delivery connection, a movable pressure responsive member for controlling said valve member and against which the fluid from said valve member is efiective in one direction, and fluid connections for applying the pressure effective at said discharge connection against said movable member in the other direction.

9. In pneumatic control apparatus, a supply connection in communication with a source or pressure fluid, a fluid delivery connection, a fluid discharge connection, means for controlling the flow of fluid to said discharge connection proportional to the square root of the absolute pressure at the discharge connection, a valve mem ber interposed between said supply connection and said delivery connection, a movable pressure responsive member for controlling said valve member and against which the fluid from said valve member is efiective in one direction, and fluid connections for applying the pressure efiective at said discharge connection against said movable member in the other direction.

COLEMAN B. MOORE.

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

UNITED STATES PATENTS Number Name Date 1,585,732 Otto May 25, 192s 1,699,676 Rush Jan. 22, 192.2;