US2811138A

US2811138A - Positioners for fluid operated motors

Info

Publication number: US2811138A
Application number: US441577A
Authority: US
Inventors: Thomas W Clements
Original assignee: Moore Products Co
Current assignee: Moore Products Co
Priority date: 1954-07-06
Filing date: 1954-07-06
Publication date: 1957-10-29
Anticipated expiration: 1974-10-29

Description

Oct. 29, 1957 1'. w. CLEMENTS 2,811,138

POSITIQNERS FOR FLUID OPERATED MOTORS Filed July 6, 1954 2 Sheets-Sheet 1 f 3 O G G r U V i J 2f A .26 27 20/ a I 1. gnu/.31, Z8 6 5:4 I 22 if i'- %f;%

4 +1 j 1 J V g o .f/

INVENTOR Thoma; W cl r ATTORNEY Oct. 29, 1957 T. w. CLEMENTS 2,811,138

POSITIONERS FOR FLUID OPERATED MOTORS Filed July 6, 1954 2 Sheets-Sheet 2 INVENTORL 771011125 NC/emems A TTORNE 1' POSITIONERS FOR FLUID OPERATED MOTORS Thomas W. Clements, Elkins Park, Pa., assignor to Moore Products Co., Philadelphia, Pa.,.a corporation of Pennsylvania Application July 6, 1954, Serial No. 441,577

Claims. (Cl. 121-41) This invention relates to positioners and more particularly to apparatus for providing accurate positioning of a fluid motor of the type employed with motor operated valves, and in other applications.

It is the principal object of the present invention to provide a positioner in which the gain or amplification between the input and output pressures may be quickly and easily determined as desired.

It is a further object of the present invention to provide a positioner which is so constructed and arranged that parts thereof for determining the throttling range are readily accessible for change as desired.

It is a further object of the present invention to provide a pilot controlled positioner in which the pilot is readily removable for cleaning.

It is a further object of the present invention to provide a positioner of the character aforesaid, having in creased capacity, enhanced stability, a minimum of friction, reduced air consumption in balanced condition, elimination of hysteresis, and long life.

It is a further object of the present invention to provide a pilot controlled positioner which is not affected by variations or changes in the supply pressure.

It is a further object of the present invention to provide a pilot controlled positioner in which low inertia of the moving parts with attendant high resonant frequency makes satisfactory operation possible under conditions of severe vibration.

Other objects and advantageous features of the invention 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 thereof, in which:

Figure 1 is a front elevational view showing the positioner applied to a motor operated valve, parts being shown in section to illustrate the construction;

Fig. 2 is a front view partly in elevation and partly in vertical section of a positioner in accordance with the invention removed from the valve of Fig. 1, and on a larger scale, the section plane being indicated by the line 22 on Fig. 3;

Fig. 3 is a longitudinal sectional view taken approximately on the line 3-3 of Fig. 2;

Fig. 4 is a fragmentary vertical sectional view approximately on the line 44 of Fig. 3;

Fig. 5 is a horizontal sectional view taken approximately on the line 5-5 of Fig. 2;

Fig. 6 is a horizontal sectional view taken approximately on the line 6-6 of Fig. 4;

Fig. 7 is a horizontal sectional view taken approximately on the line 77 of Fig. 4; and

Fig. 8 is a vertical central sectional view, enlarged, of a valve plug employed in connection with the positioner.

It should, of course, be understood that the description and drawings herein are illustrative merely, and that various modifications and changes may be made in the structure disclosed without departing from the spirit of the invention.

ice

Like numerals refer to like parts throughout the several views.

Referring more particularly to the drawings, in which a preferred embodiment of the invention is illustrated, upper and lower sections 10 and 11 of a diaphragm motor casing are shown, with a motor diaphragm 12 interposed therebetween in the usual manner and providing a fluid pressure or motor chamber 13 thereabove. The diaphragm 12 has a stem 14 connected thereto for movement therewith, and the stem 14 is connected to a valve plugtnot shown) or other controlling element to be positioned. A diaphragm return spring 15 may be provided in engagement with the diaphragm 12 for urging the diaphragm 12 upwardly in opposition to the fluid pressure applied in the chamber 13.

A casing 20 is provided for attachment to the motor housing section 11 in any desired manner and is closed by a removable front plate 21. Within the casing 20, mecha-' nism is provided for translating the position of the valve plug or other controlling element to a pneumatic unit hereinafter more fully described. The translating mechanism preferably includes a rod 22, pivotally connectedat its lower end by a pivot pin 23 to the stem 14 for movement therewith. The rod 22, at its upper end, is connected to a lever 24 carried on a pivot 25 in the casing 20. The lever 24 has an adjustable fulcrum 26 positioned. at the desired location in a slot 27 in the lever 24, for' accommodating and adjusting the positioner in accordance with the distance of travel of the stem 14. A-lever The casing 20 is provided with an opening 37 below which a housing plate 38 is mounted and held in position in any desired manner, such as by screws 39 which extend into the casing 20. The housing plate circular opening 38a of predetermined area.

Above the housing plate 38, an upper housing 40 is provided, having an opening 41 corresponding approximately in area to the opening 38a.

ring 43 is provided, above the upper housing plate 40 with an interior opening 43a corresponding approximately in area to the openings 38:: and 41. A flexible diaphragm 44 is interposed between the ring 43 and the plate 40.

Below the housing plate 38, a lower housing section "45 is provided, having an interior area corresponding approximately in area to the openings 38a and 41. A flexible diaphragm 46 is interposed between the housing plate 33 and the lower housing section 45. e

The housing ring 43, housing plate 40, and'housing section 45 are held in assembled relation to each other,

and to the housing plate 38, and with the interposed

diaphragms

42, 44 and 46 in fluid tight relation, by studs 47;

In engagement with the outer or upper face of the-- diaphragm 44, and accessible from the exterior thereof and from the interior of the casing 20, a spring abutment?- plate 48 is provided with which the lower end ofthe spring 36 is in engagement. porting plate 49 is provided,

engagement respectively with the plate 47 and forthreaded engagement with a plate 56 hereinafter identified and upper cylindrical sections extending through the plate 49,

' Patented Oct. 29, 19 57 38 has an interior A flexible diaphragm 42 e is interposed between the

plates

38 and 40. A housing- A lower diaphragm sup-"- in engagement with the lower or inner face of the diaphragm 44 and a plurality of threaded studs 50 are provided. The studs'50have: enlarged central sections 51 to provide end shoulders for" the diaphragm 44 and the spring abutment plate 48. The studs have nuts 52 thereon, engaging the plate 48, and accessible in the interior of the housing 20. The studs 50 extend freely through enlarged openings 55 in the housing plate 40 and are attached to a diaphragm supporting plate 56 engaging the upper face of the diaphragm 42. The

diaphragms

42 and 44 are thus held in predetermined spaced relation and for movement together.

- A valve body portion 57 is provided abutting against the lower face of the diaphragm 42 and secured to the supporting plate 56, and abutting against the upper face of the diaphragm 46 and has secured thereto a diaphragm supporting plate 58 which engages the lower face of the diaphragm 46. The valve body portion 57 holds the

diaphragms

42 and 46 in predetermined spaced relation and for movement together.

The valve body portion 57 has a longitudinal bore 59 with a frustoconical valve seat 60 at its inner terminus in communication witha chamber 61 from which radial passageways 62 extend. The chamber 61 is closed at its lower end by a fluid tight closure plug 64. A valve plug 65 is provided, shown in more detail in Fig. 8, having a seating portion 66 for engagement with the valve seat 60, and a stem 67 which extends through and beyond the bore 59. The plug 65 has an abutment portion 68 for engagement under certain conditions with a seat 69 on the upper housing 40. A compression spring 76 is provided, interposed between the valve plug 65 and the closure plug 64, for normally urging the seating portion 66 into engagement with the valve seat 60 but permitting the seating portion 66 to be moved away from its seat upon engagement of the abutment portion 68 with the shoulder 69.

The valve seat 69 has a bore 71 extending upwardly therefrom which bore is in communication with the atmosphere through a passageway 72.

The valve plug 65 has a passageway 73 therein of predetermined small size to provide a bleed around the valve seat 69 when the abutment portion 68 is in engagement with the seat 69.

It will be noted that a plurality of pressure fluid chambers are thus provided which include the chamber 74 in the lower housing section 45 and below the diaphragm 46, the chamber 75 in the housing plate 38 between the

diaphragms

46 and 42, and the chamber 76 in the upper housing plate 40 between the

diaphragms

42 and 44.

The lower housing section 45 is provided with a switch valve housing 77 having a fluid supply connection 78, which is connected to any suitable source of pressure regulated and filtered fluid, such as air, and has a fluid passageway 79 extending therethrough and through the

housing sections

45 and 38 to and in communication with the chamber 75.

The switch valve housing 77 is also provided with a fluid connection 80 which is connected to a source of control or instrument pressure, such as a sensing and pressure transmitting instrument or a master controller. The fluid connection 80 is connected by a fluid passageway 81 extending through the housings 77 and 45 to and in communication with the chamber 74.

The switch valve housing 77 is also provided with a fluid connection 82 which extends to the motor chamber 13 and is connected by a fluid passageway 83 which extends through the housing section 77, the housing section 45, the upper housing plate 38 and the housing section 40 to and in communication with the chamber 76.

The switch valve housing 77 has a valve member 85 therein for establishing communication between the fluid connections 78, 80 and 82, and the passageways 79, 81

mounted on a diaphragm motor having a motor chamber 13 with the stem 14 of the motor coupled to the valve positioner lever system through an

adjustable length linkage

22, 24, 26, 28. Downward motion of the motor stem 14 is eflective through the linkage to compress the valve positioner spring 36.

Pressure fluid at a controlled pressure is supplied from any suitable source, such as a master controller. (not shown) to the fluid connection 80 and through the passageway 81 to the chamber 74 beneath the diaphragm 46 where it acts in opposition to the force exerted by the spring 36.

Pressure fluid from any suitable source of pressure regulated and filtered fluid, such as air, is supplied to the fluid connection 78, and through the passageway 79 to the chamber 75 between the

diaphragms

42 and 46 and to the ports 62. 1

Upward motion of the diaphragm assembly causes the seat 60 to move upwardly with respect to the valve seating portion 66 of the valve plug 65 and admit fluid. from the chamber 75 to the chamber 76, between the diahpragms 42 and 44, from which, through the passageway 83 and the fluid connection 82 it is delivered to the motor chamber 13.

Downward motion of the diaphragm assembly causes the seat 60 to move downwardly into engagement with the seating portion 66, and upon further downward movement move the seating portion 68 away from its seat so that fluid from the chamber 76 and motor chamber 13 may escape to the atmosphere through the bore 71 and vent passageway 72.

When the positioner is in balance, the exhaust seat 69 is engaged by the seating portion 68, but the passageway 73 in the valve plug 65 bypasses the exhaust seat 69, allowing a small flow of fluid to bleed continuously to atmosphere. The supply port at the valve seat 60 will be opened just enough to make up for the air bleeding to atmosphere and to hold the pressure constant in the chamber 76 and thus in themotor chamber 13.

Upon an increase in the fluid pressure applied at the fluid connection 80, the positioner will be unbalanced, the diaphragm assembly will move upwardly and move the seat 60 away from the seating portion 66 so that an increase of pressure is effective in the chamber 76 and therefrom to the motor chamber 13. This moves the stem 14 downwardly and through the connection 23, the link 22, lever 24, adjustable fulcrum 26, lever 28, red 33, and spring abutment plate 34, the spring 36 is compressed until the force attendant upon the increased pressure is balanced.

Upon a decrease in the fluid pressure applied at the fluid connection 80 the converse will occur, with the spring 36 extended to balance the decreased force, and with discharge of fluid from chamber 76 to atmosphere past the seat 69.

tioner which will change the pressure of the fluid suppliedto the motor chamber 13 so as to restore the stem 14 to its original position.

It will be noted that both the pilot valve plug spring 70 and the supply pressure in the chamber 75 act in the same direction so that abnormally high supply pressures will not tend to force the pilot valve open and at the same time the pilot spring 70 may be light so as to avoid plunger friction.

The pilot plug 65 is readily accessible for cleaning while at the same time its mounting and support by diaphragms and its low inertia give high resonant frequency and makes satisfactory operation possible under conditions of extreme vibration.

It will also be noted that the uppermost diaphragm plate 48, which serves as a lower spring seat for the spring 36, is readily accessible, and may be easily replaced with another of different size which will change the effective area of diaphragm 44. Since

diaphragms

42 and 44 are subject to the output pressure from the pilot valve in opposite directions, any changes in the output will feed back into the diaphragm assembly a force which is proportional to the differential area of these diaphragms. The feedback will be positive if the etfective area of the diaphragm 44 exceeds the eflective area of the diaphragm 42, i. e. any change in output pressure will exert addi tional force on the diaphragm assembly in the same direction as if the input or instrument pressure had increased an additional amount. This causes the output pressure to change more than it would have Without such feedback. Changing the efiective area of the diaphragm 44 will thus change the gain or amplifying factor of the unit. It is thus also feasible to match the positioner to process conditions so as to produce stable control free from hunting.

The change of the effective area of the diaphragm 44 can be explained as follows: The diaphragm 44 is clamped at its margin or periphery between two outer rings provided by the housing ring 43 and the housing plate 40 and of a predetermined internal diameter, and separates a chamber below the diaphragm 44 from the atmosphere. The diaphragm 44 is clamped at the center thereof between clamping plates which include the spring abutment plate 48 and the plate 49, and the plate 48 has a smaller diameter than that of the ring 43. The pressure in the chamber below and bounded by the diaphragm 44 is greater than atmosphere. If now the diaphragm 44 is disposed with the marginal and the central clamped portions at the same level the diaphragm 44, at the free and unclamped portion, bulges upwardly and the dimensions of the bulged part are determined by the inside diameter of the ring 43 and the outside diameter of the portion of the plate 48 in engagement with the diaphragm 44. The diaphragm 44, being thin and flexible, can act only in tension. The point of inflection of this bulged section is, for practical purposes, the mean of the inside and outside diameters just identified or at a location half way between these two diameters.

The free area of the diaphragm 44 outside the point of inflection has a mere supporting function and all of the vertical component of force developed in this region is expended against the outer clamping ring 43 and has no effect inwardly of the point of inflection. On the other hand, all the vertical component of force developed on the free portion of the diaphragm 44 inwardly of the point of inflection and on the interior clamped portion of the diaphragm 44 in engagement with the plate 48 is effective for moving the diaphragm assembly.

The diaphragm 44, by reason of the selectivity available for the area of the plate 48, can be and accordingly is provided with a different effective area from that of the diaphragm 42 so that a differential of areas is available.

The arrangement by which the supply pressure is effective on a portion of the diaphragm assembly to balance the effect of the supply pressure on the valve plug 65 makes the accuracy independent of changes in the supply pressure.

With the pilot construction shown and with the valve plug 65 capable of seating simultaneously on supply and exhaust seats, a low air consumption is effected.

I claim:

1. In a positioner for a movable member in an expansible chamber, a plurality of spaced flexible pressure responsive members separated to provide a plurality of chambers and one of which is exteriorly exposed to the atmosphere, and member connecting said pressure responsive members together for simultaneous movement, said member including an exteriorly accessible and removable portion for determining the effective area of one of said pressure responsive members, a member extending into a first of said chambers and having an exhaust seat and a passageway from said seat to atmosphere, a connection to a control pressure connected to a second of said cham- 6 bers, a connection to a source of fluid pressure connected to a third of said chambers, an output pressure connection to said first chamber, a port connecting said first and said third chambers, and a valve member carried by said connecting member having a portion for closing said port and for closing engagement with said seat.

2. A positioner as defined in claim 1 in which the pressure responsive members are axially disposed diaphragms, and said portion is a disc.

3. In a positioner for a movable member in an expansible chamber, a lever system connected to said movable member, a resilient member connected to said lever system, a plurality of spaced flexible pressure responsive members separated to provide a plurality of chambers, a member connecting said pressure responsive members together for simultaneous movement, said member including an exteriorly accessible and removable portion for determining the effective area of one of said pressure responsive members, said resilient member engaging said portion, a member extending into a first of said chambers and having an exhaust seat and a passageway from said seat to atmosphere, a connection to a control pressure connected to a second of said chambers, a connection to a source of fluid pressure connected to a third of said chambers, an output pressure connection to said first of said chambers, a port connecting said first and said third chambers, and a valve member carried by said connecting member having a portion for closing said port and for closing engagement with said seat.

4. In a positioner for a movable member in an expansible chamber, a lever system connected to said movable member, a resilient member connected to said lever system, a plurality of spaced flexible pressure responsive members separated to provide a plurality of chambers, a member connecting said pressure responsive members together for simultaneous movement, said member including an exteriorly accessible and removable portion for determining the eifective area of one of said pressure responsive members, said resilient member engaging said portion, a member having an exhaust seat and a passageway from said seat to atmosphere, a connection to a control pressure connected to one of said chambers, a connection to a source of fluid pressure connected to another of said chambers, an output pressure connection to another of said chambers, a port connecting said other chambers, and a valve member carried by said connecting memher having a portion for closing said port and for closing engagement with said seat.

5. In a positioner for a movable member in an expansible chamber, a plurality of spaced flexible pressure responsive members separated to provide a plurality of chambers, a member connecting said pressure responsive members together for simultaneous movement, said connecting member having an exteriorly accessible and removable portion for determining the effective area of one of said pressure responsive members, a member having an exhaust seat and a passageway from said seat to atmosphere, a connection to a control pressure connected to one of said chambers, a supply port, a connection to a source of fluid pressure in communication with said port, an output pressure connection to another of said chambers, and a valve member carried by said connecting member having a portion for closing said port and for engagement with said seat.

References Cited in the file of this patent UNITED STATES PATENTS 2,185,449 Veenschoten Jan. 2, 1940 2,330,078 Otto Sept. 21, 1943 2,376,671 Dodson May 22, 1945 2,382,941 Moore Aug. 14, 1945 2,411,747 Nelson Nov. 26, 1946 2,411,748 Kelley Nov. 26, 1946 2,667,860 Henderson Feb. 2. 1954