US2858840A

US2858840A - Snap-acting pneumatic relays

Info

Publication number: US2858840A
Application number: US533711A
Authority: US
Inventors: Jr Robert C Wright
Original assignee: Worthington Corp
Current assignee: Worthington Corp
Priority date: 1955-09-12
Filing date: 1955-09-12
Publication date: 1958-11-04
Anticipated expiration: 1975-11-04

Description

Nov. 4, 1958 R. c. WRIGHT, JR z 2,858,840

SNAP-ACTING PNEUMATIC RELAYS Filed Sept. 12, 1955 ISnnentor i Ross/a7- CZ WR/GHZJ/R. a

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2,858,846 Fatented Nov. 4, 1958 SNAP-ACTING PNEUMATIC RELAYS Robert C. Wright, Jr., Hingham, Mass., assignor, by mes'ne assignments, to Worthington Corporation, New York, N. Y., a corporation of Delaware Application September 12, 1955, Serial No. 533,711 4 Claims. 01. 13'7 s2 This invention relates to'an improved pressure actuated valve, particularly to a valve in a form of a pilot or relay of the supply and exhaust type which is utilized for varying an output pressure, the valve being adapted to be opened wide and permit fluid under pressure from a source of supply to pass through the valve until the pressure from an independent source reaches a predetermined maximum, at which time the supply valve is closed and the exhaust valve is opened wide to reduce the output pressure to O p. s. i. until the pressure in such independent source drops to a predetermined minimum, thereupon to raise the output pressure to the supply pressure and maintain the output pressure at that value until the independent pressure again returns to the predetermined maximum.

The valve embodying this invention has many useful applications wherein it is desirable to provide sudden changes in output pressure between minimum and maximum Whenever the pressure from an independent source reaches either one of two selected limit values. For ex-.

ample, the valve may be used in connection with a pneumatic instrument which varies a controlling pressure in response to changes in the value of a variable, wherein it is desirable to permit the variable value to change between two selected limits. Since the instrument output or controlling pressure varies between selected limits 7 each of which are representative of a limit of variable value change, the instrument controlling pressure may be utilized to govern the valve embodying this invention on a snap-action basis for actuating a control value or the like, governing the value of a variable, between fully open and closed positions to permit the variable value to change between selected limits. This form of control is commonly known to those skilled in the art as snap-action and may be utilized in many control ap-' plications.

The valve or relay embodying this invention employs two opposed diaphragms having different efiective areas.

The diaphragm with the larger effective area is subjected to pressure from the independent source, and that having the smaller effective area is subjected to relay output pressure. By means of a biasing spring which adds to the force generated by the diaphragm having the smaller effective area and a valve member which is actuated by the combined action of the diaphragms and spring, the relay may be arranged to provide snap-action at each of two selected limits of independent pressure change without any possibility of a throttling or proportional response.

It is an object of this invention to provide a snapacting pressure control valve or relay which is of simple construction, may consist of standard parts, is capable of being manufactured at reasonable cost, and at the-same time is positive in action and is reliable in its operation over long periods of time. p

Other objects of this invention will more fully appear from the following description when taken in connection with the accompanying drawing, in which the figure is an elevation in section of a valve structure embodying this invention.

Having reference to the drawing, the valve therein illustrated consists of a body member 10 on which is mounted an intermediate plate 11 which in turn carries an end plate 12. The parts may be secured together in any well-known manner, not shown, in sealed relation 1 end by means of a threaded plug 16 and at its inner end terminates in a valve seat 17. The seat 17 fits snugly within a cylindrical recess having a diameter greater than that of the chamber 15 to provide an annular shoulder 18 which engages the lower surface of the seat, the parts being secured in fluid tight relation by any well-known means. The body member 10 is also provided with a cylindrical output pressure chamber 20, having a diameter greater than that of the seat 17 to form an annular shoulder 27, into the lower end of which chamber the valve seat extends as shown. Centrally disposed in the seat 17 is an orifice 21 which is enlarged at its upper end, as indicated at 22, toprovide a seating surface 23 for the inlet valve 24 of a supply and exhaust valve, generally indicated at 5 to be described. The upper end of the output pressure chamber 20 terminates in an enlarged cylindrical portion 26 which is disposed beneath the diaphragm 13.

The intermediate plate 11 includes an exhaust chamber 30 comprising a lower cylindrical portion 31 which corresponds in diameter to the enlarged cylindrical portion 26 of the output pressure chamber, and also includes a cylindrical portion 32 of still larger diameter,

the exhaust chamber being located between the diathe cylindrical portion 32 of the exhaust chamber and is located between the diaphragm 14 and the end wall 34 of the plate. I

The inlet chamber 15con1municates through a port 35 with a pipe 36'which connects with a suitable source of operating fluid, not shown, such as air or the like, preferably under regulated pressure. The output pressure in the chamber 20 may be utilized for any suitable purpose, such as to actuate a fluid pressure operated motor for governing the value of a variable condition, and to this end, the chamber communicates with a pipe 37 through a port 38 in the wall of the body member. Between the diaphragms 13 and Man exhaust block or spacer 40 is disposed which functions in a manner to be described. The exhaust pressure chamber 30 has a port 41 which connects the chamber with atmosphere, and the controlling pressure chamber 33 may be connected with an independent pressure source through a port 42 and pipe 43. i

The spacer 40 is generally of T shape in cross section with the atmosphere. The outside diameter of the de-- pending section 47, which extends through a central" opening in the diaphragm 13, is less than that of the head 46 and thereby provides an annular shoulder 54' which engages the diaphragm and is secured thereto in.

fluid tight relation by means of a washer 55 which may exhaust seat 50 carried by the spacer 40, and the inlet valve has a cone-shaped seating surface 9 which is adapted to cooperate with the seat 23 in the fixed inlet seat member 17. The inlet valve 24 is also preferably integral with a guide stem 59 which extends throughthe lower end=of the inlet port 21 into the inlet chamber 15, the diameter of the guide stem being such that is provided for fluid flow through the port. The supply and exhaust valve 5 is normally held closed by means of a light compression spring 61) which is confined between the exhaust valve and a diaphragm plate 61 against which the central portion of the diaphragm 14 rests.

Extensions

62 and 63 on the exhaust valve 7 and plate 61, respectively, serve as guides for the ends of the spring 60,

For purposes of assembly, the inlet valve 24 is adapted to pass through the exhaust port 49 and the diaphragm plate 61 is detachably secured to the spacer head46by screws 64 so that before the plate is attached, the supply and exhaust valve may be inserted through the spring chamber 45, the spring 643 then installed, and the assembly completed by attaching the plate to the head.

In actual practice the upper diaphragm 14 has an efie ctive area which is approximately 3.4 times the effective area of the lower diaphragm 13. Thus on this basis'for every 1 p. s. i. pressure change in the controllingchamber 33, a 3.4 p. s. i. pressure change would be required in the output pressure chamber 2%! to bring the parts to balance. However the efiect of this pressure relationship is changed by a biasing spring 70. which together with the output pressure in the chamber 20 opposes the controlling pressure in the chamber 33. The biasing spring 70 is confined between the shoulder 27 at the lower end of the chamber 29 and the disc 55 by which the spacer head 46 is clamped to the diaphragm 13. At its lower end the spring 7i) surrounds the upper part of these'at member 17, and at its upper end the spring surrounds an annular depending part 71 of the disc 55, said parts functioning as means for centering the spring in ,the chamber 20. The biasing spring 74 functions to establish the value of the low limit in the range of independent pressure change at which it is desirable to change the output pressure in the chamber 20 from O p. s. i. to the full supply, pressure. On the other hand, the difference in the effective area of the diaphragrns, the force generated by the spring 70, and the p. s. i. value of the supply pressure, establish the high limit of independent pressure change at which it is desirable to change the output pressure from full supply pressure to p. s. i.

In operation, with the independent control pressure below the selected lowilimit, the biasing spring 70 exerts a thrust on the exhaust block 40 so that the inletandexhaust valve is lifted from the inlet seat 23, the exhaust valve7 being held closed by the valve spring 60. The full supply pressure is admitted to the output pressure chamber 20 and it exerts a force on the lower diaphragm the exhaust block 40. This condition is maintained until the independent control pressure in the chamber 33 rises above its selected high limit, at which time the thrust developed on the upper diaphragm 14 exceeds the cornbined thrustofthe biasing spring 70 and the output pressure acting on the lower diaphragm 13. This condition causes the exhaust block to move downward allowing the supply and exhaust valve to clesethesupply port 21 and begin to open theexhaust port 49 permitting the output pressure to start to escape to atmosphere. The resulting reduction in output pressure in" creases the upward thrust of the lower diaphragm 13 ample spacebe more or less unreliable in operation.

which results in increasing the opening of the exhaust valve and accelerating the reduction in output pressure so that after the exhaust valve starts to open, the action is essentially instantaneous, thereby reducing the output pressure to 0 p. s. i. Since the upward thrust developed by the output pressure acting on'the lower diaphragm 13 has been removed, the downward thrust developed by the independent control pressure acting on the upper diaphragm 14 must be reduced below the upward thrust developed by the biasing springj'7t) acting alone for the reverse action to occtir. When this occurs, the exhaust block 40 is raised, thereby closing the exhaust port 49 and opening the supply port 21 to admit supply pressure to the output pressure chamber and complete the cycle. Thus the output pressure change is utilized to assist any change in valve action dictated by the independent con trol pressure.

It will be clear from the above, that the spread between the independent pressure low" limit and high limit maybe adjusted to that desired'by varying the value of the supply pressure. As the'supply pressure is increased, the spread is increased, and vice versa.

I am aware that various devices of a mechanical nature have heretofore been utilized to provide snap-action, such as spring loaded 'cletents, resilient diaphragms arranged for snap-action, and other like mechanical arrangements,'but such devices are subject to wear, their operating power factor is relatively low, and therefore they may tend to On the other hand, the device embodying this invention is of rugged construction, can be manufactured at reasonable cost, and operates under a high power factor, thereby providing .positive and reliable operation.

Having set forth theoperating prrnciples of my invention and shown and described a practical embodiment of same, what I claim and desire to secure by Letters Patent 1. In a snap-acting pneumatic relay, the combination of a first member having a selected effective area and responsive to a controlling pressure, a second member having a selected smaller effective area actingin opposition to said first member and responsive to an output pressure, a'spacer operatively connecting said members for simultaneous movement having an exhaust port connecting the output pressure with atmosphere, an inlet conneca tion for communication with a supply of fluid operating pressure, a partition downstream of the inlet connection having'an inlet port connecting the supply pressure with the output pressure, independent means coacting with the output pressurein opposition to the controlling pressure, a valve member including an exhaust valve cooperating with the exhaust port and an inlet valve cooperating with the inlet port, said valve member being operative- 13 adding to the total upward thrust acting on e the chamber, 2,0v den 7 ly connected to said spacer and actuated by the independent means in opposition to the controlling pressure to close the exhaust valve and open the inlet valve when said controlling pressure is below a selected minimum value, and when said controlling pressure tends to exceed a selected maximum value said valve member being actuated by said controlling pressure in opposition to the combined effect of said independent means and output pressure to close said inlet valve and open said exhaust valve.

2. In a snap-acting pneumatic relay, the combination of a first member having a selected effective area responsive to a controlling pressure, a second member having a selected smaller effective area acting in opposition to said first member and responsive to an output pressure, a spacer operatively connecting said members f or simultaneousmovement having an exhaust port connecting the output pressurewith atmosphere, an inlet connection for communication with a supply of fluid operating pressure, a partitiondownstream of the inletconnection having an inlet port connectingthe supply pressure withthe output pressure, an exhaust valve actuated by'said pressure responsive members and cooperating with said exhaust port, an inlet valve actuated by said pressure responsive members and cooperating with said inlet port, and independent means in operative connection with said pressure responsive members and operating in conjunction with the output pressure in opposition to the controlling pressure, said output pressure and independent means tending to close the exhaust valve and open the inlet valve and said controlling pressure tending to close the inlet valve and open the exhaust valve, said independent means being effective when the controlling pressure is below a selected minimum value to actuate said pressure responsive members in opposition to the controlling pressure to close the exhaust valve and open the inlet valve to increase the output pressure and together with the increase in output pressure to snap the inlet valve wide open and provide a maximum output pressure, and said controlling pressure being eifective when it exceeds a maximum value to actuate said pressure responsive members in opposition to e combined effect of said independent means and output pressure to close the inlet valve and open the exhaust valve to reduce the output pressure and together with the reduction in output 'pressure to snap the exhaust valve wide open and reduce the output pressure to a minimum value.

3. In a snap-acting pneumatic relay, including a casing having an inlet connection for communication with a source of fluid operating pressure, a first pressure responsive member secured to said casing and partially defining a controlling pressure chamber, a second pressure responsive member spaced from said first member and partially defining an output pressure chamber, said members together partially defining an exhaust pressure chamber communicating with atmosphere, a spacer operatively connecting said members for simultaneous movement, the etfective area of the first member being greater than the eflective area of the second member, said spacer having an exhaust port including an exhaust seat providing fluid communication between the output pressure chamber and the exhaust pressure chamber, a partition having an inlet port including an inlet seat providing fluid communication between the inlet connection and the output pressure chamber, a valve member actuated by said spacer and including an exhaust valve cooperating with the exhaust seat and an inlet valve cooperating with the inlet seat, a fluid connection from the output pressure chamber for communication with a source of demand and a fluid connection from the control pressure chamber for communication trolling pressure, and independent means in the output pressure chamber biasing said pressure responsive members against the pressure in said controlling pressure chamber, said means being eflective when the controlling pressure is below a selected minimum value to close said exhaust valve and open said inlet valve to increase said output pressure and together with the increase in output pressure to snap the inlet valve wide open to maintain the pressure in the output pressure chamber at the operating supply pressure, and the controlling pressure being eifective when it tends to exceed a selected maximum value to actuate said pressure responsive mem- With a source of con- 6 bers in opposition to the combined effect of said inde pendent means and output pressure to close the inlet valve and open the exhaust valve to reduce the output pressure and together with the reduction in output pressure to snap the exhaust valve wide open to maintain the output pressure at a minimum value.

4. A snap-acting pneumatic relay including a casing having a control pressure chamber adapted to be connected with a source of controlling pressure, an exhaust pressure chamber communicating with atmosphere, an output pressure chamber adapted to be connected with a source of demand, and an inlet connection for communication with a source of operating pressure fluid, a first pressure responsive member having a selected eifcctive area disposed between the controlling pressure chamber and the exhaust pressure chamber, a second pressure responsive member having a lesser eflective area spaced apart from said first member and disposed between the exhaust pressure chamber and the output pressure chamher, a partition between the inlet connection and the output pressure chamber having an inlet port providing fluid communication therebetween, a spacer operatively connecting said pressure responsive members for simultaneous movement, said spacer having an exhaust port providing fluid communication between the output pressure chamber and the exhaust pressure chamber, an exhaust valve actuated by the pressure responsive members and cooperating with the exhaust port to vary fluid flow therethrough, an inlet valve actuated by the pressure responsive members and cooperating with the inlet port to vary fluid flow therethrough, and independent means in operative connection with said pressure responsive members and acting with the pressure in the output pressure chamber in opposition to pressure in the controlling pressure chamber, said output pressure and independent means tending to close the exhaust valve and open the inlet valve and said controlling pressure tending to close the inlet valve and open the exhaust valve, said independent means in itself being efifective when the con trolling pressure is below a selected minimum value to actuate said pressure responsive members in opposition to the controlling pressure to close the exhaust valve and open the inlet valve to increase the output pressure and together with the increase in output pressure to snap the inlet valve wide open and provide a maximum output pressure, and said controlling pressure being effective when it exceeds a maximum value to actuate said pressure responsive members in opposition to the combined effect of said independent means and output pressure to close the inlet valve and open the exhaust valve to reduce the output pressure and together with the reduction in output pressure to snap the exhaust valve wide open and reduce the output pressure to a minimum value.

References Cited in the file of this patent UNITED STATES PATENTS 2,370,582 Rodway Feb, 27, 1945 2,610,819 Sutton Sept. 16, 1952 2,625,178 Price Jan. 13, 1953 2,714,895 Rockwell Aug. 9, 1955