US2843151A

US2843151A - Hydraulic power element

Info

Publication number: US2843151A
Application number: US345065A
Authority: US
Inventors: Frederick A Greenawalt
Original assignee: Ranco Inc
Current assignee: Robertshaw US Holding Corp
Priority date: 1953-03-27
Filing date: 1953-03-27
Publication date: 1958-07-15
Anticipated expiration: 1975-07-15
Also published as: CH333973A; DE1013139B

Description

July 15, 1958 F. A. GREENAWALT HYDRAULIC POWER ELEMENT Filed March 27. 1953 COPOLYMEB OF BUTAD/ENE AND ACRVLONITR/LE 98% I SOBU TAA 2% ISOPRENE l8 l3 l0 INVENTOR. FfifUfE/CK A. fieawmmq United States Patent 2,843,151 riYnRAULic POWER ELEMENT Frederick A.- Greenawalt, Columbus, Ohio, assignor to Rfalbco' Incorporated, Columbus, Ohio, a corporation 0 hio 7 Application March 27, 1953, Serial No. 345,065

3 Claims. (Cl. 137 -788) The present invention relates to power elements for actuating control mechanisms 'orthe like, and more particularly to a new and improved expansible power element for providing a relatively lengthy power stroke in response to relatively small changes in volume of a fluid, such as a body of confinedthermally expansible liquid.

An object of the invention is the provision of an improved pressure operated power element comprising elastic, rubber-like material in the form of ian open ended tube having a transverse wall intermediate the ends thereof forming a resilient or elastic liquid impervious partion in the tube, a relatively rigid sleeve containing the tube to prevent radial expansion thereof, annularly arranged abutment means associated with the sleeve and against which one end'of the tube abuts to prevent longitudinal movement of the tube in one direction, and a fluid inletstructure associated with the sleeve at the other end of the tube-and with which the tubeis sealingly secured so that fluid introduced into the inlet structure causes the transverse wall to'move with changes in volume of the fluidinside'the tube, the abutment means preventing longitudinal movement of the tube proper by the force of the fluid whereby the transverse wall moves longitudinally of the sleeve by flexing and internal flow of the resilient mater'ial in response to given changes in the volume of the 'fluid, whichrnovementmay' be imparted to a plunger or the like engaging the outer face of the wall. v

Although the elastic tubular element may beof a' single piece, in the preferred form of the invention described herein it comprises two resilient cup-shaped members having somewhat different physical characteristics and arranged'withthe bottom or end walls abutting one another to form the transverse wall and the open ends facing in opposite directions, one member being'formed of elastic material relatively impervious to the passage of liquidtherethrough or the absorption of liquids therein, and which is secured in'liquid sealing relationship with the fluid inlet structure, and the othermember being formed of 'mate'rialhavingrelatively quick recovery from deformations thereof andresistant to'abrasion and adapted to receive :acontrol mechanism actuating plunger or the like therein.

The invention makes possible the utilization of rubher-like material to provide an expansible element having substantially uniform power movements to actuate control mechanisms, suchas switches or valves, in response to predetermined changes in volume of. a thermally expansible liquid contained in the element and which operates under'fluid pressures of one thousand pounds per square inch and higher whereby controldevice actuating movements may be obtained in response to changes in-volume of a relatively small quantity of liquid, thus permitting relatively sensitive responses to changes in temperatures, for example. The form and arrangement'ofthe components of the improved power element are such that there is no appreciable wear on the moving parts, particularly the rubber like parts, so that 2,843,151 Fatented July 15, 1953 ice 2 the power element is long lasting and accurate in operation'. 7

Other objects-and advantages of the invention will be apparent from the following description of preferred em bodiments of the invention, reference being made to the accompanying sheet of drawings wherein:

Fig; 1 is an elevational view of a power element embodying the invention;

Figs. 2 and 3 are sectional views of the power element but on a larger scale than shown in Fig. 1, showing certain parts thereof in diflerent operative positions; and

Fig. 4 is a sectional view of another form of exparisi ble unit which may be employed in the improved power element.

As mentioned previously, the improved power element is particularlysuitable for use as a thermostat to actuate control devices, such as valves or switches, in response to changes in temperatures, although it may be employed for other uses, and it is here shown and described embodied in-a thermostatic device T. The thermostat T includes a base 10, which may be suitably attached to the housing orframe of a control mechanism (not shown), a sleeve 11 and an actuating plunger 12. The upper end of the plunger 12, as viewed in the drawings, is adapted to engage a movable control member of the control mechanism to which the thermostat is attached to provide power movements to actuate the control mechanism.

The base 10 is' preferably of relatively rigid material, such as brass, in the form of a cup having a bottom wall 13 with a central upwardly projecting stem 15. A radially extending bore 16 is formed in the bottom wall which receives one end of a capillary tube 17 which is brazed or otherwise suitably secured to the walls of the bore to form a fluid tight connection therewith. An axial bore 18 extends from the inner end of the bore 16 upwardly through the stem 15 to provide a fluid conduit from the tube 17 to the interior of the base 10. The other end of the tube 17 is not shown, but it may be sealed in any suitable manner or connected with a'bu'lb. In either event the-tube and bulb, if any,'are filled with a suitable liquid which expands and contracts in response to predetermined increases and decreases in temperature, as is well known in the'art.

-A cup-shaped member 20 is disposed in an inverted position over the stem 15 and is secured in liquid tight relation with the bottom wall of the base 10 by a flange 21 projecting radially from the open end thereof and clamped to the bottom of the base by the lower end of 'the sleeve II, which surrounds the member. The flange 21 has an upstanding bead or rim 22 and the lower end of the sleeve 11 is undercut to receive the head. The sleeve is secured in pressing engagement with the flange 21 by the upper edges of the member 10 rolled inwardly over an annular shoulder 24 formed about the sleeve 11, as shown. The member 20 is formed of a rubber material relatively impervious to liquids and particularly to the liquid employed in the tube 17. Rubber as used in this-specification and the claims includes natural and conventional synthetic rubbers. A suit-able material is known as Butyl and comprises a copolymer of about 98% isobutylene and 2% isoprene.

A second cup-shaped resilient member 26 is disposed within the sleeve 11 and its bottom wall 27 rests on the top or end wall 28 of the member 20. In assemblying the power element, the member 26 is inserted into the sleeve 11 before the sleeve is secured to the base 10, as described. Member 26 is preferably formed of elastic material resistant to abrasion and having the property of quickly returning to its original form after extension or stretching thereof. One such material is a nitrile syn: thetic rubber known as Buna-N rubber and comprising a copolymer of butadiene and acrylonitrile. The two

members

20, 26 disposed as shown form a tubular unit having a transverse wall formed by the

contiguous end walls

27, 28 of the members and which transverse walls form a fluid tight, elastic partition integral with the tubular walls of the respective members. The sides and end wall 28 form an expansible liquid tight chamber 29 in communication with the tube 17 through

bores

18, 16.

In some instances, it might be desirable to eliminate the tube 17, bores 16, 18 and confine, a body of liquid inside the chamber 29. In that event, the volume of the liquid in the chamber would vary according to the temperature of the base 10. V If desired, the two

members

20, 26 could be replaced by a single elastic member, such as that shown at 30, having tubular side walls 31, a transverse wall 32 formed integral with the tubular walls, and a radially extending flange 33 at one end similar to flange 21.

The sleeve 11 has an annular abutment or shoulder 37 formed about the inside thereof which engages the upper end edges of the member 26 when the sleeve is attached to the base 10, as described. The abutment 37 prevents upward movement of the member 26 proper, as is discussed more fully hereinafter.

A cylindrical plug 40 is disposed in the recessed portion of member 26 and is preferably formed of tetrafluoroethylene resin known as Teflon the surface of which has a waxy or soap-like character insofar as its frictional property is concerned so that the friction between the plug and the insides of the member 26 is inconsequential to operation of the power element. The lower end of the plunger 12 rests on the plug 40 and is adapted to slide freely in the sleeve 11. The upper end of the plunger, as viewed in the drawings, has a head 42 which rests on the upper end of the sleeve when the member 20 is in its normal or unexpanded condition as shown in Figs. 1 and 2.

The tube 17,

bores

16, 18 and chamber 29 are filled with a suitable liquid mentioned previously, and in use the tube 17 or a major portion thereof is disposed in an area the temperature of which is to be controlled, for example. As the temperature increases, the volume of the liquid increases and causes an increase in liquid volume inside the chamber 29 causing the end wall 28 of the member 20 to stretch and bulge upwardly. The sides of the member 20 are prevented from radial expansion by the sleeve 11, and longitudinal movement thereof is prevented by the annular abutment 37 since the sides of the

members

20, 26 are substantially non-compressible. As a result, the wall 28 bulges upwardly and causes wall 27 of member 26 to be moved upwardly as illustrated in Fig. 3. Since the material forming the sides of member 26 cannot move upwardly along the inside of the sleeve 11 it flows inwardly and upwardly causing wall 27 to increase in thickness and thereby move the plug 40 upwardly, as is illustrated in Fig. 3. This action occurs by reason of the relatively high pressures available for action on the elastic members, and it is to be noted that by the arrangement shown, these high liquid pressures can be contained by the sealing structure formed between the flange 21 and the base and sleeve 11. The movement of the intermediate wall formed by the

adjacent walls

27, 28 is such that there is no appreciable abrasion thereon and long life of consistent operation is obtained. The member 20 retains the liquid and is acted upon by the member 26 to be returned to its normal position following stretching of the wall thereof, and member 26 is resistant to 'abrading by the movement of plug 40 therein.

As mentioned previously, the movement of the plunger 12 may be relatively great with respect to the change in volume of the liquid in the chamber 23 so that the power element may be quite sensitive to changes in temperature and at the same time the power element may be relatively small and compact. For example, an element having the approximate proportions shown in the drawings in which the outside diameter of the

members

20, 26 is approximately .250" and the diameter of chamber 23 about .120", will provide a power stroke of .070" and more.

It will be seen that the improved power element may be made inexpensively and provides accurate and long lasting operation. While but two forms of the invention have been shown, it is to be understood that other forms, modifications and adaptations could be made all of which fall within the scope of the claims which follow.

I claim:

1. An expansible power element comprising a rigid base member, a rigid hollow sleeve joined at one end to said base member and having the other end open to receive a plunger, a tubular rubber element inside said sleeve and having its side walls juxtaposed to and contained by the inside walls of said sleeve, said rubber element having one end open and the other end closed by a transverse wall spaced from said open end, said open end of said rubber element facing the open end of said sleeve for receiving a plunger therein, said sleeve having the inside diameter reduced to form an abutment around the inside of said sleeve against which the open end edge of said element engages to block movement of said sidewalls of said element toward said open end of said sleeve, a plunger in said sleeve extending into the open end of said element and engaging said transverse wall, and means to apply fluid pressure to said transverse wall of said element on the side thereof opposite the side engaged by said plunger for forcing said wall toward the open end of said sleeve.

2. An expansible power element comprising a rigid base member, a rigid hollow sleeve joined at one end to said base member and having the other end open to receive a plunger, a tubular rubber element open at opposite ends and disposed inside said sleeve and having its side walls juxtaposed to and contained by the inside walls of said sleeve, rubber wall means forming a resilient partition in said element transversely thereof, one open end of said rubber element facing the open end of said sleeve for receiving a plunger therein, said sleeve having the inside diameter reduced to form an abutment around the inside of said sleeve against which the end edge of said element at said one end engages to block movement of said sidewalls of said rubber element toward said open end of said sleeve, a plunger in said sleeve extending into said open end of said rubber element and engaging said wall means, and means to apply fluid pressure to said wall means on the side thereof opposite the side engaged by said plunger for forcing said wall means toward said open end of said sleeve.

3. An expansible power element comprising a rigid base member having a fluid passage therein, a rigid hollow sleeve joined at one end to said base member and having the other end open to receive a plunger, a tubular rubber member inside said sleeve and having its side walls juxtaposed to and contained by the inside walls of said sleeve, said rubber member having one end open and the other end closed by a transverse wall, said open end of said rubber member facing the open end of said sleeve for receiving a plunger therein, said sleeve having the inside diameter reduced to form an abutment around the inside of said sleeve against which the open end edge of said member engages to block movement of said sidewalls of said rubber member toward said open end of said sleeve, a plunger in said sleeve extending into the open end of said rubber member and engaging said transverse wall, a second cup-shape rubber member having the side walls thereof juxtaposed to and contained by the inside walls of said sleeve and having a transverse wall at one end abutting the transverse wall of the first mentioned rubber member, said second cup-shape member having an open end open to said fluid passage in said base member, means compressing peripheral portions of the open end of said second cup-shape member between said sleeve and base member to form a fluidtight seal, and means to apply fluid pressure in said fluid v passage.

References Cited in the file of this patent UNITED STATES PATENTS Tatter Aug. 29, 1933 Durnin May 15, 1934 Erichsen Mar. 12, 1935 Vickers Apr. 12, 1938 Dodge Jan. 5, 1943 ONeill Apr. 19, 1949 OTHER REFERENCES Plastics and Resins (pp. 14-16 and 36), May 1946. Modern Plastics (pp. 108 and 109), November 1947.