US2514551A - Carbon graphite shoe - Google Patents

Description

July 1l, 1950 R 0 MQNROE ETAL 2,514,551

CARBQN GRAPHITE SHOE Filed May 25, 194e 3mm/WOM.

FIC-YE JUHNWH/ERDNYMUE FEI-m- MRDLLDHMDNHUE Patented July 11, 1950 UNITEDv STATES PA'l-"INI'I OFFICE CARBON GRAPHITE SHOE Michigan Application May 2,5, 1946, SeriallNo. 672,188'

3 Claims.

The present invention relates to improvements in valve mechanism, being especially concerned with valves employing a carbon graphite shoe which overlaps an orifice in aV cylindrical. wall to close the same.

In. practice, it has been found that using conventionally designed carbon graphite shoes, the valves will not holdtight over a reasonable range of temperatures and pressures. It has been eX- perienced that when the valves were tight at low pressures with cold water they leaked at the sides of the orifice at 1254isteam pressure. Also, it is foundV that when the valves are tight at 125# steam pressure they would leak at the topand bottom of the orifice when tested at lower pressures. With the high pressures developed withl steam and the low pressures with cold water, the conditions were found to be aggravated. Lapping in of the shoe to its seat on the cylindrical wall was` effective only under operating conditions approximating the temperature at which the lapping operation was performed.

The difficulties above describedV have been overcome by thinning out sections of the shoe over priorndesign` and flattening or thinning the outer surface across the cord of thearc' substantially within the area of the orice. By thinning out sections of the shoe in this manner, it has been found that the shoe will have adequate strength to withstand comparatively high pressures and any hydraulic shock that might be produced by a quick opening of the valve. At the same time, the carbon graphite shoe is capable of adjusting itself inthe cylindrical wall in such a manner that it becomes possible'toflap inor t. the-shoe at room temperature and yet have a tig-ht valve over a wide range of increasing pressures and temperatures.

With prior shoe design, the valve was limited in its general purpose use to a temperature increase in the order of from 60 to 70 degrees. With the water at 55 F., the valve is satisfactory, but presents a leaking problem as the temperature is increased to approximately 120 F. Following the principles of our new design, a tight valve is experienced over a much greater temperature and pressure range. In practice, the improved shoe is giving a tight valve with cold water :as Well as steam at 125# pressure and a temperature of 353 F.

To our knowledge, carbon graphite valve parts have heretofore always been fitted to their seats and so designed that they were relatively rigid and void of any ability to make adjustments as the character of the seat was altered by tempera- (Cl. 25d- 102) tures yor pressures or both.. The advisability of weakeningy the wall structure overstandard prac*- tice to impart characteristics of yieldability and iiexibil'ity to the carbon graphite shoe to give improved performance has apparently been unappreciated andthe results unanticipated" up to the time of our discovery;

Thus oneof the objects ofthe invention is to provide an improved valve structure embodying a carbonv graphite shoe in'combination with an arcuate seat.

Another object is to provide an improved carbonY graphite valvev for sealing orifices defined in cylindrical walls.

A further object is to provide .an'improved carbonv graphite valve of the-type described' characterize'dl by its ability to make adjustments to hold tight as the characterof the seat is altered by temperatures and pressures.

These and other objects and advantages residing in the specic detailsA of construction of the improved shoe, and the' combination, construction and` arrangement of parts will more' fully appear fromk a consideration of the following speciiication andV the appended claims.

Inthe drawings,

Fig. 1 'is a vertical.cross-sectional viewl through a valve embodying the principles. of the present invention,

Fig. 2` is a cross-sectional View taken on line II'-1I of Fig. l through. the actuating stem and the carbongraphite shoe,

Fig. 3l is a verticaly cross-sectional. view taken Onlinel Ill-III of Fig. 4 of. the carbon graphite shoe;,

Fig., 4 is a. plan. view ot'the carbonv graphite shoe shown in Fig. 1,

Figs. 5, 6 and '7 are diagrammatic views illustrating the prior art, and

Fig. 8 is a diagrammatic view illustrating the principles of the present invention.

Referring to the drawings, in Fig. 1 the valve I0 may be of the same general type and construction disclosed in our co-pending application, Serial No. 545,028, led July 15, 1944, now Patent Number 2,411,983, with pipe connections I2 and I4, and orifices I6 and I'I defined in a cylindrical wall I8. An operating stem 20 carries a transverse pin 22 upon which the shoe 24 is mounted and moves in a radial plane aroun-d the wall I8 relative to the oriiice I'I, the wall I8 defining a seat around the orifice Il with which the shoe 24 engages to seal the oriiice I'I against fluid pressure admitted through the orice I6.

The shoe 24 is fabricated from molded commercial carbon graphite, machined, as by grinding, to the form illustrated. The material for the shoe 22 is well known upon the market and made by numerous manufacturers. A relatively hard grade is used which in service takes on a characteristic high luster or glaze. The sides 26 of the shoe 24 which seal at the sides of the orifice I6, that is, the sides at the extremity of the elongated axis of the orifice, are materially thinned out as compared to accepted practice as are the sides 28 at the minor axis of the orifice I6. The sides 26 and 28 merge into the thickened boss 30 provided with a hole in which a suitable bushing 32 is press-fitted. The pin 22 has a free sliding t in the bushing 30. A light spring 34 holds the shoe 24 in sealing contact with the wall I8.

As a further departure from accepted practice, the central portion 36 of the shoe 24 has been 4 24 having been thinned out in such a manner that the fluid pressure against the shoe 2Q is capable of conforming the shoe 24 to the wall ll Within the modulus of elasticity of the molded carbon graphite structure yet the shoe 24 has proven in practice to have adequate strength to withstand relatively high pressure and hydraulic shock.

Having thus described our invention, what we consider as new and desire to cover by Letters Patent is:

l. An improved carbon graphite valve part for sealing an orice defined in a cylindrical wall,

thinned out by machining or otherwise across the cord of the arc inwardly of the sides 28 to provide a depression in the cylindrical surface in which the outer arcuate face of the sides 26 and 28 are disposed. .It will be noted from Fig. 4 that the cord intercepts the arc also inwardly of the sides 26. Thus an arcuate surface is provided -entirely around the orifice I6 to engage with the seat defined by the wall I8 to seal the orifice I6.

The principles and function of the present invention may best be understood by a comparison with accepted practice. cording to the prior art would be of the cross section shown throughout its entire extent. By lapping the shoe 38 to the wall 40 at room temperature, it will seal the orifice 42 as illustrated. Under 125# of steam pressure, expansion of the Wall 40 has created a gap m, as shown in Fig. 6, in the order of .002 for a 3A" valve and in the order of .004 for a 2" valve, permitting the valve to leak at high temperatures. If the shoe 38 is lapped in .at a temperature corresponding to 125# of steam y'7 will result from contraction of the wall 40. For

a 2" valve, the gap y is in the order of .003, peri mitting the valve to leak when used on air, cold water and other low temperature fluids. It will be understood that the leak of Fig. 6 will take place at the sides of the shoe 38 While the leak of Fig. '7 will be at the top and bottom.

In Fig. 8 is shown a Section similar to the prior art illustration of Figs. 5 to '7, inclusive, showing the manner in which the shoe 24, constructed according to the present invention follows the variations of the cylinder wall over a wide range rof pressuresand temperatures due to its flexibility and yieldabi'lity; the various sections of the shoe In Fig. 5, the shoe 38 aci310 said part having a thickened central portion adapted to receive a mounting member, relatively thin outer side portions having cylindrical faces for engaging with and overlapping the orifice, said side portions being sufficiently thin as to conform to the variations of said cylindrical wall upon expansion under the yinfluence of fluid pressure against said wall and acentral depression in the cylindrical surfacefin which said faces are disposed, said depression approximatingthe area of the orifice to be sealed. f

2. In combination, a steam valve body having a relatively high co-efficient of expansion with a cylindrical wall defining an orifice, a carbon graphite valve part having a relatively low coeflicient of expansion and supported in said body to overlap and seal said orifice and constructed and arranged to be urged to its seat by pressure in said body, said part Vhaving relativelyl thin. outer sides with cylindrical faces disposed in' the same cylindrical surface andv overlapping thefdei'lning wall structure of said c riiice,ksaidA sides being sufliciently thin as to conform to the variations of said cylindrical Wall upon-expansion, under the infiuence of fluid pressure in saidbody.

3. In the combination of -claim,2, said 'valve REFERENCES cii'iaiiiV The following references are of record in the file of this patent: vUrti'rED STATES PA'I'ENTs France i j of 19'31 Certiicate of Correction Patent No. 2,514,551 July 11, 1950 ROLLO O. MONROE ET AL.

It is hereby oertied that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 46, 'for the patent number 2,411,983 read 2,422,796;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oee.

Signed and sealed this 14th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommisszoner of Patents.

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