US3885401A

US3885401A - Refrigerating apparatus

Info

Publication number: US3885401A
Authority: US
Inventors: Ronald A Banike
Original assignee: Hollymatic Corp
Current assignee: Hollymatic Corp
Priority date: 1972-09-29
Filing date: 1974-02-27
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27

Abstract

A refrigerating apparatus having a self-cleaning valve for use with a liquid refrigerant such as carbon dioxide which exists when the pressure is released only briefly as a liquid and primarily both as a solid and a gas. The valve is self-cleaning in that opening and closing the valve dislodges solid carbon dioxide from the interior which would normally clog a valve with a liquid refrigerant of this type and with the self-cleaning feature comprising a knife edged scraping portion on either the valve seat part or the movable part so as to dislodge deposited carbon dioxide or similar refrigerant solid when the valve is operated. The disclosure also includes an apparatus including means for introducing the fluid refrigerant through a plurality of flow paths that span substantially the full width of a refrigerant chamber and with a self-cleaning valve of the above type positioned in each flow path and primarily exteriorly of the chamber.

Description

United States 1 atent 11 1 1111 3,885,401

Banike May 27, 1975 REFRIGERATING APPARATUS Primary Examiner-Meyer Perlin 75 Inventor: Ronald A. Banike, Orland Park, 111. Amid ExamnehBonald Capossela Attorney, Agent, or F1rm-Wegner, Stellman, McCord, [73] Assignee: Hollymatic Corporation, Park wu & w d

Forest, 111.

[22] Flled. Feb. 27, 1974 [57] ABSTRACT [21] Appl. N0.: 446,324 A f f t h If I l re r1 era in a ara us av11n a se -c eanm va ve Related Apphcanon Data for use with a liq i refrigerant s uch as carbon lioxide [63] Continuation-impart of Ser. No. 293,408, Sept. 29, which exists when the pressure is released only briefly 1972, 333481624- as a liquid and primarily both as a solid and a gas. The valve is self-cleaning in that opening and closing the [52] 62/303; 62/380; 137/242 valve dislodges solid carbon dioxide from the interior [5 Cl. .1 would normally clog a valve a refrig- Fleld of Search erant f ty e and the selflcleaning feature 62/303 380, 384, 388; 251/172, 333 comprising a knife edged scraping portion on either the valve seat part or the movable part so as to disl l References Cited lodge deposited carbon dioxide or similar refrigerant UNITED STATES PATENTS solid when the valve is operated. The disclosure also 2,481,968 9 1949 Atchison 62/303 includes an apparatus including means for introducing 2,759,336 8/1956 the fluid refrigerant through a plurality of flow paths 3,109,296 11/1963 Williamson et a1. 62/388 that Span substantially the full width of a refrigerant 3,608,576 9/1971 Wilhelm 137/242 chamber and with a self-cleaning valve of the above Berg positioned in each flow and primarily exteriorly of the chamber.

21 Claims, 4 Drawing Figures REFRIGERATING APPARATUS CROSS-REFERENCE TO RELATED APPLICATAION This application is a division of my copending appli cation Ser. No. 293,408. filed Sept. 29. I972 now U.S. Pat. No. 3.848.624.

BACKGROUND OF THE INVENTION A refrigerating system of the type using a liquid refrigerant that exists principally as a solid or a gas when pressure is reduced with a typical refrigerant being liquid carbon dioxide is disclosed in the copending application of R. C. Wagner Ser. No. 264.133, filed June 19, 1972 now US. Pat. No. 3,824,806 and assigned to the same. assignee as the present application. A typical refrigerant for such a system is liquid carbon dioxide which exists only briefly as a liquid when pressure is reduced and exists principally a mixture of a solid and a gas. Valves used to control the flow of the refrigerant in such a system are subject to complete blockage of flow by the solid refrigerant packing the inside of the valve. One of the features of this invention is to provide a refrigerating apparatus including a self-cleaning valve where such blockage is prevented.

The most pertinent prior art of which applicant is aware is US. Pat. No. 2,759,336 in which there is disclosed a valve for controlling the flow of liquid carbon dioxide and which is self-cleaning in one embodiment by a closing action over large surface areas between a movable part and a stationary part. In the present application the self-cleaning feature instead of utilizing a closing action over a large area functions by a scraping action by providing a scraping portion on one of the valve parts with the result that the self-cleaning is much more reliable and is faster acting.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a shortened horizontal sectional view through an insulated freezing tunnel of a refrigerating apparatus of the type disclosed in the above Wagner application and which is similar to FIG. 4 of this cpending disclosure.

FIG. 2 is a longitudinal sectional view through a valve embodying the invention.

FIG. 3 is a schematic flow diagram for providing liquid carbon dioxide to three of the valves of FIG. 2 in parallel.

FIG. 4 is an enlarged detail sectional view of the valve of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT As disclosed in FIG. 1 and in greater detail in the above Wagner application the refrigerating apparatus which is disclosed for use with liquid carbon dioxide or similar refrigerant that exists primarily under reduced pressure as a solid and a gas comprises a tunnel 11 having thermally insulated walls 12. The tunnel has an entrance end 13 and an exit end 14 through which articles as indicated at 15 are conveyed during refrigeration thereof such as for freezing food items The conveying is accomplished by an endless conveyor belt 16 that is continuously moved in the direction indicated by the arrow 17 from the entrance 13 to the exit I4 during which the articles 15 are frozen. all as described in greater detail in the above Wagner application.

The gaseous refrigerant which is formed by the volatilizing of the liquid refrigerant and the sublimation of the solid refrigerant is recirculated over the articles by a gas recirculation blower l8 driven by a shaft 19 with the recirculated carbon dioxide gas being drawn from beneath the trailing end 20 of a recirculation baffle 21 and up through a conduit section 22 as indicated by the arrows 23 and into the entrance 24 to the blower I8.

At the exit 25 from the blower 18 there are provided parallel baffles 26, 27 and 28 operating as guide means spaced from each other and having inner ends 29 spaced from each other to provide a plurality of flows paths 30, here three. spanning substantially the full width of the tunnel ll to distribute the refrigerant across this full width.

In order to provide fresh refrigerant to the apparatus 10 the inner ends of the flow paths 30 between the baffles 29 and adjacent the blower 18 are provided with a plurality of refrigerant valves .31. As can be seen from FIG. 1 each flow path 30 at its entrance which is adjacent the blower 18 is provided with its own valve 31. Also it is possible to use a single valve 31 with a horn of the type shown in the above Wagner application to spread out the flow across the tunnel 11.

With this arrangement the fluid refrigerant which includes flowable vaporizable solid particles and gaseous fluid where the refrigerant is carbon dioxide or the like is introduced into the apparatus tunnel or chamber 11 at an intermediate section between the entrance 13 and the exit 14. Because of the positioning of the valves 31 the refrigerant is introduced initially transversely to the chamber 11 and then is turned through by the baffles 2628 so that at the exits of the flow paths 30 the refrigerant is flowing countercurrently to the direction 17 of movement of the articles 15 as indicated by the directional arrows 32. Thus the apparatus including the valves as illustrated in FIG. 1 produces a manifold effect that spreads the flow of refrigerant in the flow paths 30 across the full width of the tunnel l1 and above the fluid separating baffle 21.

The flow paths of the refrigerant to the three valves 31 in the illustrated embodiment is shown semischematically in FIG. 3. Here the liquid carbon dioxide is directed through a supply valve 32 and the flow line 33 in parallel to the three valves 31. Flow through these valves 31 causes an immediate pressure drop on the liquid carbon dioxide so that the exiting refrigerant indicated at 34 is in the form of mixed solid carbon dioxide and gaseous carbon dioxide formed both from the vaporization of the liquid and the solid. The valves 31 in the illustrated embodiment are located primarily exteriorly of the chamber 11.

The structure of the valve is illustrated in FIGS. 2 and 4. As is shown there the .valve comprises a tubular valve body 35 containing a longitudinally movable part 36 therein having on its forward end a valve closing surface 37 in the form of a truncated cone with the small end joined to the valve stem 38 and the large end adjacent the exit 39 of the valve body 35.

Surrounding the surface 37 is an annular valve seat 40 that has a sealing surface 41 that engages the closing surface 37 when the valve part 36 is in closed position as shown in FIG. 2. One of the surfaces 37 and 41 is provided with a scraping portion engaging the other surface so that when the movable part 36 is moved in opening and closing the valve solid refrigerant deposited within the valve will be scraped by the scraping portion from the other surface. In the illustrated embodiment the scraping portion is in the form of a knife edge 42 on the seat part 40 to engage the closing surface 37 of the movable part 36. The result is that when the valve part 36 is moved from its closed position as shown in FIG. 2 to its open position or to the right in FIG. 2 the scraping portion 42 scraps deposited solid carbon dioxide therefrom so that it can be carried from the interior of the tubular body 35 by the flow of refrigerant as indicated by the arrow 43 into and through the valve.

The scraping portion on the seat part 40 extends around the movable valve part surface 37 in that it has an annular shape to engage the entire circumference of the surface 37.

The valve is held in closed position as shown in FIG. 2 for movement within a bushing 44 by a helical spring 45 that is positioned around the reduced rear end 46 of ,the stem 38 and has one end bearing against the bushing 44 and the other end bearing against a threaded adjustable nut 47.

The movable part 36 of the valve is moved to an open position or to the right in FIG. 2 when liquid carbon dioxide is allowed to flow into the valve as shown at 43 under a pressure greater than an initial setting on the valve. That is the valve is set at some cracking pressure by adjusting the nut 47 to compress the spring 45 to some pre-load which is transmitted to the stem 36. This pre-load is selected so that the valve will crack open at a pressure above the triple point of carbon dioxide 75 PSIA or greater.

Carbon dioxide is stored in a liquid state under a pressure of 305 PSIG and F. and will remain in a liquid state under a pressure range of 60 PSIG to 1051 PSIG and a temperature range of 69.9F. to 87.8F. To utilize the liquid carbon dioxide as a continuously controlled fluid, that is, to control the flow rate, the valving and controls must contain the carbon dioxide within these boundaries. To accomplish this directive the shear-orifice valve was developed.

The shear-orifice valve is used in conjunction with a pneumatically operated flow control needle valve as noted in the above Wagner application and here indicated generally at 32 in FIG. 3. As the needle valve modulates the flow rate, from signals transmitted from an I/P transducer and controller system, the shearorifice valve modulates. As the needle valve modulates the flow rate, the pressure drop across the valve varies and the shear-orifice valve senses this pressure variable and modulates.

Although the system is set up to contain the carbon dioxide within its liquid state boundaries, solid carbon dioxide still forms under conditions of low flow rate and at shut-off. It is also assumed that as the carbon dioxide exits the nozzle 48 of the shear-orifice valve (area of high velocity and low pressure), solid particulate flashes back within the seat 41 area. The shearorifice valve, with its knife edge, shears what solid matter is formed and self-cleans, keeping the valve open and free flowing.

This permits the liquid carbon dioxide to flow inwardly of a side entrance 52 to the valve body 35 and make a right angled turn to flow outwardly in the annular passage or nozzle 48 that is now formed between the surface 37 and the surface 41. Because this constitutes a rapid drop in pressure at the exit 39 of the valve the released refrigerant indicated at 32 in FIG. 1 and 34 in FIG. 3 becomes a mixed solid and gaseous carbon dioxide refrigerant with a substantially complete absence of liquid.

When the movable valve part 36 returns to the closed position of FIG. 3 solid carbon dioxide tends to be deposited on the interior of the valve body 35 and particularly in the area around the valve closing surface 37. In the ordinary valve this solid carbon dioxide would block the interior flow passage so that upon subsequent opening of the valve very little if any refrigerant would flow therethrough.

In the self-cleaning valve of the present invention because of the provision of the scraping surface illustrated at 42 the subsequent opening movement of the movable part 36 in the direction indicated by the arrow 53 would cause the scraping portion or knife edge 42 to scrap the solid refrigerant from the surface 37 so that the dislodged particles of solid refrigerant would be carried out through the exit 39 by the refrigerant which is now free to flow through the valve body.

In order that this scraped refrigerant does not itself block the fresh flow the seat part 40 of the valve is annularly arranged around the surface 37 and extends in the opposite direction to the direction of movement 53 of the movable part and provides a solid collecting annular pocket 54 between the tapered seat part 40 and the adjacent areas of the valve body 35. Then when the flow of liquid refrigerant is again started this temporarily received solid within the pocket 54 is itself carried out with the exiting refrigerant 34.

Having described my invention as related to the embodiment shown in the accompanying drawings, it is my intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the appended claims.

I claim:

1. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles at an intermediate section of said chamber between said entrance and exit during said passage, said means for introducing comprising guide means spanning substantially the full width of said passage of said articles for providing a plurality of side-by-side flow paths extending longitudinally of said means for passing said articles for distributing said fluid substantially uniformly through said width; and a self-cleaning valve in said flow path for a liquid refrigerant that also exists as a solid comprising a valve movable part having a valve closing surface, an annular valve seat part having a seal surface sealingly engaging said closing surface, one of said surfaces comprising a scraping portion engaging the other said surface, and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion.

2. The apparatus of claim 1 wherein said movable part is movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction, said seat part comprising a knife edged scraping portion.

3. The apparatus of claim 2 wherein said means for introducing comprises a blower means at one side of said chamber having an exit directing said fluid transversely to said chamber and said guide means is curved from a lateral direction to a longitudinal direction with respect to said chamber, the guide means thereby achieving said distribution across the full width of the chamber and directing the incoming fluid longitudinally of the chamber, said valves being located primarily exteriorly of said chamber.

4. The apparatus of claim 1 wherein said closing surface is annularly tapered for both opening and closing said valve.

5. The apparatus of claim 4 wherein said scraping portion has a knife edge and there are provided means for mounting the movable part for longitudinal movement relative to the seat part thereby varying the spac ing between said knife edge and said annularly tapered valve opening and closing surface.

6. The apparatus of claim 4 wherein said movable part is movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction and wherein said seat part extends 360 and comprises a knife edged scraping portion adjacent to a narrow annular portion contacting said movable part upon closing of said value.

7. The apparatus of claim 4 wherein said one of said surfaces comprises a knife edged scraping portion on said seat part engaging said valve closing surface.

8. The apparatus of claim 7 wherein there are provided means mounting said movable part for movement in one direction to open the valve and said scraping portion engages said movable part and extends in the opposite direction.

9. The apparatus of claim 8 wherein said scraping portion is annularly coaxial with and engages said closing surface only when the valve is closed.

10. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles at an intermediate section of said chamber between said entrance and exit during said passage, said means for introducing comprising guide means spanning substantially the full width of said passage of said articles for providing a plurality of flow paths distributing said fluid substantially uniformly through said width; a self-cleaning valve for a liquid refrigerant that also exits as a solid comprising a tubular valve body having a discharge end for said refrigerant; a longitudinally movable valve part having an annularly tapered valve opening and closing surface in said body; an annular valve seat part in said body located adjacent to the discharge end, extending inwardly thereof and spaced from said tubular body to provide an annular pocket between said seat part andsaid valve body for collecting solid refrigerant in the pocket, said valve seat part having a seal surface sealingly engaging said tapered closing surface and said seat part comprising a knide edge scraping portion engaging said valve closing surface and extending around said movable valve part; and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion.

11. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said. chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles at an intermediate section of said chamber between said entrance and exit during said passage, said. means for introducing comprising guide means spanning substantially the full width of said passage of said articles for providing a plurality of flow paths distributing said fluid substantially uniformly through said width; and a self-cleaning valve in said flow path for a liquid refrigerant that also exists as a solid comprising a valve movable part having a valve closing surface, an annular valve seat part having a sea] surface sealingly engaging saidclosing surface, one of said surfaces comprising a scraping portion engaging the other said surface, and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion, said movable part being movable in one direction for said opening and the seat part being annularly arranged around the movable part and extending in the opposite direction, said seat part comprising a knife edged scraping portion.

12. The apparatus of claim 11 wherein said means for introducing comprises a blower means at one side of said chamber having an exit directing said fluid transversely to said chamber and said guide means is curved from a lateral direction to a longitudinal direction with respect to said chamber, said guide means thereby achieving said distribution across the full width of the chamber and directing the 'incoming fluid longitudinally of the chamber, said valves being located primarily exteriorly of said chamber.

13. The apparatus of claim 11 wherein said closing surface is annularly tapered for both opening and closing said valve and wherein said scraping portion has a knife edge and there are provided means for mounting the movable part for longitudinal movement relative to the seat part thereby varying the spacing between said knife edge and said annularly tapered valve opening and closing surface.

14. The apparatus of claim 11 wherein said closing surface is annularly tapered for both opening and closing said valve, said movable part is movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction and wherein said seat part extends 360 and comprises a knife edged scraping portion adjacent to a narrow annular portion contacting said movable part upon closing of said valve.

15. The apparatus of claim 11 wherein said closing surface is annularly tapered for both opening and closing said valve and wherein said one of said surfaces comprises a knife edged scraping portion on said seat part engaging said valve closing surface.

16. The apparatus of claim 15 wherein there are provided means mounting said movable part for movement in one direction to open the valve and said scraping portion engages said movable part and extends in the opposite direction.

17. The apparatus of claim 16 wherein said scraping portion is annularly coaxial with and engages said closing surface only when the valve is closed.

18. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles during said pas sage; and a self-cleaning valve for a liquid refrigerant that also exists as a solid comprising a valve movable part having a valve closing surface, an annular valve seat part having a seal surface sealingly engaging said closing surface, one of said surfaces comprising a scraping portion engaging the other said surface, and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion, said movable part being movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction, said seat part comprising a knife edged scraping portion.

19. The apparatus of claim 18 wherein said closing surface is annularly tapered for both opening and closing said valve and said scraping portion has a knife edge and there are provided means for mounting said movable part for longitudinal movement relative to said seat part thereby varying the spacing between said knife edge and said annularly tapered valve opening and closing surface.

20. The apparatus of claim 19 wherein said movable part is movable in one direction for said opening and the seat part is annularly arranged around said movable part and extends in the opposite direction and wherein said seat part extends 360 and comprises a knife edged scraping portion adjacent to a narrow annular portion contacting said movable part upon closing of said valve.

21. The apparatus of claim 19 wherein said one of said surfaces comprises a knife edged scraping portion on said seat part engaging said valve closing surface, there are provided means mounting said movable part for movement in one direction to open the valve and said scraping portion engages said movable part and extends in the opposite direction and said scraping portion is annularly coaxial with and engages said closing surface only when the valve is closed.

Claims

5. The apparatus of claim 4 wherein said scraping portion has a knife edge and there are provided means for mounting the movable part for longitudinal movement relative to the seat part thereby varying the spacing between said knife edge and said annularly tapered valve opening and closing surface.

6. The apparatus of claim 4 wherein said movable part is movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction and wherein said seat part extends 360* and comprises a knife edged scraping portion adjacent to a narrow annular portion contacting said movable part upon closing of said value.

10. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles at an intermediate section of said chamber between said entrance and exit during said passage, said means for introducing comprising guide means spanning substantially the full width of said passage of said articles for providing a plurality of flow paths distributing said fluid substantially uniformly through said width; a self-cleaning valve for a liquid refrigerant that also exits as a solid comprising a tubular valve body having a discharge end for said refrigerant; a longitudinally movable valve part having an annularly tapered valve opening and closing surface in said body; an annular valve seat part in said body located adjacent to the discharge end, extending inwardly thereof and spaced from said tubular body to provide an annular pocket between said seat part and said valve body for collecting solid refrigerant in the pocket, said valve seat part having a seal surface sealingly engaging said tapered closing surface and said seat part comprising a knide edge scraping portion engaging said valve closing surface and extending around said movable valve part; and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion.

11. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles at an intermediate section of said chamber between said entrance and exit during said passage, said means for introducing comprising guide means spanning substantially the full width of said passage of said articles for providing a plurality of flow paths distributing said fluid substantially uniformly through said width; and a self-cleaning valve in said flow path for a liquid refrigerant that also exists as a solid comprising a valve movable part having a valve closing surface, an annular valve seat part having a seal surface sealingly engaging said closing surface, one of said surfaces comprising a scraping portion engaging the other said surface, and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion, said movable part being movable in one direction for said opening and the seat part being annularly arranged around the movable part and extending in the opposite direction, said seat part comprising a knife edged scraping portion.

12. The apparatus of claim 11 wherein said means for introducing comprises a blower means at one side of said chamber having an exit directing said fluid transversely to said chamber and said guide means is curved from a lateral direction to a longitudinal direction with respect to said chamber, said guide means thereby achieving said distribution across the full width of the chamber and directing the incoming fluid longitudinally of the chamber, said valves being located primarily exteriorly of said chamber.

14. The apparatus of claim 11 wherein said closing surface is annularly tapered for both opening and closing said valve, said movable part is movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction and wherein said seat part extends 360* and comprises a knife edged scraping portion adjacent to a narrow annular portion contacting said movable part upon closing of said valve.

18. Apparatus for refrigerating articles, comprising: means defining a thermally isolated chamber having an entrance and an exit for passage of said articles through said chamber; means for passing said articles through said chamber; means for introducing a fluid refrigerant including flowable vaporizable solid particles and gaseous fluid into contact with said articles during said passage; and a self-cleaning valve for a liquid refrigerant that also exists as a solid comprising a valve movable part having a valve closing surface, an annular valve seat part having a seal surface sealingly engaging said closing surface, one of said surfaces comprising a scraping portion engaging the other said surface, and means for moving said movable part relative to said seat part for simultaneously opening and closing said valve and scraping solid refrigerant from the other said surface with said scraping portion, said movable part being movable in one direction for said opening and the seat part is annularly arranged around the movable part and extends in the opposite direction, said seat part comprising a knife edged scraping portion.

20. The apparatus of claim 19 wherein said movable part is movable in one direction for said opening and the seat part is annularly arranged around said movable part and extends in the opposite direction and wherein said seat part extends 360* and comprises a knife edged scraping portion adjacent to a narrow annular portion cOntacting said movable part upon closing of said valve.