VALVE, IN PARTICULAR FOR COMPRESSORS

Abstract

Valve, in particular for compressors, comprising a seat (1) provided with at least one flow way (111), an obturator member (4) able to obstruct said flow way (111) and movable with respect to said seat in a given direction, and means (5) for resiliently stressing said obturator (4), which are able to force said obturator (4) into a given position and are active in the direction of movement thereof; said resilient stressing means (5) comprise at least one cylindrical helical compression spring (5), characterized by the presence, between all the turns and along the entire working length of the spring (5), of inter-turn apertures.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a valve, and in particular relates to a valve for reciprocating compressors of the reciprocating type.

The valves of the type currently used in said compressors are normally automatic valves, comprising a valve body, called the seat, consisting of a plate having, formed therein, a plurality of axial flow channels which may be concentric or non-concentric. The opening and closing of said channels is performed by the obturator, a member which may consist of a plurality of elements or a single element. In all cases the obturators are subject to the action of resilient stressing means, typically metal, cylindrical helical, compression springs. The springs are housed inside a valve body (called “counter-seat”) consisting of a plate in which the flow through channels are formed. The abovementioned spring housings may also contain spring protection elements which are preferably made of thermoplastic material and which have the function of eliminating metal contact between the surface of the spring and the external metal parts, such as, for example, the walls of the housing formed in the counter-seat or the obturator itself.

Most of the said springs are of the compression type with a cylindrical helix or conical helix. Said springs, which are made of steel wire, are formed by a total number of turns, equivalent to the sum of the active turns and the non-active turns. The non-active turns are in contact with the adjacent turns and moreover said turns are suitably ground at the ends to ensure a good axial stability of the said spring.

The springs constitute one of the most critical parts of the valve; in fact, the high opening/closing frequencies produce, on them and on the parts in contact with them, wear of varying nature and varying degrees. According to the state of the art, most of said wear, which is produced by the movement of the spring, has been analyzed and defined, and may be classified as follows:

A) wear between the external surface of the spring and the surface of the housing cavity, which is eliminated by the introduction of plastic elements which are inserted between the spring and the housing;

B) wear between the bottom end of the spring and the housing cavity support surface, which is eliminated by the introduction of plastic elements;

C) wear between the top end of the spring and the surface of contact with the obturator, which is eliminated by the introduction of plastic elements or by the introduction of plastic obturators.

Despite these improvements, the spring continues to be one of the most critical parts of the valve and the cause of malfunctions. The development of increasingly faster compressors and the continuous efforts to eliminate the oil in the compressed gas have resulted in an increase in the problems of reliability of the abovementioned components.

The object of the present invention is therefore to provide a valve for compressors, in which the wear characteristics of the springs are optimized compared to that known in the state of the art, ensuring a greater working life of the compressor.

The present invention therefore relates to a valve, in particular for compressors, comprising a seat provided with at least one flow way, an obturator member able to obstruct said flow way and movable with respect to said seat in a given direction and means for resiliently stressing said obturator, which are able to force said obturator into a given position and are active in the direction of movement thereof; said resilient stressing means comprise at least one cylindrical helical compression spring characterized by the presence, between all the turns and along the entire working length of the said spring, of inter-turn apertures.

According to a still further feature of the valve according to the present invention, the said cylindrical helical compression spring is provided, between all the turns and over the whole working length, of inter-turn apertures and where the difference in diameter between the end turns, which are preferably open conical terminal turns, and the immediately adjacent turns is in the region of at least one-and-a-half times, and preferably twice, the cross-section of the metal wire which forms the said spring.

In a preferred embodiment, the end turns both have dimensions smaller than those of the immediately adjacent turns. Advantageously, the valve according to the present invention may be provided with protection members which are preferably made of plastic material and are arranged inside the housing which accommodates the spring, so as to preserve further the wear thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and characteristic features of the device according to the present invention will emerge from the following description of an embodiment thereof, provided solely by way of a non-limiting example, with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an embodiment of the valve according to the present invention;

FIG. 2 is a cross-sectioned detail of the valve according to FIG. 1, in another operative configuration;

FIG. 3 is a plan view of the spring used in the valve according to the invention; and

FIGS. 4A and 4B are two cross-sectional views of the spring, in the rest condition and compression condition, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 shows an embodiment of the valve according to the present invention; 1 denotes the seat of the said valve, comprising a plate 101 provided with a plurality of axial and eccentric through-holes 111 acting as flow ways for the fluid and having a central, axial, threaded, through-hole 201 with which the threaded end 306 of the bolt 6 mates. The plate 101 also has formed therein the grooves 121 which communicate with the through-holes 111. The central portion of the bolt 6 also has, mounted thereon, the bush 406 and the counter-seat 2 provided with a central axial through-hole 302; the seat 1, bush 406 and counter-seat 2 are fixed together by means of the nut 106 screwed onto the threaded end 206 of the bolt 6. The axial through-ducts 102 are formed in the counter-seat 2.

The obturator 4 is arranged between the seat 1 and the counter-seat 2, being coaxial and concentric with the bush 406 and axially slidable along it by means of its central axial hole 304. The obturator has, formed therein, eccentric apertures 104 which are staggered axially with respect to the axial holes 111 of the plate 101 of the seat 1, while these apertures are in alignment with the ducts 102 formed in the counter-seat 2. The seat 1 and counter-seat 2 are moreover joined together by means of the pin 401 which is inserted inside the blind hole 301 formed in the plate 101 and passes through the hole 204 of the obturator 4 and enters into the blind hole 202 of the counter-seat 2.

The counter-seat 2 is also provided with the cylindrical housing 402 inside which the cylindrical helical compression spring 5 is arranged, the end turns 105 having a diameter smaller than that of the turns 205 immediately adjacent to them. The inserts 412 and 422 are arranged inside the housing 402, said inserts being preferably made of thermoplastic material or the like and having the function of eliminating metal contact of the spring 5 with the associated housing 402. The end wall of the insert 412 presses, owing to the action of the spring 5, against the surface of the obturator 4 which in the figure is shown open as a result of the action of the fluid flow which passes through the holes 111 in the plate 101 of the seat 1. The spring 5 in this figure is shown compressed inside the housing 402.

FIG. 2 shows a cross-sectioned detail of the valve according to FIG. 1; identical parts are indicated by the same numbers. The valve is shown here in the closed condition, with the obturator 4 which is in contact with the grooves 121 in the plate 101 which communicate, as can be seen in FIG. 1, with the holes 111 through which the fluid flows. The spring 5 is shown here in the equilibrium condition, expanded compared to the condition shown in FIG. 1.

FIG. 3 shows a plan view of the spring 5 which acts on the obturator 4 of the valve; as can be noted, the end turn 105 visible in the figure has a diameter smaller than that of the turn 205 adjacent to it. FIGS. 4A and 4B, on the other hand, highlight the fact that the presence of the inter-turn apertures, together with the difference in diameter between the open conical end turns 105 and the immediately adjacent turns 205 result in non-interference of all the turns over the useful working section.

The operating principle of the valve according to the present invention will become obvious from the description below. The valve of the type shown in FIG. 1 is normally used in compressors and operates with decidedly high opening and closing frequencies. Consequently, the resilient stressing means which act on the obturator 4 are subject to considerable wear and this irremediably affects proper operation of the valve. The spring 5 has characteristics such as to ensure that it is damaged to a considerably lesser extent than the normal cylindrical helical springs. One of the main causes of wear of the springs in question is associated with the fact that the said end turns lie in planes parallel to each other, perpendicular to the axis of the spring, but inclined with respect to the plane of extension of the helix, namely to the planes in which the other turns of the spring lie. This different inclination causes in fact a poor distribution of the load on the spring and makes it more prone to wear.

In this case this wear effect is greatly reduced and even almost eliminated entirely, owing to the presence of the inter-turn apertures together with the reduction in the diameter of the said end turns 105 compared to the immediately adjacent turns. As can be noted from FIGS. 4A and 4B, the characteristics of this spring, presence of apertures between the turns and difference in diameter between the said end turns are such as to ensure, during compression of the said spring, the absence of interference between all the turns over the entire useful working section (see FIG. 4B); consequently the turns of the spring will tend not to wear, the spring will tend to function in the manner closest to the initial configuration and its working life will be markedly improved.

Advantageously, by inserting the thermoplastic inserts 412 and 422 inside the housing 402, metal contact between the spring 5 and the walls of the counter-seat 2 and/or the obturator 4 is further eliminated.

The valve thus designed is able, on the one hand, to ensure, also at high frequencies, a precise operation and, on the other hand, the average life of the resilient stressing means and therefore the valve itself is prolonged considerably.

Claims

1. Valve for reciprocating compressors, comprising a seat (1) provided with at least one flow way (111), an obturator member (4) able to obstruct said flow way (111) and movable with respect to said seat in a given direction, and means (5) for resiliently stressing said obturator (4), which are able to force said obturator (4) into a given position and are active in the direction of movement thereof; said resilient stressing means (5) comprise at least one helical compression spring (5), characterized by the presence, between all the turns and along the entire working length of the spring (5), both in the rest condition (FIG. 4A) and in the compression condition (FIG. 4B) of inter-turn apertures, and further characterized by a taper ratio variation of both end turns in that the difference in diameter between the end turns (105) and the immediately adjacent turns (205) is in the region of at least one-and-a-half times the cross-section of the metal wire which forms the said spring.

2. Valve according to claim 1, in which the difference in diameter between both end turns (105) and the turns (205) immediately adjacent to them is half times or more the cross-section of the metal wire which forms the said spring.

3. Valve according to claim 1, in which both end turns (105) have a diameter less than that of the immediately adjacent turns (205).

4. Valve according to claim 1, in which both end turns (105) have a diameter more than that of the immediately adjacent turns (205).

5. Valve according to claim 1 in which one end turn (105) has a diameter less than that of the immediately adjacent turns (205) and the other end turn (105) has a diameter more than that of the immediately adjacent turns (205).

6. Valve according to claim 3, in which said end turns are ground.

7. Valve according to claim 1, in which the pitch of said springs is variable.

8. Valve according to claim 7, in which said resilient stressing means (5) are arranged inside a housing (402) which is suitably positioned with respect to said obturator member (4).

9. Valve according to claim 8, in which protection members (412, 422), preferably made of plastic material, are arranged inside the housing which accommodates the spring.

10. Valve according to claim 3, in which said end turns are conical.