WO2007135704A1

WO2007135704A1 - Check valve for gaseous fluids

Info

Publication number: WO2007135704A1
Application number: PCT/IT2007/000351
Authority: WO
Inventors: Andrea Di Foggia; Mariano Migliaccio; Ottavio Pennacchia
Original assignee: La.Me. S.R.L.
Priority date: 2006-05-23
Filing date: 2007-05-16
Publication date: 2007-11-29
Also published as: ITNA20060063A1

Abstract

Check valve, in which the assembly formed by the plug (5) and the closing spring (6) is not fixed 'a priori' in the valve body, but is received instead inside a housing or outer plug (10) which in turn is equipped with a pushing spring (9) having a stiffness (rigidity) greater than that of the spring (6) which directly acts on the (inner) plug (5). This solution/approach allows to realise a check valve without taking account of strict tolerance requirements, except for the manufacture of the inner plug (5). The movable housing (10), which is connected to the valve body by a threaded coupling, renders possible to adjust the most appropriate end-of-stroke position of the check valve, thereby adapting its operation to various needs.

Description

Check valve for gaseous fluids

Technical Field

The device according to the present invention relates to a check valve of new construction. Referring to an already known check valve, as shown in Fig. 1, which is mounted on the input or delivery duct (1) of a compressor and which is connected to the storage tank (2) of compressed fluid, this valve, by its spring (4) and seal element (5) prevents accidental emptying of the storage tank when, upon reaching the maximum pressure, the compressor is turned off, allowing the delivery duct (1) of the latter to be connected to the outside environment (3), in order to permit the restart of the compressor in absence of a counterpressure (back pressure) that would otherwise act should the delivery duct remain under pressure.

A common, already known check valve, must be manufactured taking into account an exact geometry in the region occupied by the plug and the closure spring, in order to insure its closing within the least possible operation time, so as to prevent a partial emptying of the storage tank. The present invention modifies the structure and design of the check valve by realising the same as indicated in Fig. 2. In this Fig. 2 it can be noted that the assembly consisting of the (inner) plug (5) and the closure spring (4) is not fixed "a priori" in the valve body; instead, it is lodged inside a housing (outer plug) which in turn is equipped with a compression spring having a stiffness greater than that of the spring acting directly on the seal element. This solution allows to produce a check valve without being forced to comply with strict size and tolerance requirements. Due to the movable housing (outer plug), which is connected to the valve body by means of a threaded coupling, it is possible to select, each time, the most appropriate end-of-stroke position of the check valve, so as to adapt the operation to different conditions.

The device of the present invention may for instance form an accessory (fitting) for gaseous fluid compression plants utilising reciprocating, positive-displacement compressors. These mechanical work performing machines are usually provided with a check valve, located in the delivery duct connecting the compressor to the storage tank for the compressed fluid. This valve, apart from allowing the fluid flow to move from the compressor to the storage tank, after opening itself under the action of the pressure developed on the compressor delivery side, accomplishes its actual task of check valve when a maximum desired pressure in the tank is reached, which is set beforehand to an appropriate "set-point" value, usually available on the electric supply and control board of the compression system. The signal indicating that the maximum pressure has been reached is in fact used to establish a fluid communication between the delivery duct of the compressor and a vent hole, and to possibly turn off at the same time the drive motor of the compressor itself. Then, since no pressure is acting on the compressor delivery side, the check valve immediately closes under the pushing action exerted on it by the pressure inside the tank which is present on the circuit connecting the valve to the tank, thereby preventing a fluid communication to be established between the storage tank and the outside environment, and therefore preventing also the emptying of the storage tank. Check valves therefore accomplish the following main tasks:

They prevent compressed fluid inside the storage tank from returning to the compressor by passing through the delivery duct, or from escaping through the vent hole opened by the compressor control system when the maximum pressure of the storage tank is reached; - They lower the pressure existing inside the delivery duct, which is directly connected to the compressor, by establishing a fluid communication towards the outside environment (atmospheric pressure), with the principal aim to drastically reduce the counterpressure (back pressure) which otherwise must be overcome by the compressor at each restart.

Background Art

In the following description of the background art the numbers are in parentheses. In Fig. 3 there is shown an already known and commonly used check valve, inserted along the delivery duct of a compressor. Duct (1) originates in the compressor. Duct (2) serves to guide the fluid flow to the storage tank. Duct (3) allows fluid discharge to take place through it when a mechanically, electrically, or pneumatically operated valve opens, at the instant of time when the maximum pressure value is reached, thereby establishing a fluid communication between this duct and the outside environment (which is at ambient pressure). Reference (4) denotes the check valve, which in Fig. 4 is illustrated in cross-section to better illustrate its components. Reference (4) also denotes in this figure 3 the valve body, (1) denotes the pipe fitting of the delivery duct to the compressor, (2) denotes the pipe fitting to the storage tank, (3) denotes the connection to the (mechanically, electrically or pneumatically operated) valve which allows fluid discharge, (5) indicates a plug designed to receive the check valve proper.

The latter is formed by a low-stiffness helical spring (6) urging a suitable seal element (8) (of rubber-like or in any case easily compressible material) against an appropriate seat (7) of circular form.

When the compressor is not operating, the check valve closes the passage in the direction leading from duct (2) to duct (1), being possibly facilitated in its task by a possible pressure existing in the storage tank, that may be greater than the pressure existing (inside duct (I)) upstream of the seal element, and this pressure gradient generates a closing force urging gasket (8) against its seat (7). On the other hand, when the compressor is operating, until the pressure inside the delivery duct (1) remains below the maximum pressure value set (selected) on the control board of the compressor, the valve - formed by the components (6) and (8) - remains open, or it opens under the pressure imposed by the compressor, thereby allowing air pushed by the compressor to flow from duct (1) to duct (2) and to finally reach the storage tank. Once the maximum pressure is reached inside the storage tank, the delivery side (delivery duct) of the compressor, that is duct (1), is set in fluid communication with the atmosphere through the duct (3) which ends in a hole (whose valve is operated electrically, mechanically or pneumatically), whereas the check valve - formed by the components (5, 6, 7, 8) - moves to its closure position and prevents the storage tank from becoming empty. Obviously, the above given description is only illustrative and does not leave out other possible applications or embodiments of the check valve shown in Figs. 3 and 4, the latter being extensively used in this configuration in current technology and allowing to perform a very useful function in practical applications. There exist in fact various relevant applications concerning both the handling of compressed air and of other compressed gases, and applications in the field relating to the motion of other (pressurised) fluids.

Brief Description of Drawings

The present invention will now be described only for illustrative and non-limitative purposes with reference to its embodiments shown in the drawings, wherein:

FIGURES 1 and 2 serve to directly compare a known check valve (Fig. 1) to a possible check valve embodiment according to the invention (Fig. 2);

FIGURES 3 and 4 show a valve of the prior art in side elevation view (Fig. 3) and in cross-section respectively (Fig. 4), wherein, in contrast with Fig. 1 more components have been indicated by respective reference numbers;

FIGURE 5 shows in cross-section, a check valve according to the present invention, in a first embodiment, wherein more components have been indicated than in Fig. 2;

FIGURES 6a and 6b show, once again in cross-section, two other embodiments of the invention which have additional advantages;

FIGURE 7 shows in a perspective, exploded view, the check valve according to the second embodiment shown in cross-section in Fig. 6a.

Description of Preferred Embodiments In Fig. 5 there is shown a check valve (nonreturn valve) which takes advantage of the innovative concept according to the present invention. To better illustrate how such a modified valve operates, a kind of valve is disclosed which is very similar to that already shown in Figs. 3 and 4 but which is equipped with components according to the present invention. First of all, referring again to Figs. 3 and 4, it should be noted that the "core" of a conventional check valve is substantially formed by the components 5, 6, 7 and 8, that is, by a cover or plug 5, a spring 6, a seat 7 with sealing function, and a gasket or seal element 8. It is unavoidable, in this arrangement, to define with a certain accuracy the distance (space) occupied by the cylindrical, helical spring 6, between the cover inner side (cover bottom) and the gasket or seal element. Thus, the spring, by its mechanical and dimensional properties, as well as by its constituent material, influences both the initial force required to open the valve and the actual compression stroke of the spring 6 during the delivery phase of the compressor. In any case, in order to obtain a satisfactory result, an accurate machining of the plug/cover 5 is required, as well as for the threaded portion of the valve (body) where the same is to be mounted. AU this requires a complex machining to be performed on the valve, which must take into account specific tolerances, ultimately resulting in additional costs for the valve itself. Now, comparing Fig. 5 to Fig. 4, other two components of the check valve appear in the former, which are indicated by reference numbers 9 and 10. Actually, the components 5, 6, 7 and 8 are identical, with regard to their function and size, to those of Fig. 4, except that the plug 5 is in this case somewhat different from the original one, since it is not fixed (stationary), being urged instead against its own support seat by a conical helical spring 9 of high stiffness (rigidity), which abuts on an outer plug (outer cover) 10.

By using this spring it is possible to avoid to perform, for the whole valve body, an accurate machining of that portion where the plug is to be mounted (compare component 5 of Fig. 4), and moreover, it becomes possible to adopt a certain processing accuracy only during the machining of component 5 of Fig. 5, for which is it certainly easier to comply with dimensional tolerances. This means that according to the present approach the valve body can be manufactured with tolerances which are less strict, while accurate machining is limited only to the inner plug 5 of Fig. 5, which can be manufactured independently, can be easily checked at the end of its processing, and in any case can be inexpensively obtained as a moulded part.

Moreover, from the foregoing it also follows that a check valve can be constructed which is not only simpler than that of Fig. 4 but also simpler than that of Fig. 5. Actually, in Figures 6a and 6b two embodiments of the valve are illustrated (that on the left for a single input flow, that on the right for two input flows), which - though functionally identical to the embodiment of Fig. 5 - have the advantage that they were obtained from very simple elements, all exempt from strict tolerance requirements, except component 5 which is designed to perform the actual function of a nonreturn valve. In these embodiments, the element 10, in addition to its task of providing an abutment surface for the spring 9, also forms a communication duct to the storage tank for the flow of compressed fluid, and it could even be realised integrally with the tank (not shown). The valves in Fig. 6 (a and b) also have the advantage of using some commercially available elements, which may be easily obtained in this field of components used in pneumatic and hydraulic systems. For greater clearness, Fig. 7 shows the valve of Fig. 6a in perspective and exploded view.

Claims

1. Check valve received inside a valve body with one or more input ducts (1) connectable each to a respective compressor, at least one vent duct (3) located at said one or more input ducts (1), and a duct (2) connectable to a storage tank for compressed fluid, characterised in that the main components of the check valve are formed by:

- an outer plug (10) mounted on the outer part of the valve body;

- a first spring (9) acting between an inner surface of the outer plug (10) and an outer surface of an inner plug (5) which is lodged inside said outer plug (10) and inside said valve body; - a second spring (6) lodged inside said inner plug (5) and acting between an inner surface of the inner plug (5) and a movable seal element (8), wherein

- said movable seal element (8) interacts with a valve seat (7);

- said first spring (9) urges the inner plug (5) against a stationary seat of the valve body and has a greater rigidity than that of the second spring (6).

2. Check valve according to claim 1, characterised in that said first spring (9), having an increased rigidity, is mounted with a greater preload than the preload of the second spring (6) acting on the movable seal element (8).

3. Check valve according to claim 1 or 2, characterised in that the inner plug (5) is realised using manufacturing tolerances more accurate than those used for the other components of the check valve.

4. Check valve according to any of the preceding claims, characterised in that the outer plug (10) has an adjustable position.

5. Check valve according to claim 4, characterised in that the outer plug (10) is mounted on the valve body by means of a threaded portion which allows to adjust its axial position.

6. Check valve according to any of the preceding claims, characterised in that said stationary seat of the valve body, against which said first spring (9) of increased rigidity urges the inner plug (5), is located outside the valve seat (7) against which said movable seal element (8) abuts when the valve closes.

7. Check valve according to any of the preceding claims, characterised in that: said second spring (6) has the task of permitting the flow of fluid pushed by the compressor towards the interior of the storage tank, only in the direction towards the tank, in case of a positive pressure difference along said direction, while preventing the occurrence of any flow in case of a negative pressure difference along the same direction;

- the first spring (9) has the task of urging said inner plug (5), that is, the functional part of the valve proper, against said stationary seat of the valve body, with a force exceeding the maximum force that can be produced by the pressure difference existing between said one or more input ducts (1) and said duct (2) connectable to the storage tank.

8. Check valve according to any of the preceding claims, characterised in that said movable seal element (8) forms a gasket made of an easily compressible material, for instance a rubber-like material.

9. Check valve according to any of the preceding claims, characterised in that said outer plug (10) has an annular abutment surface in contact with an end of said first spring (9), said outer plug (10) being integrally formed with the duct (2) connected to the storage tank of compressed fluid.

10. Check valve according to claim 9, characterised in that the duct (2) connected to the storage tank of compressed fluid is coaxial with the inner plug (5), the two springs (6, 9), and an end portion of the input duct (1) which ends at the valve seat O)-

11. Check valve according to any of the preceding claims, characterised in that at least one of the springs (6, 9) is a metallic, helical spring.

12. Check valve according to claim 11, characterised in that at least one of the springs (6, 9) is a helical, conical spring.