WO1990002899A1

WO1990002899A1 - High pressure valve usable particularly in a fluid jet cutting tool

Info

Publication number: WO1990002899A1
Application number: PCT/FR1989/000456
Authority: WO
Inventors: Philippe Descottes
Original assignee: Societe Etudes Recherches Fabrication Industrielle (Serfi)
Priority date: 1988-09-12
Filing date: 1989-09-11
Publication date: 1990-03-22
Also published as: FR2636400A1; FR2636400B1; AU4217489A

Abstract

The present invention relates to a valve for very high pressure fluid pipe comprising a valve body (13) wherein there is arranged a high pressure pipe (15), supplying downstream a fluid outlet pipe (16), the outlet pipe having a seat (12) wherein bears one of the extremities of a return stem (8), the assembly of said seat and said stem forming the valve itself, characterized in that there is arranged about said stem (8) an extensible tube (7) of which one of the ends is sealingly made integral with the valve body and of which the other end is sealingly made integral with, on the one hand, the other end (10) of said stem (8), and on the other hand, a connection flange (6) which is itself integral with a compressed air jack (1, 2, 3, 4), said extensible tube (7) and said stem (8) being provided, at their union, with means allowing the compression of said stem (8) to the seat (12).

Description

High pressure valve usable in particular in a fluid jet cutting tool

The present invention relates to a high pressure valve usable, in particular, in a fluid jet cutting tool. The present invention relates more particularly to a sealed valve device the opening of which is controlled, from the outside, by the action of a jack.

The valve according to the invention has been designed more particularly for use in a cutting device employing the kinetic energy of a jet of .fluid under very high pressure as a cutting tool; this is why the valve will be described in the context of such use. However, it goes without saying that the use of the valve according to the invention is not limited to this specific application. It is known that cutting devices employing the kinetic energy of a jet of fluid use high pressures reaching, for example, values of 4,500 bars. The fluid, once pressurized by a booster, is conveyed, by means of appropriate pipes, to a generally mobile cutting head above a work surface. The interruption of the high pressure jet is checked on this cutting head. For this, we use a high pressure valve whose presentation is conventional. There is indeed a shutter member such as a needle resting on a conical seat, a shutter control member such as a cylinder for example, and finally a return member such as a rod for example , which transmits the movement from the control member to the shutter member. The whole difficulty with this type of valve comes from the need to isolate the chamber receiving the fluid under high pressure and in which the obturator member is located, relative to the exterior, knowing that the wall of this chamber is necessarily crossed by the actuator return rod. In order to combat leaks at this precise location, sealing devices such as gaskets or cable glands must be installed which must not impede the movement of the return rod. Given the very high pressure of the fluid whose flow is to be interrupted, considerable efforts are applied to the different parts of the chamber. This has several drawbacks. First of all, the return rod receives a very large pushing force tending to push it outwards (450 N per mm of resulting surface subjected to 4500 bars). It is thus common to have forces of the order of 5000 N. On the other hand, the sealing device located at the passage of the return rod is itself subjected to such forces. It must therefore be dimensioned so as to resist it and this results in a tightening force around the considerable return rod, which force considerably hardens the displacement of the return rod. In addition, wear and tear occurs at this point, eventually destroying the seal, which must then be changed. Finally, for safety reasons inherent in the use of such a cutting means, it is necessary that the valve be of the "normally closed" type, that is to say that in the absence of s gnal on the control member the flow of high pressure fluid is canceled. This function is ensured by an elastic element such as a spring or stack of elastic washers (BelleviLle type) which constantly pushes the needle of the shutter on its seat by means of the return rod. Given the presence of the effort mentioned above, which tends to push the return rod out of the room. The spring must be dimensioned so as to counter this effort. These three main drawbacks lead to a fourth which is the general dimensioning of the valve. Indeed, given the different forces involved listed above, the control member must be calculated so as to counter these forces and thus be able to open the valve, and this as quickly as possible. This control member, by virtue of its position on a mobile carriage, must necessarily be remote-controlled. It is therefore practical to use a compressed air cylinder, this type of energy being by far the easiest to transport and the least expensive. Thus, it is common to use, for an air pressure of 6 bars, a cylinder with a diameter of 100 to 120 mm. The object of the present invention is to eliminate the drawbacks mentioned above and to propose a size valve. reduced allowing to integrate for example on a cutting carriage, to reduce maintenance interventions and to have a very high reliability.

The valve according to the invention comprises a valve body (13) in which a high pressure fluid inlet pipe (15 ⁾ has been arranged, supplying downstream a fluid outlet pipe (16), said outlet pipe comprising a seat (12) on which one end of a return rod (8) rests, the assembly of said seat and said rod forming the valve proper which is characterized in that it is arranged around said rod (8) an extensible tube (7) one end of which is made integral, in a sealed manner, with said valve body and the other end of which is made integral, in sealed manner, on the one hand end ⁽ 10 ⁾ of said rod (8) and on the other hand of a connecting flange ⁽ 6), itself integral with a compressed air cylinder (1) (2) (3) (4), said extensible tube (7) and said rod (8) comprising, at the level of their joining, means allowing the compression of said rod (8) on the seat (12).

Various other characteristics will be given during the following explanation, which will be better understood in the light of the following diagrams:

- Figure 1: cross section of a complete cutting head, including the valve, object of the invention;

- Figure 2: detail of the valve. The description is made according to a preferred embodiment, but however it is clear that various modifications can be made without departing from the essential characteristics of the invention.

In Figure 1, there are two sub-assemblies: - a) cutting nozzle

- b) the jet interruption valve.

These two sub-assemblies are connected together by a rigid pipe (16) and are fixed on a support (20), which support is itself fixed on any mobile carriage. The cutting nozzle is constituted by a nozzle (18) responsible for calibrating the fluid jet and a nozzle support (19), which is screwed onto a nozzle body (17). The nozzle body (17) is connected to the pipe (16) by means of a connector (21) of the high pressure type known elsewhere.

The valve essentially comprises:

- a valve body (13) serving as general support,

- an inlet tube (15) for the pressurized fluid which is connected to said body by means of a fitting (23), - an outlet tube (16) for the pressurized fluid which is connected to said body by means of a connector (22), said inlet tube and Said outlet tube being obviously connected together.

The end of the outlet tube (16) is machined so as to receive a part (12) serving as a seat on which a return rod (8) is supported. This return rod has an axis which coincides with that of the part (12) and extends beyond the valve body by means of a fitting (5) of the same type as the fittings (22) and (23).

We will now refer more particularly to FIG. 2 which illustrates the closure principle involving the seat (12) and the return rod (8).

In this figure, we find:

- The inlet pipe (15) (or more precisely the ^" connection pipe between said inlet pipe and the pipe comprising the shutter (12) (8)),

- The seat (12)

- the return rod (8) which is located in the axis of said seat and extends beyond the body of the valve,

- and the body of the valve (13); moreover, it can be seen that around the return rod (8) there is an extendable tube (7).

This extendable tube is a metal tube having a certain elasticity; One end (24) of the extendable tube is held in abutment against a bore formed in the body of the valve; the other end of the extendable tube is made integral from the end of the return rod by means of a file¬ tage which constitutes the end of the internal face of said tube and of a screw (11) which constitutes the end of the shank (8); moreover, this same end of the extendable tube is made integral by means of a part (9), of a connecting flange (6) soli¬ dary of a jack. A plug (10) screwed onto said connecting flange (6) comes to bear on the end of the extensible tube (7) thereby achieving a complete seal.

A compressed air cylinder (see Figure 1) is mounted around the tube (7); this cylinder is constituted by a cylinder (1) fitted on the connector (5) and by a piston (2), sliding freely on the same cylinder connector (5). Conventional O-rings seal the compressed air to the outside. Air is introduced inside the cylinder at the connection (4). It is a single acting cylinder. The action of the piston (2) is trans¬ put to the connecting flange (6) by a spacer (3) which acts as a pusher. Rubber pads of the ⁽¹⁴⁾ ^'disposed within the cylinder for damping the movement of the piston (2).

The description of the various elements being made, we will now explain the operation. The principle of the invention is based on an elementary observation specific to the use made of it. Indeed, the fluid put under high pressure is calibrated, at the outlet of the nozzle, by a nozzle (18) whose diameter is generally between 0.08 and 0.15 mm. If the fluid is water and its pressure has been brought to around 4,500 bars. The flow rate of passage through the nozzle is then of the order of 0.5 L / min, which is very low. On the other hand, the speed of the fluid, at the outlet of the nozzle, is very high, of the order of 1000 m / s: it is also thanks to this high speed that we have a very important kinetic energy, hence the action of cutting the jet.

In order not to disturb the characteristics of the jet at the nozzle, it is necessary to have, upstream, much larger passage sections for the fluid, which has the effect of reducing the speed of circulation. It is then that we realize that it suffices to lift the shutter very little to have a very large passage section compared to that of the nozzle. For example, if we consider a shutter diameter of 1.5 mm, it is enough to lift it by 0.35 mm to have a passage section about 200 times larger than that of the nozzle.

To create this relatively small shutter opening, one can then play on the elasticity of the extendable tube (7). Consider that the valve is initially adjusted so that the rod (8) is just in contact with the seat (12) and that the cylinder (1-2-3-4) is not actuated. The pressurized fluid has not yet been sent. Now put this _yanne under pressure, which fluid pressure is then distributed in a volume comprised between the internal wall of the extensible tube (7), that of the valve body (13) and the external wall of the return rod (8). These elements are therefore subjected to significant forces due to the high pressure. More particularly, the extensible tube (7) lengthens (its radial swelling is neglected because it is very weak) as well as the rod C8) under the effect of the compression exerted radially. The elongation of the latter is greater than that of the tube (7), this situation arising from the relative dimensioning of the parts between them imposed by the invention, which has the effect of leaving the valve in the closed position.

If the actuator (1-2-3-4) is actuated, the piston of the latter, by means of the spacer (3), pulls on the end of the tube (7) and the elongate. The end (11) of the rod (8) follows the movement of the tube (7). There comes a point when the elongation of the tube (7) is such that it compensates for the initial elongation of the rod (8). There is then separation of the end of the rod (8) from above the seat (12) and the fluid can circulate: The valve is open. There exists at this time a new phenomenon, complementary: The end of the rod (8) no longer being in contact with the seat (12), it is subjected to the pressure of the fluid and therefore receives a thrust which tends to compress it axially and thus reinforces the action of the jack. The presence of this force then prevents the valve from closing when the action of the jack is removed. which is not the desired result. To combat this phenomenon, it is necessary to have the greatest possible elongation of the tube (7) before the rod (8) comes off from its seat. This difficulty should be remedied and for this:

- On the one hand, the material constituting the rod (8) will be suitably chosen; this material will have a modulus of elasticity as large as possible to minimize said shortening,

- on the other hand, we will subject said rod (8) to a compression preload; for that, we. provided according to the invention that the joining of the end of the tube (7) and the end of the rod (8) is effected by means of a thread and a screw (11); action on said screw will subject the rod (8) to a necessary prestress. Finally, there is a balance between the forces exerted by the pressure of the fluid, the tension of the extensible tube

(7) and compression of the rod (8). It is the breaking of this balance, by pulling on the Connection flange (6), which creates the opening of the valve. The effort required depends on the preload previously adjusted and is relatively low (2,000 to 3,000 N).

It is produced by the piston (2) and transmitted by the spacer (3).

A compressed air cylinder, with a diameter of 80 mm, may very well be suitable for this.

If the material used for the extensible tube is steel, the elongations are relatively small for the forces involved, but sufficient to cause an opening of the shutter of a few tenths of a millimeter. The dimensions of this tube are determined according to the nature of the material, the difference in section between its inside diameter and the outside diameter of the return rod and the pressure of the cutting fluid.

A valve is thus obtained, adaptable in particular to a cutting head, the advantages of which are as follows:

- very small footprint and very low weight very few parts very simple operation, with only one moving part (the cylinder).

Claims

1. Valve for piping of fluid under very high pressure comprising a valve body (13) in which a high pressure pipeline (15) of fluid inlet has been placed, supplying downstream a fluid outlet pipeline (16 ), said outlet pipe comprising a seat (12) on which one of the ends of a return rod (8) rests, the assembly of said seat and said rod forming the valve proper, characterized in that L 'there is arranged around said rod (8) an extendable tube (7) one end of which is made integral, in a sealed manner, with said valve body and the other end of which is made integral, in a sealed manner, of one part of the other end (10) of said rod (8) and secondly of a connecting flange (6), itself secured to a compressed air cylinder (1) (2) (3 ) (4), said extendable tube (7) and said rod (8 ⁾ comprising, at the level of their attachment, means allowing the compression of said rod (8) on the seat (12).

2. Valve according to claim 1, characterized in that the extendable tube (7) acts as a return element now The valve in the normally closed position.

3. Cutting device using a fluid under very high pressure, characterized in that it comprises a valve according to one of claims 1 and 2.