EP1608912A1

EP1608912A1 - A valve unit for controlling the delivery of a combustible gas

Info

Publication number: EP1608912A1
Application number: EP03720855A
Authority: EP
Inventors: Lorenzo Zulian; Michele Benvenuto
Original assignee: Sit La Precisa SpA
Current assignee: Sit La Precisa SpA
Priority date: 2003-04-02
Filing date: 2003-04-02
Publication date: 2005-12-28
Also published as: WO2004088206A1; AU2003224429A1; AR043969A1

Abstract

A valve unit for controlling the delivery of a combustible gas comprises a first and a second valve seat (19, 20), coaxial with the cover and arranged in series with each other along a gas delivery channel (4), a first sealing closure means (17) associated with the first valve seat (19) and a second closure means (18) regulating the delivery pressure associated with the second valve seat (20), and also actuator means (23) acting on the first and second closure means (17, 18) to cause the respective valve seats (19, 20) to open, against resilient return means applying a loading to the closure means tending to close the corresponding valve seats. The resilient return means comprise a first sealing spring (30) acting on the first closure means (17) and a separate and distinct second spring (31) acting on the second regulating closure means (18) so that the resilient return action of the first sealing spring (30) is independent of the resilient action exerted by the second spring (31) and consequently the sealing force on the first closure means (17) is exerted solely by the first spring (30).

Description

A valve unit for controlling the delivery of a combustible gas Technical field

The invention relates to a valve unit for controlling the delivery of a combustible gas according to the preamble to the main claim no. 1 Technological background

Valve units of the above-mentioned type are widely used to regulate the delivery rate of a combustible gas delivered to a burner or other similar device. In these units it is known practice to regulate the delivery of gas by means of controlled regulation of the delivery pressure, between a minimum and a maximum pressure value.

A typical application provides for the valve unit to be equipped with a pair of valve seats coaxial with each other, arranged in series with each other on the same delivery channel, associated with respective closure means controlled by actuator means of the electromagnetic type. One of these closure means is assigned the function (safety closure) of sealing the gas path while the other closure means is used to regulate the delivery pressure. Each of the closure means are associated with a respective spring which performs the function of resilient return of the closure means to the position of closure of the valve seats. An example of a valve unit having the above-mentioned characteristics is known from the European patent application published as no. 978688.

A limitation found in these known applications is that the spring provided for the sealing function is also used in the regulating function, otherwise known in the sector in question as "offset calibration". To assign the above-mentioned functions to the same resilient return means normally represents a compromise choice between two conflicting requirements. Thus on the one hand the sealing action of the valve would preferably require the use of a sealing spring with low stiffness (to obtain a sealing force substantially independent of the degree of compression of the spring), while on the other the offset calibration function would instead require a spring with high stiffness for more precise control of the modulation force when varying the degree of compression of the spring, and also to avoid positions of neutral equilibrium along the calibration curves.

A principal limitation of the compromise choice mentioned above lies in the fact that the sealing force of the valve is exerted by the offset calibration spring, the stiffness characteristic of which varies as a function of the selected calibration, accordingly making the sealing force of the valve uncertain and non-controllable, which is also contrary to the stipulated technical safety standards.

Another limitation found consists in the fact that the closure force, meaning the force required to open the air gaps between the magnetically coupled parts of the actuator, is exerted solely by the offset calibration spring, without any assistance from the resilient action exerted by the sealing spring. Description of the invention

The problem addressed by the invention is that of making available a valve unit for controlling the delivery of a combustible gas, structurally and functionally designed so as to overcome the unwelcome limitations noted with reference to the known technology cited. This problem is solved by the invention by means of a valve unit produced in accordance with the following claims. Brief description of the drawings

Other characteristics and advantages of the invention will become clear from the following detailed description of a preferred form of embodiment illustrated, purely by way of non-limiting example, with reference to the appended drawings in which

- figure 1 is a schematic view in section of a first example of a valve unit produced according to the invention, - figures 2, 3 and 4 are views in section of a detail of the valve unit in figure 1 in respective and distinct operating positions,

- figure 5 is a schematic view in section of a variant of the valve unit according to the invention. A preferred mode of embodiment of the invention

With reference initially to figure 1, the number 1 indicates as a whole a valve unit for controlling the delivery of a combustible gas delivered to a burner or other similar device, not shown in the drawing. The gas is supplied to the unit 1 at a feed opening 2 and is delivered from it through a delivery opening 3. Between the openings 2 and 3 is formed a main channel 4 through which the gas passes.

In the channel 4 a first solenoid safety valve 5 is provided, with a respective closure means 6 associated with a corresponding valve seat 7. A spring 8 is provided for the resilient return of the closure means 6 to close the valve seat 7.

Downstream of the solenoid safety valve 5, a service channel 9 is open to the main channel 4 and is used to deliver a predetermined flow of gas to the pilot burner.

The unit 1 also comprises a pressure regulating device 10, in itself of conventional design, comprising a diaphragm 11 with the feed pressure of the gas acting on it on one side and on the other the resilient action of a spring 12, the loading of which can be adjusted by means of a screw 13. Connected to the diaphragm 11 is a closure element 14 associated with a valve seat 15 made in the channel 4.

Downstream of the pressure regulator 10, the unit 1 further comprises a sealing and regulating valve 16 with double closure means 17, 18. More particularly, the valve comprises, in the channel 4, a first and a second valve seat

19, 20, coaxial with each other (axis X), and arranged in series with each other, respectively associated with the first and second closure means 17, 18.

The first closure means 17 is arranged downstream of the second closure means 18, relative to the direction of flow of the gas delivered in the channel 4, and between the respective valve seats 19, 20 an auxiliary bypass channel 21 for the minimum is open, and this is in communication with the channel 4, upstream of the second closure means 18. The cross-section of the bypass channel can be adjusted by means of an adjusting screw 22.

The number 23 indicates as a whole actuator means for controlling the closure means 17, 18 comprising a movable component 24 of an electromagnet

25. The movable component 24 is guided slidably along the axis X and is connected to a control rod 26 to cause the opening of closure means 17, 18. More particularly, the control rod 26 has opposite axial ends 26a, 26b respectively joined by means of corresponding connections of the tilting type, to the movable component 24 and to a head 27 of the sealing closure means 17. The end 26b is mushroom-shaped and its widened portion is held, with radial and axial clearance, in a respective seat 27a on the head of the closure means 27, while the opposite end 26a is arranged with a seat 28 capable of holding, with appropriate radial and axial clearance, a mushroom-shaped portion 24a made at the free end of the movable component 24.

Between the ends 26a, 26b, the control rod 26 also has a central section 26c to which is fitted, so that each can slide relative to the other along the axis X, a sleeve formation 29 having at one of its axial ends a shoulder forming the second regulating closure means 18. At the opposite axial end, the sleeve formation 29 has a surface capable of abutting against a corresponding surface, facing it, on the head of the closure means 17. By means of the mutual abutment contact between the above-mentioned surfaces, the second closure means 18 can be driven by the sealing closure means 17 in the axial movement of the latter controlled by the electromagnetic actuator.

It may be noted that, because of the double tilting connection of the rod

26, it is possible to secure the movable component of the electromagnet loosely to both closure means 17, 18, which advantageously provides compensation if the connection of the closure means with the respective valve seats should be misaligned or not perfectly concentric, ensuring effective closure of these in any operating condition. The valve unit 1 also comprises resilient return means capable of applying a loading to the closure means 17, 18 tending to close the respective valve seats. Said means comprise a first spring 30 acting on the first sealing closure means 17 and a separate and distinct spring 31 acting on the second closure means 18. More particularly, the first spring 30 has its opposite ends abutting respectively against a fixed seating 32 on the valve and against the movable component 24. The second spring 31 has opposite ends abutting between the second closure means 28 and a fixed structure on the valve unit.

It should be noted that the resilient return action of the first sealing spring

30 is independent of the resilient action of the second spring 31, so that the sealing force on the first closure means 17 is exerted solely by the first spring 30.

Advantageously, the second spring 31 has higher stiffness characteristics compared with the first spring 30. In this way, because the sealing function of the valve is assigned solely to the resilient action of the first spring 30, a spring with relatively low stiffness is chosen, so that the sealing force is substantially independent of the degree of compression of the spring and in any operating condition always ensures adequate resilient return action for safety closure of the valve seats.

On the other hand, because the function assigned to the second spring 31 is to regulate the delivery pressure, a spring with somewhat high stiffness is chosen, so as to ensure greater precision in the control and calibration of the degree of compression and also to avoid conditions of neutral equilibrium which may compromise the reliability of the calibration system.

Figure 2 shows a first non-operating condition with both valve seats 19, 20 shut off.

Figure 3 shows a second operating condition of the valve unit in which the sealing closure means 17 is made to open the respective valve seat 19 as a result of operation of the electromagnetic actuator 23 against the resilient action of the sealing spring. In this situation, the closure means 18 remains closed on the corresponding valve seat 20.

Figure 4 shows a third operating condition in which, as a result of a further operation of the electromagnetic actuator, the head of closure means 27 is moved axially until it runs into the sleeve formation 29, thus causing simultaneous lifting of the closure means 18 against the resilient action of the spring 31.

Figure 5 shows a variant embodiment of the invention, in which components similar to those in the previous example are indicated using the same reference numbers. This variant differs mainly from the preceding example in that means of adjusting the stiffness characteristics of the second spring 31 are provided, for appropriate calibration of the spring, in order to obtain modulation of the pressure of the gas delivered through the valve unit.

Said regulating means comprise a plate 33 providing a seating for the end of the second spring opposite the one acting on the closure means 18, and a screw device acting on the plate 33 to move in an adjustable manner the position of the plate so as to vary the degree of compression of the spring as desired by adjusting the stiffness coefficient of the spring as a function of the selected calibration.

More particularly, an appendage 34 extends radially from the plate 33 and is joined to a shaft 35 which is in turn fitted, with a screw-nut connection, to a fixed portion 36 of the valve unit 1. The appendage 34 is held axially on the shaft but secured rotatably to it, so that when the shaft 35 rotates (screws up/unscrews), the appendage, and the plate integral with it, is moved axially and consequently compresses/decompresses the coils of the second spring 31. Naturally, different devices for adjusting the calibration, equivalent to the one described, may be provided without thereby departing from the scope of the invention.

The invention thus solves the problem proposed and offers numerous advantages compared with known solutions.

A main advantage consists in the fact that, with the valve unit according to the invention, the sealing force on the sealing closure means is exerted by a spring independent of the adjustment of the offset calibration, ensuring greater reliability and precision of the gas seal in the valve seat, and at the same time, as a separate spring can be reserved for the offset calibration function, the latter is advantageously selected to have suitable stiffness characteristics with consequent improved efficiency and reliability.

Another advantage of the valve unit according to the invention is that it ensures a closure force, meaning the force which is required to open the air gaps of the magnetic coupling (to move the closure means towards the closure position), exerted by both springs of the respective closure means.

Claims

1. A valve unit for controlling the delivery of a combustible gas, comprising:

- a first and a second valve seat (19, 20), coaxial with each other and arranged in series with each other along a gas delivery channel (4), - a first sealing closure means (17) associated with the first valve seat (19) and a second closure means (18) for regulating a delivery pressure, associated with the second valve seat (20),

- actuator means (23) acting on said first and second closure means (17, 18) to control the opening of the respective valve seats (19, 20), working against resilient return means applying a loading to the closure means tending to close the corresponding valve seats, characterized in that said resilient return means comprise a first sealing spring (30) acting on the first closure means (17) and a separate and distinct second spring (31) acting on the second regulating closure means (18) in such a way that a resilient return action of the first sealing spring (30) is independent of a resilient action exerted by the second spring (31) and consequently a sealing force on the first closure means (17) is exerted solely by said first spring (30).

2. A valve unit according to claim 1, in which said first sealing closure means (17) are arranged downstream of said second closure means (18) relative to the direction of flow of gas delivered through said channel (4).

3. A valve unit according to claim 1 or 2, in which said second spring (31) has higher stiffness characteristics compared with the first sealing spring (30).

4. A valve unit according to one or more of the preceding claims, comprising means of adjusting the stiffness characteristics of the second spring (31), for calibrating this when modulating the delivery pressure of the gas.

5. A valve unit according to claim 4, in which said adjusting means comprise a plate (33) providing a seating for one end of the second spring (31), the other opposite end acting on the second closure means (18), and screw means acting on the plate (33) to move the position of this adjustably so as to obtain stiffness coefficient values for the spring correlating with the selected calibration.

6. A valve unit according to claim 5, comprising an appendage (34) extending from said plate (33) and joined to a shaft (35) fitted with a screw-nut connection in a fixed portion (36) of the valve unit, so that, when the shaft (35) rotates, movement is generated of the appendage (34) and of the plate (33) integral with it.

7. A valve unit according to one or more of the preceding claims, in which said actuator means (23) are of the electromagnetic type and comprise a movable component (24) associated with an electromagnet (25) and connected to a rod (26) controlling the closure means.

8. A valve unit according to claim 7, in which said first closure means (17) comprises a closure means head (27) joined by a tilting connection to a first end of the control rod (26).

9. A valve unit according to claim 8, in which said tilting connection comprises a portion of said first end of the rod (26), said portion being held in a seat (27a) in said head (27), with radial and axial clearance.

10. A valve unit according to one or more of claims 7 to 9, in which said rod (26) comprises a second opposite end joined, via a second tilting connection, to the movable component (24) of the electromagnetic actuator.

11. A valve unit according to claim 10, in which said second tilting connection comprises an end portion (24a) of the movable component (24) fitted, with radial and axial clearance, in a respective seat (28) in said second end of the control rod (26).

12. A valve unit according to one or more of claims 7 to 11, in which said control rod (26) comprises a section (26c) extending between said first and second rod ends, on which is fitted, so that it can slide relative to the rod, a sleeve formation (29) carrying the second closure means (18).

13. A valve unit according to claim 12, in which said second closure means (18) is formed by a shoulder on said sleeve formation (29).

14. A valve unit according to claim 13, in which, at the opposite end to said shoulder, the sleeve formation (29) is capable of abutting against a surface on the head (27) of said first closure means (17), so that the second closure means (18) is moved so as to open the respective valve seat (20), against the corresponding spring (31), as a result of the axial movement of the control rod (26) caused by the electromagnetic actuator.