WO2001090650A1

WO2001090650A1 - A valve unit for controlling the delivery of a fuel gas, particularly for water-heating devices

Info

Publication number: WO2001090650A1
Application number: PCT/EP2000/008377
Authority: WO
Inventors: Stefano Zanella; Alessandro Toniolo; Massimo Giacomelli
Original assignee: Sit La Precisa SpA
Current assignee: Sit La Precisa SpA
Priority date: 2000-05-22
Filing date: 2000-08-28
Publication date: 2001-11-29
Anticipated expiration: 2002-11-22
Also published as: IT1315698B1; ITPD20000138A1; AU7414400A

Abstract

A valve unit for controlling the delivery of a fuel gas comprises a thermostatic valve (30) with an actuator means (31) which is sensitive to the variation of the water temperature in order to bring about the shutting-off of a main gas-delivery duct (4), a servo-valve (8) having a first closure member (9) with diaphragm control (12), the diaphragm being subjected to the gas-delivery pressure (Pu) on one side and to a pilot pressure (Pt) established in a pilot chamber (13) of the servo-valve on the other side, and a pressure-regulator device associated with the servo-valve (8) and comprising a regulation valve for controlling the pilot pressure (Pt) in the pilot chamber (13).

Description

Title

A valve unit for controlling the delivery of a fuel gas, particularly for water-heating devices Technical Field The present invention relates to a valve unit for controlling the delivery of a fuel gas according to the preamble to main Claim 1. Technological background

As is well known, valve units of the type referred to are used for controlling gas delivery in water-heating apparatus, particularly in domestic water-heaters.

A unit of this type typically comprises a thermostatic valve with a valve seat formed in the main gas delivery duct and a corresponding closure member controlled by a thermomechanical actuator. The actuator normally comprises an element which is sensitive to the variation of the water temperature, placed in contact with the water to be heated and operatively connected to the closure member of the valve . As a result of the thermal expansion of this element, the rod controlling the closure member is displaced, by means of a bistable resilient device, with a displacement which is correlated with the variation of the water temperature and as a result of which the closure member is closed onto the corresponding valve seat in order to shut off the gas flow when a predetermined temperature is exceeded.

Although, on the one hand, these control devices, so- called "thermomechanical thermostats", have the advantage that they do not require any external electrical supply for their operation, on the other hand, they have some limitations. In particular, the thermal expansions which can be achieved with the materials normally used for thermostatic bulbs, within the temperature ranges typically encountered in the heating of water for domestic use, lead to extensions of the temperature-sensitive elements which are quite small in comparison with the much larger movements of the closure member which are required for an adequate gas flow. Description of the invention

The problem upon which the present invention is based is that of improving the functionality of valves with thermomechanical thermostatic control by providing a valve unit for controlling the delivery of a fuel gas which is designed structurally and functionally so as to avoid the disadvantages complained of with reference to the prior art mentioned.

This problem is solved by the invention by means of a valve unit formed in accordance with the following claims. Brief description of the drawings

The characteristics and the advantages of the invention will become clearer from the following detailed description of a preferred embodiment thereof, described by way of non- limiting example with reference to the single appended drawing which is a schematic view showing, in section, a valve unit formed in accordance with the present invention. Preferred embodiment of the invention

With reference to the drawing mentioned, a valve unit, formed in accordance with the present invention, for controlling the delivery of a fuel gas supplied to a water- heating device (not shown) , such as a domestic water-heater, is generally indicated 1. The gas is supplied to the unit 1 through a supply opening 2 and is delivered thereby through a delivery opening 3. A main gas-flow duct 4 is defined between the openings 2 and 3. The valve unit 1 comprises a safety valve 5 operated by a magnetic unit 6 which is armed manually by means of an arming member including an operating rod 7 so as to open the safety valve 5 and to allow the gas to flow towards the delivery opening 3.

A servo-valve 8 mounted in the main duct 4 comprises a closure member 9 which is urged resiliently into closure on a valve seat 10 by the resilient load of a spring 11 and can be opened by a diaphragm 12 sensitive to the pressure differential existing between the delivery pressure Pu existing in the region of the opening 3, on one side, and to the pressure value Pt in a pilot chamber 13, on the other side. The pressure value Pt is controlled by the operation of a servo-assisted diaphragm pressure-regulator device, indicated 14.

The device 14 comprises a pressure-regulation valve 15 having a diaphragm 16 fixed to a closure member 17 associated with a corresponding valve seat 18. The diaphragm 16 is subjected, on one side, to a load exerted by a spring 19 and adjustable by the screwing of a spring-holder 20 and, on the other side, to the pressure existing in a chamber 21. The chamber 21 is in communication with the pilot chamber 13 by means of the valve seat 18 and by means of a duct 22, and with the delivery opening 3 by means of a transfer duct 23. The transfer duct 23 and the duct 22 are connected to one another and in fluid communication by means of a duct 24 in which there is a constriction 25.

A tapping duct, indicated 26, opens at one of its ends into the main duct 4, upstream of the servo-valve 8, in order to tap off a fraction of the gas flow supplied to the inlet of the valve unit 1. The opposite end of the duct 26 opens into a chamber 27 in which there is in turn a valve seat 28 associated with a corresponding closure member 29. The seat 28 and the closure member 29 are parts of a thermostatic valve, generally indicated 30. The valve seat 28 is connected to the duct 22 in a manner such that the valve 30 selectively puts the tapping duct 26 into communication with the duct 22, as will be explained in detail below.

The duct 26 also has a constriction 26a such as to induce a loss of pressure in order to derive the pilot pressure Pt from the fraction of the gas-flow tapped off from the flow supplied through the main duct 4 at the inlet of the valve unit .

The valve 30 comprises a thermomechanical actuator 31 for opening/closing the closure member 29 relative to the respective valve seat 28. The actuator 31 comprises a tubular element 32a which is sensitive to the variation of the temperature of the water to be heated and which is preferably made of a material with a high thermal expansion coefficient, and a second, rod-like element 32b with a low coefficient of thermal expansion, one end of which is coupled to the element 32a. The element 32a is immersed in the water held in a tank 33, shown only partially in the drawing, and is preferably housed in a sleeve 35 connecting the valve unit to the tank.

One end of the rod-like element 32b abuts the base of the element 32a and its opposite end acts on a lever arrangement 36 operatively connected to a control rod 37 of the closure member 29. More particularly, the lever arrangement comprises a second-order lever 36a having a fulcrum 38 at one end and acting, at the opposite end, on a thrust means 39 guided for sliding in a stationary structure _la of the unit 1. The lever 36a abuts the rod-like element 32b in an intermediate position between the fulcrum 38 and the point of connection with the thrust means 39. A quick-release resilient means 40 is interposed between the thrust means 39 and the rod 37 of the closure member 29 for acting on the closure member 29 resiliently so as to open the valve seat 28. The quick release of the resilient means 40 is activated by the force exerted by the rod-like element 32, by means of the thrust means 39 and the lever 36a, as a result of the extension of the rod-like element 32 due to the thermal expansion which it has undergone . When a predetermined value of the thermoelastic force applied to the resilient means is reached, the latter snaps into an operative position (shown in broken outline in the drawing) such as to bias the closure member 29 into closure onto the seat 28, consequently shutting off the tapping duct 26, as will become clear from the following description of the operation of the valve unit of the invention. The position of the fulcrum 38 of the lever is adjustable by means of a rod 41 supported rotatably on the stationary structure la of the valve unit and acting on the fulcrum 38 with one of its axial ends. The rod 41 has an external thread 42 which can be engaged by screwing in a female thread 43 formed inside a bush 44. The bush is fixed to the stationary structure la so that, as a result of the male-and-female screw coupling, if the rod 41 is rotated, it correspondingly slides axially away from or towards the fulcrum 38 in order to shift the position of the fulcrum in an adjustable manner.

This adjustment enables the distance between the lever 36a and the sensitive element 32 acting on the rod to be varied so as consequently to adjust the value of the thermoelastic extension required to activate the quick- release resilient means 40. Geared transmission means provided for the rotation of the rod 41 comprise a set of teeth 45 formed on a cylindrical portion of the rod and meshed with a respective ring gear 46. The ring gear 46 is fixed to and coaxial with an operating knob 47 supported for rotation on the valve unit l.

An optional diaphragm pressure-regulator for supplying a pilot burner (not shown) with a preselected pressure through a duct 49 is indicated 48.

In operation, the delivery pressure Pu is regulated to a predetermined value by the control of the pilot pressure Pt, with the control mediated by the pressure regulator 14 in which the pressure value Pt is preset at the calibration stage by adjustment of the spring 19, by screwing of the spring-holder 20. The pressure regulator 14 keeps the pressure in the chamber 13 constant at the value determined by the calibration performed, and the diaphragm 12 fixed to the closure member 9 consequently keeps the delivery pressure Pu constant by maintaining a constant ratio between the delivery pressure Pu and the pilot pressure Pt .

As the temperature of the water to be heated increases, the sensitive element 32b is subjected to a thermal gradient and undergoes an extension due to thermoelastic expansion which in turn induces a load on the lever 36a, which load is transferred to the rod of the closure member 29 by the thrust means 39. When the load threshold value for the activation of the resilient means 40 is reached, the latter is snapped to the position shown in broken outline in the drawing, biasing the closure member 29 into closure on the valve seat 28, consequently shutting off the tapping duct 26. A pressure equal to the delivery pressure Pu is thus established in the duct 22 and in the pilot chamber 13 and the diaphragm 12 is subjected to the same pressure Pu on both sides. The closure member 9 in the main duct 4 is consequently urged into closure on the valve seat 10 by the resilient action of the spring 11, thus shutting off the flow of gas in the main duct 4. It will thus be noted that the shutting-off of the duct 4 is achieved by the operation of the thermostatic valve 30 for shutting off the tapping duct 26. By adjusting the position of the fulcrum 38, it is also possible to associate the intervention load of the quick release resilient means 40 with different values of the thermoelastic extension of the sensitive element 32 so that, for each temperature value or range of values preselected (by means of index marks on the knob 47) , the thermostatic valve is operated so as to shut off the tapping duct 26 when the temperature value which has been set is exceeded.

The invention thus solves the problem set, achieving many advantages in comparison with known solutions. A principal advantage lies in the fact that, since the thermostatic valve controlled by the element which is sensitive to the variation of the water temperature is provided in a tapping duct (also known as a "leakage circuit") of the servo pressure-regulator, the distances travelled which are necessary to open/close the tapping duct are an order of magnitude smaller than in known direct shut- off systems in which shut-off takes place in the main duct, and accurate and reliable regulation is permitted even with the small extensions of thermoelastic origin which can normally be achieved in the temperature-sensitive element of the thermomechanical actuator.

Moreover, the pressure losses brought about in the region of the thermostatic valve are advantageously low by virtue of the fact that the shut-off and regulation functions are incorporated in a single valve rather than in a pair of valves as in the case of a separate pressure-regulator.

Claims

1. A valve unit for controlling the delivery of a fuel gas, particularly for water-heating devices, of the type comprising a thermostatic valve (30) with an actuator means (31) which is sensitive to the variation of the water temperature in order to bring about the shutting-off of a main gas-delivery duct (4) in dependence on the temperature reached in the water, characterized in that it comprises:

- a servo-valve (8) disposed in the main duct (4) and having a first closure member (9) with diaphragm control (12) , the diaphragm being subjected to the gas-delivery pressure (Pu) on one side and to a pilot pressure (Pt) established in a pilot chamber (13) of the servo-valve on the other side,

- a pressure-regulator device associated with the servo-valve (8) and comprising a regulation valve (15) for controlling the pilot pressure (Pt) in the pilot chamber (13) ,

- a tapping duct (26) for tapping off a fraction of the gas- flow from the main duct (4) , upstream of the first closure member (9) , the tapping duct (26) being in fluid communication with the pilot chamber (13) and the pressure regulator, and in that the thermostatic valve (30) is provided in the tapping duct (26) in order to bring about closure of the first closure member (9) of the main gas duct (4) by means of the shutting-off of the tapping duct, with a control mediated by the pressure-regulator device.

2. A valve unit according to Claim 1, in which the thermostatic valve (30) comprises a second closure member (29) associated with a respective second valve seat (28) in the tapping duct (26) , a quick-release resilient means (40) being interposed between the second closure member (29) and the actuator means of the thermostatic valve (30) for acting on the second closure member (29) so as to open the second valve seat (28) , the quick-release resilient means (40) being activated by the load exerted by the actuator means (31) as a result of the thermal expansion thereof, in order to snap so as to bias the second closure member (29) into closure on the respective second seat (28) when a predetermined load value is exceeded.

3. A valve unit according to Claim 1 or Claim 2, in which the actuator means (31) comprises a pair of elements

(32a, 32b) with a high differential thermal expansion coefficient .

4. A valve unit according to Claim 3 , in which the pair of elements acts on the second closure member (29) by means of a lever arrangement (36) .

5. A valve unit according to Claim 4 , in which the lever arrangement (36) comprises a second-order lever (36a) .

6. A valve unit according to Claim 5, in which the fulcrum (38) of the lever (36a) is adjustable.

7. A valve unit according to one or more of Claims 4 to

6, in which the quick-release resilient means (40) acts between a control rod (37) of the second closure member (29) and a thrust means (39) operatively connected to the lever

(36a) , the resilient means (40) being movable, by means of the pair of elements (32a, 32b) , so as to snap between a first operative position in which the second closure member (29) is acted on resiliently so as to open the second valve seat (28) and a second operative position in which the closure member (29) is biased into closure on the respective seat (28) as a result of the snapping of the resilient means (40) .