A valve unit for regulating the flow-rate of a fuel gas

Abstract

 A valve unit for regulating the flow-rate of a fuel gas delivered through a delivery duct (3) is described and comprises a servo-valve (4) having a closure element (5) controlled by a diaphragm (8), the diaphragm being subjected to the gas-delivery pressure on one side and to a reference pressure established in a control chamber (9) of the servo-valve on the other side, a pressure-regulator device associated with the servo-valve (4) and comprising a regulation valve (10; 51) for controlling the reference pressure in the control chamber (9), additional regulator means for modulating the delivery pressure and/or the output flow-rate of gas through the delivery duct (3) in dependence on an external control, the additional regulator means acting alternatively on the pressure-regulator device or on means (53) for choking the delivery duct in order to modulate the delivery pressure, or to modulate the flow-rate delivered through the delivery duct (3), respectively, and actuator means for the additional regulator means, comprising a reversible motor (32) having a rotor (31) connected to a male-and-female screw coupling (28, 29; 58, 57) acting on the pressure-regulator device or on the choking means, for the operative control thereof.

Description

[0001] The invention relates to a valve unit for regulating the flow-rate of a fuel gas, according to the preamble to the main claim.

[0002] As is well known, valve units of this type are used for regulating the flow-rate of a fuel gas delivered to a burner or to another similar user through a delivery duct.

[0003] Units are known, in which the gas-flow is regulated by controlled regulation of the delivery pressure between minimum and maximum pressure values by means of a servo-valve subservient to a modulation unit with diaphragm control. The diaphragm of a unit of this type is acted on, on one side, by the gas delivery pressure as detected in the delivery duct to the user and, on the other side, by a resilient load which is subjected to the action of the movable element of an electromagnetic actuator. The delivery pressure can thus be modulated in a manner correlated with the electrical current which is supplied to the solenoid of the electromagnetic actuator and which is variable between a minimum value and a maximum value.

[0004] One of the problems encountered with units of this type is that the mechanical and, in particular, the magnetic hysteresis produced in the electromagnetic actuator in the course of regulation between the minimum and maximum pressure values lead to inaccuracies in the positioning of the actuator such that various delivery-pressure values are produced (because of the hysteresis curves) for a given current supplied to the solenoid. These inaccuracies cannot be tolerated in applications in which precise control of the modulation of the gas-flow supplied to the user is required. There are also known valve units in which the flow-rate is regulated by keeping the supply pressure constant and regulating the opening of a gas-outlet aperture in the delivery duct in controlled manner. However, the actuators provided for operating the closure element associated with this outlet aperture, particularly the electromagnetic actuators normally used in gas technology, have the same disadvantages as indicated above and are not therefore well suited to applications in which a high degree of accuracy is required in the modulation of the flow-rate of the gas delivered.

[0005] The problem upon which the present invention is based is that of providing a device for regulating the flow-rate of a gas which is designed structurally and functionally to prevent all of the problems complained of with reference to the prior art mentioned.

[0006] The characteristics and the advantages of the invention will become clearer from the following detailed description of two preferred embodiments thereof, described by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a schematic view showing, in section, a first embodiment of a valve unit formed in accordance with the invention,

Figure 2 is a schematic view showing, in section, a second embodiment of the valve unit according to the invention,

Figure 3 is a partial view showing a detail of the valve unit of Figure 2, in section and on an enlarged scale,

Figure 4 is a front elevational view showing a detail of the valve unit of Figure 2,

Figure 5 is a view corresponding to that of Figure 4 showing a variant of the detail of Figure 4,

Figure 6 is a plan view of a further detail of the valve unit of Figure 2,

Figure 7 is a section taken on the line VII-VII of Figure 6.

[0007] With reference to Figure 1, a valve unit for regulating the flow-rate of a fuel gas delivered to a burner or to another similar user, not shown in the drawing, is generally indicated 1. The gas is supplied to the unit 1 through a supply duct 2 and is delivered thereby through a delivery duct 3.

[0008] The ducts 2 and 3 are separated by a servo-valve 4 comprising a closure element 5 which is acted on resiliently so as to close a seat 6 by the resilient load of a spring 7, and which can be opened by a diaphragm 8 which is sensitive to the pressure differential existing between the pressure Pu in the delivery duct 3 on one side and the pressure value Pt in a control chamber 9 on the other side. The pressure value Pt is controlled by means of a diaphragm pressure-modulation valve, indicated 10, which, with the servo-valve 4, constitutes a servo-assisted diaphragm pressure-regulator device.

[0009] The modulation valve 10 comprises an operating rod 11 one axial end of which is screwed into a cup-shaped element 12. A spring 13 acts between the cup-shaped element 12 and a plate 14 carrying a closure element 15 which can shut off a seat 16. The plate 14 is fixed to a modulation-valve diaphragm 17 which is subjected to the load exerted by the operating rod 11 on one side and to the pressure existing in a chamber 18 on the other side. The chamber 18 is in communication with the delivery duct 3 by means of a transfer duct 19 and with a second chamber 20 by means of the valve seat 16. The second chamber 20 is always in communication with the control chamber 9 by means of a second transfer duct 21, whereas it communicates selectively with a tapping-off duct 22 for the gas supplied to the input of the valve unit and with a duct 23 opening into the chamber 18 via an on-off valve generally indicated 24.

[0010] The on-off valve 24 comprises a closure element 25 which is acted on so as to close a seat 26 and is movable so as to close an opposed seat 27 so that the seats 26, 27 are opened or closed alternatively by the operation of the on-off valve. In the duct 22, there is a choke 22a such as to bring about a loss of pressure in order to derive the control pressure Pt from a fraction of the gas-flow tapped off from the flow supplied through the duct 2 at the input of the valve unit.

[0011] The operating rod 11 has a male thread 28 which can be engaged by screwing in a female thread 29 formed inside a bush 30. The bush 30 is connected rigidly and coaxially to the rotor 31 of an electric motor 32 associated with the valve 10. The motor 32 is a direct-current electric motor and is preferably a stepper motor.

[0012] The operating rod 11 is connected to the hollow shaft of the rotor 31 by the male-and-female screw coupling with a unitary transmission ratio.

[0013] The operating rod 11 also has a pair of diametrally-opposed, radial projections 33 for engaging respective grooves 34 formed in a casing 35 of the motor connected rigidly to the stator portion of the motor. By virtue of the engagement of the grooves 34 by the projections 33, the threaded operating rod 11 is guided in the direction of its axis in a manner such that, by virtue of the male-and-female screw coupling, a rotation of the bush 30 causes corresponding axial sliding of the rod 11 with a consequent variation in the resilient load generated on the spring 13 and in turn produced on the diaphragm 17.

[0014] A spring 36 acts between the cup-shaped element 12 and the casing 35 (which is fixed to the stator portion of the motor) and serves to keep the corresponding sides of the thread of the male-and-female screw coupling continuously in contact with one another, thus eliminating the play which is present in the coupling.

[0015] An adjustable stop element, indicated 37, is formed on the surface of a screw 38 screwed into an axial threaded hole 39 of the casing of the motor 32.

[0016] A safety solenoid valve, generally indicated 40, is disposed upstream of the valve unit 1 and serves to shut off the main gas-flow supplied through the duct 2.

[0017] As a result of a rotation of the motor 32, the operating rod 11 is moved axially between a first position in which it is in abutment with the stop element 37 in order to produce a minimum resilient load on the spring 13 and consequently a minimum delivery-pressure value Pu, and a second position in which the rod is moved so as to compress the spring in order to produce a preselected maximum resilient load correlated to the maximum permissible delivery pressure value Pu for the modulator valve.

[0018] In operation, the motor 32 is rotated for a preselected number of revolutions, this number of revolutions being correlated, by means of the pitch of the thread in the male-and-female screw coupling, with a predetermined axial travel of the operating rod. The travel performed by the rod is such as to produce a resilient load in the spring 13 which in turn is correlated proportionally with the delivery pressure Pu produced in the delivery duct 3 by the modulation valve 10, as explained in greater detail in the following description.

[0019] The resilient load of the spring 13 presses on the diaphragm 17 which partially closes the closure element 15 onto the corresponding seat 16. This partial closure brings about an increase in the pressure Pt existing in the chamber 20 and, via the transfer duct 21, in the control chamber 9. This increased pressure Pt acts on the diaphragm 8, urging the closure element 5 to open. As a result of a reduction in the pressure losses, the partial opening of the closure element 5 leads to an increase in the delivery pressure Pu. This pressure Pu also acts, via the duct 19, on the side of the diaphragm 17 facing the chamber 18, consequently balancing the resilient load exerted by the spring 13. Finally, the value of the delivery pressure Pu thus achieved is correlated with the flow-rate delivered through the delivery duct 3. A pressure value Pu and a flow-rate which are proportionally correlated with one another are thus achieved for each value of the resilient load exerted on the diaphragm 17 (which is proportional to the number of revolutions performed by the rotor 31). The flow-rate of gas can thus be regulated continuously by the operation of the motor 32 associated with the modulation valve 10.

[0020] The motor 32 has a rotor 31 the rotation of which is reversible, so that the gas-delivery pressure can be modulated continuously from the maximum value to the minimum value and vice versa as a result of the rotation of the rotor 31 in one direction of rotation or in the opposite direction, respectively.

[0021] Figure 2 shows a second embodiment of the valve unit of the invention, generally indicated 50, in which parts corresponding to those of the previous embodiment are indicated by the same reference numerals.

[0022] The valve unit 50 differs form the unit 1 in that, instead of the modulation valve 10 of the unit 1, it has a regulation valve 51 comprising a screw 52 for regulating the maximum value of the pressure Pu. The screw 52, with which the spring 13 is in abutment, maintains a preselected resilient load on the diaphragm 17, this load being correlated proportionally with a delivery pressure Pu in the duct 3. As in the previous embodiment, the pressure Pu is the pressure detected through the duct 19.

[0023] The unit 50 also comprises means for choking the delivery duct 3, the means comprising a closure element 53 which is acted on so as to close a gas outlet aperture 54.

[0024] The aperture 54 is formed in a plate-like partition 55 (Figure 4) which is mounted in the duct 3 and against which the closure element 53 bears. The closure element comprises a first plate-shaped portion 53a which is acted on resiliently so as to close the aperture 54. The plate-shaped portion 53a is connected to a second, bent portion 53b constituting a resilient means which in turn is extended by a third portion 53c extending from the second portion (Figures 6 and 7) at right angles. The third portion 53c has opposed appendages 53d which extend in the same direction from a central portion 53e and by means of which the closure element is connected rigidly to the outer wall of a bush 56. The axial cavity of the bush 56 has a female thread 57 which can be engaged by screwing on an externally threaded rod 58 connected rigidly to the rotor 31 of the motor 32. The rod 58 is preferably connected to the shaft of the rotor 31 by means of a coupling 59 keyed to the motor shaft and having an axial projection 59a shaped like the tip of a flat-bladed screwdriver and housed in a corresponding seat of the rod. The end of the rod remote from the coupling 59 is housed in a recess 60 formed in the body of the valve unit 1. A spring 61 acting between the bush 56 and the stator portion of the motor serves to take up the play in the male-and-female threaded coupling in exactly the same manner as described in the previous embodiment.

[0025] As a result of a rotation of the motor 32 and consequently of the rod 58, the bush 56 and the closure element 53 fixed thereto are moved axially between a first position in which the aperture 54 is completely shut off by the portion 53a of the closure element and a second position to which the closure element is moved so as to open the aperture completely. The portion 53c for attaching the closure element to the bush 56, preventing the bush from rotating about its own axis, also constitutes guide means for guiding the axial movement of the bush due to the male-and-female threaded coupling, as a result of the rotation of the rod 58 about its axis.

[0026] During the mounting of the closure element, the portion 53b is pivoted towards the portion 53a and serves to exert on the latter a resilient load to keep the closure element in continuous sliding contact with the outlet aperture 54 during the movement of the closure element 53 from the first position to the second. A bush, indicated 62, for adjusting the minimum value of the travel of the closure element 53 is screwed onto a portion of the body of the valve unit 1.

[0027] In operation, the motor 32 is rotated for a preselected number of revolutions, this number of revolutions being correlated proportionally, by means of the pitch of the thread in the male-and-female screw coupling, with the axial travel of the closure element 53 and consequently with the choking of the outlet aperture 54. A value of the outlet cross-section and consequently of the flow-rate delivered, which are correlated with one another proportionally, is thus achieved for each positioning of the closure element 53 between the first and the second position (this positioning being proportional to the number of revolutions performed by the rotor 31). The flow-rate of gas can thus be modulated continuously by control of the motor 32 associated with the valve for choking the delivery duct 3.

[0028] As in the previous embodiment, the motor 32 has a rotor the rotation of which can be reversed so that the flow-rate of gas can be modulated continuously from the maximum value to the minimum value and vice versa as a result of the rotation of the rotor 31 in one direction of rotation or in the opposite direction, respectively.

[0029] It should be noted that the law according to which the flow-rate is modulated is also correlated with the shape of the outlet aperture 54. The aperture 54 preferably has a triangular shape (Figure 4) in which a straight or curved shape is selected for at least two sides (Figure 5) to achieve different values for the flow-rate of gas delivered for a given positioning of the closure element.

[0030] The invention thus solves the problem set, achieving the advantages mentioned above in comparison with known solutions.

[0031] In particular, it is clear that the valve unit of the invention achieves greater accuracy in the modulation of the gas flow-rate than known devices in which mechanical and magnetic hystereses lead to errors in the positioning of the operating rod of the pressure regulator or of the closure element in the delivery duct. The unit according to the invention advantageously enables a clearly defined pressure value and/or flow-rate to be achieved for each value of the positioning travel of the operating rod of the pressure regulator or of the closure element in the delivery duct.

[0032] The improved accuracy in the modulation of the pressure and/or of the flow-rate achieved by the valve unit according to the invention also leads to the advantage that the range of regulatable pressures can be widened and it is thus possible to regulate minimum pressures lower than those which can be regulated by known units. With the valve unit of the invention, minimum pressures of the order of about 1% of the maximum permissible pressures can be regulated, with minimum powers consequently of the order of 10% of the maximum powers.

[0033] A further advantage is that these minimum powers which can be achieved, which are lower than the values achieved by known solutions (for given maximum powers achieved by known devices), enable a minimal combustion to be maintained in the equipment, avoiding frequent cycles of extinguishing/ lighting of the gas, achieving a considerable reduction in harmful emissions of exhaust gases which, as is well known, increase with frequent lighting and extinguishing.

Claims

1. A valve unit for regulating the flow-rate of a fuel gas delivered through a delivery duct (3), the unit comprising:

- a servo-valve (4) having a closure element (5) controlled by a diaphragm (8), the diaphragm being subjected to the gas-delivery pressure on one side and to a control pressure established in a control chamber (9) of the servo-valve on the other side,

- a pressure-regulator device associated with the servo-valve (4) and comprising a regulation valve (10; 51) for controlling the control pressure in the control chamber (9),

- additional regulator means for modulating the delivery pressure and/or the output flow-rate of gas through the delivery duct (3) in dependence on an external control, the additional regulator means acting alternatively on the pressure-regulator device or on means (53) for choking the delivery duct in order to modulate the delivery pressure, or to modulate the flow-rate delivered through the delivery duct (3), respectively, and

- actuator means for the additional regulator means, characterized in that the actuator means comprise a reversible motor (32) having a rotor (31) connected to a screw coupling with male and female screws (28, 29; 58, 57) acting on the pressure-regulator device or on the choking means, for the operative control thereof.

2. A valve unit according to Claim 1, in which the motor (32) is a direct-current electric motor.

3. A unit according to Claim 2, in which the motor (32) is a stepper motor.

4. A unit according to one or more of the preceding claims, in which one or other of the male (28,58) and female (29,57) screws is connected to the rotor (31) of the motor (32) by direct coupling with a unitary transmission ratio.

5. A unit according to one or more of the preceding claims, in which the regulation valve (10) comprises an operating rod (11) acting on a closure element (15) controlled by a diaphragm (17), the rod (11) being rigidly connected to one or other of the male and female screws (28, 29).

6. A unit according to Claim 5, in which the female screw (29) is formed in a bush (30) coaxial with and rigidly connected to the rotor (31) of the motor (32) and in screwing engagement with the operating rod (11).

7. A unit according to Claim 5 or Claim 6, in which guide means (33, 34) are provided on the regulation valve for guiding the operating rod (11) axially during the operation of the closure element (15) as a result of a rotation of the rotor (31) about its own axis.

8. A unit according to one or more of Claims 5 to 7, in which resilient means (36) are provided, acting between the operating rod (11) and the stator portion of the motor (32) for taking up the play in the screw coupling.

9. A unit according to one or more of Claims 1 to 4, in which the choking means comprise a second closure element (53) connected rigidly to one or other of the male and female screws (58, 57).

10. A unit according to Claim 9, in which the female screw (57) is formed in a second bush (56) in screwing engagement with a rod (58) carrying the male screw, the rod being fixed for rotation with the rotor (31).

11. A unit according to Claim 10, in which the second closure element (53) comprises a plate-like element (53a) which is acted on resiliently so as to close an aperture (54) of the choking means, the plate-shaped element being fixed for translation with the second bush (56).

12. A unit according to Claim 11, in which the plate-shaped closure element (53a) is urged into sliding contact with the aperture (54) in order to choke the aperture as a result of a translation of the second bush (56).

13. A unit according to Claim 11 or Claim 12, in which the aperture (54) has a substantially triangular shape.

14. A unit according to one or more of Claims 10 to 13, in which resilient means (61) are provided between the second bush (56) and the stator portion of the motor (32) for taking up the play in the screw coupling.

Drawing