EP0697563A1

EP0697563A1 - Gas boiler valve assembly

Info

Publication number: EP0697563A1
Application number: EP95112769A
Authority: EP
Inventors: Giorgio Scanferla
Original assignee: INTEGRA Srl
Current assignee: INTEGRA Srl
Priority date: 1994-08-17
Filing date: 1995-08-14
Publication date: 1996-02-21
Also published as: ITMI941747A0; IT1274622B; ITMI941747A1

Abstract

A gas boiler valve assembly comprises a gas path (3) extending between a gas inlet opening (4) and a gas outlet opening (5) to a burner, adjustably intercepted by a disk (17) operated by respective membrane control means (21). Advantageously, the valve assembly comprises control devices (22, 23) capable of driving in a broad modulation range the membrane control means (21) in response to the air flow fed to the burner and, respectively, to an electrical signal proportional to the thermal power required to the burner.

Description

The present invention relates to a gas boiler valve assembly of the type comprising:

a valve body in which is defined a gas path extending between a gas inlet opening and a gas outlet opening to a burner;
a first valve seat formed in said body in said gas path;
a first disk cooperating with said first valve seat wherein it is adjustably positioned - against respective spring means - by membrane means driven by the air flow fed to the burner and operated by a limiting device of the gas flow leaving said valve body, said limiting device including: a gas passageway for by-passing said first valve seat, a second valve seat formed in said by-pass passageway and a second disk cooperating with said second valve seat.

More particularly, the valve assembly of the present invention finds a preferred, although not exclusive, use in gas boilers of the so-called combined type equipped with a so-called "aired" burner.
In the following description and appended claims, the term: boiler of the so-called combined type, is meant to indicate a boiler capable of delivering either hot water for space heating or primary water and hot water for sanitary use.
By the term: "aired" boiler, is meant a burner in which the combustion air is partly premixed with the combustible gas downstream of the nozzles feeding the gas to the burner (primary air) and partly fed downstream of the latter for completing combustion (secondary air).
In the field of heating equipment for civil use and in particular in the field of gas boilers, the need for achieving an ever more flexible control of the thermal power in a broad range of values is well known.
It is also known that to meet this need the main problem to be solved is that of ensuring that the burner is always fed with air-gas mixtures in the correct proportions regardless of the thermal power required.
This to the purpose of ensuring, on the one hand, a correct operation of the burner with a stable and clean flame and, on the other hand, of avoiding that the excess air sent to the burner exceeds the design limits.
In this case, in fact, the boiler efficiency would drop rapidly and significantly.
To meet the above mentioned need of controlling and correctly feeding the burner, there have long been used in the art valve assemblies of the so-called air-gas type, which regulate the gas flow in response to the air flow fed to the burner and, hence, in response to the thermal power required.
In valve assemblies of this type, the gas flow fed to the burner is controlled between a minimum and a maximum value by intercepting a gas supply path, defined in the valve body and fed by the external gas distribution mains.
More particularly, the above mentioned control is performed, starting from the maximum flow rate value, by means of a disk driven, as a function of the air flow fed to the burner, by a membrane controlled by a complex mechanical amplification system provided with levers.
In order to keep the boiler power within the maximum design values, the above mentioned membrane means are also operated, if necessary, by a gas flow limiting device, which drives the disk intercepting the gas supply path so as to limit the gas flow leaving the valve assembly below a predetermined maximum value.
Although essentially serving the purpose, the air-gas valve assemblies of the known type exhibit the acknowledged shortcoming of being unable to continuously control the thermal power of the burner over the whole variation range thereof.
The response limits of the membrane means designed to intercept the combustible gas path, in fact, do not allow to reduce the gas flow leaving the valve assembly below a minimum threshold value, below which an extremely irregular gas delivery with a resulting instability of the entire boiler control system is observed.
It follows that the maximum ratio of maximum to minimum thermal power of the burner, or "modulation ratio", achievable by the air-gas valve assemblies of conventional type does not exceed 3.5-3:1.
This ratio is, however, far below the modulation ratio required by nearly all boilers in use today which varies in the region of 6.5-7:1.
The impossibility of continuously controlling the gas flow implies an on-off operation of the valve assembly and burner and causes further undesirable shortcomings such as a delivery of hot sanitary water at oscillating temperatures (hunting), a high boiler noise and a significant emission of unburnt gas upon every on-off cycle of the burner.
The arise of hysteresis phenomena of the membrane and the presence of an inevitable friction in the levers of the mechanical amplification system, furthermore, introduce a regulation error in the gas flow fed to the burner which progressively worsens in time the modulation capability of the valve assembly as well as the boiler performance.
The technical problem underlying the present invention is thus to make available a gas boiler valve assembly which allows to continuously control the thermal power of the burner over the entire variation range thereof, while overcoming at the same time the shortcomings cited with reference to the above-mentioned prior art.
This technical problem is solved according to the present invention by a valve assembly of the above mentioned type which is characterized in that it further comprises, in said limiting device, means for adjustably positioning said second disk in said second valve seat, said means being driven in response to the thermal power required to the burner to adjustably position said first disk in said first valve seat by means of said membrane means.
According to the present invention, the disk designed to intercept the combustible gas path and regulate the gas flow leaving the valve assembly is controlled in a first modulation range by a pneumatic control device, sensitive to any variation in the air flow fed to the burner and, in a second modulation range, by a solenoid-operated limiting-regulating device, operated by an electrical signal proportional to the thermal power required to the burner.
Advantageously, the solenoid-operated limiting-regulating device can modulate the gas flow (thermal power) either simultaneously with the pneumatic control device, or outside the sensitivity limits of the latter.
In this manner, it is possible to continuously reduce the gas flow fed to the burner down to the minimum values compatible with a stable burner operation, moving freely over the entire modulation range required by the boilers in trade today (7:1).
The above mentioned advantages, furthermore, are readily achievable by making limited modifications to the flow limiting device already existing in the air-gas valve assemblies of conventional type, to the benefit of production costs.
Further characteristics and advantages of the invention will be better apparent from the description of an embodiment thereof, given hereinbelow by way of non-limiting example with reference to the only figure of the annexed drawing, in which said valve assembly is shown in longitudinal cross section.
With reference to the figure, reference number 1 indicates a valve assembly designed to control the flow rate of a combustible gas fed to a conventional aired burner (not shown), of a boiler of the so-called combined type also of conventional type and not shown.
The valve assembly 1 essentially comprises a valve body 2 in which a gas path 3, extending between a gas inlet opening 4 and a gas outlet opening 5, is defined.
Specifically, the openings 4, 5 are internally threaded to be coupled by means of screwing to the free ends of ducts 6, 7 by means of which the gas is fed into the valve body 2 and, respectively, conveyed to the burner.
A core member indicated by reference 8 is integrally formed within the valve body 2 and divides the gas path 3 in two upstream 3a and downstream 3b consecutive sections.
The core member 8 is also appropriately shaped so as to define in the upstream section 3a of the gas path 3 two contiguous chambers 9, 10 in mutual fluid communication through an opening 11 which essentially constitutes a valve seat on which a disk 12 is positionable in a gas-tight manner against the action of a spring 13.
Said disk is mounted in a conventional manner at one end of a stem 14 operated in a conventional manner not shown by a solenoid 15 driven by a flame sensor also not shown because entirely conventional.
The above mentioned upstream and downstream sections 3a, 3b of the fluid path 3 are also in mutual fluid communication through an opening 16, essentially coplanar to the previous one, also constituting a valve seat in which a disk 17 may be adjustably positioned, in a gastight manner, against the action of respective spring means 18.
To the sole purpose of simplifying the present description, the valve seat 16 and the disk 17 will be indicated below by the terms: main valve seat and, respectively, main disk.
The main disk 17 is mounted, in a conventional manner, on one end of a stem 19 slidably guided in a corresponding seat 20 formed in the core member 8, whose other end is operated by a membrane 21.
According to the present invention, the membrane 21 is operated in turn by a control device 22, which is driven by the air flow rate fed to the burner, and/or by a control and limiting device 23 which is operated in response to an electrical signal proportional to the thermal power required to the burner and which will be described in more detail hereinbelow.
In the valve assembly 1, the chamber 10 formed in the upstream section 3a of the gas path 3 is selectively connected to an airspace 24 defined between the membrane 21 and the valve body 2, by means of a first duct 25, a chamber 26 and a second duct 27 which constitute together a gas path placed in parallel to the gas path 3.
To this end, the outlet opening of the duct 25 is selectively intercepted by a disk 29 mounted, in a conventional manner, on one end of an arm 28 supported in a rotating manner in the chamber 26 and whose other end is operated by the core member 31 of a solenoid 32.
More particularly, the disk 29 moves between opposite positions in which it closes and, respectively, opens the duct 25 against the action of counteracting spring means 30.
The chamber 10 is also in selective fluid communication with the downstream section 3b of the gas path 3, through a passageway 35 by-passing the main valve seat 16, comprising: the duct 25, the chamber 26 and a pair of calibrated ducts 33, 34 formed in the valve body 2 between the chamber 26 and the above-mentioned downstream section 3b.
According to the present invention, the above mentioned by-pass passageway 35 forms an integral part of the gas flow control and limiting device 23, by which it is adjustably intercepted by means of a disk 36, cooperating with a respective valve seat 37 formed at an end of the duct 33 opposite the chamber 26.
The disk 36 is connected in a conventional manner to a membrane 38 and is operated against the action of counteracting spring means 39 by the moving core member 40 of a solenoid 41, driven in a known manner by an electrical signal proportional to the thermal power required to the burner.
The moving core member 40 is in particular mounted in a hole 58 axially formed within a central body of the solenoid 41 in which it is slidably guided against the action of a counteracting spring 56.
According to the present invention, the opposite ends of the spring 56 abut against the moving core member 40 and, respectively, the fixed core member 55 of the solenoid 41, which may be adjustably and variably positioned within the hole 58.
A nut 57, operable from the outside of the valve assembly 1 blocks the fixed core member 55 in the selected position.
By appropriately positioning the fixed core member 55, the compression degree of the spring 56 and, accordingly, the force exerted by the spring 56 on the core member 40, may be adjusted.
Advantageously, the stroke of the core member 40 and thus the maximum opening of the by-pass passageway 35 may also be adjusted by means of a rod 42, operable from the outside of the valve assembly of the present invention, which essentially constitutes an adjustable stop for the core member.
The regulating device 22 operating the membrane 21 comprises a unit 46, sensitive to the air flow fed to the burner, which drives a disk 45 allowing a selective fluid communication between the airspace 24 and the downstream section 3b of the gas path 3.
More particulalry, the disk 45 intercepts a further gas passageway by-passing the main valve seat 16, including a pair of ducts 43, 44 formed in the valve body 2 downstream of the airspace 24.
The disk 45 is conventionally supported by a stem 47, slidably guided in a corresponding seat formed in the valve body 2, which is fixed in turn to one end of an arm 48 operated in a conventional manner by a membrane 49 against the action of first and second spring means 50, 51.
More particulalry, the membrane 49 is supported within a chamber 52 which is divided thereby in two portions 52a, 52b connected upstream and, respectively, downstream of a device, not shown, designed to detect any variation in the air flow fed to the burner.
In the regulating device 22 as well the force exerted by the spring means 50 and 51 on the disk 45 and, respectively, on the membrane 49 may be adjusted by providing appropriate pretensioning means entirely conventional and not shown.
In operation, the valve assembly 1 described above allows to regulate the gas flow (thermal power) of a boiler from a minimum to a maximum value including the entire range of intermediate values.
This is achieved by means of the regulating device 22, driven by the air flow fed to the burner, and by the control and limiting device 23 driven by an electrical signal energizing the solenoid 41 and proportional to the required thermal power.
Whenever hot sanitary water and/or water for space heating is required, a special control unit provided in the boiler body activates a blower feeding air to the burner and starts the opening step of the valve assembly 1.
This takes place by operating solenoids 15 and 32 which cause a virtually simultaneous displacement of the disks 12 and 29 away from the corresponding valve seat 11 and from the duct 25.
In this way, the gas is free to flow sequentially into the chamber 10 of the upstream section 3a of the gas path 3, into the duct 25, into the chamber 26, and into the duct 27 up to the airspace 24 located below the membrane 21 operating the main disk 17.
The pressure created in the airspace 24 causes a gradual upward movement of the main disk 17 from the corresponding valve seat 16, allowing gas to flow into the downstream section 3b of the gas path and then to be discharged from the valve assembly 1.
As soon as the opening transient is terminated, the valve assembly 1 switches to the gas flow control mode, so that the gas flow is adjusted, depending upon the thermal power required to the burner, either by the regulating device 22 as a function of a pressure drop (ΔP) appropriately amplified by the unit 46 and/or by the control and limiting device 23 as a function of an electrical signal sent to the solenoid 41.
In a first control or modulation range - proximate to a preset maximum boiler thermal power - the gas flow fed to the boiler and thus the power delivered thereby is controlled by the device 22, which drives the main disk 17 in response to any variation of the air flow detected and appropriately amplified by the unit 46.
Thus, for each decrease in the air flow there is a corresponding decrease in the pressure drop (ΔP) detected by the unit 46: this implies a decreased pressure on the membrane 49 counteracted by the spring 51, with an upward movement of the membrane and a corresponding clockwise rotation (viewing the figure) of the arm 48.
Consequent upon this rotation, the stem 47 is lowered with a gradual displacement of the disk 45 away from the outlet of the duct 43.
In this manner, a fluid communication is established between the airspace 24 and the vent duct 44 with a downward movement of the main disk 17 towards its valve seat 16 and, hence, with a decrease of the gas flow leaving the valve assembly 1.
In other words, the gas flow through the main valve seat 16 and the gas path 3 is modulated by the disk 45 (modulating disk) in response to the air flow variations detected by the unit 46.
On the contrary, each increase in the air flow will induce a corresponding increase in the pressure drop (ΔP) detected by the unit 46: this implies an increased pressure on the membrane 49 against the action of the spring 51, with an ensuing downward movement of the membrane and a corresponding counterclockwise rotation of the arm 48 (viewing the figure).
Consequent upon this rotation, the stem 47 rises with gradual closing of the duct 43 by the disk 45.
In this way, a pressure build up occurs in the airspace 24 with a corresponding upward movement of the main disk 17 away from its valve seat 16 and, hence, with an increase in the gas flow leaving the valve assembly 1.
In connection to the gas flow control around the maximum value thereof, it is to be observed that this value may not exceed a threshold value, set during design and determined by the control and limiting device 23.
More particularly, by calibrating the spring 39 acting on the disk 36 it is possible to cause an "automatic" upward movement of the disk 36 whenever the gas pressure in the downstream section 3b exceeds the preset threshold value.
When this occurs, the gas pressure in the downstream section 3b is able to overcome the force exerted by the spring 39 and cause an upward movement of the disk 36, with a corresponding opening of the by-pass passageway 35.
There ensues an immediate gas outflow from the airspace 24 to the downstream section 3b of the gas path 3, with a progressive downward movement of the main disk 17 and a consequent decrease of the pressure (flow rate) of the gas leaving the valve assembly 1.
According to the present invention, the calibration of the spring 39 may be readily effected by adjusting the compression degree of the spring 56, acting on the moving core member 40, which possesses a force greater than that of the spring 39.
This adjustment is performed by locking in a predetermined position the fixed core member 55 in the hole 48 by means of the nut 57.
By appropriately calibrating the springs 50 and 51, may also be set in advance either the minimum pressure drop (ΔP) capable of displacing the membrane 49, or the maximum extent of the opening stroke of the disk 45 to which corresponds the maximum opening of the duct 43 (lower regulation limit of the device 22).
In the valve assembly 1 of the present invention, the gas flow regulation carried out by the device 22 takes place in a modulation range spanning from the maximum flow to approximately 1/3 of this value (maximum modulation ratio 3.5-3:1), i.e. up to the sensitivity limits of the membrane 49.
If the power required to the burner falls below this value, the valve assembly 1 carries out the desired gas flow regulation by means of the control and limiting device 23, directly driven by the boiler control unit.
In this second modulation range, the solenoid 41 of the control device 23 effects a progressive upward movement of the core member 40 and, along therewith, a progressive upward upward movement of the disk 36, proportional to the decrease in required power.
This causes a progressive opening of the by-pass passageway 35 accompanied by a progressive gas outflow from the airspace 24 towards the downstream section 3b of the gas path 3.
Again in this case there is a downward movement of the main disk 17 and, along therewith, a pressure (flow rate) reduction of the gas leaving the valve assembly 1.
In other words, the gas flow through the main valve seat 16 and the gas path 3 is modulated by the disk 36 (modulating disk) in response to an electrical signal sent to the solenoid 41 and proportional to the required thermal power.
According to the present invention, the gas flow regulation carried out by the control and limiting device 23 takes place in a modulation range spanning from approximately 1/3 of the maximum flow up to a minimum compatible with a steady burner operation.
Typically, this value is less than the minimum thermal power required to the gas boilers presently available on the market.
Thanks to this advantageous feature, the valve assembly of the present invention is capable of adjusting with continuity the gas flow (thermal power) and thus ensure modulation ratios higher than the maximum values required today (6-7:1).
According to another advantageous feature of the present invention, the minimum flow (thermal power) achievable may be controlled, depending upon the boiler characteristics, by merely positioning the stop rod 42 in the solenoid 41.
The above description clearly shows the numerous advantages achieved by the valve assembly of the present invention.
A first significant advantage is related to the possibility, on the one hand, to broaden the gas flow (thermal power) modulation range up to the maximum extent thereof and, on the other hand, to ensure a high efficiency of the burner substantially over the entire modulation range.
Thanks to the dual control system it is also possible to change the ratio of the air and gas flows in the pneumatic flow-modulation range, by driving through the solenoid 41 the disk 36 and, along therewith, the main disk 17 independently of and simultaneously with the device 22.
Finally, the valve assembly of the present invention allows to achieve the above mentioned relevant advantages at a cost quite comparable with that of the air-gas control units presently available on the market.

Claims

Gas boiler valve assembly of the type compupward movement:
- a valve body (2) in which is defined a gas path (3) extending between a gas inlet opening (4) and a gas outlet opening (5) to a burner;

- a first valve seat (16) formed in said body (2) in said gas path (3);

- a first disk (17) cooperating with said first valve seat (16) wherein it is adjustably positioned - against respective spring means (18) - by membrane means (21), driven by the air flow fed to the burner and operated by a limiting device (23) of the gas flow leaving said valve body (2), said limiting device (23) including: a gas passageway (35) for by-passing said first valve seat (16), a second valve seat (37) formed in said by-pass passageway (35) and a second disk (36) cooperating with said second valve seat (37);
characterized in that it further comprises, in said limiting device (23), means (40, 41) for adjustably positioning said second disk (36) in said second valve seat (37), said means (40, 41) being driven in response to the thermal power required to the burner to adjustably position said first disk (17) in said first valve seat (16) by means of said membrane means (21).
Valve assembly according to claim 1, characterized in that said second disk (36) is adjustably positionable in said second valve seat (37) by a core member (40) driven as a function of the thermal power required to the burner.
Valve assembly according to claim 2, characterized in that said core member (40) is slidably driven by a solenoid electromagnetic device (41).
Valve assembly according to claim 3, characterized in that said core member (40) is in sliding engagement within a central body of said solenoid electromagnetic device (41) against respective spring means (56) having an adjustable compression degree.
Valve assembly according to claim 3, characterized in that it further comprises stop means (42) for said core member (40) manually operable from the outside of said valve body (2).
Gas boiler characterized in that it comprises a valve assembly according to any one of claims 1 to 5.