[0001] The present invention relates to a valve unit for automatically regulating the flow-rate
of a fuel gas to a device for heating a fluid in dependence on variations in the flow-rate
of the fluid flowing through the heating device, in accordance with the preamble to
main Claim 1.
[0002] Within the specific technical field of the present invention, there is a need to
regulate the flow-rate of gas supplied to water-heating devices such as domestic water-heaters
or boilers in dependence in variations in the flow-rate of water flowing through the
heating device. The regulation of the flow-rate of fuel gas, which is performed in
a manner correlated with and proportional to the flow-rate of water flowing through
the heating device, advantageously enables a temperature of the water output from
the heater device to be kept substantially uniform and such as to ensure adequate
comfort for the user.
[0003] A first known system for automatically regulating the flow-rate of gas provides for
the use of an actuator with a diaphragm supplied with a pressure differential which
is brought about in the pipe through which the water flows and is correlated with
the flow-rate thereof. The diaphragm actuator supplied with this water-pressure differential
generates a displacement signal which is transferred directly to the closure member
of a valve located in the gas-supply duct so as to regulate the flow-rate of fuel
gas in a manner correlated with the flow-rate of water required by the user.
[0004] Amongst the disadvantages found in this regulation system is the fact that, because
the pressure differential brought about in the water pipe is correlated proportionally
with the square of the flow-rate of water, the law governing the variation of the
lifting of the closure member of the gas-supply duct is not linear and consequently
renders the regulation of the fuel-gas flow rather complex. Moreover, this law may
vary in dependence on the geometry of the closure member and is also variable in dependence
on the type of gas used. Compensation systems may be used to solve these problems
partially, but these systems are quite complex and expensive so that their use is
in any case not justified in apparatus such as gas water-heaters or boilers for domestic
use.
[0005] A second known system for automatically regulating the flow-rate of gas provides
for the diaphragm actuator, which is supplied with the water-pressure differential,
acting on the means for regulating the gas flow-rate by means of the control mediated
by a pressure regulator device. An example of such a system is known from the abstract
of the Japanese patent application published with No. 58024756. The pressure regulator
device disclosed therein comprises a servo-valve located in a gas-supply duct and
having a closure member with a diaphragm control, the diaphragm being subject to the
gas-delivery pressure on one side and to a reference pressure established in a pilot
chamber of the servo-valve on the other side, and a modulation valve, the diaphragm
of which is subject, on one side, to the gas delivery pressure and, on the other side,
to the resilient load exerted directly, by means of the diaphragm actuator, by the
pressure differential which is brought about in the fluid and is correlated with the
flow-rate thereof. Since the diaphragm actuator acts directly on the control rod of
the modulation valve, friction and consequent hysteresis phenomenons opposing the
movement of the lever are generated, particularly in the areas of the hydraulic seals
provided as separation of the gas from the water. Such hysteresis phenomenons have
influence on the law of proportionality between the water pressure differential and
gas delivery pressure, by reducing the accuracy in the control and gas regulation.
[0006] Electronically-controlled gas-flow regulation systems which detect the temperature
of the water flowing through the heater device and electronically regulate the flow-rate
of fuel gas supplied to the device are also known. However, these are more complex
and sophisticated than the above-mentioned known systems and involve quite expensive
applications which are unsuitable for inexpensive use in the above-mentioned apparatus.
[0007] The problem upon which the present invention is based is that of providing a valve
unit for automatically regulating the flow-rate of a fuel gas which is designed structurally
and functionally so as to prevent all of the problems complained of with reference
to the prior art mentioned.
[0008] This problem is solved by the invention by means of a valve unit formed in accordance
with the following claims.
[0009] 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 appended drawings, in which:
Figure 1 is a schematic view showing a valve unit according to the invention, in section,
Figure 2 is a view corresponding to that of Figure 1, showing a variant of the invention,
Figure 3 is a partially-sectioned view of a variant of a detail of the valve unit
of Figure 1,
Figure 4 is a functional diagram of apparatus equipped with the valve unit of the
present invention.
[0010] With reference to Figure 1, a valve unit, generally indicated 1, is for automatically
regulating the flow-rate of a fuel gas delivered to a water-heating device such as,
for example, a domestic water-heater or boiler, not shown in the drawings, in dependence
on variations in the flow-rate of water flowing through the heating device. The gas
is supplied to the valve unit by a supply duct 2 and is output by the valve unit through
a delivery duct 3 to a burner of the heating device, not shown in the drawing.
[0011] The ducts 2, 3 are separated by a servo-valve 4 comprising a first closure member
5 which is urged resiliently into closure on a first seat 6 by the resilient load
of a spring 7 and which can be opened by a first 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 Pt in a pilot chamber 9 on the other side. The pressure
Pt in the pilot chamber 9 is controlled by the control mediated by a diaphragm pressure-modulation
valve, indicated 10, constituting, with the servo-valve 4, a servo-assisted, diaphragm
pressure-regulator.
[0012] The pressure-modulation valve 10 comprises a control rod 12 screwed into a cup-shaped
element 13 which is kept in abutment with a stationary structure of the valve unit
by the resilient load of a first spring 14. A second spring 15 acts between the cup-shaped
element 13 and a plate 16 carrying a closure member 17 which can shut off a seat 18.
The plate 16 is fixed to a diaphragm 19 of the modulation valve which is subject to
the load exerted by the control rod 12 on one side and to the pressure existing in
a chamber 20 on the other side. The chamber 20 is in communication with the delivery
duct 3 through a transfer duct 21, and with a second chamber 22 through the valve
seat 18. The second chamber 22 is always in communication with the pilot chamber 9
through a second transfer duct 23, whereas it communicates selectively with a duct
24 for tapping off the gas supplied to the input of the valve unit and with a duct
25 communicating with the chamber 20 through an on-off valve 26. The valve 26 comprises
a closure member 27 which is urged into closure on a third seat 28 and is movable,
by the action of a control rod 29 of the closure member, so as to close onto a fourth
seat 30 in a manner such that, when the third seat 28 is closed, the fourth seat 30
remains open and vice versa. In the duct 24, there is a constriction 24a such as to
bring about a loss of pressure in order to derive the piloting pressure Pt from a
fraction of the gas flow tapped off, at the input of the valve unit, from the flow
supplied through the duct 2.
[0013] The control rod 12 of the modulation valve acts on the diaphragm 19 by means of a
first-order lever 31 pivotable, in an intermediate position of the lever, on a fulcrum
32 associated with a bracket 32a fixed to the stationary structure of the valve unit
1. The lever 31 acts directly on a shoulder 12a of the control rod 12 which is adjustable
by screwing. This adjustment enables the distance between the shoulder 12a and the
portion of the lever 31 which acts on the shoulder to be varied so as consequently
to adjust the pressure-modulation activation threshold of the valve 10.
[0014] On the opposite side of the fulcrum 32 to the control rod 12, the lever 31 is movable
by means of a rod 33 having opposite ends fixed to respective diaphragms 34, 35 of
a diaphragm actuator indicated 35a. The diaphragms 34, 35 are subject to the pressures
detected in adjacent portions of a water-supply pipe 36a, downstream and upstream
of a constriction 36 of the pipe 36a, respectively. The actuator 35a is thus supplied
with the pressure differential brought about in the pipe 36a and generates a load
which is transferred directly to the rod 33 by the diaphragms 34, 35, and which is
correlated with the pressure-differential value.
[0015] In a variant shown in Figure 3, the actuator 35a comprises a single diaphragm 35b
which is subject, on its opposite sides, to the pressures detected upstream and downstream
of the constriction 36, respectively. The single diaphragm 35b is fixed to one end
of a rod 33a to the opposite end of which the lever 31 is connected. The end portion
of the lever 31 facing towards the rod 33a is surrounded by a sealing element 33b.
The sealing element is fitted on the lever 31 and its opposite ends are connected
in a hydraulically leaktight manner to the lever and to the stationary portion of
the valve unit, respectively. The hydraulic seals provided are thus advantageously
static and such as to permit the pivoting movement of the lever about its fulcrum
without generating substantial friction opposing the movement of the lever.
[0016] With further reference to the valve unit of Figure 1, the lever 31 is moved relative
to the fulcrum 32 by the load exerted as a result of the pressure differential supplied
to the diaphragm actuator 35a. Since the flow-rate of water in the pipe 36a is correlated
proportionally with the pressure differential acting on the diaphragms 34, 35, as
explained further below, for each value of the water flow-rate, the position of the
control rod 12 of the modulation valve is controlled directly by means of the lever
31, in a correlated manner, by the water-pressure differential brought about in the
pipe 36a.
[0017] A minimum adjustment screw associated with the control rod 12 of the modulation valve
is indicated 37. The travel of the rod 12 is adjusted by means of the screw 37 so
as to ensure a minimum resilient load on the spring 15 and consequently a minimum
pressure value of the valve.
[0018] The lever 31 is extended, on the same side of the fulcrum 32 as the rod 33, by an
appendage 38 which is acted on resiliently by a respective spring 39 the resilient
load of which serves to keep the lever in abutment with a shoulder of the rod 33.
[0019] On the same side of the fulcrum 32 as the control rod 12, the lever 31 is further
extended by first and second adjacent portions 40, 41. The first portion 40 bears
against a shoulder of an adjustment screw 42 for regulating the maximum pressure value
permissible for the modulation valve.
[0020] The second portion 41 is constituted by a resilient plate fixed to one end of the
lever and in abutment at its opposite end with a catch projection of a control rod
43 of the closure member 27. The rod 43 in turn acts on a control element of a snap-action
switch indicated 44, the operating threshold of which is adjustable by the screwing
of a bush 45. The switch 44 is acted on by the resilient load of the plate 41 and,
for a predetermined value of this load, the rod 43 is moved, as a result of the snap
action of the switch 44, with a predetermined travel such as to snap the closure member
27 into closure on the seat 30.
[0021] In operation, as a result of a reduction in the required flow-rate of water, the
pivoting of the lever 31 is such as to reduce the resilient load exerted by the spring
15 on the diaphragm 19 and, conversely, to increase the resilient load exerted by
the plate 41 on the rod 43. When a predetermined threshold value of the flow-rate,
equal to the minimum permitted flow, is reached, the resilient load of the plate operates
the snap-action mechanism of the switch 44, the control element of which moves the
rod 43 with a travel the length of which is such as to switch the on-off valve 26
and to bring the closure member 27 into closure on the seat 28. The diaphragm 8 is
thus subject to the same pressure on both sides and the closure member 5 is operated
by the spring 7 so as to close the seat 6, shutting off the flow of gas through the
valve unit.
[0022] During lighting or extinguishing, the snap-action switch 44 also performs the function
of a control element for devices (not shown) which are normally provided in apparatus
equipped with the valve unit of the invention for lighting the burner and monitoring
the flame.
[0023] The switch 44 may additionally be arranged to bring about the closure of a solenoid
valve 45a disposed upstream of the valve unit, by means of the signal produced by
the snap action, so as to shut off the main gas flow supplied through the duct 2.
[0024] In Figure 1, the valve unit 1 is shown in an operative condition in which the closure
member 27 is closed onto the seat 30 so that the gas pressure tapped off through the
duct 24 acts in the pilot chamber 9 through the transfer duct 23 and the chamber 22,
as well as in the chamber 20 of the pressure-regulator 10. In this condition, the
closure member 5 is acted on so as to open the seat 6 partially, so as to ensure delivery
of the gas to the output of the valve unit 1.
An increase in the flow-rate of water required by the user causes a proportional increase
in the water-pressure differential to which the diaphragms 34, 35 are subject (from
a fluid-dynamics point of view, the flow-rate is proportional to the square root of
the pressure differential) which acts on the control rod 12 by means of the lever
31, producing a resilient load on the spring 15. This load presses the diaphragm 19,
which partially closes the closure member 17 in the corresponding seat 18. This partial
closure brings about an increase in the pressure Pt existing in the chamber 22 and,
through the transfer duct 23, in the pilot chamber 9. This increased pressure Pt acts
on the diaphragm 9, opening the closure member 5. The partial opening of the closure
member 5 as a result of a reduction in the pressure loss brings about an increase
in the delivery pressure Pu. This pressure Pu also acts, through the duct 21, on the
side of the membrane 19 facing the chamber 20 so as consequently to balance the resilient
load exerted by the spring 15. A pressure and a gas flow-rate correlated proportionally
with the pressure-differential and the flow-rate of water detected in the pipe 36a
is thus achieved for each value of the resilient load on the diaphragm 19.
[0025] Conversely, for a reduction in the flow-rate of water required by the user, the pressure
differential detected in the water pipe reduces proportionally and a corresponding
load is transmitted to the control rod 12 and, from the control rod 12 to the diaphragm
19, by means of the spring 15. In this case, the reduction in the resilient load of
the spring 15 causes partial opening of the seat 18 and a consequent reduction of
the pilot pressure Pt existing in the chambers 22 and 9. The closure member of the
servo-valve 4 therefore partially closes the seat 6 so as to bring about a reduction
in the delivery pressure Pu owing to the increase in the pressure loss. This delivery
pressure acts in the chamber 20 through the duct 21, balancing the resilient load
acting on the diaphragm 19, thus achieving a value of the gas pressure delivered as
well as a flow-rate value which are correlated proportionally with the water-pressure
and flow-rate differential detected in the pipe 36a.
[0026] The delivery pressure Pu of the gas thus varies in direct proportion to the water-pressure
differential detected in the supply pipe 36a. Upon the assumption that the gas-pressure
differential at the output of the valve unit is substantially equal to the delivery
pressure (since it is related to atmospheric pressure), the ratio between the water-pressure
differential and the gas delivery pressure consequently remains substantially constant
with variations in the required flow-rate of water. Since the flow-rates vary proportionally
with the pressure differential (substantially with the square root of the pressure
differential), the ratio between the gas flow-rate and the water flow-rate is kept
constant in operation. This constant ratio between the gas and water flow-rates consequently
ensures a substantially constant temperature differential between the water input
to and output from the heater device. Since the water-input temperature can be considered
approximately constant or at most variable in a limited manner and over long time
intervals (for example, seasonal temperature variations), the water-output temperature
remains substantially constant and such as to ensure adequate comfort for the user
in all operating conditions.
[0027] According to a further characteristic of the valve unit according to the invention,
a throttle element 48 is provided in the constriction 36 of the supply pipe, the various
positions of this throttle element enabling different pressure losses and consequently
different values of the pressure differential generated in the region of the constriction
36 to be brought about for a given flow-rate of water passing through the pipe 36a.
It is thus possible to vary the ratio between the pressure differential and the gas-delivery
pressure so as to vary the gas-delivery flow-rate selectively and consequently to
vary the temperature of the water output by the heating device for a given flow-rate
of water required by the user. The throttle element thus constitutes an element for
regulating the ratio between the water pressure differential and the gas delivery
pressure. Alternatively, the throttle element 48 may be disposed in the gas-supply
pipe, downstream of the valve unit 1, in order to perform the function of an element
for regulating the ratio between the pressure differentials and hence between the
water and gas flow-rates, as described above.
[0028] Figure 2 shows a variant of the valve unit of the invention, generally indicated
50, in which parts corresponding to those of the preceding embodiment are marked with
the same reference numerals. The valve unit 50 is suitable, in particular, for applications
in which a user such as an instantaneous water heater for domestic use is associated
with a gas central-heating boiler. Figure 4 is a functional diagram of a combined
installation of the aforesaid type. The installation provides for a first water circuit
with heating elements R such as room radiators, connected to a boiler C with an associated
burner B supplied by a fuel-gas delivery line G. A second circuit is also provided
for supplying washing water to a corresponding heating device such as a heat-exchanger
S. The water is supplied to the user by means of a line W for supplying water to the
heat exchanger S through which the fluid of the first circuit, diverted by means of
a three-way valve V, is made to flow.
[0029] With particular reference to Figure 2, the valve unit 50 differs from the unit of
the previous embodiment in that a second servo-valve 51 is provided, in addition to
the modulation valve 10. The servo-valve 51 has a diaphragm 52 fixed to a plate 53
carrying a closure element associated with a corresponding valve seat 54. The diaphragm
52 is subject, on one side, to a load exerted by a spring 55 and adjustable by screwing
of a spring-holder 56 and, on the other side, to the pressure existing in a chamber
60. The chamber 60 is in communication with the chamber 22 through the valve seat
54 and with the pilot chamber 9 through the transfer duct 23. The chamber 60 also
communicates selectively with the duct 21 through the valve seat 30, which is opened
by the on-off valve 26. In this variant of the invention, the valve 26 constitutes
a switching valve which can switch operation alternatively from the servo-valve 51
to the modulation valve 10, as elements for modulating the gas-delivery pressure.
[0030] In Figure 2, the valve unit is shown in an operative condition in which the delivery
pressure Pu, and consequently the gas flow-rate, is regulated by the servo-valve 51
and the modulation valve 10 is excluded from operation. In this condition, the chamber
60 is in communication with the duct 21 through the valve seat 30 and the pilot pressure
Pt is obtained from the balance between the pressure Pu acting on the diaphragm 52
and the resilient load acting thereon by means of the spring 55. Adjustment of the
travel of the spring holder 56 regulates the maximum permissible value of the delivery
pressure (and flow-rate), which is selected in dependence on the power of the heating
device of the installation. In this operative condition, water is flowing through
the heating elements R, whereas the flow to the heating device S of the washing-water
circuit is shut off by the closure of the three-way valve. As a result of a request
for washing water by the user and hence of a flow of water along the supply line W,
the water-pressure differential detected by the diaphragm actuator 35 brings about
switching of the valve 26 by means of the lever 31 in the manner provided for in the
valve unit 1, by means of the snap-action switch 44 and the resilient plate 41. As
a result of the switching, the delivery pressure Pu, and hence the gas flow-rate,
are regulated by the modulation valve 10 and the servo-valve 51 is excluded from operation.
The pressure Pu is regulated in the manner described above with reference to the valve
unit 1 and, for each value of the water flow-rate required, the gas-delivery pressure
varies in direct proportion to the water-pressure differential detected in the supply
pipe. In this second operative condition, the switching brought about by the valve
26 opens, by means of the switch 44, the three-way valve V by means of which the water
flow of the first circuit is diverted towards the heat-exchanger S for heating the
washing water.
[0031] The invention thus solves the problem set, achieving the advantages set out above
in comparison with known solutions.
1. A valve unit for automatically regulating the flow-rate of a fuel gas to a device
for heating a fluid in dependence on variations in the flow-rate of the fluid through
the heating device, comprising:
- means (36) for bringing about, in the fluid, a pressure differential correlated
with the flow-rate of fluid flowing through a pipe (36a),
- actuator means (35a) which are supplied with the pressure differential in order
to generate a signal correlated with the pressure differential, and
- means (4,10), controlled by the actuator means (35a), for regulating the flow-rate
of fuel-gas in order to vary the flow-rate of gas in a manner correlated with the
fluid-pressure differential, said means for regulating the gas flow-rate comprising
a pressure-regulator with a diaphragm (19), and said actuator means (35a) acting on
the regulating means by means of the control mediated by the pressure regulator, said
pressure regulator comprising:
- a servo-valve (4) located in a gas-supply duct (2) and having a closure member (5)
with diaphragm control (8), the diaphragm of the servo-valve being subject to the
gas-delivery pressure (Pu) on one side and to a reference pressure (Pt) established
in a pilot chamber (9) of the servo-valve on the other side, and
- a modulation valve (10), including the diaphragm (19) of the pressure regulator,
for controlling the reference pressure (Pt) in the pilot chamber (9), the diaphragm
(19) of the modulation valve (10) being subject, on one side, to the gas-delivery
pressure (Pu) and, on the other side, to the resilient load exerted directly, by means
of the actuator means (35a), by the pressure differential which is brought about in
the fluid and is correlated with the flow-rate thereof, characterized in that the
resilient load exerted on the diaphragm (19) of the modulation valve (10) is generated
by means of a first-order lever (31), the lever being acted on, on one side of its
fulcrum point (32) by the actuator means (35a) and, on the other side of its fulcrum
point by the spring (15) loading the modulation valve, so that the resilient load
is correlated proportionally with the pressure differential supplied to the actuator
means (35a).
2. A valve unit according to Claim 1, in which the actuator means comprise a diaphragm
actuator (35a), the diaphragm actuator acting on the diaphragm (19) of the modulation
valve (10) by means of a spring loading the diaphragm (19) of the modulation valve
(10) in order to transfer to the diaphragm of the modulation valve a load correlated
with the signal generated by the diaphragm actuator (35a) upon variations of the fluid-pressure
differential.
3. A valve unit according to Claim 1 or 2, in which the diaphragm actuator is of the
type with a single diaphragm (35b), the diaphragm being subject, on its opposite sides,
to the pressures which define the pressure differential and which are detected in
adjacent portions of the pipe (36b) through which the fluid flows.
4. A valve unit according to one or more of the preceding Claims, comprising a sealing
element (33b) fitted on the lever (31) and having opposite ends connected in a hydraulically
leaktight manner to a stationary portion of the valve unit and to the lever (31).
5. A valve unit according to Claim 4, in which the hydraulic seals are static seals.
6. A valve unit according to Claim 1 or 2, in which the diaphragm actuator (35a) comprises
a pair of facing diaphragms (34,35) which are subject, respectively, to one and to
the other of the pressures which define the pressure differential and which are detected
in adjacent portions of the pipe (36) through which the fluid flows, the diaphragms
(34,35) being connected to one another by means of a rod (33) connected to the lever
(31), the lever being pivoted about its fulcrum (32) as a result of the movement of
the rod which is acted on, by means of the pair of diaphragms, by the pressure differential
supplied to the actuator (35a), the lever (31) being housed at least partially within
a chamber which is disposed between the diaphragms (34,35) and which is closed in
a leaktight manner without contact between the lever and the fluid.
7. A valve unit according to one or more of the preceding claims, further comprising
an on-off valve (26) for shutting off the supply of gas to the pilot chamber (9),
the on-off valve (26) comprising a closure member (27) movable selectively so as to
close a first or, alternatively, a second valve seat (28,30), the closure member (27)
being moved between the valve seats by a control element of a snap-action switch (44)
acting on the control rod (43) of the closure member (27) of the on-off valve (26),
the snap-action control element being activated by the resilient load of a resilient
element (41) fixed to the lever (31).
8. A valve unit according to Claim 7, comprising a second servo-valve (51) with a diaphragm
(52), the on-off valve (26)constituting a switching valve for switching operation
alternatively from the second servo-valve (51) to the modulation valve (10) and consequently
modulating the gas-delivery pressure (Pu).
9. A valve unit according to one or more of the preceding claims, in which the means
for bringing about the pressure differential in the pipe through which the fluid flows
comprise a constriction (36) between adjacent portions of the pipe, the pressures
defining the differential being detected in the adjacent portions and transferred
to the actuator means (35a) in order to generate the signal correlated with the pressure
differential, throttle means (48) being provided between the adjacent portions for
selectively varying the cross-section for the flow of the fluid and consequently bringing
about different pressure-differential values for a given flow-rate.
10. A valve unit according to Claim 8, comprising a three-way diverter valve (V) interposed
between a first circuit and a second circuit for the fluid, for selectively diverting
the flow of the fluid from the first circuit to the second, the first circuit being
provided with room-heating elements (R), the second circuit being provided with a
heat-exchanger (S) for heating washing water, lighting and flame-monitoring members
being associated with a device for heating the fluid, the snap-action switch (44)
constituting a control element for the lighting and flame-monitoring members and/or
for the three-way valve (V) for selectively controlling the change from room-heating
operation to washing-water-heating operation.