GB2136936A

GB2136936A - Gas-Fired Flow Heater

Info

Publication number: GB2136936A
Application number: GB08404559A
Authority: GB
Inventors: Karl-Ernst Vaillant; Harry Schulz; Hans Putz
Original assignee: Joh Vaillant GmbH and Co
Current assignee: Vaillant GmbH
Priority date: 1983-02-23
Filing date: 1984-02-21
Publication date: 1984-09-26
Also published as: IT1173351B; LU85225A1; AT384883B; FR2541434A1; CH666113A5; GB8404559D0; IT8419762A0; GB2136936B; FR2541434B1; NL8400561A; ATA52984A

Abstract

A gas-fired flow heater (1) comprises a heat exchanger (3) which is heated by a burner (2) and to which water is supplied through a water valve (7) having a housing in which a flow rate limiter (15) and a venturi nozzle (22) are arranged one behind the other in the direction of flow, wherein the space between the flow rate limiter (15) and the venturi nozzle (22) communicates with a diaphragm chamber (21) by which pressure is applied to one side of the diaphragm with the other side of the diaphragm communicating with the throat of the venturi nozzle, and wherein two by-pass lines (10, 26) for the venturi nozzle are provided with one of the by-pass lines beginning downstream of the flow rate limiter and being controlled by a valve which is adjustable in dependence on the position of the diaphragm and the other by-pass line beginning upstream of the flow rate limiter and ending downstream of the heat exchanger. In an alternative, the other by-pass line may end upstream of the heat exchanger with that line extending through the final control element of the flow rate limiter and ending downstream of the heat exchanger. <IMAGE>

Description

SPECIFICATION Gas-Fired Flow Heater This invention relates to a gas-fired flow heater comprising a heat exchanger which is heated by a burner and to which water is supplied through a water valve having a housing in which a flow rate limiter and a venturi nozzle are arranged one behind the other in the direction of flow, wherein the space between the flow rate limiter and the venturi nozzle communicates with a diaphragm chamber by which pressure is applied to one side of the diaphragm, while the other side of the diaphragm communicates with the throat of the venturi nozzle, and wherein two by-pass lines for the venturi nozzle are provided with one of these by-pass lines beginning downstream of the flow rate limiter and being controlled by a valve which is adjustable in dependence on the position of the diaphragm and the other by-pass line being provided with a throttle valve.

A gas-fired flow heater of this construction has been disclosed by our appliances of Type MAG W. It has been found, however, that a disadvantage of these appliances resides in that a second by-pass line for the venturi nozzles opens downstream of the venturi nozzle but upstream of the heat exchanger proper so that the entire water flows through the heat exchanger. This is undesirable because water cannot be conducted at an unlimited flow rate past the limiter and past the heat exchanger, so that the consumer cannot vary the temperature of the tapped water when the flow heater operates approximately at its rated power.

It is an aim of the present invention to permit such operation and with this in view the other bypass line begins upstream of the flow rate limiter and ends downstream of the heat exchanger.

As a result of this arrangement, the temperature of the tapped water can be varied even when the pressure at the connection to the water main is low.

Two examples of heaters in accordance with the invention are shown in the accompanying drawings, in which: Figure 1 is a diagrammatic view showing the water flow path in one form of gas-fired flow heater; Figure 2 is a graph; Figure 3 is another diagrammatic representation of the water flow path in a modified gas-fired flow heater; Figure 4 is an enlarged sectional view showing a water valve; and Figure 5 shows a detail of the water valve.

In all Figures, like reference characters designate like details.

The central part of the gas-fired flow heater 1 shown in Figure 1 consists of a heat exchanger 3, which is heated by a gas burner 2 and is connected on its downstream side to a discharge line 4, which is controlled by a tap valve 5. The cold water flows in the direction indicated by an arrow 6 from a cold water main to a valve 7, which comprises in a housing an inlet 8 and a junction 9. From the junction 9, a by-pass line 10 leads directly to the discharge line 4, to which the by-pass line is connected at a point that is downstream of the heat exchanger 3 and upstream of the tap valve 5. The by-pass line 10 incorporates an adjusting valve 11 and a throttel valve 13, which is controlled by a handle 12.A line 14 which is parallel to the by-pass line 10 extends from the junction 9 to a flow rate limiting valve 15, which is mounted in the housing and can be removed when a screw 1 6 has been removed.

The flow rate limiting valve 1 5 is succeeded by a diaphragm chamber 17, in which a diaphragm 19, provided with a diaphragm disc 18, is gripped along its rim in a pressure-tight manner so that a diaphragm-defined vacuum chamber 20 and a diaphragm-defined pressure chamber 21 are provided in the housing. The flow rate limiting valve 1 5 constitutes an inlet to the diaphragmdefined pressure chamber 21. An outlet from said chamber 21 is constituted by a venturi nozzle 22.

A line 24 opens at the throat 23 of the venturi nozzle 22 and leads to the diaphragm-defined vacuum chamber 20.

A connecting line 25 extends from the outlet of the venturi nozzle 22 and connects the valve 7 to the inlet of the heat exchanger 3. A second bypass line 26 branches from the diaphragmdefined pressure chamber 21 at a valve seat 27, which is still part of the diaphragm-defined pressure chamber 22 of the valve 7. The by-pass line 26 opens at 33 into the line 25 between the venturi nozzle and the heat exchanger. The valve seat 27 is controlled by a valve cone 28, which is connected by a rod 29 to the diaphragm disc 1 8.

Another rod 30 is connected to the diaphragm disc and extends to a valve member 31 of a gas valve, which is incorporated in a gas supply line 32 that is connected to the burner 2.

Figure 2 is a graph in which the water flow rate in dm3 min-1 is plotted against the pressure P in bars and the temperature rise At in C.

The mode of operation of the flow heater shown in Figure 1 will now be explained more fully with reference to Figure 2. It is assumed that the appliance is initially at rest, the adjusting valve 11 is in an opened intermediate position and the tap valve 12, the valve 27/28 and the gas valve 31 are closed. There is no flow of gas or water.

When the tap valve 5 is opened to initiate the operation of the gas-fired flow heater, water will flow immediately through the diaphragm-defined pressure chamber 21, the venturi nozzle, the lines 25 and 4 and the heat exchanger 3 at a rate which is limited by the flow rate limiting valve 1 5.

That flow of water acts through line 24 to establish a vacuum at the venturi nozzle and in the diaphragm-defined vacuum chamber 20 so that the diaphragm 1 9 is raised against the restoring force of a compression spring 76. As the diaphragm is raised, it causes the rod 30 to lift the valve member 31 from its valve seat so that the gas valve is opened.

As soon as the gas valve is opened, the valve 27/28 is opened too to permit a flow through the by-pass line 26. The by-pass line is gradually opened so that an increase of the water flow rate causes by means of the by-pass line a lower pressure to be established at the venturi nozzle.

As a result, the opening of the gas valve is proportional to the water flow rate but increases less strongly than the water flow rate. All water flowing through the venturi nozzle and the by-pass conduit 26 is heated in the heat exchanger 3 and is supplied through the discharge line 4 to the tap valve. For this purpose, water at a rate controlled by the throttle and adjusting valves 13, 11 can by-pass the heat exchanger and be made directly available to the person who is operating the tap valve.

The graph shown as Figure 2 contains a family of curves 40, 41, 42 and 43, which extend from the origin and by which certain flow rates are associated with certain maximum water supply pressures in the mains. Curve 40 will be obtained when the water pressure is 6 bars and the throttle valve 1 3 is more or less opened. The curve indicates the rate of water flowing through the by-pass line at a given maximum water pressure in the main. Curve 41 is obtained in case of a maximum water supply pressure of 4 bars and curve 43 at a maximum water supply pressure of 1 bar.

Curve 44 is the characteristic of the flow rate limiting valve 1 5. From a water pressure of O to 1 bar the curve rises steeply from the origin to a point 45 and then turns into an almost horizontal direction. This shows that a water supply pressure in excess of 1 bar will have no effect on the rate of water flow through lines 14 and 25 and through the heat exchanger.

Curve 46 is the result of the addition of curve 40 to the associated curve 44. The other curve 47 is the result of an addition of curves 42 and 44.

Curves 46 and 47 terminate at the largest temperature rise that can be effected by the appliance and in the present case amounts to 250C or at the maximum rate of water flow amounting to 10 dm3 min-1. It is apparent from curves 46 and 47 that the rate of water flow in the by-pass line 10 can be changed by an adjustment of the throttle valve 1 3 and that the temperature of the entire water which is tapped and the flow rate can thus be varied in dependence on the existing water supply pressure.

By means of the adjusting valve, the fitter of the appliance can adjust an average flow rate in dependence on the water supply pressure which exists at the place where the appliance is installed. That average flow rate will constitute the maximum rate of by-pass flow. The user of the appliance can actuate the throttle valve 13 to decrease that flow rate but cannot increase it.

If the flow area of the tap valve 5 is smaller than the constricted flow area of the flow rate limiting valve 15, the flow rate will vary in dependence on the position of the tap valve until the limiting valve becomes effective. In that case the flow rate will vary in accordance with curve 48 in Figure 2. The flow rate limiting valve becomes effective at point 45 of that curve and from that point the rate of water flow is constant or almost constant, as represented by curve 44, regardless of the position of the tap valve.

When the throttle valve 13 is then opened by means of the handle 12, the flow of water in line 10 will not be controlled by the flow rate limiting valve 1 5. That rate of water flow can be infinitely increased or decreased by means of the throttle valve 13. If the constructed flow area of the throttle valve is smaller than the flow area that has been adjusted at the adjusting valve 11, then the rate of by-pass flow will be controlled by the throttle valve 13. If the constructed flow area is larger, then the total rate of water flow will be controlled by the flow area of the adjusting valve 11. If the flow area of the throttle valve is smaller, the flow rate will correspond to curve 49 as far as to point 50, at which the flow rate limiting valve becomes effective so that the curve 49 is continued by curve 46 after a salient point.The curves 49, 46 are the result of the addition of the curves 48 and 44 to one of curves 40 to 42.

Curves 40 to 42 alone constitute only the rate of by-pass flow. The slope of each of curves 40 to 42 depends on the position of the smallest valve flow area in the by-pass path.

When the user of the appliance has found a control curve which best meets his desires, the adjusting valve 11 will be adjusted to that flow area with which the curve has been found by the adjustment of the handle 1 2 of the throttle valve 1 3. That flow area and the corresponding curve have now been fixedly adjusted in the appliance.

By changing the position of the throttle valve 1 3 the user of the appliance can decrease the rate of cold water by-pass flow. As such decrease of the rate of cold water by-pass flow is not accompanied by a change of the rate of flow through the heat exchanger, the total flow rate will be decreased and the temperature of the hot water which is discharged will be increased.

The same result can be achieved when the positions of valves 11 and 1 3 are not changed and the tap valve 5 is adjusted to a smaller flow area. If the rate of flow through the heat exchanger 3 is mainly controlled by the flow rate limiting valve 15, a throttling of the tap valve 5 will result only in a change (decrease) of the rate of by-pass flow. This produces the same result, namely, a temperature of the tapped water in conjunction with a slight decrease of the rate at which water is discharged. This solution affords the advantage that the user can change the temperature of the water which is discharged, in conjunction with a change of the rate of said water, simply by an adjustment of the tap valve.

Curve 47 in Figure 2 will be obtained if the water supply pressure amounts only to 2 bars because the rated water flow rate will be obtained in case of that supply pressure. The curved branch 47 is the result of an addition of curves 44 and 42.

The flow heater shown in Figure 3 serves to produce hot water for consumption and its central part consists of a heat exchanger 3, which is heated by a gas burner 2 and is connected on its downstream side to a discharge line 4, which is controlled by a tap valve 5. The cold water flows in the direction indicated by an arrow 6 from a cold water main to a water valve 7, which comprises in a housing an inlet 8 and a junction 9.

In an alternative indicated in dotted lines in Figure 3, a by-pass line 1 0 leads from the junction 9 directly to the discharge line 4, to which the bypass line is connected at a point that is downstream of the heat exchanger 3 and upstream of the tap valve 5. The by-pass line 10 incorporates an adjusting valve 11 and a throttle valve 13, which is controlled by a handle 12. A line 14 which is parallel to the by-pass line 10 extends from the junction 9 which is controlled by a constriction 60, which is defined by a throat formed in the housing 7 and by a valve member 61 of a flow control valve 62.On that side of the constriction 60 which is opposite to the junction 9 the line 14 extends through a diaphragm chamber 17, in which a diaphragm 19 provided with a diaphragm disc 1 8 is gripped in a pressuretight manner along its rim so that a diaphragmdefined vacuum chamber 20'and a diaphragmdefined pressure chamber 21 are provided in the housing. The constriction 60 of the flow control valve constitutes the inlet to the diaphragmdefined pressure chamber 21. An outlet from said chamber 21 is constituted by a venturi nozzle 22.

A connecting line 25 extends from the outlet of the venturi nozzle 22 and connects the water valve 7 to the inlet of the heat exchanger 3. A second by-pass line 26 branches from the diaphragm-defined pressure chamber 21 at an opening 63 and a central bore 64 in the valve member 61 downstream of the constriction 60 of the control valve 62 and by-passes the venturi nozzle and connects the pressure chamber to the line 25 at an opening 33, which is disposed downstream of the venturi nozzle and upstream of the heat exchanger.

The final control element 61 consists of a valve member and by means of the extension member containing the bore 63 and the central passage 64 is rigidly connected to the diaphragm disc 1 8.

On its underside, remote from the diaphragm disc 18, the final control element 61 constitutes a sleeve 65, which accommodates a compression spring 66, which bears on an abutment 67 that is secured to the housing.

The venturi nozzle 22 together with the diaphragm chamber 1 7 and the final control element 61 constitutes a water flow control valve, the reference value for which is determined by the degree to which the tap valve is opened and which ensures that the rate of water flow determined by the opening of the water tap valve 5 will be maintained constant.

In accordance with another alternative within the scope of the invention the second by-pass line 10 instead of its arrangement indicated by a dotted line in Figure 3 may open into the connecting line 25 upstream of the heat exchanger 3, as is indicated by a solid line, rather than into the discharge line 4 downstream of the heat exchanger 3.

The gas burner 2 is supplied via a gas supply line 32, which incorporates a gas valve 31, which has a valve member that is operable by means of a rod 30, which is secured to the diaphragm disc 1 8 on that side thereof which is remote from the final control element 61.

The design of the water valve is apparent from Figure 4, which shows the valve in operative position. It is apparent that the water valve is composed of an upper housing section 68 and a lower housing section 69, which are connected by means of pins and screws and between which the diaphragm 1 9 is gripped. The upper section 69 comprises a bushing 70, through which the rod 30 extends to form a gas- and water-tight joint. The diaphragm disc 18 is supported by means of a compression spring 76 on the under side of the upper section 69 so that that section and the diaphragm tend to move to the lower end position. The underside of the diaphragm is engaged by the head 72 of the final control element 61, which is biased by the return spring 66. The spring 66 has a smaller spring constant than the spring 71 so that the latter overrides the former.As a result, the gas valve 31 is closed when the flow heater is in position of rest but in that condition the final control element 61 exposes the constricted flow area 60 of the flow control valve. The abutment 67 consists of a screw, which is screwed in a bore 73 in the housing 68. The lines 8 and 26 are connected to the bore 73. The abutment screw is tubular and has a hollow internal cavity 74, which communicates through a radial bore 75 with the interior of the line 26, which consists of a bore.

The outside peripheral surface of the abutment screw is sealed by an O-ring against the inside surface of the bore 73. The inside surface of the bore 74 is sealed by O-rings against the outside peripheral surface of the final control element 61, which is mounted in the bore 74. As a result, there is a flow path from the inlet 8 through the constriction 60, controlled by the final control element 61, and through the bores 63 and 64 in the interior of the final control element 61 and the adjoining bore 74 and then through the radial bore 75 and the line 26 downstream of the venturi nozzle and to the connecting line 25. That flow path constitutes a by-pass shunting the throat 23 of the venturi nozzle 22 and its flow area is controlled by means of the final control element 61 defining the constriction 60 and by the sleeve 65, which is adapted to close the bore 75.When the flow heater is in position of rest, the sleeve 65 extends over and thus closes the bore 75 whereas the constricted flow area 60 is entirely opened. In the other end position the constricted flow area 60 is closed by the final control element 61 but the bore 75 is opened because the sleeve 65 has been raised above the cross-section of that bore.

Figure 4 shows the position for automatic control when the tap valve 5 is open. As is apparent from Figure 3 showing the flow heater in position of rest, the line 26 is closed in that position so that the operation of the appliance cannot be initiated unless the entire water flow passes through the opened constriction. In that case the opening of the tap valve 5 causes a superatmospheric pressure to be established in the pressure chamber 21. That superatmospheric pressure is vented in part through the venturi nozzle 22 and in part through the by-pass line 10.

The rate of the pressure drop will depend on the flow area of the throttle valve 13. When it is closed, the pressure will be vented only through the venturi nozzle so that a correspondingly high differential pressure will be developed between the two diaphragm chambers. As a result, the water valve will respond very quickly and the gas valve will open quickly because the diaphragm 1 9 will be suddenly deflected in an upward direction against the restoring force of the spring 71.

Owing to the restoring force of the spring 66 the final control element 61 follows the movement of the diaphragm so that the constriction 60 will be further constricted. But as the final control element 61 follows the movement of the diaphragm, the by-pass line 26 is opened so that water by-pass the venturi nozzle 22 and the differential pressure between the diaphragmdefined chambers is decreased. As a result, immediately after the beginning of the movement to open the gas valve the rate of gas flow varies in proportion to the rate of water flow through the appliance but the factor of proportionality can be further decreased.

Figure 5 shows the design of the abutment 67 and its radial bore 75. The abutment 67 is a cylindrical member, which has a plurality of steps and comprises a first sleeve section 77, which is hollow-cylindrical. That sleeve section surrounds with its inside peripheral surface the outside peripheral surface of the sleeve 65, which constitutes part of the valve mernber 61. An Oring is held on the outside peripheral surface of the sleeve section 77 and seals the outside peripheral surface of the abutment against the inside peripheral surface of the bore 73.The bore 75 is disposed between the end 79 of the sleeve section 77 and the first step 80, at which the abutment merges into a portion 81 in which its outside peripheral surface is larger in diameter and which has external screw threads 82, with which the abutment is screwed in internal screw threads of the bore 73. The portion 81 is succeeded by another step 83 and the end portion 84 of the abutment 64. The end portion 84 is largest in diameter and may be polygonal so that it can be screwed by means of an implement into the water valve 7.

It is apparent from the figure that the bore 75 is not round but approximately triangular. The triangle is so oriented that during a movement of the lower edge of the sleeve 65 the apex portion of the triangle is exposed first so that during a progressive (upward) movement of the sleeve 65 the extent to which the cross-section of the bore 75 is exposed is progressively increased.

The abutment 67 may be formed with a single triangular bore 75 or with a plurality of such bores. The apex angle of the triangle will be selected in dependence on the design of the water heater. The factor of proportionality of the change of the gas supply rate in response to a change of the rate of water flow will depend on the apex angle.

Whereas in the illustrative embodiment shown in Figure 4 the sleeve 65 constitutes an inner member and the abutment constitutes an outer member, these two members may be interchanged, i.e., the sleeve 65 may constitute the outer member and the abutment 67 constitute the inner member. The same result will be produced when the triangular bore 75 is formed in the sleeve and is covered to a larger or smaller extent by an edge of the abutment.

Claims

1. A gas-fired flow heater comprising a heat exchanger which is heated by a burner and to which water is supplied through a water valve having a housing in which a flow rate limiter and a venturi nozzle are arranged one behind the other in the direction of flow, wherein the space between the flow rate limiter and the venturi nozzle communicates with a diaphragm chamber by which pressure is applied to one side of the diaphragm with the other side of the diaphragm communicating with the throat of the venturi nozzle, and wherein two by-pass lines for the venturi nozzle are provided with one of the bypass lines beginning downstream of the flow rate limiter and being controlled by a valve which is adjustable in dependence on the position of the diaphragm and the other by-pass line being provided with a throttle valve, in which the other by-pass line begins upstream of the flow rate limiter and ends downstream of the heat exchanger.

2. A gas-fired flow heater according to claim 1, in which the by-pass line incorporates an additional adjusting valve.

3. A gas-fired flow heater comprising a heat exchanger which is heated by a burner and to which water is supplied through a water valve having a housing in which a flow rate limiter and a venturi nozzle are arranged one behind the other in the direction of flow wherein the space between the flow rate limiter and the venturi nozzle communicates with a diaphragm chamber by which pressure is applied to one side of the diaphragm with the other side of the diaphragm communicating with the throat of the venturi nozzle, and wherein two by-pass lines for the venturi nozzle are provided with one of the bypass lines beginning downstream of the flow rate limiter and being controlled by a valve which is adjustable in dependence on the position of the diaphragm and the other by-pass line being provided with a throttle valve, in which the flow rate limiter comprises a flow rate stabilizer, and the other by-pass line begins downstream of the adjustable opening of the stabilizer and extends through the final control member of the stabilizer and ends upstream of the heat exchanger.

4. A gas-fired flow heater comprising a heat exchanger which is heated by a burner and to which water is supplied through a water valve having a housing in which a flow rate limiter and a venturi nozzle are arranged one behind the other in the direction of flow, wherein the space between the flow rate limiter and the venturi nozzle communicates with a diaphragm chamber by which pressure is applied to one side of the diaphragm with the other side of the diaphragm communicating with the throat of the venturi nozzle, and wherein two by-pass lines for the venturi nozzle are provided with one of the bypass lines beginning downstream of the flow rate limiter and being controlled by a valve which is adjustable in dependence on the position of the diaphragm and the other by-pass line being provided with a throttle valve, in which the flow rate limiter comprises a flow rate stabilizer, and the other by-pass line begins downstream of the adjustable opening of the flow rate stabilizer and extends through the final control member of the stabilizer and ends downstream of the heat exchanger.

5. A gas-fired flow heater according to claim 3 or claim 4, in which the final control element of the flow rate stabilizer is sleeve-shaped with one end engaging the diaphragm and the other end mounted in a bearing bore of the water valve and subjected to the restoring force of a spring.

6. A gas-fired flow heater according to any one of claims 3 to 5, in which the bearing bore for the final control element is part of a mounting screw which is screwed in a bore of the water valve, the final control element being mounted in the bore of the screw and the interior of the bore communicating through at least one radial bore with a passage which constitutes the by-pass line.

7. A gas-fired flow heater according to claim 6, in which the radial bore is triangular in crosssection and the triangle is so oriented that, when the bore is initially closed when the flow heater is in a position of rest, an apex of the triangle is exposed first and a triangular cross-section having a progressively increasing base area is subsequently exposed.

8. A gas-fired flow heater substantially as described herein with reference to Figures 1 and 2 or Figures 3 to 5 of the accompanying drawings.