GB1585695A - Gas-fired continuous-flow water heater - Google Patents

Description

(54) GAS-FIRED CONTINUOUS-FLOW WATER HEATER (71) We, ROBERT BOSCH GMBH., a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to gas-fired continuous-flow water heater having an hydraulic adjusting member which is subjected to a pressure difference derived from the flow of the circulating water and which influences a valve device controlling the supply of gas to the burner.

There is provided by the present invention a gas-fired continuous-flow water heater having an hydraulic adjusting member which is subjected to a pressure difference derived from the flow of the circulating water and which influences a valve, controlling the supply of gas to the burner, such that the supply of gas to the burner is interrupted below a predetermined first rate of flow of water, such that a minimum quantity of gas required for igniting the burner is released, through a throttle and a thermostatic valve, between the first and a predetermined second rate of flow of water, and such that, above the second rate of flow of water, the gas is released, by by-passing of the throttle, through the thermostatic valve, which controls the supply of gas to maintain, within the proportional range of deviation of the thermostat of the valve, the heated water at a nominal temperature between said second rate of flow and the maximum rated flow of water, the nominal temperature being that which can be mam- tained at the full rated heat output of the heater at the maximum rated flow of water; wherein the hydraulic adjusting member and the means for producing the pressure difference are constructed and matched to one another such that the minimum quantity of gas required for the igniting of the burner is released at a rate of flow of the water such that the quantity of gas heats the water to the nominal temperature.

Advantageously, said rate of flow of water which is maintained at the nominal temperature by said minimum quantity of gas is at its maximum equal to said second rate of flow.

In known apparatus of the above type (German Offenlegungsschrift 2,331,625), the hydraulic adjusting member acts upon two valves located one behind the other in the path of the gas, the thermostatically controlled valve being connected as a separate component downstream of the two valves. The hydraulic adjusting member has a displaceable plunger which passes through the closure member of the first valve which is surrounded by a throttled by-pass. The plunger is connected in a play-free manner to the closure member of the second valve which is connected downstream and which is the only valve to be opened from when the predetermined first rate flow of the water is attained until the predetermined second rate of flow has been attained, and which allows the quantity of gas, flowing through the by-pass, to flow to the burner by way of the thermostatic valve.

Upon attaining the predetermined second rate of flow of the water, a stop on the plunger of the adjusting member strikes against the closure member of the first valve and also lifts the latter valve from its valve seat, whereupon the full quantity of gas can flow through the two valves, and the thermostatic valve can assume its regulating function.

In these known water heaters, the hydraulic adjusting member and the means for producing the differential pressure are constructed and matched to one another such that, with the by-passing of the throttle, the path for the gas through the thermostatic valve is opened at the so-called "switching-on quantity" of water of approximately 3 litres per minute, as is customary in continuous flow water heaters without thermostatic regulation of the outflow temperature of the water.However, in a water heater having thermostatic regulation, and which is operated with a mixing head connected downstream, this may be disadvantageous, since the quantity of water required per unit of time from the water heater by the mixing head in the lower range of the desired value of the mixing head, also lies below the switching on quantity of water of the water heater, and thus water, whose temperature is non-regulated or too low, can flow to the mixing head, so that the mixing head might not be able to regulate in a satisfactory manner.

In contrast to this, the water heater in accordance with the invention has the advantage that the predetermined value of the outflow temperature of the water is maintained, even when the quantity of water is less than that required for switching on the apparatus, since the minimum quantity of gas required for the igniting of the burner also sufficiently heats the small quantity of water flowing through the heat exchanger. A quantity of water of approximately 1.4 litres per minute can be drawn from the apparatus in a temperatureregulated manner at a desired value of the outflow temperature of 60"C, the apparatus thus functioning like, and having the advantages of, a hot-water reservoir.

An embodiment of the invention is illustrated in the accompanying drawings in which: Figure 1 shows, diagrammatically, a water heater in accordance with the invention; Figure 2 is a cross section through the gas fitting and the thermostatic regulating device of the water heater of Figure 1, and Figure 3 is a graph showing the function c.f the water heater of Figure 1.

The water heater has a cold-water connection 11 which opens into the chamber 12 of an hydraulic adjusting member 13 acting as a flow monitor or a water deficiency safety device. A line 14 leads from the chamber 12 by way of a venturi 15, acting as a pressure-difference producer, to a heat exchanger 16 through which the line 14 passes in the form of a serpentine pipe.

A discharge line 17 leads from the heat exchanger 16 to a tap 18 from which hot water may be drawn from the apparatus.

A throttled line 19 leads from the narrowest flow-across section of the venturi 15 to a second chamber 20 of the adjusting member 13, the chamber 20 being separated from the first chamber 12 by means of a diaphragm 21. A plunger 22 is secured to the diaphragm 21 and extends upwardly out of the housing of the adjusting member 13 in a sealed manner and extends into a gas fitting 23 which is secured to the housing of the adjusting member 13.

The gas fitting 23 has a first chamber 26 (Figure 2) into which a gas feed line 27 (Figure 1) opens. The chamber 26 communicates with a second chamber 29 by way of a passage 28. The passage 28 is controlled by two valves 31 and 32 which are influenced by the hydraulic adjusting member 13 in the manner which will be further described hereinafter. The chamber 29 is connected, by way of a thermostatically operated valve 34, to an outlet connection piece 35 which is connected by way of a line 36 to a gas burner 37 which heats the heat exchanger 16.

The plunger 22 of the adjusting member 13 cooperates with a pin 40 on which the closure member of the valve 31 is displaceably mounted. The closure member of the valve 32 is mounted on the free end of the pin 40 and is subjected to the force of a closing spring 41. An annular collar 42 is provided on the pin 40 and comes into abutment against the closure member of the valve 31 after the adjusting member 13 has effected a specific part of its full stroke.

The valve 31 is surrounded by a throttled by-pass 44 whose flow-through cross section is adjustable by means of a screw 45. The thermostatic valve 34 has a closure member 48 which is loosely and displaceably mounted on a pin 49 secured relative to the housing, the closure member 48 being pressed by means of a spring 50 against the free end of a lever 52 whose other end is supported on an adjustable stop 53.

The sensor 55 of a thermostat 56 is secured to the discharge line 17, and the adjusting member 57 of the thermostat acts upon the lever 52 at 58. As the temperature in the line 17 increases, the lever 52 is pivoted in a clockwise direction and the flow-through cross section of the valve 34 is reduced, and vice versa. The valve 34 and the thermostat 56 together with the mechanical transmission members are combined to form a structural unit 60 which is screwed to the gas fitting 23.

When water is drawn off by opening the tap 18, a pressure difference is produced between the two chambers 12 and 20 of the adjusting member 13 by means of the venturi 15 and exerts a resultant force upon the diaphragm 21. However, this pressure difference can only build up slowly owing to the throttling of the line 19, so that the diaphragm 21 and the plunger 22 only move upwardly slowly. The valve 32 is thereby opened in the first instance so that only a limited quantity of gas can flow by way of the by-pass 44 and the thermostatic valve 34 to the burner where the gas is ignited by means not illustrated. The valve 31 is also opened after a further partial stroke of the diaphragm 21, whereupon gas flows in a non-throttled manner to the thermostatic valve 34 which controls the flow of gas to the burner 37 in accordance with the temperature of the water in the discharge line 17.When the tap 18 is closed, a valve (not illustrated), which counteracts the throttling of the line 19, produces rapid pressure equalization between the two chambers 12 and 20 of the adjusting member 13, thus resulting in the rapid closing of the two valves 31 and 32.

In the mode of operation described above, it is assumed that the tap 18 is opened rapidly and fully, so that the two switching steps of the valves 31, 32, namely the release of a limited supply of gas in the first instance and then the release of the full supply of gas, are effected solely in accordance with the delayed response of the adjusting member 13. In this case, the dependence of the adjusting stroke upon the rate of flow, or the quantity of water flowing through per unit of time, has no effect.

However, in order to comprehend the present invention it is necessary to consider the static state of the adjusting member 13 and of the two valves 31 and 32 at various rates of flow or specific flow-through quantities of the water after the adjusting member 13 has completed its stroke corresponding to the prevailing rate of flow.

These relationships will be seen from the function graph of Figure 3. The quantity of water drawn off is plotted in litres per minute on the abscissa of the graph, and the temperature of the outflowing water is plotted in degrees Celsius on the ordinate.

The thermostatic regulator is adjusted such that the discharge temperature of the water is 60"C. This temperature is maintained from a so-called switching-on quantity x of water, which will be further explained hereinafter, up to a quantity y of water within the deviation of the thermostat shown in the graph by the two dash-dot lines spaced apart by the distance p. Between the two quantities x and y of water, the dependence of the discharge temperature upon the quantity of water drawn off is represented as a straight line a which drops from x to y by the value p.When the quantities of water drawn off exceed y litres per minute, which represents the maximum rated flow of water the heater is designed for, the performance of the apparatus is no longer sufficient to heat the water to 60"C i.e. the maximum heat output the heater is rated for is no longer sufficient to maintain the water temperature. Thus, beyond y, the dependence curve of temperature and quantity drops more steeply in accordance with an exponential curve b.

The switching-on quantity x of water is the specific flow-through quantity at which the adjusting member 13 opens the two valves 31 and 32 and allows the gas to flow through these valves in a virtually unthrottled manner. In addition to the switching-on quantity x, the specific flowthrough quantity z is of importance below which the pressure difference produced at the venturi 15 is insufficient to overcome the force of the closing spring 41, i.e. to open the valve 32.The apparatus does not start when the flow-through quantity is less than z, so that the outflowing water and the inflowing water are at the same temperature which, in the present embodiment, is assumed to be 10 C. The following occurs when steady states with increasing specific flow-through quantities are set successively: The water is not heated when the flowthrough quantity is less than the flowthrough quantity z. The water is heated by the preliminary quantity of gas in the range between the flow-through quantities z and x. The two valves 31 and 32 are open when the flow-through quantity is in excess of the flow-through quantity x, and the thermostatic regulating valve 32 maintains the outflow temperature constant within the proportional thermostat deviation p.In accordance with the invention, the so-called first switching-on step lying between the flow-through quantities z and x is chosen such that the quantity of water flowing through in this range is also heated to a temperature of approximately 60"C by the preliminary quantity of gas. The temperature curve up to the switching-on quantity x of water then follows the line c which, owing to the early intervention of the thermostatic regulator in this range, and with this throttling of the quantity of gas to approximately 30% of the full quantity of gas, is kept within the proportional deviation p.

The graph shows that, by virtue of the fact that, in accordance with the invention, the adjusting member and the pressuredifference producer are matched to one another, a regulated outflow temperature results within the proportional deviation p from a flow-through quantity of approximately 1.4 litres per minute onwards.

For the purpose of comparison, the temperature characteristic in a known apparatus of the same performance is shown by a broken line. It will be seen that, in this apparatus, the temperature characteristic c' established in the first switching-on stage lies below the proportional deviation p, and that, in this apparatus, a relatively large temperature transient is effected upwardly into the proportional region when the switching-on quantity x' of water is attained. In an apparatus of this type, matching has to be effected very carefully by means of a mixing head connected downstream, if the mixing head is also to fulfil its regulating function in the lower range of temperature.In the apparatus constructed in accordance with the invention, matching with a mixing head connected downstream is substantially simpler, since, even with substantially smaller flow-though quantities of water, the apparatus operates with an outflow temperature regulated to the desired value.

WHAT WE CLAIM IS: 1. A gas-fired continuous-flow water heater having an hydraulic adjusting member which is subjected to a pressure difference derived from the flow of the circulating water and which influences a valve, controlling the supply of gas to the burner, such that the supply of gas to the burner is interrupted below a predetermined first rate of flow of water, such that a minimum quantity of gas required for igniting the burner is released, through a throttle and a thermostatic valve, between the first and a predetermined second rate of flow of water, and such that, above the second rate of flow of water, the gas is released, by by-passing of the throttle, through the thermostatic valve, which controls the supply of gas to maintain, within the proportional range of deviation of the thermostat of the valve, the heated water at a nominal temperature between said second rate of flow and the maximum rated flow of water, the nominal temperature being that which can be maintained at the full rated heat output of the heater at the maximum rated flow of water; wherein the hydraulic adjusting member and the means for producing the pressure difference are constructed and matched to one another such that the minimum quantity of gas required for the igniting of the burner is released at a rate of flow of the water such that that quantity of gas heats the water to the nominal temperature.

2. A water heater as claimed in claim 1, wherein said rate of flow of water which is maintained at the nominal temperature by said minimum quantity of gas, is at its maximum equal to said second rate of flow.

3. A gas-fired continuous-flow water heater substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. in accordance with the invention, matching with a mixing head connected downstream is substantially simpler, since, even with substantially smaller flow-though quantities of water, the apparatus operates with an outflow temperature regulated to the desired value. WHAT WE CLAIM IS:

1. A gas-fired continuous-flow water heater having an hydraulic adjusting member which is subjected to a pressure difference derived from the flow of the circulating water and which influences a valve, controlling the supply of gas to the burner, such that the supply of gas to the burner is interrupted below a predetermined first rate of flow of water, such that a minimum quantity of gas required for igniting the burner is released, through a throttle and a thermostatic valve, between the first and a predetermined second rate of flow of water, and such that, above the second rate of flow of water, the gas is released, by by-passing of the throttle, through the thermostatic valve, which controls the supply of gas to maintain, within the proportional range of deviation of the thermostat of the valve, the heated water at a nominal temperature between said second rate of flow and the maximum rated flow of water, the nominal temperature being that which can be maintained at the full rated heat output of the heater at the maximum rated flow of water; wherein the hydraulic adjusting member and the means for producing the pressure difference are constructed and matched to one another such that the minimum quantity of gas required for the igniting of the burner is released at a rate of flow of the water such that that quantity of gas heats the water to the nominal temperature.

2. A water heater as claimed in claim 1, wherein said rate of flow of water which is maintained at the nominal temperature by said minimum quantity of gas, is at its maximum equal to said second rate of flow.

3. A gas-fired continuous-flow water heater substantially as hereinbefore described with reference to the accompanying drawings.