Gas manifold

Abstract

A gas manifold allows each distribution chamber to be fed with fuel gas at an appropriate flow rate irrespective of an increase in the number of distribution chambers included in the gas manifold. A gas manifold distributes fuel gas flowing in through an inlet to a plurality of distribution chambers through a main channel. The main channel includes a flow guide that guides the fuel gas toward a maximum distribution chamber and reduces the fuel gas flowing into other distribution chambers. This allows fuel gas at a sufficient flow rate to be fed more easily to the maximum distribution chamber than to the other distribution chambers for a larger number of distribution chambers included in the gas manifold, allowing the plurality of distribution chambers to be fed with fuel gas at appropriate flow rates.

Claims

1. A gas manifold installable in a combustion apparatus to distribute fuel gas to a plurality of burners for burning the fuel gas included in the combustion apparatus, the plurality of burners being grouped into a plurality of burner sets, the combustion apparatus performing stepwise switching of the number of burners to burn the fuel gas by causing each of the plurality of burner sets to burn the fuel gas, the gas manifold comprising: a main channel configured to allow passage of the fuel gas fed from outside; a plurality of distribution chambers each located for a corresponding burner set of the plurality of burner sets, the plurality of distribution chambers being configured to receive, from the main channel, the fuel gas to be fed to the plurality of burners in the plurality of burner sets; a plurality of nozzles each located for a corresponding burner of the plurality of burners, the plurality of nozzles being configured to feed the plurality of burners with the fuel gas flowing into the plurality of distribution chambers; a plurality of distribution channels branching from the main channel and connecting the main channel to the plurality of distribution chambers; and a plurality of on-off valves each located at a corresponding distribution channel of the plurality of distribution channels to open or close the corresponding distribution channel, wherein the plurality of distribution chambers include a maximum distribution chamber and distribution chambers other than the maximum distribution chamber, and the maximum distribution chamber includes more burners in the corresponding burner set than each of the other distribution chambers, the main channel includes a flow guide configured to guide the fuel gas toward a maximum distribution channel being a distribution channel included in the plurality of distribution channels connected to the maximum distribution chamber, and the flow guide comprises a projection structure that makes a narrow passage in the main channel, a sectional area of the narrow passage being constant and narrower than that of an upstream passage and a downstream passage thereof.

2. The gas manifold according to claim 1, wherein the main channel includes a part narrowed by the flow guide, and the narrowed part has a channel area larger than a total opening area of the distribution channels other than the maximum distribution channel at branches of the other distribution channels from the main channel.

3. The gas manifold according to claim 1, wherein a branch of the maximum distribution channel from the main channel is disposed at an outer side of branches of the other distribution channels from the main channel, and the fuel gas flows into the main channel through an inlet located between the branch of the maximum distribution channel from the main channel and a branch of a distribution channel next to the maximum distribution channel from the main channel.

4. The gas manifold according to claim 3, wherein the plurality of distribution chambers include a minimum distribution chamber and distribution chambers other than the minimum distribution chamber, and the minimum distribution chamber includes fewer burners in the corresponding burner set than each of the other distribution chambers, and the minimum distribution chamber is connected to a minimum distribution channel being a distribution channel included in the plurality of distribution channels, and the minimum distribution channel branches from the main channel at a most upstream position of a plurality of distribution channels branching from the main channel downstream from the flow guide.

5. The gas manifold according to claim 1, wherein the main channel is defined by a manifold cover placed over a channel groove on a manifold body, the plurality of distribution chambers are defined by the manifold cover placed over a plurality of recesses adjacent to the channel groove on the manifold body, the fuel gas flows into the main channel through an inlet that is open from the manifold body to the manifold cover, and the plurality of distribution channels are open in the channel groove nearer a bottom of the channel groove than the manifold cover.

6. The gas manifold according to claim 5, wherein the manifold cover and the manifold body hold a sealing member comprising a compressible material, and the sealing member is located between the manifold cover and the manifold body in a compressed state, the flow guide protrudes from the bottom of the channel groove toward an opening as a wall, and the flow guide protrudes by a height smaller than a depth of the channel groove and is in contact with the sealing member located between the manifold cover and the manifold body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram of a water heater 1 including a combustion apparatus 10.

(2) FIG. 2 is a view of a gas manifold 100 and a burner 12 according to an embodiment showing their structures.

(3) FIG. 3 is an exploded view of the gas manifold 100 according to the embodiment.

(4) FIG. 4 is a perspective view of a channel groove 111 showing the detailed shape of an opening 113c in its side wall.

(5) FIG. 5 is a view of the gas manifold 100 according to the embodiment showing fuel gas flows in the manifold.

(6) FIG. 6 is a diagram describing a comparison between the numbers of burners 12 fed with fuel gas from distribution chambers 102a to 102d in the gas manifold 100 according to the embodiment.

(7) FIG. 7 is a diagram describing a basic mechanism for allowing fuel gas at appropriate flow rates to be distributed to the distribution chambers 102a to 102d through the gas manifold 100 according to the embodiment.

(8) FIG. 8 is a front view of the gas manifold 100 according to the embodiment showing specific shapes of the channel groove 111 and recesses 112a to 112d on a manifold body 110.

DETAILED DESCRIPTION

(9) FIG. 1 is a diagram of a water heater 1 including a combustion apparatus 10. The water heater 1 includes the combustion apparatus 10 that burns fuel gas, and a heat exchanger 20 that uses hot combustion gas generated in the combustion apparatus 10 to produce hot water. The heat exchanger 20 is connected to a water supply channel 21 that receives service water, and a hot-water supply channel 22 that feeds the hot water produced in the heat exchanger 20. The water supply channel 21 has, on its course, a flow sensor 23 that detects the flow rate of service water flowing into the heat exchanger 20. In addition, the hot-water supply channel 22 has a hot-water supply faucet 24 connected to its end.

(10) The combustion apparatus 10 includes a combustion case 11 that defines a combustion chamber in its inner space, a plurality of burners 12 installed in the combustion case 11, a gas manifold 100 that feeds the burners 12 with fuel gas, a combustion fan 13 that feeds the combustion case 11 with combustion air for burning the fuel gas, a spark plug 14 that lights the burners 12, and a flame rod 15 that detects the flame of the burners 12. The gas manifold 100 is connected to a gas channel 16 that feeds the fuel gas, and the gas channel 16 includes, on its course, a main valve 17 that opens or closes the gas channel 16, and a proportional valve 18 that regulates the flow rate of the fuel gas downstream from the main valve 17.

(11) As shown in FIG. 1, the combustion apparatus 10 according to the present embodiment includes 19 burners 12. The burners 12 are grouped into four burner sets 12a to 12d each including a different number of burners 12. In the illustrated example, the burner set 12a includes eight adjacent burners 12, the burner set 12b includes two adjacent burners 12, the burner set 12c includes three adjacent burners 12, and the burner set 12d includes six adjacent burners 12.

(12) The gas manifold 100 includes a plurality of nozzles 101 that feed the burners 12 with fuel gas. Each nozzle 101 is associated with one burner 12 in advance and feeds the burner 12 with the fuel gas. The gas manifold 100 also includes four internal distribution chambers 102a to 102d. The four distribution chambers 102a to 102d correspond to the four burner sets 12a to 12d described above. An electromagnetic on-off valve 19a is installed upstream from the distribution chamber 102a, an electromagnetic on-off valve 19b upstream from the distribution chamber 102b, an electromagnetic on-off valve 19c upstream from the distribution chamber 102c, and an electromagnetic on-off valve 19d upstream from the distribution chamber 102d. The electromagnetic on-off valves 19a to 19d may be open or closed to feed the distribution chambers 102a to 102d individually with the fuel gas. The electromagnetic on-off valves 19a to 19d in the present embodiment correspond to on-off valves in the aspects of the present invention.

(13) As described above, each nozzle 101 feeds fuel gas to the specific burner 12 associated with it in advance, and the nozzles 101 that feed fuel gas to the burners 12. The nozzles 101 that feed fuel gas to the burners 12 in the burner set 12a receive the fuel gas from the distribution chamber 102a. Likewise, the nozzles 101 that feed fuel gas to the burners 12 in the burner set 12b receive the fuel gas from the distribution chamber 102b, the nozzles 101 that feed fuel gas to the burners 12 in the burner set 12c receive the fuel gas from the distribution chamber 102c, and the nozzles 101 that feed fuel gas to the burners 12 in the burner set 12d receive the fuel gas from the distribution chamber 102d. The electromagnetic on-off valves 19a to 19d may be open or closed to cause each of the burner sets 12a to 12d to individually start or stop feeding fuel gas to the burners 12. Each of the burner sets 12a to 12d may thus individually start or end the combustion of the fuel gas by the burners 12.

(14) In the above water heater 1, when a user of the water heater 1 opens the hot-water supply faucet 24 on the hot-water supply channel 22, the heat exchanger 20 is fed with service water through the water supply channel 21. When the flow sensor 23 detects the flow rate of the service water reaching at least a predetermined flow rate, burners 12 start combustion. In accordance with intended thermal power, the degree of opening of the proportional valve 18 is controlled, and the electromagnetic on-off valves 19a to 19d are open or closed. This allows multi-level switching of the number of burners 12 to burn the fuel gas. The hot combustion gas generated in the combustion passes through the heat exchanger 20 above the combustion apparatus 10. During the passage, the hot combustion gas exchanges heat with the service water passing through the heat exchanger 20 to generate hot water, which flows through the hot-water supply channel 22 and out of the hot-water supply faucet 24. The combustion gas with the temperature lowered by the heat exchange is discharged from the water heater 1 through an outlet 2 above the heat exchanger 20.

(15) FIG. 2 is a view of the gas manifold 100 and a burner 12 according to the present embodiment showing the positional relationship between them. As described above, the water heater 1 according to the present embodiment includes the 19 burners 12. To simplify the drawing, FIG. 2 shows one burner 12 without the 18 other burners 12.

(16) The burner 12 includes combined metal plates and has two gas inlets 12o (upper gas inlets 12o and lower gas inlets 12o) in its side surface to receive fuel gas. When injected into each gas inlet 12o, fuel gas flows into the burner 12 through the gas inlets 12o together with the surrounding air. The fuel gas and air mix in the burner 12 into mixed gas, and then the mixed gas flows out through a plurality of burner ports 12f formed in the top surface of the burner 12. The mixed gas is ignited with the spark plug 14 (refer to FIG. 1) to start combustion by the burner 12.

(17) In correspondence with the two gas inlets 12o (upper and lower gas inlets) in the burner 12 according to the present embodiment, the nozzles 101 in the gas manifold 100 according to the present embodiment are arranged in two lines (upper and lower lines). A pair of upper and lower nozzles 101 injects fuel gas into the upper and lower gas inlets 12o in the burner 12. As described above, the water heater 1 according to the present embodiment includes the 19 burners 12. Each burner 12 is associated with one pair of upper and lower nozzles 101, and thus the gas manifold 100 includes 38 (=19×2) nozzles 101 in total. As described above, the 19 burners 12 are grouped into the four burner sets 12a to 12d, and thus the 38 nozzles 101 for feeding fuel gas to the burners 12 can be grouped into a nozzle set 101a for feeding fuel gas to the burners 12 in the burner set 12a, a nozzle set 101b for feeding fuel gas to the burners 12 in the burner set 12b, a nozzle set 101c for feeding fuel gas to the burners 12 in the burner set 12c, and a nozzle set 101d for feeding fuel gas to the burners 12 in the burner set 12d.

(18) As shown in FIG. 2, the four electromagnetic on-off valves 19a to 19d are attached below the nozzles 101. Under the electromagnetic on-off valves 19a to 19d, an inlet 103 is located to receive fuel gas. When the electromagnetic on-off valve 19a is open with the inlet 103 receiving fuel gas, the fuel gas is fed through the gas manifold 100 and the nozzles 101 in the nozzle set 101a to the burners 12 in the burner set 12a. The internal structure of the gas manifold 100 will be described later. When the electromagnetic on-off valve 19b is open, the fuel gas is fed through the nozzles 101 in the nozzle set 101b to the burners 12 in the burner set 12b. Likewise, when the electromagnetic on-off valve 19c is open, the fuel gas is fed through the nozzles 101 in the nozzle set 101c to the burners 12 in the burner set 12c. When the electromagnetic on-off valve 19d is open, the fuel gas is fed through the nozzles 101 in the nozzle set 101d to the burners 12 in the burner set 12d.

(19) FIG. 3 is an exploded view of the gas manifold 100 according to the present embodiment. As shown in the figure, the gas manifold 100 includes a die-cast or cast manifold body 110, a sealing member 120 formed from a compressible material such as rubber, and a sheet-metal manifold cover 130 attached to the manifold body 110 with multiple mounting screws 140 with the sealing member 120 between the manifold body 110 and the manifold cover 130. The manifold cover 130, which is formed from sheet-metal in the present embodiment, may be die-cast or cast.

(20) As shown in the figure, the manifold body 110 has four recesses 112a to 112d located in line and a channel groove 111 immediately below the recesses 112a to 112d. When the manifold cover 130 is fitted to the manifold body 110 with the sealing member 120 between them, the recess 112a is covered with the manifold cover 130 to define the distribution chamber 102a (refer to FIG. 1). The recess 112b defines the distribution chamber 102b (refer to FIG. 1), the recess 112c defines the distribution chamber 102c (refer to FIG. 1), and the recess 112d defines the distribution chamber 102d (refer to FIG. 1). In FIG. 3, the numeral in parentheses (102a) below the recess 112a indicates that the recess 112a will form the distribution chamber 102a when the manifold cover 130 is attached to it. Likewise, in FIG. 3, the numeral (102b) below the recess 112b indicates that the recess 112b will form the distribution chamber 102b, the numeral (102c) below the recess 112c indicates that the recess 112c will form the distribution chamber 102c, and the numeral (102d) below the recess 112d indicates that the recess 112d will form the distribution chamber 102d. In addition, a main channel 104 is defined by the manifold cover 130 placed over the channel groove 111 on the manifold body 110. In FIG. 3, the numeral (104) below the channel groove 111 indicates that the channel groove 111 will form the main channel 104.

(21) The recess 112a also has, in its lower part (adjacent to the channel groove 111), a valve port 114a for the electromagnetic on-off valve 19a (refer to FIG. 2), and the valve port 114a connects to the valve chamber for the electromagnetic on-off valve 19a. Likewise, the recess 112b has, in its lower part, a valve port 114b for the electromagnetic on-off valve 19b (refer to FIG. 2), the recess 112c has, in its lower part, a valve port 114c for the electromagnetic on-off valve 19c (refer to FIG. 2), and the recess 112d has, in its lower part, a valve port 114d for the electromagnetic on-off valve 19d (refer to FIG. 2). The valve port 114b connects to the valve chamber for the electromagnetic on-off valve 19b, the valve port 114c connects to the valve chamber for the electromagnetic on-off valve 19c, and the valve port 114d connects to the valve chamber for the electromagnetic on-off valve 19d.

(22) In addition, the valve chambers for the electromagnetic on-off valves 19a to 19d each have an opening in the side corresponding to the side wall of the channel groove 111. An opening 113b in FIG. 3 in the side wall of the channel groove 111 connects to the valve chamber for the electromagnetic on-off valve 19b. An opening 113c in FIG. 3 in the side wall of the channel groove 111 connects to the valve chamber for the electromagnetic on-off valve 19c. An opening 113d in FIG. 3 in the side wall of the channel groove 111 connects to the valve chamber for the electromagnetic on-off valve 19d. An opening 113a in the side wall of the channel groove 111 also connects to the valve chamber for the electromagnetic on-off valve 19a although the opening 113a is not shown in FIG. 3.

(23) FIG. 4 is a perspective view of the channel groove 111 showing the detailed shape of the opening 113c in its side wall as viewed in the direction indicated by arrow P in FIG. 3. The opening 113a, the opening 113b, and the opening 113d have the same shape as the opening 113c and are not shown. In FIG. 4, the numerals in parentheses (113a, 113b, 113d) below the opening 113c indicate that the opening 113c represents these openings.

(24) As shown in FIG. 4, the channel groove 111 has a side wall 111a and a bottom 111b, and the opening 113c in the side wall 111a at a position adjacent to the bottom 111b. The opening 113c connects to a valve chamber 19cc for the electromagnetic on-off valve 19c (refer to FIG. 2). The valve chamber 19cc accommodates a valve element 19cv in the electromagnetic on-off valve 19c. The valve element 19cv is urged against the valve port 114c by a spring 19cs for the electromagnetic on-off valve 19c. In FIG. 4, the numerals in parentheses (114a, 114b, 114d) below the valve port 114c indicate that the valve port 114c represents the valve port 114a, the valve port 114b, and the valve port 114d. In FIG. 4, the numerals (19ac, 19bc, 19dc) below the valve chamber 19cc indicate that the valve chamber 19cc represents a valve chamber 19ac, a valve chamber 19bc, and a valve chamber 19dc, and the numerals (19av, 19bv, 19dv) below the valve element 19cv indicate that the valve element 19cv represents a valve element 19av, a valve element 19bv, and a valve element 19dv. In addition, the numerals (19as, 19bs, 19ds) below the spring 19cs indicate that the spring 19cs represents a spring 19as, a spring 19bs, and a spring 19ds.

(25) In this manner, the channel groove 111 connects to the recess 112a (refer to FIG. 3) through the opening 113a, the valve chamber 19ac, and the valve port 114a. Thus, the electromagnetic on-off valve 19a shown in FIG. 2 is open to define a channel connecting the channel groove 111 and the recess 112a. The channel from the channel groove 111 to the recess 112a corresponds to a distribution channel in the aspects of the present invention. Likewise, the electromagnetic on-off valve 19b is open to define a channel connecting the channel groove 111 and the recess 112b (refer to FIG. 3). The electromagnetic on-off valve 19c is open to define a channel connecting the channel groove 111 and the recess 112c (refer to FIG. 3). The electromagnetic on-off valve 19d is open to define a channel connecting the channel groove 111 and the recess 112d (refer to FIG. 3). The channel from the channel groove 111 to the recess 112b, the channel from the channel groove 111 to the recess 112c, and the channel from the channel groove 111 to the recess 112d also correspond to distribution channels in the aspects of the present invention.

(26) FIG. 5 is a view of the gas manifold 100 according to the present embodiment with the structure described above, showing fuel gas flows in the manifold. The fuel gas fed through the inlet 103 flows first into the main channel 104. As described above with reference to FIG. 3, the main channel 104 is defined between the channel groove 111 on the manifold body 110 and the manifold cover 130. The four distribution chambers 102a to 102d are located above the main channel 104. As described above with reference to FIG. 3, the four distribution chambers 102a to 102d are defined between the four recesses 112a to 112d on the manifold body 110 and the manifold cover 130. The distribution chamber 102a connects to the main channel 104 with the electromagnetic on-off valve 19a (refer to FIG. 2). The distribution chamber 102b connects to the main channel 104 with the electromagnetic on-off valve 19b (refer to FIG. 2). The distribution chamber 102c connects to the main channel 104 with the electromagnetic on-off valve 19c (refer to FIG. 2). The distribution chamber 102d connects to the main channel 104 with the electromagnetic on-off valve 19d (refer to FIG. 2). When the electromagnetic on-off valves 19a to 19d are open, the fuel gas in the main channel 104 flows into the distribution chambers 102a to 102d through the electromagnetic on-off valves 19a to 19d. Thick dash-dot arrows indicate fuel gas flows. After flowing into the distribution chambers 102a to 102d, the fuel gas is fed to the burners 12 through the nozzles 101 in the distribution chambers 102a to 102d.

(27) As described above with reference to FIG. 1 or 2, the distribution chamber 102a feeds the eight burners 12 with the fuel gas. The distribution chamber 102b feeds the two burners 12 with the fuel gas. The distribution chamber 102c feeds the three burners 12 with the fuel gas. The distribution chamber 102d feeds the six burners 12 with the fuel gas. Each burner 12 burns fuel gas at the same maximum flow rate, and the flow rates of fuel gas to be fed to the distribution chambers 102a to 102d rise as the number of burners 12 to burn the fuel gas increases. Thus, as shown in FIG. 6, a comparison between the distribution chamber 102a including the largest number of burners 12 and the distribution chamber 102b including the smallest number of burners 12 shows as large as a four-fold difference (=8/2) in the flow rates of fuel gas to be fed to these distribution chambers. The distribution chamber including the largest number of burners 12 (the distribution chamber 102a in this embodiment) will be referred to as “the maximum distribution chamber”. The distribution chamber 102 including the smallest number of burners 12 (the distribution chamber 102b in this embodiment) will be referred to as “the minimum distribution chamber”.

(28) As described above with reference to FIG. 4, the main channel 104 connects to the distribution chambers 102a to 102d through the openings 113a to 113d, the valve chambers 19ac to 19dc, and the valve ports 114a to 114d. Moreover, the valve chambers 19ac to 19dc accommodate the valve elements 19av to 19dy and the springs 19as to 19ds in the electromagnetic on-off valves 19a to 19d. Thus, increasing the size of the valve ports 114a to 114d or the electromagnetic on-off valves 19a to 19d may not prevent a certain channel resistance. With about a four-fold difference in the flow rate of fuel gas to be fed between the maximum distribution chamber (the distribution chamber 102a in this embodiment) and the minimum distribution chamber (the distribution chamber 102b in this embodiment), the channel resistance that cannot be reduced by the increase of the size may cause shortage of the fuel gas to be fed to the maximum distribution chamber. This can cause inappropriate flow rates of fuel gas to the distribution chambers 102a to 102d. To distribute fuel gas at appropriate flow rates to the distribution chambers 102a to 102d, the gas manifold 100 according to the present embodiment has the structure below.

(29) FIG. 7 is a diagram describing a basic mechanism for allowing fuel gas at appropriate flow rates to be distributed to the distribution chambers 102a to 102d through the gas manifold 100 according to the present embodiment. As described above, after flowing into the main channel 104 through the inlet 103, the fuel gas flows into the distribution chambers 102a to 102d from the main channel 104. FIG. 7 shows a distribution channel 105a representing the channel from the main channel 104 to the distribution chamber 102a described above with reference to FIG. 4 (or the passage from the opening 113a through the valve chamber 19ac to the valve port 114a). Likewise, a distribution channel 105b represents the channel from the main channel 104 to the distribution chamber 102b (the passage from the opening 113b through the valve chamber 19bc to the valve port 114b). A distribution channel 105c represents the channel from the main channel 104 to the distribution chamber 102c (the passage from the opening 113c through the valve chamber 19cc to the valve port 114c). A distribution channel 105d represents the channel from the main channel 104 to the distribution chamber 102d (the passage from the opening 113d through the valve chamber 19dc to the valve port 114d).

(30) The distribution channels 105a to 105d branch from the main channel 104 at different positions. The branch of the distribution channel 105a (hereinafter, the maximum distribution channel) to the maximum distribution chamber (the distribution chamber 102a in this embodiment) is nearer an end position than (upstream from) the branches of the distribution channels 105b to 105d to the three other distribution chambers (the distribution chambers 102b to 102d in this embodiment). An orifice plate 115 that narrows the main channel 104 is located between the branch of the maximum distribution channel (the distribution channel 105a in this embodiment) and the branches of the three other distribution channels 105b to 105d. The inlet 103, which allows fuel gas to flow into the main channel 104, is adjacent to the branch of the maximum distribution channel (the distribution channel 105a in this embodiment).

(31) In this structure, the fuel gas pressure in the main channel 104 is higher in an area upstream from the orifice plate 115 than in an area downstream from the orifice plate 115. In FIG. 7, the main channel 104 from the inlet 103 to the orifice plate 115 is hatched more densely to represent a fuel gas pressure higher than in the remaining part. The distribution channel 105a branches from the main channel 104 upstream from the orifice plate 115, allowing the distribution chamber 102a to be fed with sufficient fuel gas although the channel resistance may not be reduced in the distribution channel 105a.

(32) The orifice plate 115 narrows the main channel 104 into a narrow part 116 having a larger area than the total area of the branches of the distribution channels 105b to 105d from the main channel 104 other than the maximum distribution channel (the distribution channel 105a in this embodiment). The orifice plate 115 thus does not cause the distribution chambers 102b to 102d to be fed with insufficient fuel gas.

(33) The fuel gas to be fed to the three distribution chambers 102b to 102d other than the maximum distribution chamber passes through the main channel 104 downstream from the orifice plate 115, and correspondingly the fuel gas pressure decreases in the flow direction of the main channel 104 downstream from the orifice plate 115. Although a higher flow rate causes a larger reduction in the pressure, the flow rate of the fuel gas flowing downstream from the orifice plate 115 may not be too high because this fuel gas is the gas remaining after the distribution chamber 102a, or the maximum distribution chamber, is fed with fuel gas. Thus, the pressure in the main channel 104 downstream from the orifice plate 115 may not decrease greatly. In FIG. 7, a thick dash-dot arrow indicates a fuel gas flow in the main channel 104 downstream from the orifice plate 115. The main channel 104 downstream from the orifice plate 115 is hatched more sparsely in the flow direction to indicate a gradually decreasing fuel gas pressure. The main channel 104 downstream from the orifice plate 115 has a slight pressure gradient caused by a fuel gas flow. Thus, the fuel gas pressure is substantially the same at the positions at which the three distribution channels 105b to 105d branch from the main channel 104. This allows the distribution channels 105b to 105d to be fed with fuel gas at appropriate flow rates in accordance with the channel resistances of the distribution channels 105a to 105d.

(34) Additionally, in the gas manifold 100 according to the present embodiment, as shown in FIG. 7, the distribution channel 105b (hereinafter, the minimum distribution channel) to the minimum distribution chamber (the distribution chamber 102b in this embodiment) branches from a position immediately downstream from the orifice plate 115. This is to feed fuel gas at more appropriate flow rates to the distribution channels 105b to 105d based on the pressure gradient in the main channel 104 downstream from the orifice plate 115. This will be described below.

(35) As described above, the valve ports 114a to 114d and the electromagnetic on-off valves 19a to 19d defining the distribution channels 105a to 105d are sized depending on the flow rate of fuel gas to be fed through the distribution channels 105a to 105d. For the distribution channel 105b that is the minimum distribution channel, the valve port 114b is smaller than the other valve ports 114a, 114c, and 114d and the electromagnetic on-off valve 19b is also smaller than the other electromagnetic on-off valves 19a, 19c, and 19d. The valve chamber 19bc for the electromagnetic on-off valve 19b is also smaller than the valve chambers 19ac, 19cc, and 19dc for the other electromagnetic on-off valves 19a, 19c, and 19d. The small size of the valve chamber 19bc, which accommodates the valve element 19by and the spring 19bs of the electromagnetic on-off valve 19b, is likely to cause the minimum distribution channel (the distribution channel 105b in this embodiment) to have a channel resistance higher than a design resistance. Thus, the minimum distribution channel (the distribution channel 105b) branches from the position immediately downstream from the orifice plate 115, which has the highest pressure in the main channel 104 downstream from the orifice plate 115. This minimum distribution channel allows fuel gas at an appropriate flow rate to be fed with a channel resistance greater than the design resistance.

(36) FIG. 8 is a front view of the gas manifold 100 according to the present embodiment showing specific shapes of the channel groove 111 and the recesses 112a to 112d on the manifold body 110. As described above with reference to FIG. 3, when the sealing member 120 and the manifold cover 130 are fitted to the manifold body 110, the channel groove 111 defines the main channel 104, the recess 112a defines the distribution chamber 102a (the maximum distribution chamber in the present embodiment), the recess 112b defines the distribution chamber 102b (the minimum distribution chamber in the present embodiment), the recess 112c defines the distribution chamber 102c, and the recess 112d defines the distribution chamber 102d.

(37) As shown in FIG. 8, the recess 112a (to define the maximum distribution chamber), out of the four recesses 112a to 112d, is at the rightmost position in the figure. On the left of the recess 112a, the recess 112b (to define the minimum distribution chamber) is located, and on its left, the two other recesses 112c and 112d are located. The channel groove 111 extending in the horizontal direction is below and adjacent to the four recesses 112a to 112d in the figure. Thus, the channel groove 111 has, in its side wall, the opening 113a into the recess 112a, the opening 113b into the recess 112b, the opening 113c into the recess 112c, and the opening 113d into the recess 112d in this order from right to left in the figure.

(38) The four recesses 112a to 112d may be located in the reverse direction (or from left to right in the figure). In this case, the four openings 113a to 113d are also in the channel groove 111 in the reverse order. The recess 112a connecting to the opening 113a defines the distribution chamber 102a, or the maximum distribution chamber, and thus the opening 113a into the recess 112a will be referred to as “the largest opening”. Similarly, the recess 112b connecting to the opening 113b defines the distribution chamber 102b, or the minimum distribution chamber, and thus the opening 113b into the recess 112b will be referred to as “the smallest opening”.

(39) As shown in FIG. 8, the channel groove 111 on the manifold body 110 according to the present embodiment includes the openings 113a to 113d aligned horizontally, the inlet 103 between the opening 113a (the largest opening) and the opening 113b (the smallest opening) for receiving a fuel gas inflow, and a flow guide 117 that guides the fuel gas inflow toward the opening 113a (the largest opening). The flow guide 117 protrudes from the bottom 111b of the channel groove 111 as a wall. Although the height of the flow guide 117 from the bottom 111b is smaller than the depth of the channel groove 111, the upper end of the flow guide 117 comes in contact with the sealing member 120 when the manifold cover 130 is fitted to the manifold body 110 with the sealing member 120 between them. The protruding flow guide 117 narrows the channel groove 111 to define the narrow part 116.

(40) The gas manifold 100 according to the present embodiment includes the flow guide 117, which functions as the orifice plate 115 in FIG. 7. The mechanism described above with reference to FIG. 7 thus allows sufficient fuel gas to be fed to the recess 112a defining the maximum distribution chamber. The opening 113b (the smallest opening) first branches from the channel groove 111 at a position downstream from the flow guide 117. This allows sufficient fuel gas to be fed to the recess 112b defining the minimum distribution chamber. All the recesses 112a to 112d are thus fed with fuel gas at appropriate flow rates.

(41) As shown in FIG. 8, the inlet 103 for receiving a fuel gas inflow is located between the opening 113a (the largest opening) and the opening 113b (the smallest opening), and the flow guide 117 guides the fuel gas flow toward the opening 113a. As indicated by a thick dash-dot arrow in FIG. 8, the fuel gas flow is guided away from the opening 113b, and the fuel gas does not easily flow toward the openings 113b to 113d. As a result, with the narrow part 116 in the channel groove 111 having an area larger than the total area of the openings 113b to 113d, the fuel gas does not excessively flow into the openings 113b to 113d.

(42) Without the flow of fuel gas guided away from the opening 113b, the area of the narrow part 116 in the channel groove 111 may be reduced to prevent the fuel gas from excessively flowing into the openings 113b to 113d. The narrow part 116 with an area smaller than the total area of the openings 113b to 113d may disable the openings 113b to 113d from being fed with fuel gas at sufficient flow rates. However, in the gas manifold 100 according to the present embodiment, the narrow part 116 in the channel groove 111 may have an area larger than the total area of the openings 113b to 113d, thus allowing the recesses 112b to 112d to be fed with fuel gas at sufficient flow rates. The four recesses 112a to 112d are thus fed with fuel gas at appropriate flow rates.

(43) Further, the inlet 103 is located in the bottom 111b of the channel groove 111. Thus, after flowing in through the inlet 103, fuel gas flows toward the manifold cover 130 (from the depth toward the near side in FIG. 8). After flowing into the main channel 104, the fuel gas (at least the main flow of the fuel gas) flows along the manifold cover 130 (or away from the bottom 111b of the channel groove 111). However, as shown in FIG. 4, the openings 113a to 113d are located in the side wall 111a of the channel groove 111 adjacent to the bottom 111b. Thus, the fuel gas flowing along the manifold cover 130 does not directly flow into the openings 113a to 113d. This prevents the fuel gas from flowing intensively into some of the openings 113a to 113d. The four recesses 112a to 112d are thus fed with fuel gas at appropriate flow rates.

(44) Further, the openings 113b to 113d downstream from the flow guide 117 are located in parts of the side wall 111a of the channel groove 111 that protrude in an arc toward the middle of the channel groove 111. With one of the openings 113b to 113d located in a part of the side wall 111a of the channel groove 111 that recedes inward, the opening may not easily receive fuel gas. However, in the present embodiment, all the openings 113b to 113d are located in the arc-shaped parts of the side wall 111a of the channel groove 111, with no opening disabled from being fed with fuel gas. This allows any of the recesses 112a to 112d to be fed with fuel gas at an appropriate flow rate.

(45) The flow guide 117 located in the channel groove 111 has a height from the bottom 111b of the channel groove 111 smaller than the depth of the channel groove 111 by the compression allowance of the sealing member 120 (refer to FIG. 3). Thus, when the manifold cover 130 is fitted to the manifold body 110 with the sealing member 120 between them, the upper end of the flow guide 117 comes in contact with the sealing member 120, but applies no reaction force on the sealing member 120 or the manifold cover 130. The structure including the flow guide 117 can avoid a decrease in the contact stress between the sealing member and the main channel 104 and thus avoid leakage of the fuel gas flowing through the main channel 104.

(46) Although the gas manifold 100 according to the present embodiment has been described, the present invention is not limited to the above embodiment, but may be modified variously without departing from the spirit and scope of the present invention.

REFERENCE SIGNS LIST

(47) 1 water heater 2 outlet 10 combustion apparatus 11 combustion case 12 burner 12a to 12d burner set 12f burner port 12o gas inlet 13 combustion fan 14 spark plug 15 flame rod 16 gas channel 17 main valve 18 proportional valve 19a to 19d electromagnetic on-off valve 19ac to 19dc valve chamber 19as to 19ds spring 19av to 19dv valve element 20 heat exchanger 21 water supply channel 22 hot-water supply channel 23 flow sensor 24 hot-water supply faucet 100 gas manifold 101 nozzle 101a to 101d nozzle set 102a to 102d distribution chamber 103 inlet 104 main channel 105a to 105d distribution channel 110 manifold body 111 channel groove 111a side wall 111b bottom 112a to 112d recess 113a to 113d opening 114a to 114d valve port 115 orifice plate 116 narrow part 117 flow guide 120 sealing member 130 manifold cover 140 mounting screw