JP6321348B2 - Hot water storage tank - Google Patents

Description

  The present invention relates to a hot water storage tank.

  Conventionally, in a hot water storage tank used for an electric water heater, a heater insertion hole is formed on the surface of a cylindrical hot water storage tank body, and a heater supported by a heater fixing plate is inserted into the hot water storage tank body from the heater insertion hole. Yes. Furthermore, a screw (heater mounting screw) is welded around the heater insertion hole of the hot water storage tank body, and a screw hole (heater mounting hole) is provided in the heater fixing plate that supports the heater. The heater is fixed to the hot water storage tank main body by inserting a heater mounting screw into the heater mounting hole and fastening a nut to the heater mounting screw.

  However, if the water pressure used in the electric water heater is high and excessive force is applied to the welded part of the heater mounting screw, the welded part of the heater mounting screw is caused by metal fatigue due to repeated boiling of water in the heater. May crack and leak from the hot water storage tank. In particular, hot water storage tanks used in electric water heaters tend to crack easily at the welded portion of the heater mounting screw because the base material of the hot water storage tank body is thin.

This will be described in more detail with reference to FIG. FIG. 7 is an enlarged cross-sectional view of a conventional hot water storage tank cut in a direction perpendicular to a heater fixing plate with a heater mounting screw.
When fixing the heater fixing plate 120 to the hot water storage tank body 110, the heater mounting screw 111 is inserted into the heater mounting hole 121, and the nut 130 is fastened to the heater mounting screw 111 via the washer 140 (FIG. 7 ( a)). At this time, if the nut 130 is further tightened, the welded portion of the heater mounting screw 111 is pulled in the axial direction of the heater mounting screw 111, and stress is applied to the welded portion of the heater mounting screw 111 (FIG. 7B). ). The welded portion that is stressed by tightening the nut 130 is also a portion that is stressed when the water pressure of the water used in the electric water heater is high, and is likely to crack due to metal fatigue. Therefore, in tightening the nut 130 to the heater mounting screw 111, strict torque management is required, and the work process when mounting the heater fixing plate 120 to the hot water tank main body 110 becomes complicated.

  In response to these problems, measures to reinforce the entire hot water storage tank by thickening the base material of the hot water storage tank body, and reducing the pressure receiving area of the heater fixing plate by reducing the heater insertion hole, Measures are taken to reduce the stress load on the welded part.

  In addition, a technique is known in which stress is concentrated to reinforce by forming a bead around a portion where a heater mounting screw of a hot water storage tank body is welded (see, for example, Patent Document 1). Furthermore, a technique is known in which a plurality of heater mounting screws are welded to an annular flat plate, and the flat plate is welded to the hot water storage tank body to reinforce the periphery of the heater mounting screw and then fix the heater fixing plate with a nut. (For example, see Patent Documents 1 and 2).

JP 2000-121168 A Japanese Patent Laid-Open No. 10-238865

  However, when the base material of the hot water storage tank body is made thick, the material cost of the entire hot water storage tank increases, making it difficult to increase the size of the hot water storage tank. Moreover, when the heater insertion hole is made small, it is necessary to make the pipe diameter of the heater small. In this case, in order to maintain the water heating capability, it is necessary to make the heater pipe long and bend a large number, so that the processing cost increases.

  In addition, when a bead is formed around the portion where the heater mounting screw of the hot water storage tank body is welded, the concave shape generated by forming the bead becomes the starting point of occurrence of cracks due to metal fatigue. There is. Furthermore, if the heater fixing plate is fixed to the hot water storage tank main body via an annular flat plate, the stress can surely be relieved, but if a flat plate that is a separate member from the hot water storage tank main body and the heater is used, the material cost will increase. Further, the manufacturing process becomes complicated.

  Thus, even when the base material of the hot water storage tank main body is thin, without requiring a complicated manufacturing process, the storage tank that can sufficiently suppress the occurrence of cracks in the welded portion of the heater mounting screw. The current situation is that it has not been obtained.

  The present invention has been made in view of the above problems, and even when the base material of the hot water storage tank main body is thin, the occurrence of cracks in the welded portion of the heater mounting screw is not required without requiring a complicated manufacturing process. It aims at providing the storage tank which can fully be suppressed.

The present invention has a hot water storage tank body (for example, a heater insertion hole (for example, a heater insertion hole 311 to be described later) formed), and one end side of a screw (for example, a screw 312 to be described later) is welded to the outer surface around the heater insertion hole. , A hot water storage tank body 31 described later, a heater (for example, a heater 32 described later) that is provided in the hot water storage tank body and heats the water in the hot water storage tank body, and a screw hole (for example, And a heater fixing plate (for example, a heater fixing plate 33 described later) that supports and fixes the heater, and a nut (for example, a screw hole 331) that is inserted into the screw hole. When the nut 35 described later is fastened, the heater insertion hole is closed by the heater fixing plate and the heater is fixed. The screw includes a flange portion (for example, a flange portion 313 described later) provided on the one end side and welded to the hot water storage tank body, and the flange portion is provided on the hot water storage tank body side of the heater fixing plate. The present invention relates to a hot water storage tank (for example, a hot water storage tank 30 described later) in contact with a surface (for example, the surface 317).
According to the present invention, since the flange formed on the screw is in contact with the surface of the heater fixing plate on the hot water storage tank body side, the stress when the nut is fastened to the screw is applied to the flange. The Thereby, it can prevent that the stress at the time of fastening a nut to a screw is directly applied to the location where the screw was welded to the hot water storage tank body. Therefore, even when the base material of the hot water storage tank main body is thin, it is possible to suppress the occurrence of cracks at the locations where the screws are welded to the hot water storage tank main body. Moreover, since it is only necessary to weld the screw provided with the flange to the outer surface of the hot water storage tank main body, it is possible to sufficiently suppress the occurrence of cracks in the welded portion of the heater mounting screw without requiring a complicated manufacturing process. it can.

Moreover, it is preferable that the said heater fixing plate has a level | step difference (for example, level | step difference 332 mentioned later) formed when the circumference | surroundings of the said screw hole bulge to the opposite side to the said hot water storage tank main body side.
According to this invention, the gap between the hot water storage tank body and the heater fixing plate is narrower on the peripheral side of the heater insertion hole than on the outer peripheral side of the heater fixing plate.
If there is no step formed on the heater fixing plate, both the outer peripheral side and the inner peripheral side of the region where the O-ring is arranged in the hot water storage tank body can be used to deeply form the groove used for positioning the O-ring. Needs to be deformed so as to be closer to the heater fixing plate. In this case, the manufacture of the hot water storage tank main body becomes complicated.
On the other hand, in the present invention, since the gap between the hot water storage tank main body and the heater fixing plate is narrow at the periphery of the heater insertion hole, the groove used for positioning the O-ring is formed deeply without going through complicated steps. Can do. Therefore, the manufacturing cost of the hot water storage tank body can be suppressed.

  According to the present invention, even when the base material of the hot water storage tank body is thin, the storage tank that can sufficiently suppress the occurrence of cracks in the welded portion of the heater mounting screw without requiring a complicated manufacturing process. Can be provided.

It is a permeation | transmission perspective view of the electric water heater which has the hot water storage tank which concerns on one Embodiment of this invention. It is a figure which shows the use condition of the electric water heater which has the hot water storage tank which concerns on the said embodiment. It is the perspective view of the hot water storage tank which concerns on the said embodiment, and is the figure which looked at the hot water storage tank of FIG. It is an expansion exploded perspective view of the hot water storage tank concerning the above-mentioned embodiment. It is an expanded sectional view of the hot water storage tank concerning the above-mentioned embodiment, and is a figure shown about the state where the nut was fastened to the screw in the hot water storage tank. It is an expanded sectional view of the hot water storage tank concerning the modification of the above-mentioned embodiment, and is a figure shown about the state where the nut was fastened to the screw in the hot water storage tank. It is an expanded sectional view of the conventional hot water storage tank, (a) is a figure showing the state where the nut was fastened to the heater mounting screw, (b) after tightening the nut further to the heater mounting screw It is a figure shown about the state fastened.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a transparent perspective view of an electric water heater 1 having a hot water storage tank 30 according to an embodiment of the present invention. As shown in FIG. 1, an electric water heater 1 is a small electric hot water composed of a water supply unit 2, a hot water storage unit 3, a hot water supply unit 4, an expanded water discharge unit 5, and a substantially rectangular parallelepiped casing 6. It is a vessel. In the electric water heater 1, water supplied by the water supply unit 2 is heated by the hot water storage unit 3 and stored as hot water, and the stored hot water is supplied by the hot water supply unit 4. Further, the expanded water generated during heating in the hot water storage unit 3 is discharged to the outside by the expanded water discharge unit 5.

The water supply unit 2 includes a pipe joint 21, a water supply pipe 22, a pressure reducing valve 23, a bypass pipe 24, and a water supply port 25.
The pipe joint 21 is provided on the upper surface of the casing 6, and the upstream end of the water supply pipe 22 is connected to the downstream side thereof. In addition, a direct pressure water supply pipe 71 connected to a water pipe is connected to the upstream side of the pipe joint 21 via a stop cock 72 described later.

  The water supply pipe 22 extends downward and is connected to the hot water tank main body 31 via a pressure reducing valve 23 described later. Thereby, water is supplied into the hot water storage tank 30.

  The pressure reducing valve 23 is a pressure regulating valve (regulator) provided in the middle of the water supply pipe 22. The pressure reducing valve 23 depressurizes high-pressure water introduced through the pipe joint 21. Thereby, the decompressed water is supplied into the hot water storage tank main body 31.

  The bypass pipe 24 is branched from the first branch portion 221 of the water supply pipe 22 on the downstream side of the pressure reducing valve 23. The bypass pipe 24 extends upward and is connected to a water supply port 25 described later.

  The water supply port 25 is provided on the upper surface of the casing 6, and the opening thereof faces substantially in the horizontal direction. A same-pressure water supply pipe 73 connected to a faucet fitting 7 described later is connected to the downstream side of the water supply port 25. Thereby, the water decompressed by the pressure reducing valve 23 is supplied from the water supply port 25 to the faucet fitting 7 through the same pressure water supply pipe 73.

The hot water storage unit 3 includes a hot water storage tank 30 and a drain valve 30a.
The hot water storage tank 30 includes a hot water storage tank main body 31 and a heater 32. In the hot water storage tank 30, the water supplied from the water supply pipe 22 to the inside of the hot water storage tank body 31 is warmed by the heater 32 and discharged to the hot water supply pipe 41.
The hot water storage tank 30 will be described in detail later.

  The drain valve 30 a is provided at a connection portion between the lower part of the hot water tank main body 31 and the water supply pipe 22. The drain valve 30a is opened by pushing a drain pin 213 provided in a pipe joint 21 described later for the purpose of maintenance and freezing prevention. Thereby, the water in the water supply pipe 22 is discharged outside.

The hot water supply unit 4 includes a hot water supply pipe 41, a hot and cold water mixing valve 42, and a hot water supply port 43.
The upstream side of the hot water supply pipe 41 is connected to the hot water storage tank body 31. Moreover, the downstream side is connected to the hot water supply port 43 mentioned later.

  The hot water mixing valve 42 is provided in the middle of the hot water supply pipe 41. A bypass pipe 24 branched from the water supply pipe 22 is connected to the hot water mixing valve 42. Thereby, the water supplied from the water supply pipe 22 and the hot water supplied from the hot water supply pipe 41 are mixed. An automatic temperature controller such as a thermostat (not shown) is provided inside the hot and cold mixing valve 42. With this automatic temperature controller, the mixing ratio of hot and cold water is controlled so that the hot water after mixing has a predetermined temperature suitable for use (for example, 38 ° C. to 42 ° C.).

  The hot water supply port 43 is provided on the upper surface of the casing 6, and the opening thereof faces substantially in the horizontal direction. The downstream side of the hot water supply port 43 is connected to the faucet fitting 7 via a hot water discharge pipe 74 described later. As a result, hot water mixed with hot water with the hot water mixing valve 42 and adjusted to an appropriate temperature is supplied to the faucet fitting 7.

The expansion water discharge unit 5 includes an expansion water discharge pipe 51, a relief valve 52, and an expansion water discharge port 53.
The expansion water discharge pipe 51 is provided to be branched from the second branch part 222 of the water supply pipe 22 on the downstream side of the first branch part 221. The expansion water discharge pipe 51 extends upward and is connected to an expansion water discharge port 53 described later.

  The relief valve 52 is provided in the middle of the expansion water discharge pipe 51. The relief valve 52 is a safety valve that opens when the internal pressure exceeds a predetermined pressure and closes when the internal pressure falls below the predetermined pressure. When the relief valve 52 is opened, the expanded water generated during heating by the heater 32 is introduced into the expanded water discharge pipe 51. The relief valve 52 includes a test pin 521 provided on the front surface of the casing 6, and can be opened and closed by operating the test pin 521 during maintenance.

  The expansion water discharge port 53 is provided on the upper surface of the casing 6, and its opening faces substantially in the horizontal direction. An expansion water discharge hose 75 connected to a drainage device 76 described later is connected to the downstream side of the expansion water discharge port 53. Thereby, the expanded water generated during heating by the heater 32 is discharged to the outside.

FIG. 2 is a diagram illustrating a usage state of the electric water heater 1 having the hot water storage tank 30 according to the present embodiment.
As shown in FIG. 2, the electric water heater 1 is disposed below a wash basin 70 provided with a faucet fitting 7. As described above, the electric water heater 1 is used while being fixed to a narrow space. The electric water heater 1 is driven by connecting a power cord 8 to a wall outlet 9 and turning on a power switch 61 provided on the front surface of the casing 6.

  As described above, the pipe joint 21 is connected to the direct pressure water supply pipe 71 connected to the water pipe through the water stop cock 72. The direct pressure water supply pipe 71 extends from the water stop cock 72 and bends toward the electric water heater 1 and then extends in a substantially horizontal direction. The high-pressure water supplied from the water pipe flows through the direct pressure water supply pipe 71.

  The same-pressure water supply pipe 73 connected to the faucet fitting 7 is connected to the water supply port 25. The same-pressure water supply pipe 73 extends from the water supply port 25 in a substantially horizontal direction (rightward in FIG. 2) and then extends obliquely upward. In the same pressure water supply pipe 73, the water depressurized by the pressure reducing valve 23 flows.

  A hot water outlet pipe 74 connected to the faucet fitting 7 is connected to the hot water supply port 43. The hot water outlet 74 extends from the hot water supply port 43 in a substantially horizontal direction (rightward in FIG. 2) and then extends obliquely upward. Hot water that has been adjusted to an appropriate temperature by mixing hot water and water by the hot water mixing valve 42 flows through the hot water supply pipe 74.

  An expansion water discharge hose 75 connected to a drainage device 76 to be described later is connected to the expansion water discharge port 53. The expansion water discharge hose 75 extends from the expansion water discharge port 53 in a substantially horizontal direction (right direction in FIG. 2), then extends obliquely upward, and again extends in a substantially horizontal direction (right direction in FIG. 2). The expanded water discharge hose 75 circulates expanded water generated during heating by the heater 32.

  The downstream side of the drainage device 76 is connected to a drainage pipe 77 provided at the lower part of the basin 70. Inside the drainage device 76, a trap-type sealing portion 76a is provided. The sealed water in the sealed water portion 76a prevents the odor in the sewage pipe connected to the downstream side of the drain pipe 77 from rising and entering the room.

  With the electric water heater 1 used as described above, water is supplied to the faucet fitting 7 from the same pressure water supply pipe 73 and hot water is supplied from the hot water supply pipe 74. The water and hot water supplied to the faucet fitting 7 are mixed and then discharged from the water outlet 7a.

Next, the hot water storage tank 30 according to this embodiment will be described.
FIG. 3 is a perspective view of the hot water storage tank 30 as viewed from the direction of arrow A in FIG. FIG. 4 is an enlarged exploded perspective view of the hot water storage tank 30. As described above, the hot water storage tank 30 includes the hot water storage tank main body 31, the heater 32, and the heater fixing plate 33.
The hot water storage tank body 31 is configured by a thin cylindrical tank having a substantially cylindrical shape extending in the vertical direction. The hot water storage tank body 31 has a hot water storage tank water supply port 315 on the lower side and a hot water storage tank hot water supply port 316 on the upper side. The hot water storage tank water supply port 315 is connected to the water supply pipe 22, and the hot water storage tank hot water supply port 316 is connected to the hot water supply pipe 41.

Furthermore, as shown in FIG. 4, a heater insertion hole 311 is formed in the hot water storage tank main body 31, and one end side of the screw 312 is welded to the outer surface around the heater insertion hole 311.
The heater insertion hole 311 is formed on the lower side in the vertical direction of the side periphery of the hot water storage tank body 31. The heater insertion hole 311 is a long hole that extends in the vertical direction and has a size that allows insertion of a heater 32 to be described later. A groove 314 is formed on the periphery of the heater insertion hole 311 in the hot water storage tank body 31. An O-ring 34 is disposed in the groove portion 314.

  Two screws 312 are arranged on the upper peripheral edge of the heater insertion hole 311, two on the lower peripheral edge of the heater insertion hole 311, and two on the central peripheral edge in the longitudinal direction of the heater insertion hole 311. . The screw 312 includes a flange 313 provided on one end side of the hot water storage tank main body 31 side. The shape of the collar part 313 is circular. The diameter of the flange portion 313 is larger than the diameter of the screw 312, and the flange portion 313 extends from the periphery of the screw 312. The flange 313 is welded to the hot water storage tank body 31. The screw 312 is configured as an integral member including the flange portion 313.

  The cylindrical hot water storage tank body 31 has a shape in which the periphery of the heater insertion hole 311 is flat. In particular, on the outer surface of the hot water storage tank body 31, the places where the two screws 312 on the upper side of the heater insertion hole 311 and the two screws on the lower side are arranged are flat.

  The inner wall of the hot water tank main body 31 is provided with a temperature controller and an overtemperature prevention device (not shown). These temperature regulators and overheat prevention devices raise the temperature of the water in the hot water storage tank main body 31 to an appropriate temperature and prevent overheating.

  The heater 32 is composed of a heater pipe and is provided in the hot water storage tank main body 31. The heater 32 has end portions 321 and 321 arranged outside the hot water storage tank body 31. The heater 32 is curved inside the hot water storage tank body 31. In particular, the heater 32 is bent and bent in a U shape at the intermediate portion 322 thereof. The heater 32 is connected to a power source (not shown) at the end portions 321 and 321. The heater 32 is heated by being energized, and heats the water in the hot water storage tank body 31.

  The heater fixing plate 33 has a rectangular plate shape. The heater fixing plate 33 is penetrated by the heater 32 at two places aligned in the longitudinal direction. The heater fixing plate 33 is integrated with the heater 32 by welding. The heater fixing plate 33 supports and fixes the heater 32. Further, the heater fixing plate 33 closes a heater insertion hole 311 described later.

  As shown in FIG. 4, a screw hole 331 through which the screw 312 is inserted is formed in the heater fixing plate 33. The screw holes are formed at a total of six locations around the four corners of the heater fixing plate 33 and the central portion of each long side of the heater fixing plate 33.

  The heater fixing plate 33 has a step 332 formed by the periphery of the screw hole 331 bulging to the side opposite to the hot water storage tank main body 31 side. The step 332 can be formed by pressure molding.

  By fastening the nut 35 to the screw 312 inserted through the screw hole 331, the heater insertion hole 311 is closed by the heater fixing plate 33 and the heater 32 is fixed. A washer 36 is disposed between the nut 35 and the heater fixing plate 33.

Next, the state where the nut 35 is fastened to the screw 312 of the hot water storage tank 30 according to the present embodiment will be described in more detail.
FIG. 5 is an enlarged cross-sectional view of the hot water storage tank 30 cut in a direction perpendicular to the heater fixing plate 33 with the screw 312, and is a view showing a state where the nut 35 is fastened to the screw 312 in the hot water storage tank 30. The flange portion 313 is in contact with the surface 317 of the heater fixing plate 33 on the hot water storage tank main body 31 side. Since the flange portion 313 is in contact with the surface 317 of the heater fixing plate 33, stress when the nut 35 is fastened to the screw 312 is applied to the flange portion 313. Thereby, the stress when the nut 35 is fastened to the screw 312 can be prevented from being directly applied to the location where the screw 312 is welded to the hot water storage tank body 31. As described above, since the screw 312 is configured as an integral member including the flange portion 313, the flange portion 313 is more resistant to stress than the welded portion.

By forming the step 332, the heater fixing plate 33 approaches the hot water storage tank body 31 side on the side in contact with the O-ring 34 (the side where the heater insertion hole 311 is formed) rather than the periphery of the screw hole 331. . The heater fixing plate 33 abuts the hot water tank main body 31 around the step 332.
The O-ring 34 is sandwiched and pressed between the hot water storage tank body 31 and a heater fixing plate 33 described later, thereby preventing water leakage from the hot water storage tank 30.

According to this embodiment, the following effects are produced.
(1) In the present embodiment, one end of the screw 312 provided with the flange 313 at one end and the flange 313 is welded to the outer surface around the heater insertion hole 311 of the hot water storage tank body 31. Further, the flange portion 313 was brought into contact with the surface 317 of the heater fixing plate 33 on the hot water storage tank body 31 side.
Since the flange portion 313 is in contact with the surface 317 of the heater fixing plate 33, stress when the nut 35 is fastened to the screw 312 is applied to the flange portion 313. Thereby, the stress when the nut 35 is fastened to the screw 312 can be prevented from being directly applied to the location where the screw 312 is welded to the hot water storage tank body 31. Therefore, even when the base material of the hot water storage tank main body 31 is thin, it is possible to suppress the occurrence of cracks at the locations where the screws 312 are welded to the hot water storage tank main body 31. Moreover, since it is only necessary to weld the screw 312 provided with the flange portion 313 to the outer surface of the hot water storage tank main body 31, it is possible to sufficiently suppress the occurrence of cracks in the welded portion of the screw 312 without requiring a complicated manufacturing process. be able to.

(2) In the present embodiment, a step 332 that bulges on the opposite side to the hot water storage tank body 31 side is formed around the screw hole 331 of the heater fixing plate 33.
Thereby, the clearance gap between the hot water storage tank main body 31 and the heater fixing plate 33 is a peripheral side (B side of FIG. 5) of the heater insertion hole 311 rather than the outer peripheral side (A side of FIG. 5) of the heater fixing plate 33. Narrow.
If the step 332 is not formed on the heater fixing plate 33, the outer peripheral side of the region where the O-ring 34 is disposed in the hot water storage tank body 31 can be used to deeply form the groove 314 used for positioning the O-ring 34. It is necessary to deform so that both (the A side in FIG. 5) and the inner peripheral side (the B side in FIG. 5) approach the heater fixing plate 33 side. In this case, the manufacture of the hot water storage tank body 31 becomes complicated.
On the other hand, in the present embodiment, since the gap between the hot water tank main body 31 and the heater fixing plate 33 is narrow at the periphery of the heater insertion hole 311, the groove portion 314 used for positioning the O-ring 34 is subjected to complicated steps. Without being deeply formed. Therefore, the manufacturing cost of the hot water storage tank body 31 can be suppressed.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
In the above embodiment, the step 332 is formed around the screw hole 331 of the heater fixing plate 33, but the present invention is not limited to this. For example, as shown in FIG. 6, the heater fixing plate 33A of the hot water storage tank 30A may be a flat plate-like member having no step. Even if the heater fixing plate 33A has no step around the screw hole 331A, the nut 35A is brought into contact with the surface 317A of the heater fixing plate 33A on the hot water storage tank body 31A side by contacting the flange 313A. The stress at the time of fastening to the screw 312A can be prevented from being directly applied to the location where the screw 312A is welded to the hot water storage tank body 31A.

DESCRIPTION OF SYMBOLS 1 ... Electric water heater 30 ... Hot water storage tank 31 ... Hot water storage tank main body 311 ... Heater insertion hole 312 ... Screw 313 ... Saddle 32 ... Heater 33 ... Heater fixing plate 331 ... Screw hole 332 ... Level difference

Claims (1)

A hot water storage tank body in which a heater insertion hole is formed and one end of a screw is welded to the outer surface around the heater insertion hole;
A heater provided in the hot water storage tank body, for heating water in the hot water storage tank body;
A screw hole through which the screw is inserted, and a heater fixing plate for supporting and fixing the heater,
A hot water storage tank in which the heater is fixed while the heater insertion hole is closed by the heater fixing plate by fastening a nut to the screw inserted into the screw hole,
The screw includes a flange portion provided on the one end side and welded to the hot water storage tank body,
The flange is in contact with the surface of the hot water storage tank body of the heater fixing plate,
The heater fixing plate, said periphery of the screw hole and the hot water storage tank main body by bulging to the opposite side, a step is formed in the side in contact with the peripheral and the O-ring of the screw hole, the step is substantially hot water tank the heater fixing plate a thickness of the flange portion you contact with the hot water storage tank body on the side in contact with the O-ring.

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