GB1567643A

GB1567643A - Water heater

Info

Publication number: GB1567643A
Application number: GB40157/76A
Authority: GB
Original assignee: SMITH Ltd H
Current assignee: SMITH Ltd H
Priority date: 1977-10-10
Filing date: 1977-10-10
Publication date: 1980-05-21

Description

(71) We, HERMAN SMITH LIMITED, a British Company of Cinderbank Works, Netherton, Dudley, West Midlands, 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: This invention relates to a water heater for use in an aircraft to provide a supply of hot water inter alia for the preparation of beverages. Such water heaters are normally constructed as units which can readily be removed from the aircraft for maintenance purposes and which require connection only to an electrical power supply, a cold water supply and a drain to become fully operational.

In modern aircraft, the cold water supply is under pressure, for example of 25 psi above the ambient pressure within the aircraft. Some water heaters which are in use in aircraft at the present time are so arranged that, in use the pressure within the heater is at least as great as the cold water supply pressure. These known heaters have electrical heating elements controlled by temperature sensing devices intended to maintain the temperature of the water in the heater at a predetermined value which is near to the boiling point of the water under ambient pressure. If the temperature sensing device should become faulty during the service life of the heater, the water in the heater may be raised to a much higher temperature.There is thus a risk of water being drawn off from the heater at a pressure considerably above the ambient pressure and a temperature considerably above the boiling point under ambient pressure conditions.

These known water heaters also have a pressure relief valve intended to open at or above a predetermined pressure which is typically 125 psi. During the service life of a heater, its pressure relief valve may become contaminated with scale or affected in some other way which prevents its opening when subjected to the predetermined pressure differential. There is thus the possibility, if both the temperature sensing device and the pressure relief valve fail to operate properly, of there being established within the heater a pressure which is sufficiently high to burst the heater and there have been incidences of aircraft water heaters exploding in use.

According to the present invention there is provided a water heater suitable for installation in an aircraft and comprising a closed tank, a heating element in the tank, a water inlet to the thank, a main outlet through which hot water may be discharged from the tank in use, valve means for so controlling flow of water through the inlet and main outlet that, in use, water can flow into the tank through the inlet only when the main outlet is open for discharge of water from the tank, and a safety outlet which is permanently open to ambient pressure to permit fluid to escape from the tank whenever the pressure therein exceeds the ambient pressure by a predetermined amount, the safety outlet being so arranged that water does not escape from the tank through the safety outlet when the pressure in the tank is no greater than the ambient pressure.

Since the safety outlet of a water heater in accordance with the invention is permanently open, the pressure which can be established within the heater is limited to a value equal to the sum of the ambient pressure and said predetermined amount.

The safety outlet can be so arranged that the predetermined amount is small so that the risk of discharge of water through the main outlet under high pressure can be substantially avoided. It will be understood that the maximum temperature to which (54) WATER HEATER water can be heated is equal to the boiling point at the maximum pressure which can be established in the heater.

By a closed tank we mean a tank which is not open-topped and from which fluids can escape only among predetermined paths defined by pipes and the like.

The safety outlet may be in the form of an inverted U tube extending upwardly from the top of the tank a short distance.

The excess pressure in the tank required to cause fluid to be discharged through the safety outlet is then equal to the head of water between the water level within the tank and the top of the U tube.

The invention will now be described by way of example with reference to the accompanying drawings, wherein: FIGURE 1 shows a perspective view of the heater and FIGURE 2 is a diagram of an electrical circuit of the heater.

The heater comprises an outer casing 10 which is fabricated of sheet metal and is provided at its upper side with a handle 11.

From the rear of the casing there extends a flexible hose 12, one end of which is connected in use to a water supply tank or other source of cold water. There also projects from the rear of the casing an electrical connector through which electrical power can be supplied to an electrical circuit of the heater. The heater can readily be disconnected for removal from an aircraft in which it is installed for maintenance purposes, by disconnecting the hose 12 from the source of cold water and disconnecting an electrical power cable (not shown) from the electrical connector.

Within the case 10 there is mounted a closed tank 14, also fabricated of sheet metal. Below the tank and within the casing there is also a sump 15 from which an overflow pipe 16 extends through the rear of the casing 10. A safety outlet 17 connects the interior of the tank 14 with the interior of the sump 15. The safety outlet is in the form of a tube of inverted U-shape, with the base of the U extending above an upper wall of the tank. A shorter limb of the U-tube, extends downwardly into the tank and terminates a short distance below the upper wall thereof. A long limb of the U-tube extends downwardly through the tank into the sump. The safety outlet is permanently open and the sump 15 is open to the ambient atmosphere through the overflow 16.Accordingly, water can flow from the tank 14 through the safety outlet into the sump whenever the pressure within the tank 14 exceeds the ambient pressure by a value sufficient to raise water from the tank to the base of the U-shape of the safety outlet. The pressure within the tank 14 can never exceed the ambient pressure by more than a predetermined value which, typically, is a few ounces per square inch.

Within the casing 10 there are mounted two valves, namely a three-way valve 18 and a two-way valve 19. Rotary operating members of these valves are coupled together and coupled to an operating knob 20 situated outside a front wall of the casing 10. There also projects through the front wall of the casing an end portion of a delivery duct 21 through which water is discharged from the heater in use. The delivery duct is connected with a main outlet 22 in the upper wall of the tank 14 through a first orifice defined by the two-way valve 19. The delivery duct is also connected through the three-way valve 18 with a feed duct 23 inside the casing which in turn is connected to the hose 12. A water inlet to the tank 14 in the form of a pipe 24 extends from the three-way valve 18 to a position within the tank and near to the bottom thereof.This inlet connects with the feed duct through a second orifice defined by the valve 18.

The valves 18 and 19 are operated together by the knob 20. In a central position of the knob, both of the valves are closed so that water is prevented from entering the heater through the feed duct 23, prevented from leaving the heater through the delivery duct 21 and prevented from entering and leaving te tank through the inlet 24 and main outlet 22. If the knob 20 is rotated through 90" in one direction from the central position, the orifice of the valve 19 remains closed by a closure element but the valve 18 establishes the feed duct 23 in communication with the delivery duct 21 so that cold water is fed directly from the supply to the delivery duct. In this position of the knob 20, the second orifice (which is defined by the valve 18) also remains closed by a respective closure element. If the knob is rotated in the opposite direction through 90" from the central position, the valve 19 is opened to permit discharge of water from the tank 14 through the delivery duct 21 and the valve 18 establishes the feed duct 23 in communication through the second orifice with the inlet 24 so that cold water enters the bottom of the tank. It will be noted that as the main outlet 22 is in the upper wall of the tank, water can be discharged from the tank, through the main outlet only if the tank is maintained completely full of water and, during discharge from the tank, the discharged water is displaced by water entering through the inlet 24.

To permit the establishment within the tank 14 of a pressure sufficient to discharge water through the main outlet 22, this outlet, the valve 19 and the delivery duct 21 are all situated below the base of the U shaped safety outlet 17.

Within the tank 14 there are disposed three electrical heating elements El, E2 and E3. The elements E2 and E3 are situated near to the bottom of the tank and the element El is situated in the upper half of the tank. As shown in Figure 2, there is connected in series with each heating element a respective thermal limited TL3, TL4 and TL5, which opens the circuit to the heating element if the temperature of the thermal limiter rises to a predetermined value. The thermal limiters are situated within and near to the top of the tank 14.

The thermal limiters are arranged to prevent energisation of the heating elements under abnormal conditions which may give rise to risk of damage to the heater or danger to personnel. Typically, the thermal limiters open their respective circuits at a temperature of 149"C.

Within the tank 14 at a level above the heating element El but below the upper wall of the tank, there is disposed a thermostat TS2. This thermostat remains open, provided that it is submerged in the body of water in the tank. Should the heating element El be energised when the surface of the body of water in the tank is below the thermostat TS2, electrical contacts of the thermostat close after energisation of the heating element for approximately 45 seconds and cause relay R1 to de-energise all of the heating elements, A further thermostat TSl, in the tank 14 controls energisation of the heating elements in accordance with the temperature of the water in the tank.The thermostat TS1 can be adjusted in accordance with the ambient pressure conditions under which the heater is to be used to de-energise the heating ele ments when the water is at the boiling point.

Water can be drained from the tank 14 through a drain orifice normally closed by a plug 25 which is accessible at the front of the casing 10. To refill the tank 14, the control knob 20 is turned to the hot water delivery position until water begins to emerge through the delivery duct 21. The control knob is then returned to its central position and the heating elements can be energised.

The electrical circuit shown in Figure 4 also includes indicator lights L1 to L4 to indicate various conditions of the electrical circuit.

The pressure which can be established within the tank 14 is limited to a maximum value which is independent of the pressure under which water is supplied to the heater through the hose 12. This maximum pres sure is equal to the sum of the ambient pressure and the head of water between the water level in the tank (normally the uppermost part of the upper wall) and the base (junction between the limbs) of the safety outlet 17. Water can be supplied to the heater at a pressure of 25 psi without risk of hot water being discharged from the heater at this pressure.

The longer limb of the safety outlet 17 comprises a lower portion 26 of larger diameter and an upper portion 27 of smaller diameter which extends downwardly into the lower portion a short distance. At the upper end of the lower portion, there is an annular air inlet 29 which is exposed to the ambient pressure and prevents the safety outlet functioning as a siphon. Thus, a small quantity of water can escape from the tank through the safety outlet without the level of water in the tank necessarily falling to the level of the thermostat TS2 and deenergising the heating elements.

Alternatively, siphoning of water through the safety outlet may be prevented by the formation of a small vent, typically 0.075 inch diameter, in the longer limb of the safety outlet just below the level of the top of the tank 14. If such a vent is provided, the joint between the upper and lower parts of the longer limb is sealed.

The flow through the feed duct 23 is restricted, so that water cannot enter the tank 14 at a greater rate than it can be discharged therefrom. Since flow into the tank through the inlet 24 can take place only when water is being discharged through the main outlet 22, the pressure within the tank does not rise during normal operation and loss of water through the safety outlet does not normally occur.

WHAT WE CLAIM IS:- 1. A water heater suitable for installation in an aircraft and comprising a closed tank, a heating element in the tank, a water inlet to the tank, a main outlet through which hot water may be discharged from the tank in use, valve means for so controlling flow of water through the inlet and main outlet that, in use, water can flow into the tank through the inlet only when the main outlet is open for discharge of water from the tank, and a safety outlet which is permanently open to ambient pressure to permit fluid to escape from the tank whenever the pressure therein exceeds the ambient pressure by a predetermined amount, the safety outlet being so arranged that water does not escape from the tank through the safety outlet when the pressure in the tank is no greater than the ambient pressure.

2. A heater according to Claim 1 wherein the safety outlet is in the form of an inverted U tube extending upwardly from the top of the tank a short distance.

3. A heater according to Claim 1 or Claim 2 further incorporating a sump for

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. shaped safety outlet 17. Within the tank 14 there are disposed three electrical heating elements El, E2 and E3. The elements E2 and E3 are situated near to the bottom of the tank and the element El is situated in the upper half of the tank. As shown in Figure 2, there is connected in series with each heating element a respective thermal limited TL3, TL4 and TL5, which opens the circuit to the heating element if the temperature of the thermal limiter rises to a predetermined value. The thermal limiters are situated within and near to the top of the tank 14. The thermal limiters are arranged to prevent energisation of the heating elements under abnormal conditions which may give rise to risk of damage to the heater or danger to personnel. Typically, the thermal limiters open their respective circuits at a temperature of 149"C. Within the tank 14 at a level above the heating element El but below the upper wall of the tank, there is disposed a thermostat TS2. This thermostat remains open, provided that it is submerged in the body of water in the tank. Should the heating element El be energised when the surface of the body of water in the tank is below the thermostat TS2, electrical contacts of the thermostat close after energisation of the heating element for approximately 45 seconds and cause relay R1 to de-energise all of the heating elements, A further thermostat TSl, in the tank 14 controls energisation of the heating elements in accordance with the temperature of the water in the tank.The thermostat TS1 can be adjusted in accordance with the ambient pressure conditions under which the heater is to be used to de-energise the heating ele ments when the water is at the boiling point. Water can be drained from the tank 14 through a drain orifice normally closed by a plug 25 which is accessible at the front of the casing 10. To refill the tank 14, the control knob 20 is turned to the hot water delivery position until water begins to emerge through the delivery duct 21. The control knob is then returned to its central position and the heating elements can be energised. The electrical circuit shown in Figure 4 also includes indicator lights L1 to L4 to indicate various conditions of the electrical circuit. The pressure which can be established within the tank 14 is limited to a maximum value which is independent of the pressure under which water is supplied to the heater through the hose 12. This maximum pres sure is equal to the sum of the ambient pressure and the head of water between the water level in the tank (normally the uppermost part of the upper wall) and the base (junction between the limbs) of the safety outlet 17. Water can be supplied to the heater at a pressure of 25 psi without risk of hot water being discharged from the heater at this pressure. The longer limb of the safety outlet 17 comprises a lower portion 26 of larger diameter and an upper portion 27 of smaller diameter which extends downwardly into the lower portion a short distance. At the upper end of the lower portion, there is an annular air inlet 29 which is exposed to the ambient pressure and prevents the safety outlet functioning as a siphon. Thus, a small quantity of water can escape from the tank through the safety outlet without the level of water in the tank necessarily falling to the level of the thermostat TS2 and deenergising the heating elements. Alternatively, siphoning of water through the safety outlet may be prevented by the formation of a small vent, typically 0.075 inch diameter, in the longer limb of the safety outlet just below the level of the top of the tank 14. If such a vent is provided, the joint between the upper and lower parts of the longer limb is sealed. The flow through the feed duct 23 is restricted, so that water cannot enter the tank 14 at a greater rate than it can be discharged therefrom. Since flow into the tank through the inlet 24 can take place only when water is being discharged through the main outlet 22, the pressure within the tank does not rise during normal operation and loss of water through the safety outlet does not normally occur. WHAT WE CLAIM IS:-

1. A water heater suitable for installation in an aircraft and comprising a closed tank, a heating element in the tank, a water inlet to the tank, a main outlet through which hot water may be discharged from the tank in use, valve means for so controlling flow of water through the inlet and main outlet that, in use, water can flow into the tank through the inlet only when the main outlet is open for discharge of water from the tank, and a safety outlet which is permanently open to ambient pressure to permit fluid to escape from the tank whenever the pressure therein exceeds the ambient pressure by a predetermined amount, the safety outlet being so arranged that water does not escape from the tank through the safety outlet when the pressure in the tank is no greater than the ambient pressure.

3. A heater according to Claim 1 or Claim 2 further incorporating a sump for

receiving water which leaves the tank \nroueay oue,

4. A heater according to any preceding claim wherein the valve means defines a first orifice communicating with the main outlet and a second orifice communicating with the inlet, there being respective valve elements for closing the first and second orifices and said valve elements being movable together by means of a single operating member which is accessible to a user.

5. A heater according to Claim 4 comprising a delivery duct with which the main outlet communicates through said first valve orifice and a feed duct through which water is supplied to the heater, the valve means being adapted to establish the feed duct in communication selectively with one of the inlet duct and the delivery duct.

6. A heater according to any preceding claim including means responsive to energisation of the heating element when the tank is only partly filled with water the deenergise the heating element.

6. A heater according to any preceding claim wherein tile valve means: t cmD a unit which can be removed from the air craft for maintenance.

7. A heater substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.

8. A heater according to Claim 7 having an electric circuit substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.