EP0164816B1

EP0164816B1 - Electrically operated water heating device

Info

Publication number: EP0164816B1
Application number: EP19850301074
Authority: EP
Inventors: John David Holland
Original assignee: STEAMY PRODUCTS (PRIVATE) Ltd
Current assignee: STEAMY PRODUCTS (PRIVATE) Ltd
Priority date: 1984-02-20
Filing date: 1985-02-19
Publication date: 1990-10-24
Anticipated expiration: 2005-02-19
Also published as: NZ211161A; AP8500007A0; ES540515A0; AU580578B2; ATE57758T1; ES8603057A1; EP0164816A3; ZW2984A1; AP41A; PT79976A; ZA851153B; PT79976B; EP0164816A2; AU3871985A; DE3580191D1

Description

This invention relates to an electrically operated water heating device of the kind adapted to give substantially instantaneous hot water without the need for pre-heating and storage. More specifically the invention relates to an electrically operated water heating device comprising a housing having a water inlet and a water outlet, a water heating chamber containing an electrical heating element arranged between the inlet and outlet such that water passing between the inlet and outlet must pass through the chamber in contact with the element and pressure responsive means displaceable in response to water pressure in the chamber to cause contact between fixed and movable electrical contacts to complete an electrical circuit supplying current to the element such that the element is energised to heat water in the chamber only when there is a predetermined water pressure in the chamber.
A device of the above kind is known from AU―B―489438. One of the most serious problems associated with water heating devices in which water passes in contact with an electrically energised heating element is the danger of current leakageto the water. In the event of failure of the earthing system such current leakage is potentially lethal, especially in the confines of a shower cubicle.
The present invention alleviates this problem in that the outlet comprises a nozzle which will limit the volume of water passing through the device and atomise water leaving the outlet, i.e. convert it into an aerosol spray.
A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which Figure 1 is a side elevation and Figure 2 is a side sectional elevation of a device in accordance with the invention.
The device indicated generally at 10 is a water heater with combined shower head. The tubular housing 52 of the device is closed at its top end by a cap assembly 34 and at its lower end terminates in a shower rose head 18. The housing 52 has a lateral water inlet 12 through which water enters a water heating chamber 20. Water leaves the chamber 20 via an outlet nozzle 16 at the upper end of a downwardly directed outlet tube 51 which opens at its lower end to the shower rose 18. The inlet 12 has a restriction 14 related to the restriction represented by the nozzle 16 such that the volume of water entering the heating chamber 20 cannot exceed the volume escaping from it. Furthermore the nozzle 16 is adapted to atomise the water entering the tube 51, i.e. to turn it into an aerosol spray, before it emerges from a shower rose head 18. This process of atomising the water through nozzle 16 enhances the safety of the device 10 since any current leakage to the water is dissipated almost entirely.
A coiled heating element 22 is mounted on a support assembly 24 in the heating chamber 20. The element 22 is a coiled, non-ferrous bare or uninsulated element wound around the support assembly 24, the latter preferably being moulded from a light weight, strong thermoplastics material with a melting point of up to 400 degrees centigrade. The assembly 24 comprises four separate, identical segments which interlock on assembly. The individual segments have holes 26 to enable free passage of water so that the water will come into contact with a high proportion of the surface of the element 22. Because of the design of the assembly 24 combined with use of an uninsulated heating element 22 greater thermal efficiency is achieved thereby allowing the element 22 to be of a relatively low resistance type, resulting in longer life expectancy and lower current consumption. The non-ferrous element 22 is corrosion resistant which should further enhance the life expectancy of this component.
An electrical switching mechanism to control the supply of current to the element 22 comprises a pair of movable contacts 28 mounted in a watertight manner by a rigid support washer 30 on a flexible diaphragm 32 which forms the roof of the heating chamber 20. The terminals 28 are connected at their lower ends to the ends of the element 22 and a semi-rigid wire support (not shown) connects the support assembly 24 to the flexible diaphragm 32 in a spaced-apart relation but such that the element 22 on its support 24 moves up and down in sympathy with the diaphragm 32.
The cap assembly 34 is secured to the housing 52 by cooperating screw threads 53 during assembly of the device 10. The periphery of the diaphragm 32 is thus clamped between the cap 34 and housing 52 and forms a watertight seal. Mounted on the cap 34 are fixed contacts 36 positioned so that they will touch the respective movable contacts 28 when the latter rise with the diaphragm 32. As shown in Figure 2 the device 10 is in an inoperative mode. Under the influence of gravity the element 22 and its support assembly 24 have pulled the diaphragm 32 downward so that the fixed 36 and movable 28 contacts are spaced apart. When water is admitted to the heating chamber 20 through the inlet 12 its pressure will raise the diaphragm 32 until the contacts 28 touch the contacts 36 so that the heating element 22 is energised.
There is additionally mounted on the cap 34 an earth terminal 38 from which a wire 39 depends, passing through the diaphragm 32 so that its free end, which is stripped of insulation, hangs in the area 40 at the lower end of the outlet tube 51 where the aerosol spray from the restriction 16 passes to the shower rose 18. This is an additional safety feature intended to minimise current leakage.
The upper ends of the fixed contacts or terminals 36 and 38 have respectively connected to them the live, neutral and earth wires of an electric cable (not shown) entering the device 10 through a terminal cover 42 mounted on the cap 34. An inlet duct 54 of the terminal cover is externally threaded to receive a cable gland. The terminal cover 42 is rotatable relative to the cap 34 to provide freedom of cable positioning during installation of the device 10. The duct 54 has a restriction 44 intended to minimise the possibility of water entering the area of the electrical contacts from this source. However, in the event that some moisture should gain access to the interior of the terminal cover 42 the cap 34 has a peripheral well or recess 46 in which water can collect to keep it away from the electrical contacts.
So as to avoid the contacts 36 and 38 turning in the cap 34 while wires are being secured to them their shafts are knurled vertically where they pass through the cap thus locking them in position.
The removable shower head or rose cap 18 is connected to the housing 52 by a quick-release thread 55 such that it will release from the housing 52 in approximately a quarter turn. The rose cap 18 includes an integrally moulded sealing formation 48 which removes the necessity for a rubber sealing ring or the like which can become detached and lost. Sealing is automatic as the rose head 18 is screwed onto the housing 52.
The outlet holes 50 of the rose cap 18 are each tapered similarly to a funnel. It has been found that this allows easy cleaning of the shower rose 18 since dirt lodges in the tapered holes and can be removed merely by releasing the rose 18 from the unit and banging lightly in an inverted position against a firm surface. This arrangement contrasts favourably with conventional roses the holes of which normally have to be cleaned individually e.g. by pushing a pin through the hole.
Tests have established that notwithstanding the use of a bare or uninsulated heating element 22 the maximum current leakage without any earthing arrangement is in the region of 0.001 to 0.007 milli-amps. This leakage could never lead to accidental electrocution as has been known to happen with some existing devices. To the best knowledge of the Inventor, this is the first time an arrangement using a bare element has been safely used for the heating of water, with the above earth leakage results.
The disclosed switching method although simple is extremely robust and in operation it is expected that the contacts will not need attention during the lifetime of the device. This contrasts favourably with devices using micro switches which do not adequately cope with the 5 to 7 kw current passing through them so that they burn and require early replacement.
In its preferred form the device is primarily made from moulded durable plastics material which is of course non-conductive or corrosive.
As mentioned previously, the use of the bare or uninsulated element 22 has allowed greater thermal efficiency. This is highlighted when it is appreciated that a device in accordance with the preferred embodiment of the invention will operate satisfactorily using only 2 to 3 kw while known devices achieving the same degree of heating are using in the order of 5 to 7 kw. Water temperature is governed by the volume of water passing through the heating chamber, such that the more water that is allowed to pass the cooler it will become. Calibration is such that at minimum flow the temperature cannot exceed 60 degrees centigrade which means that one cannot be accidentally scalded, while the restriction in the water inlet ensures that the volume of water passing through will never be such that water will not be "hot". An unexpected benefit which has been discovered lies in the field of general health/hygiene, since most known bacteria in the water are destroyed by a combination of the action of heat and low voltage electrocution. This combination renders water passing through the device of the invention semi-sterilised. This combined with the many other advantages of the invention make it eminently suitable for use in hospitals and like institutions.
In spite of the fact that current leakage without an earth system is extremely low, the device of the invention would normally include an earth arrangement in the form of a length of wire bared (i.e. stripped of insulation) at one end and located in the zone of the emergent aerosol spray and taken separately to earth. This arrangement could be advantageous in areas prone to frequent electrical thunder storms.

Claims

1. An electrically operated water heating device (10) comprising a housing (52) having a water inlet (12) and a water outlet (51), a water heating chamber (20) containing an electrical heating element (22) arranged between the inlet (12) and outlet (51) such that water passing between the inlet (12) and outlet (51) must pass through the chamber (20) in contact with the element (22) and pressure responsive means (32) displaceable in response to water pressure in the chamber (20) to cause contact between fixed (36) and movable (28) electrical contacts to complete an electrical circuit supplying current to the element (22) such that the element (22) is energised to heat water in the chamber (20) only when there is a predetermined water pressure in the chamber (20), characterised in that the outlet (51) comprises a nozzle (16) which will limit the volume of water passing through the device (10) and atomise water leaving the outlet (51).

2. A device as claimed in claim 1, characterised in that the element (22) is uninsulated.

3. A device as claimed in claim 1 or claim 2, characterised in that the outlet is in the form of a downwardly directed outlet tube (51) with the nozzle (16) positioned in the region of its upper end.

4. A device as claimed in any one of the preceding claims, characterised in that an earth wire (40) is provided having a bared or uninsulated portion suspended in the zone (40) of the aerosol spray leaving the outlet (51).

5. A device as claimed in any one of the preceding claims, characterised in that the electrical element (22) is made from a non-ferrous material.

6. A device as claimed in any one of the preceding claims, characterised in that the electrical element (22) is mounted on a support assembly (24) made of a thermoplastics material of high melting point and comprising four substantially identical segments which interlock on assembly to support the element (22) in a manner allowing water to come into contact with the greater proportion of the surface area of the element (22).

7. A device as claimed in any one of the preceding claims, characterised in that a shower rose (18) is provided arranged to receive water from the outlet (51), the shower rose (18) having tapered holes (50).

8. A device as claimed in claim 7, characterised in that the rose (18) is connected to the housing (51) by a self-sealing arrangement (40) in combination with quick release threads (55).