GB2158926A

GB2158926A - Electric flow heater

Info

Publication number: GB2158926A
Application number: GB08510208A
Authority: GB
Inventors: Royston Leonard Edwards
Original assignee: IMI Santon Ltd
Current assignee: IMI Santon Ltd
Priority date: 1984-04-24
Filing date: 1985-04-22
Publication date: 1985-11-20
Also published as: GB8510208D0; GB8410428D0

Abstract

An electric instantaneous water heater of the open-outlet type has an electronic control circuit which permits the water to run only for a predetermined time interval. After a first preset time interval the electric current to the heater is switched off, but the control circuit permits water to continue flowing through the heater for a second preset time interval.

Description

SPECIFICATION Electric flow heater This invention relates to electric flow heaters for liquids, and in particular to "instantane outs ' water heaters having an open outlet and typically used as hand washers.

One problem encountered with instantaneous water heaters arises from the thermal heat capacity or heat content of the sheathed electric element employed to heat the water.

When the power supply to the element is switched off, residual heat from the element and its sheath continues to be given up to the water in the heater. If the water is turned off at the same time as the power to the element is switched off, the water in the heater, which is usually in a very small capacity container, can rise to an uncomfortable temperature to any user who operates the instantaneous water heater immediately after it has been turned off. It is an object of the present invention to overcome this problem, and to ensure that the water leaving the heater prior to ceasing its flow is at a suitable temperature. It is a further object of the invention to conserve water by avoiding needless flushing of the heater with cold water from the inlet.

According to one aspect of the invention we provide an electric flow heater for liquids adapted to be connected to a supply of liquid under pressure, said heater including an electric heating element adapted to heat liquid as it passes through a container, said container having an inlet for liquid to be heated and an open outlet, an electrically operable valve in the inlet, and user operable means adapted to initiate a predetermined control sequence by means of a control circuit, said control circuit comprising means for actuating said valve to open in response to a first signal so as to admit liquid to be heated to the container, means for simultaneously switching electric power to said element, means for switching off electric power to said element at a predetermined first time interval after the initiation of the control sequence, and means for actuating the valve to close at a predetermined second time interval after the end of the first time interval.

The electrically operable valve is preferably a solenoid valve. The heater may also incorporate a flow switch in the inlet to the container which is operable in response to movement of liquid into the container.

The control circuit suitably includes an electronic timer set with two predetermined time intervals in cascade of one another. The user operable means is typically a piezo ceramic push button, the operation of which triggers the timer, thus initiating the first predetermined time interval. The output from the timer may be applied to a triac, thus switching on the solenoid valve and allowing liquid to pass through the container to an open outlet. Liquid flowing through the inlet to the container may then operate the flow switch which typically closes the contacts of a reed switch. This action may activate a zero voltage switching circuit which provides on/off control for a load triac which controls the electricity supply to the heater element. The load triac is typically cooled by mounting it on the inlet for the liquid to be heated.

The control circuit is typically adapted to produce signals to switch off both the solenoid valve and the heating element at the end of the first predetermined time interval, the solenoid valve being re-activated before it can respond to its signal so that it remains open until a signal is produced from the timer at the end of the second time interval. An input differentiater may be associated with the timer so that the second predetermined time interval is initiated at the end of the first predetermined time interval. The time intervals may be preset by adjustment of components in the control circuit.

One 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 schematic diagram of a handwasher according to the invention, and Figure 2 is an electric diagram of the control circuit of the hand-washer of Fig. 1.

The hand-washer supplies water heated by electricity as it passes through a container 1 0.

A sheathed electrical element 11 enters container 10 from above, and is typically rated at 3KW. Cold water under pressure enters container 10 via inlet 12, the heated water leaving container 10 by an open outlet 1 3. In the inlet 1 2 and typically within a casing (not shown) for the hand-washer are a solenoid valve 14 and a magnet operated reed-switch 1 5 acting as a flow switch upstream of solenoid valve 14. A thermal cut-out device 1 6 is positioned on the top of container 10 and acts as a safety device which cuts the power supply to element 11 if its temperature reaches above a certain value.

The casing of the container has a pushbutton 1 7 (see Fig. 2) which is of the piezoceramic type, which when operated by the hand-washer user triggers a type 556 timer 1 8 (which may be considered as two timers in cascade) to initiate a first predetermined time interval, say 1 6 seconds. The output from timer 18 is applied by line 1 9 to a triac 20 which turns on solenoid valve 1 4 thereby permitting water to pass through inlet 1 2 into container 1 0. The flow of water through inlet 1 2 causes the contacts of reed switch 1 5 to close, thereby turning on an SL 446A zero voltage switch 21.

Zero voltage switch 21 provides on/off control for a load triac 22 which operates on the power supply to element 11. The zero voltage switching minimises any radio frequency interference which would otherwise occur. The heating element 11 is thus switched on in response to the pressing of push-button 1 7.

Whilst element 11 operates at mains supply voltage, typically 240V, the control circuit operates at 8.5V DC through the current regulation provided by rectifier 23 and load resistance 24 which is mounted on the water inlet 1 2 for purposes of heat dissipation. If for any reason there is a failure in the water supply to the heater, or the pressure drops to a very low level, the magnet in the flow will fall under gravity, causing the current to the element to be immediately switched off.

At the end of the first predetermined time interval, ie 1 6 seconds, a second predetermined time interval, say 4 seconds, is initiated by timer 1 8 in conjunction with an input differentiator circuit. At the same time, signals from timer 1 8 turn off zero voltage switch 21, thereby causing it to switch off the power supply to load triac 22, and also switches off power to solenoid valve 1 4. Almost instantaneously, timer 1 8 also provides a signal on line 25 to cause triac 20 to maintain solenoid valve 14 open.Thus, element 11 is switched off after 1 6 seconds, whereas solenoid valve 14 remains open permitting cold water to enter container 10 and to leave container 10 via open outlet 1 3. Although element 11 is no longer under load, the residual heat in its sheath and the heat in the container 10 continue to heat the water for several seconds. The length of the second predetermined time interval is selected so that the water has extracted a large proportion of the element/container residual heat before it is cut off. This is done by a signal from timer 1 8 to triac 22 which causes solenoid valve 14 to close thereby stopping water entering container 10. The length of the first predetermined time interval can be adjusted by changing the value of resistor 26, and the length of the second predetermined time interval by changing the value of resistor 27.

When the hand-washer is used again immediately after its cycle, there is no problem with very hot water from container 10, having absorbed residual heat from element 11, immediately causing discomfort to the user. The system also makes maximum utilisation of power supplied to element 11 in each wash operation.

Claims

1. An electric flow heater for liquids adapted to be connected to a supply of liquid under pressure, said heater including an electric heating element adapted to heat liquid as it passes through a container, said container having an inlet for liquid to be heated and an open outlet, an electrically operable valve in the inlet, and user operable means adapted to initiate a predetermined control sequence by means of a control circuit, said control circuit comprising means for actuating said valve to open in response to a first signal so as to admit liquid to be heated to the container, means for simultaneously switching electric power to said element, means for switching off electric power to said element at a predetermined first time interval after the initiation of the control sequence, and means for actuating the valve to close at a predetermined second time interval after the end of the first time interval.

2. An electric flow heater as claimed in Claim 1 in which the electrically operable valve is a solenoid valve.

3. An electric flow heater as claimed in Claim 1 or Claim 2 which incorporates a flow switch in the inlet to the container which is adapted to be operable in response to movement of liquid into the container.

4. An electric flow heater as claimed in any preceding claim in which the control circuit includes an electronic timer set with two predetermined time intervals in cascade of one another.

5. An electric flow heater as claimed in Claim 4 in which the user operable means is a piezo ceramic push button, the operation of which is adapted to trigger the timer, thus initiating the first predetermined time interval.

6. An electric flow heater as claimed in Claim 4 or Claim 5 in which the output from the timer is applied to a triac, thereby switching on the solenoid valve and allowing liquid to pass through the container to an open outlet.

7. An electric flow heater as claimed in Claim 6 incorporating the reed switch wherein liquid flowing through the inlet to the container operates the flow switch which then closes the contacts of the reed switch.

8. An electric flow heater as claimed in Claim 7 in which closure of the contacts of the reed switch is adapted to activate a zero voltage switching circuit to provide on/off control for a load triac adapted to control the electrical supply to the heater element.

9. An electric flow heater as claimed in Claim 4 when dependent upon Claim 2 wherein the control circuit is adapted to produce signals to switch off both the solenoid valve and the heating element at the end of the first predetermined time interval, the solenoid valve being re-activated before it can respond to the signal it receives so that it remains open until a signal is received from the timer at the end of the second time interval.

1 0. An electric flow heater as claimed in Claim 4 and incorporating an input differentiater associated with the timer such that the second predetermined time interval is initiated at the end of the first predetermined time interval.

11. An electric flow heater as hereinbefore described with reference to and as shown in the accompanying drawings.