IE80655B1

IE80655B1 - Instantaneous electric water heater

Info

Publication number: IE80655B1
Application number: IE950236A
Authority: IE
Inventors: Andrew Ian Mattocks
Original assignee: Caradon Mira Ltd
Priority date: 1994-04-09
Filing date: 1995-04-03
Publication date: 1998-11-04
Also published as: GB2289323B; GB2289323A; IE950236A1; GB2289323C; GB9407119D0

Abstract

An instantaneous electric water heater has an inlet 3 for connection to a supply of cold water, an outlet 4 for heated water and, between the inlet 3 and outlet 4, a pump 5, an on/off valve 6, a flow regulator 7 and a heat exchanger 8. The on/off valve 6 and flow regulator 7 are operable independently with the pump 5 being operable on opening the valve 6 to boost the water pressure and the heat exchanger 8 being operable on opening the valve 6 when the water pressure reaches a pre-determined value. The flow regulator 7 (Fig.7, not shown) comprises a cylinder sliding through an O-ring, the cylinder having axially extending slots, of different length, in its outer surface. Pressure increase can expand the O-ring.

Description

INSTANTANEOUS ELECTRIC WATER HEATER This invention concerns improvements in or relating to instantaneous electric water heaters wherein water is heated as it flows through the heater. For a given power input, the water temperature is controlled by adjusting the flow rate. As a consequence, the range of flow rates and hence temperatures that can be selected is limited if the water supply pressure is low or unreliable.

This is undesirable for many applications where, depending on the water supply temperature, the user may be unable to obtain a desired water temperature.

Thus, the water supply temperature in summer can be considerably higher than in winter with the result that the flow rate required to achieve the same water temperature is much higher in summer than in winter for a given power input.

It has been proposed to compensate for variations in the water supply temperature by providing different power inputs. This can result in problems if there is insufficient overlap between the range of temperatures provided by each power input.

The present invention has for its object to provide an instantaneous electric water heater capable of providing adjustable selection of a wide range of flow rates at low water supply pressures.

According to the present invention there is provided an instantaneous electric water heater having a water inlet for connection to a supply of cold water, a water outlet for heated water and, between the water inlet and water outlet, a pump, an on/off flow control valve, a flow regulator and a heat exchanger having at least one electric heating element, the flow control valve and flow regulator being operable independently, switch means responsive to water pressure for controlling the power supply to the heat exchanger, the pump and switch means being upstream of the flow regulator and operable in response to actuation of the flow control valve such that the pump is activated when the flow of water is turned on and the switch means is responsive to the water pressure to the flow regulator.

By the provision of the pump, a wide range of flow rates can be obtained even at low water supply pressures for a given power input enabling the user to select any desired temperature. -2δ 0 ό b b Furthermore, by arranging for the pump and heat exchanger to be operable in response to actuation of the flow control valve with the flow regulator being independently operable, user operation and control of water temperature is simplified.

Advantageously, the flow control valve is arranged on closing to allow water to flow for a short period of time after the switch means for the heat exchanger has interrupted the power supply to the heat exchanger.

Preferably, the flow regulator is operable to vary the flow rate and is adapted to maintain constant a selected flow rate.

Advantageously, the pump is a centrifugal pump having an inlet coaxial with an impeller mounted on an output shaft of a high speed motor, and an outlet communicating with a chamber at the periphery of the impeller.

Preferably, the pump includes a pressure relief valve arranged to open if the water pressure exceeds a pre-determined value.

Advantageously, the flow control valve and flow regulator are independently operable by separate rotatable control members.

Preferably, the heat exchanger has a plurality of electric heating elements and rotation of the control member for the flow control valve is arranged to select different combinations of the heating elements to vary the power setting of the heat exchanger.

Other features, benefits and advantages of the invention will be apparent from the following description of an exemplary embodiment with reference to the accompanying drawings, wherein:FIGURE 1 is a front view of an instantaneous electric water heater embodying the invention; FIGURE 2 is a front view of the heater shown in Figure 1 with the front cover removed; FIGURE 3 is a front view, to an enlarged scale, of the on/off flow control valve, flow regulator and switch assembly shown in Figure 2; FIGURE 4 is a rear view, partly in section, of the on/off flow control valve, flow regulator and switch assembly shown in Figure 3 with the flow control valve shown closed; -3FIGURE 5 is a rear view, similar to Figure 4, with the flow control valve shown open; FIGURE 6 is a side view, partly in section, of the on/off flow control valve, flow regulator and switch assembly shown in Figure 4; FIGURE 7 is a section through the flow regulator shown in Figure 2; and FIGURE 8 is a section through the pump shown in Figure 2; With reference to the drawings, there is depicted an instantaneous electric water heater 1 comprising a rectangular casing 2 adapted for wall mounting with an inlet 3 at the rear for connection to a supply of cold water such as the incoming mains and an outlet 4 at the bottom for connection to an ablutionary appliance such as a shower.

Connected in series between the inlet 3 and the outlet 4 there is a centrifugal pump 5, an on/off flow control valve 6, a flow regulator 7 and a heat exchanger 8.

The on/off valve 6 and flow regulator 7 are incorporated in a valve body 9 having an inlet 10 connected to an outlet 11 from the pump 5, and an outlet 12 connected to an inlet 13 of the heat exchanger 8.

The on/off valve 6 is controlled by a rotatable control knob 14 20 mounted on a spindle 15 and the flow regulator 7 is controlled by a separate rotatable control knob 16 mounted on a spindle 17.

The power supply to the pump 5 is controlled by rotation of the knob 14 so that the pump 5 is energised to boost the water pressure when the valve 6 is opened and is de-energised when the valve 6 is closed.

The power supply to the heat exchanger 8 is controlled by a pressure switch 18 downstream of valve 6 so that the heat exchanger 8 is energised at a pre-determined water pressure when the valve 6 is opened and is deenergised when the valve 6 is closed.

The on/off valve 6 comprises a rubber diaphragm 19 with a flow guide 20 slidably received in a passageway 21 leading to outlet 12. The diaphragm 19 is biased by a spring 22 to engage an annular seat 23 to close the passageway 21 in a first position of the control knob 14 designated stop on the front of the casing 2.

The diaphragm 19 is displaced away from the seat 23 to open the passageway 21 by a push rod 24 actuated by pivotal movement of a bell crank lever 25 under the control of a cam 26 mounted on spindle 15 in each -4of three further positions of the control knob 14 designated cool, low and high on the front of the casing 2. The control knob 14 is located at each selected position by means of a detent spring 27.

The power supply to the pump 5 is controlled by a micro switch 28 under the control of a cam 29 mounted on the spindle 15 to energise the pump 5 in each of the cool, low and high positions of the knob 14 and to de-energise the pump 5 in the stop position of the knob 14.

The heat exchanger 8 has two electric heating elements 30,31 controlled by respective micro switches 32,33 actuated by pivotal movement of associated bell crank levers 34,35 under the control of the pressure switch 18.

The pressure switch 18 comprises a rubber diaphragm 36 responsive to the water pressure flowing through the passageway 21 to control movement of a push-rod 37 biased towards the diaphragm 36 by a return spring 38.

The levers 34,35 engage opposite ends of a beam 39 carried by the push-rod 37 and biased away from the diaphragm 36 by a weak spring 40 that allows pivotal movement of the levers 34,35 to be selectively blocked by respective cams 41,42 on the spindle 15.

In this way, the power setting of the heat exchanger 8 can be adjusted so that neither, one or both heating elements 30,31 is energised when the water pressure in the passageway 21 overcomes the biasing of the return spring 38 corresponding to the cool, "low and high positions of the control knob 14 respectively.

When the control knob 14 is rotated to the stop position to close the valve 6, movement of the diaphragm 19 towards the seat 23 is damped by the provision of a vent hole 43 so that the water continues to flow for a short period of time after the pressure switch 18 has interrupted the power supply to the heat exchanger 8.

In this way, the residual heat of the heating elements 30,31 is reduced preventing the water remaining in the heat exchanger being heated to an elevated temperature so as to avoid an initial flow of hot water if the valve 6 is opened soon after having been closed.

The heat exchanger 8 has a thermal cut-out 44 arranged to sense the outlet water temperature and to interrupt the power supply to the heating elements 30,31 if the temperature exceeds a pre-determined safe value, and -5a pressure relief valve 45 arranged to open if the pressure of the water in the heat exchanger 8 exceeds a pre-determined safe value. A neon lamp 46 on the front of the casing 2 is illuminated to provide a visual warning to the user when the cut-out 44 has interrupted the power supply.

As best shown in Figure 7, the inner end of the flow regulator spindle 17 threadably engages a piston 47 non-rotatably mounted in a cover member 48 secured to the body 9 by screws 49 so that the piston 47 is axially movable in response to rotation of the spindle 17 by the control knob 16.

The piston 47 is provided with a cylindrical extension 50 having a plurality of axially extending slots (not shown) in the outer surface that cooperate with a surrounding O-ring 51 to define openings through which water can flow. The slots are of different axial length so that the number of openings available changes with axial movement of the piston 47 to vary the flow rate and hence the temperature to which the water is heated for a given power setting of the heat exchanger 8.

Each slot is of uniform cross-section along its length and the Oring 51 is resiliently deformable to change the area of the opening in response to variations in the pressure of the water so that, for a given position of the extension 50, the selected flow rate is constant.

As best shown in Figure 8, the pump 5 has an impeller 52 mounted on a shaft 53 of a high speed brush motor 54 and a coaxial inlet 55 connected to the water inlet 3. A chamber 56 at the periphery of the impeller 52 communicates with the outlet 11 and with a pressure relief valve 57.

The valve 57 comprises a rubber ball 58 located in an opening 59 with the ball 58 being compressed so as to be ejected from the opening 59 if the pressure of the water exceeds a pre-determined value for any reason. For example, if the pump 5 is not de-energised when the valve 6 is closed.

The high speed brush motor 54 ensures that the water pressure is boosted sufficiently to enable the flow rate and hence water temperature to be adjusted over a wide range with the available ranges of temperatures on different power settings overlapping so that temperature selection gaps between different power settings are avoided.

In known manner, the water heater 1 is connected to an incoming power supply via a remote isolating switch (not shown) which allows the power supply to be switched off for servicing and/or repair of the water -6heater 1. A neon lamp 60 on the front of the casing 2 is illuminated to provide a visual warning to the user when the power supply is switched on.

As will be appreciated from the description of the exemplary embodiment, the arrangement of the controls is simplified by using a single control knob to control water flow, the pump and the heat exchanger with a separate control knob to control flow rate and thus water temperature for a given power setting.

It will be understood that the invention is not limited to the embodiment above-described. For example, the heat exchanger may have one or more heating elements arranged to provide a single power setting or any combination of different power settings as desired with an appropriate switch arrangement for selecting each power setting.

The arrangement of the pump, on/off valve, flow regulator and heat exchanger may be altered. For example, the pump may be positioned downstream of the on/off valve.

The on/off valve and/or flow regulator may be replaced by any other type of on/off valve or flow regulator suitable for the intended purpose as will be familiar to those skilled in the art.

Claims

Claims:

1. An instantaneous electric water heater having a water inlet for connection to a supply of cold water, a water outlet for heated water and, between the water inlet and water outlet, a pump, an on/off flow control valve, a flow regulator and a heat exchanger having at least one electric heating element, the flow control valve and flow regulator being operable independently, switch means responsive to water pressure for controlling the power supply to the heat exchanger, the pump and switch means being upstream of the flow regulator and operable in response to actuation of the flow control valve such that the pump is activated when the flow of water is turned on and the switch means is responsive to the water pressure to the flow regulator.

2. An instantaneous electric water heater according to Claim 1 wherein the flow control valve is arranged on closing to allow water to flow for a short period of time after the switch means for the heat exchanger has interrupted the power supply to the heat exchanger.

3. An instantaneous electric water heater according to any one of the preceding Claims wherein the flow regulator is operable to vary the flow rate and is adapted to maintain constant a selected flow rate.

4. An instantaneous electric water heater according to any one of the preceding Claims wherein the pump is a centrifugal pump having an inlet coaxial with an impeller mounted on an output shaft of a high speed motor, and an outlet communicating with a chamber at the periphery of the impeller.

5. An instantaneous electric water heater according to Claim 4 wherein the pump includes a pressure relief valve arranged to open if the water pressure exceeds a pre-determined value.

6. An instantaneous electric water heater according to any one of the preceding Claims wherein the flow control valve and flow regulator are independently operable by separate rotatable control members.

7. An instantaneous electric water heater according Claim 6 wherein the heat exchanger has a plurality of electric heating elements and rotation of the control member for the flow control valve is arranged to select different combinations of the heating elements to vary the power setting of the heat exchanger. -88.

8.An instantaneous electric water heater for an ablutionary appliance such as a shower comprises a water inlet for connection to a supply of cold water, a water outlet for connection to the appliance and, between the water inlet and water outlet, a pump for boosting the water pressure, an on/off flow 5 control valve, a flow regulator for controlling flow rate, and a heat exchanger having at least one electric heating element for heating the water, a first rotatable control member for operating the on/off flow control valve, a second rotatable control member for operating the flow regulator independently of the on/off flow control valve, first switch means for 10 operating the pump, and second switch means for operating the heat exchanger, the first switch means being operable to actuate the pump in response to rotation of the first control member to open the flow control valve, and the second switch means being operable to actuate the power supply in response to a pre-determined water pressure upstream of the flow 15 regulator.

9. An instantaneous electric water heater substantially as hereinbefore described with reference to the accompanying drawings.