GB2142809A - Immersion heater - Google Patents

Abstract

In an immersion heater having a cap (8) which encloses the head (5) of the thermostat (4) and the heater terminals (3a, 3b), and in which adjustment of the thermostat is effected by rotation of a spindle (17) carried by the thermostat head, the spindle is associated with an extension (13) which extends in a rotatable manner through and closes an opening in the cap, to permit the thermostat to be adjusted without removal of the cap, thereby enabling it to be done by an unskilled person in complete safety. The extension may be in the form of a knob captive in the opening in the cap but engageable with the thermostat spindle when the cap is fitted to the thermostat. <IMAGE>

Description

SPECIFICATION Immersion heater This invention relates to electric immersion heaters of the kind having a mounting head arranged to be fitted in a liquid-tight manner within an opening in the wall of a liquid container, more especially a domestic hot water tank, and carrying one or more electric heating elements arranged to extend into the container when the head is so fitted, together with a thermostat for controlling the tempera ture to which the liquid is heated in use of the heater.

Such immersion heaters normally incorpo rate a cap which is arranged to be secured to the exterior of the mounting head so as to enclose the heater terminals and the head of the thermostat. The latter is usually adjustable, and for this purpose the thermostat head is provided with a rotatable spindle by which the temperature setting of the thermostat can be altered.

In immersion heaters of the kind referred to in common use at the present time it is necessary to remove the cap in order to enable the thermostat to be adjusted. However the removal of the cap also exposes the heating element terminals, and this could provide a hazard if adjustment of the thermostat is carried out by inexperienced persons. Moreover access is often limited, making adjustment awkward. However in the interests of energy conservation it is desirable that immersion heater thermostats be capable of easy adjustment by the users, and an object of the invention is to provide a form of thermostat by which this can be readily achieved.

According to the invention in an immersion heater of the kind referred to incorporating a cap of insulating material arranged to be fitted to the mounting head so as to enclose the head of the thermostat and the heater terminals, and in which the thermostat has a rotatable spindle by which the thermostat setting can be adjusted, the spindle is associated with an extension which projects through an opening in the cap, at least when the cap is fitted to the mounting head, the extension effectively closing the opening but being rotatable within it, and rotation of the extension producing a corresponding rotation of the thermostat spindle.

As the projection extends through the opening, adjustment of the thermostat can be effected without removal of the cap. In addition the closure of the opening by the extension ensures that the introduction of a foreign body, such as a finger or screwdriver, into the interior of the cap, when in its operative position, with the consequent risk of touching an electrically "live" part of the heater, is effectively prevented. Consequently the invention provides a form of heater whose thermostat can readily be adjusted by an inexperi enced person with complete safety.

The extension may in some cases be inte gral with the main part of the thermostat spindle, or it may comprise a separate mem ber engageable with it. Thus the extension, which may form an integral part of, or be fitted to, the thermostat spindle may be ar ranged to project through a suitably positioned hole in the cap when the latter is fitted to the mounting head of the heater.

Preferably, however, the extension comprises a separate member, conveniently in the form of a knurled knob, captive within the associated opening in the cap, and arranged to engage the thermostat spindle in a manner which permits the rotation of the member to be transmitted to the spindle when the cap is secured to the mounting head.

For example the end part of the spindle may be of square or other non-circular crosssection, with a correspondingly shaped recess being formed in the inner end of the extension member, the recess being arranged to engage said end part of the spindle when the cap is fitted to the mounting head. Preferably also the head of the thermostat is springloaded outwards away from the mounting head, the spring loading assisting in retaining the spindle and the extension member in engagement with each other.

The cap may be formed as a single moulding of plastics material, although in some cases it may be formed in two parts, the first part providing the side walls of the cap, and the second part providing at least part of the end wall of the cap and carrying said extension member, the second part of the cap being securable to the mounting head and engageable with the first part in a manner which retains the latter in position on the mounting head.

One immersion heater in accordance with the invention will now be described by way of example with reference to Figures 1 to 3 of the accompanying schematic drawings, in which Figure 1 represents an end view of the immersion heater, Figure 2 represents a similar view of the immersion heater with the cap removed, and Figure 3 represents a transverse cross-section of the head part of the heater.

The immersion heater comprises, in the usual way, a dish-shaped mounting head 1 in the form of a brass casting, exteriorly threaded and provided around its rim with an outwardly directed flange 2. The threaded part of the mounting head is arranged to be inserted into a corresponding opening in the wall of a liquid container such as a hot water tank, and is arranged to be secured in position by a nut (not shown), a gasket (also not shown) being arranged to be clamped between the flange 2 and the outer surface of the container around the opening.

The mounting head 1 carries a sheathed wire electric heating element 3 (shown only in part) having two limbs 3a, 3b which project through corresponding openings in the base of the mounting head and are secured thereto in a liquid-tight manner.

The mounting head 1 is also arranged to accommodate a rod type thermostat 4, comprising a head 5 from which protrudes a sleeve 6 closed at its outer end and housing the thermostate actuator rod (not shown). The sleeve 6 is arranged to fit into a tube 7 which is also sealed in a liquid-tight manner into a corresponding opening in the base of the mounting head 1.

In use, the ends of the two limbs 3a, 3b of the heating element 3, and the head 5 of the thermostat 4, are enclosed by a cap 8 of synthetic plastics material secured to the mounting head 1 by means of a screwthreaded rod 11 and slotted nut 1 2.

In accordance with the invention, the cap 8 carries a thermostat adjustment member 1 3 captively but rotatably secured in an opening in the end wall of the cap 8. The external end 14 of the member 1 3 is in the form of a knurled knob, and the inner end 1 5 is formed with a square-sectioned recess 1 6 which fits on to a similarly sectioned end of the thermostat spindle 1 7. A light helical compression spring 18 between the head 5 of the thermostat 4 and the base of the mounting head 1 ensures that the end of the spindle 1 7 is held in engagement with the adjustment member 13, such that rotation of the member is transmitted to the spindle, thereby enabling the setting of the thermostat to be altered without removal of the cap 8. The outer surface of the cap conveniently carries markings as at 1 9 showing the direction in which the member needs to be rotated in order to obtain an increase or reduction in water temperature.

Fitting of the cap 8 on to the mounting head 1 in the correct position is facilitated by the provisions of a ledge 20 on the inner surface of the end wall 21 of the cap, the ledge being arranged to engage a respective side of the thermostat head 4 when the cap is fitted to the mounting head, and also securing the thermostat against rotation when the adjustment member 1 3 is itself rotated to adjust the thermostat setting.

In the element illustrated the end wall 21 of the cap 1 3 is shown as a separate plate which fits into a recess at the outer end of the cap and serves to retain the remainder of the cap in position when the nut 1 2 is screwed on to the threaded rod 11. However the cap can be formed as a single moulding, with the sides and end integral with one another, if desired.

In practice, the cap 1 3 is provided with an opening (not shown) through which electric current supply leads pass. The end of one limb 3b of the heating element 3 is provided with a terminal screw 22 for connection to one supply lead conductor, the other conductor of the supply lead being connected to one terminal (not shown) of the thermostat 4, the other limb 3a of the element being connected directly to the other terminal of the thermostat 4. The threaded rod 11 carries a further nut 23 for clamping the earth lead to the mounting head. All connections have, however, been omitted from the drawing for simplicity.

Claims (10)

1. An immersion heater of the kind referred to incorporating a cap of insulating material arranged to be fitted to the mounting head so as to enclose the head of the thermostat and the heater terminals, and in which the thermostat has a rotatable spindle by which the thermostat setting can be adjusted, wherein the spindle is associated with an extension which projects through an opening in the cap, at least when the cap is fitted to the mounting head, the extension effectively closing the opening but being rotatable within it, and being such that rotation of the extension produces a corresponding rotation of the thermostat spindle.

2. An immersion heater according to Claim 1 in which the extension is integral with the main part of the thermostat spindle.

3. An immersion heater according to Claim 1 in which the extension comprises a member separate from the thermostat spindle but engageable with it when the cap is fitted to the mounting head.

4. An immersion heater according to Claim 3 wherein the extension member is captive within said opening.

5. An immersion heater according to Claim 4 wherein the end part of the spindle is of square or other non-circular cross-section and the inner end of the extension member is formed with a correspondingly shaped recess engageable with the end part of the spindle when the cap is fitted to the mounting head.

6. An immersion heater according to Claim 4 or 5 wherein the head of the thermostat is spring-loaded outwards away from the mounting head, such that the end part of the spindle is held resiliently in engagement with the extension member.

7. An immersion heater according to any one of Ciaims 3 to 6 wherein the cap is formed in two parts, the first part providing the side walls of the cap, and the second part providing at least part of the end wall of the cap and carrying said extension member, the second part of the cap being securable to the mounting head and engageable with the first part in a manner which retains the latter in position on the mounting head.

8. An immersion heater according to any one of Claims 3 to 6 wherein the cap is formed as a single moulding.

9. An immersion heater according to any preceding Claim wherein the outer surface of the part of the cap surrounding the extension carries markings indicating the direction that the extension needs to be rotated in order to obtain an increase or reduction in water temperature.

10. An immersion heater of the kind referred to substantially as shown in and as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawing.