WO2009026921A2

WO2009026921A2 - A thermostat for controlling a valve

Info

Publication number: WO2009026921A2
Application number: PCT/DK2008/000304
Authority: WO
Inventors: Bjarne Frederiksen; Anders Ostergaard Clausen
Original assignee: Danfoss A/S
Priority date: 2007-08-28
Filing date: 2008-08-26
Publication date: 2009-03-05
Also published as: WO2009026921A3

Abstract

The invention provides a thermostat which is attachable to a valve, e.g. of a radiator for controlling the temperature of an environment. The thermostat comprises a handle by which a user may set a desired temperature set-value, and a thermo sensitive element which controls the valve based on a sensed temperature. To enable temporary changes, the thermostat further comprises a switch function which can be activated to change the setting of the valve without changing the set-value.

Description

A THERMOSTAT FOR CONTROLLING A VALVE

INTRODUCTION

The invention relates to a thermostat comprising a base which is attachable to a valve, a handle, a thermo sensitive element, a set-value structure for selecting a set-value by movement of the handle relative to the base, and a shoulder movable relative to the base to set a flow through the valve, wherein the set-value structure is arranged to position the shoulder in a control position based on a selected set-value, and the thermo sensitive element is arranged to modify the control position based on a sensed temperature.

BACKGROUND OF THE INVENTION

Thermostats of the above mentioned kind are typically applied for controlling flow through a heating installation such as a radiator for controlling indoor temperature. The set-value indicates a desired temperature, and the thermo sensitive element adjusts the position of the shoulder based on a sensed temperature. The associated valve typically has a spindle which is slidingly received in a valve house and which controls the position of a valve member relative to a valve seat. The shoulder abuts the spindle, and the spindle therefore moves when the shoulder is moved towards the spindle, and the flow through the valve is therefore changed depending on the movement of the shoulder.

In commonly known thermostats, the set-value is selected by rotation of a knob, and security elements have already been developed which prevent access to the knob, e.g. for protecting against undesired changing of the set-value. Thermostats can be applied for controlling thermal conditions in an environment both in combination with refrigeration and air conditioning systems where the thermal installation is adapted to cool down the environment and in combination with heating systems where the thermal installation is adapted to heat up the environment. In the following, it is considered that the thermostat in question controls a valve and thus a thermal condition of an environment, and it may be applied both in combination with a heating and a refrigerating system.

DE2625421 and DE2932884 illustrate a commonly known radiator thermostat for a heating system.

Typically, a constant indoor temperature, e.g. 20 degrees Celsius, is desired, and all thermostats in a thermal installation are adjusted to a corresponding set-value. Since a change in the set-value of one thermostat among several thermostats is typically counteracted by the other thermostats and since it typically requires a relatively long period of time before the effect of the change can be determined, it is often difficult to set the set-values correctly, and typically, the user will adjust the set- values of the thermostats up and down for a few days before the thermal condition in the environment is satisfactory.

DESCRIPTION OF THE INVENTION

The present invention improves the known thermostats by providing a thermostat comprising a switch function which can be activated to move the shoulder away from the control position without changing the set- value, and which can be deactivated to allow the shoulder to move back to the control position.

By use of the switch function, the release of thermal energy from the thermal installation can be changed momentarily without having to change the setting of the set-value, and the previous characteristics of the installation can be reinstated by deactivation of the switch function. Accordingly, a momentary change in the thermal conditions of the environment or in the release of thermal energy from the thermal installation may be obtained without having to readjust the set-values of the thermostats of the installation.

In general, the invention may be useful whenever it is desired to change a thermal condition of an indoor environment away from a normally desired thermal condition. In particular, the invention may be useful when a window is opened or a ventilation system is turned on to momentarily exchange indoor air with fresh air from an ambient space.

The base may form a flange or cavity with a structure which facilitates connection of the thermostat to a matching structure of a valve. The base therefore serves to hold the thermostat in a fixed or at least a releasably fixed connection with the valve. The base may even form part of the valve so that the thermostat is an integrated part of the valve.

The handle may be formed as a knob of a shape corresponding to the knob of thermostats which are known in the art. In particular, the handle and the base may form a shell structure which encapsulates the thermo sensitive element, the set-value structure, and optionally other parts of the thermostat.

The handle may be allowed to rotate around an axis, e.g. an axis which extends through the shoulder. In particular, the rotation axis may be parallel or coaxial with an axis along which the spindle of the valve slides towards and away from the thermostat during movement of the shoulder.

The thermo sensitive element could be of the kind known from existing thermostats, e.g. where a substance changes volume based on its temperature or of the kind where a wax changes from solid to liquid state, and where a rod is pushed towards the associated valve by the increasing volume of the substance. The shoulder may form part of the rod, or it may be attached to the rod, e.g. at a free end of the rod. Typically, the spindle is moved outwardly towards the thermostat by a spring force which is provided in the valve. Upon movement in the direction towards the valve, the shoulder must, in this case, counteract the spring force. In this embodiment, the shoulder and the spindle does not need to be fixed to each other, and the shoulder may simply be a surface, e.g. a concave or inwardly bulging surface in the free end of the rod. In other embodiments, no spring force is provided in the valve, and the shoulder should move the spindle in both directions. This would require engagement between the shoulder and the spindle, and the shoulder may therefore comprise such means for catching and fixating the spindle.

The set-value structure may e.g. be adapted to move the thermo sensitive element including the rod which forms the shoulder relative to the base and thus relative to the valve in a direction towards the valve or in a direction away from the valve. At a given, fixed, temperature, the set-value structure may therefore be used for setting a desired flow through the valve. Subsequently, the thermo sensitive element will serve to adjust the position of the shoulder based on the sensed temperature. The set-value structure is typically provided so that it moves the shoulder based on rotational movement of the handle relative to the base, and to support adjustment of the set-value, the handle and base may comprise a matching dial indicating the set-value.

In the following, the control position is a position of the shoulder and thus of the spindle of a valve which is controlled by the thermostat. The control position is a position which is determined by the set-value selected by the user and by the thermo sensitive element based on a sensed temperature. Typically, a movement towards the valve will press the spindle of the valve into the valve house, and in many existing valves, this will decrease the flow. Valves having an opposite characteristics may exist. In any case, the switch function may be arranged to move the shoulder away from the control position either in a direction towards the associated valve or in a direction away from the associated valve. The movement may either reduce or increase the flow through the valve, and in one embodiment, the switch may be adapted to completely prevent a flow through the valve, e.g. in order to momentarily prevent heating or cooling of the environment.

Typically, a movement away from the valve will release a pressure on the spindle of the valve. In common valves, the spindle will be lifted outwardly from the valve by spring means included in the valve, and the flow through the valve will increase. In this case, the switch function may be adapted for a momentary release of extra thermal energy from the radiator to which the thermostat is applied, e.g. to conduct a fast raising of the temperature of the environment.

The switch function could be activated by movement of the entire thermostat including the base between a first and a second position relative to the valve. In order to make a simple interface to the valve and an easy control of the switch function, it may be desired to activate and deactivate the switch function by movement of the handle relative to the base. If the set-value is selected by rotation of the handle around an axis, the switch function could be operated by sliding the handle towards and away from the base along the axis.

If, in the activated state of the switch function, the shoulder has counteracted a spring force which is built into the valve, the spring force of the valve may act on the shoulder when the switch function is deactivated and bring the shoulder back to the control position. In this case, the switch function may be controlled by a control means which is capable of moving the shoulder only in the direction which counteracts the built in spring force.

Since activation of the switch function may also move the shoulder in a direction which is supported by the spring force of the valve, or since the valve may not even provide a spring force, the switch function may alternatively be controlled by a control means which are capable of moving the shoulder both towards and away from the valve. Alternatively, or as a supplement, the thermostat may comprise first biasing means which biases the shoulder towards the control position. In this case, the user counteracts the force of the first biasing means when activating the switch function. To deactivate the switch function, the user releases a deactivation mechanism and the first biasing means brings the shoulder back to the control position. The first biasing means may e.g. comprise one or more springs, e.g. disc or helically coiled springs, or the first biasing means may comprise a gas which is compressed during movement of the shoulder away from the control position and which is decompressed during returning of the shoulder to the control position.

The switch function may be controlled and/or provided by a configuration element which is slideable relative to the base and which is arranged to move the shoulder.

In the following text, "forward" indicates a movement towards the base and valve, and "rearward" indicates a movement away from the base and valve. The configuration element may be arranged to be moved forward and thereby to push the shoulder towards the valve, or to be moved rearward and thereby to allow the shoulder to return to the control position, e.g. under influence of the first biasing means or under influence of a built in spring force in the valve. To maintain the switch function in the activated state, the thermostat may comprise locking means adapted to lock the configuration element in a closed position of the configuration element relative to the base, i.e. at a position where the configuration element prevents the shoulder from returning to the control position. The locking means may provide a forward end-stop limiting movement in the forward direction beyond the closed position and a rearward end-stop limiting movement in the rearward direction beyond an open position of the configuration element relative to the base.

In one embodiment, the locking means is adapted to lock the configuration element in the closed position by rotation of the configuration element relative to the base. This feature may be advantageous, e.g. in combination with a timer which will be described later.

As it will be understood in connection with the detailed description of a preferred embodiment and the corresponding drawing, a safe-feature which prevents unintended change of the set-value, e.g. for preventing children from operating the thermostat, may be obtained by locking means which is adapted to prevent rotation of the configuration element relative to the base unless the configuration element is in the closed position. This will be obtainable by use of a T-shaped groove cooperating with a protrusion, the groove and protrusion being arranged in opposite surfaces of the base and the configuration element. The T-shaped groove prevents rotation of the configuration element, and due to the engagement between the handle and the configuration element, the handle is prevented from rotating in the neutral position. This is explained further with reference to Fig. 9.

To simplify the design of the thermostat, to provide only one control handle for the user to operate both the set-value structure and the switch function, or to improve the operating interface, e.g. by application of dials which are only visible in states wherein the corresponding function can be operated, the handle may be adapted for translatoric displacement along an axis relative to the base. In particular, the handle may be adapted for sliding in the previously introduced forward/rearward direction. The configuration element may be arranged between the base and the handle, so that, by forward movement, the handle can push the configuration element in the same direction. In this manner, the handle may, by rotation be used for operating the set-value structure and by sliding be used for operating the switch function. In particular, the handle may be adapted for translatoric displacement forward from a neutral position towards a forward position and rearward from the neutral position towards a rearward position. For this purpose, the thermostat may include second biasing means for biasing the handle towards the neutral position, i.e. somewhere between the forward and rearward positions of the handle relative to the configuration element and set-value structure.

The handle may have a double function, i.e. in the rearward position, the handle may engage the set-value structure, and rotation of the handle in the rearward position may thus change the set-value. In the forward position, the handle may have moved the configuration element to its closed position, and it may thus have activated the switch function.

The previously mentioned safe-feature which prevents unintended change of the set-value may be obtained by engagement between the handle and both of the set-value structure and configuration element when the handle is in the neutral position. This feature depends on the previously mentioned T-groove which prevents rotation of the configuration element except in the closed position thereof. Further explanation is provided later with reference to Fig. 9.

E.g. in combination with ventilation, it may be desired to turn off the heating for a certain period of time. In order not to forget to deactivate the switch function or to simplify the use of the switch function, the thermostat may comprise a timer arranged to deactivate the switch function after expiry of a period of time. In this regards, the term "timer" may cover any kind of structure which is capable of deactivating the switch function after a period of time. The timer may e.g. comprise a spring mechanism which can be wound up or a compressed volume of gas where the gas is released whereby a chamber changes volume and deactivates the switch function. In both cases, the duration before deactivation can be set by a friction between the configuration element when it rotates to an unlocked position or the duration may be set by the degree to which the spring is deformed or the gas is compressed. If the timer is based on compressed gas, the system may comprise two chambers between which the gas flows. When the timer is activated, gas is displaced from one chamber to the other, and when the gas contents in the chambers has leveled out, the switch may be deactivated.

The period of time could be selectable e.g. by movement of the handle relative to the base. In particular, the selection of the period of time, i.e. the duration of the period during which the switch function is activated, may be selected by rotation of the handle, when the handle is in the forward position and the configuration element is therefore in the closed position. One embodiment of the timer is explained further with reference to the Figs. 1 and 8. In this case, the timer is adapted to unlock the configuration element from the closed position by rotating the configuration element relative to the base. For this purpose, the illustrated timer comprises a mechanism which can be wound up by rotation of a spindle in one rotational direction upon which it rotates in the opposite direction in a period of time. The configuration element engages the spindle so that the timer can be wound up via the handle, and so that the timer, subsequently, can rotate the configuration element. To support setting of the timer, the thermostat may comprise a dial indicating the length of the period of time. Since another dial of the thermostat may indicate the set-value, it may be confusing for the user to understand the meaning of each of the dials. For simplicity in use of the thermostat, the handle may cover the dial indicating the timer unless the handle is in the forward position. Correspondingly, the handle may cover the dial indicating the set-value unless the handle is in the rearward position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In the following, a preferred embodiment of the invention will be explained in further details with reference to the drawing in which:

Fig. 1 illustrates a thermostat according to the invention;

Fig. 2 illustrates the thermostat in Fig. 1 in an exploded view;

Fig. 3 illustrates an exploded, elevational view;

Fig. 4 illustrates the thermostat from Fig. 1 with the handle pulled rearward;

Fig. 5 illustrates the thermostat from Fig. 4 after rotation of the handle and therefore after the set-value has been changed;

Fig. 6 illustrates the thermostat from Fig. 5 after the handle has returned to the neutral position;

Fig. 7 illustrates the thermostat from Fig. 1 with the handle pushed forward; Fig. 8 illustrates details of the interaction between the timer and the configuration element, and

Fig. 9 illustrates details of the locking means for locking the configuration element in the closed position.

Fig. 1 illustrates a cross-section of a thermostat according to the invention and the same thermostat is illustrated in an exploded view in Fig. 2. Fig. 3 illustrates an exploded, elevational view of the thermostat. The thermostat 1 comprises a base 2 comprising a front opening 3 by which a valve may be partly inserted into the base and be attached thereto. The thermostat further comprises a handle 4, a thermo sensitive element 5, a set-value structure 6 for selecting a set-value by movement of the handle 4 relative to the base 2, and a shoulder 7 movable relative to the base 2 to set a flow through the valve (not shown).

Traditionally, the shoulder 7 is positioned by use of the set-value structure 6, and the position is modified by the thermo sensitive element 5 which contains a medium which expands or contracts in response to temperature changes. This position of the shoulder 7 is called the controlled position.

The thermostat further comprises locking means in the form of a T-shaped groove 8 which is only partly visible, and a configuration element 9 which is slidable in the direction indicated by the arrows 10, 11 and which can be locked in a foremost, closed position in which the configuration element 9 pulls the thermo sensitive element 5 forwardly towards the front opening 3 in the base 2. During this movement, the shoulder 7 is also moved forward in the direction indicated by the arrow 10, and a flow through a corresponding valve is changed (depending on the valve in question, the indicated forward movement will typically reduce or prevent the flow in the valve). When the configuration element 9 is not in the foremost, closed position, rotation of the configuration element 9 is prevented by the T- shaped groove 8. As it may be apparent, the switch function is primarily provided by interaction between the configuration element 9, which is arranged between the base and the thermo sensitive element, and the thermo sensitive element.

To provide the previously mentioned double function of the handle 4, the illustrated thermostat 1 comprises a circumferential toothing 12 provided on an inner surface of the handle 4. The inner toothing 12 cooperates with a circumferential outer toothing 13 on an outer surface of the configuration element 9 to form a first engaging means. The first engaging means can be shifted between a first coupled state and a first decoupled state by sliding of the handle 4 relative to the configuration element 9 in the direction of the arrows 10, 11. The arrow 10 indicates a forward direction and the arrow 11 indicates a rearward direction.

In the first coupled state, rotation of the handle 4 is transferred to the configuration element 9, and provided that the T-shaped groove 8 does not prevent rotation of the configuration element, it can be rotated by use of the handle 4. Like the configuration element 9, the set-value structure 6 also comprises an outer toothing 14 provided on an outer surface thereof. The inner toothing 12 also cooperates with the outer toothing 14 to form second engaging means which provides a second coupled state and a second decoupled state by sliding of the handle 4 relative to the set-value structure 6 in the direction indicated by the arrows 10, 11. In the second coupled state, rotational movement of the handle 4 around the axis is transferred to the set-value structure 6, and rotation of the handle 4, provided that such rotation is not prevented by the first engaging means, rotates the set-value structure 6 which in turn changes the position of the thermo sensitive element 5 and the shoulder 7.

In Fig. 1 , the illustrated neutral position of the handle 4 provides both the first and the second coupled states. Since the configuration element 9 is in a rearmost, open position in which the switch function is deactivated and in which rotation of the configuration element 9 is prevented by the locking T-groove 8, the handle 4, by its engagement with the configuration element 9, is also prevented from rotating. This provides a safe-feature which prevents unintended changing of the set-value.

To change the set-value, the user will have to slide the handle in the direction indicated by the arrow 11. This will move the first engaging means to the first decoupled state and thereby allow rotation of the handle 4. Via the second engaging means, the rotation of the handle can be transferred to the set-value structure 6. The set-value structure 6 comprises an internal threading 15 which drives the outer threading 16 provided on the outer surface of the thermo sensitive element 5 and thus moves the thermo sensitive element 5 and the shoulder 7 in the direction of the arrows 10, 11 depending on the direction of rotation. Accordingly, rotation of the handle 4 changes the set-value.

As indicated in any of the Figs. 1-8, the thermostat comprises a timer 17 (indication numbers of the timer are provided in Figs. 1 and 7) which has a spindle 18 which forms part of the rod from the thermo sensitive element 5 to the shoulder 7, and which has a lower surface forming the shoulder 7. The spindle 18 of the timer 17 can be wound up in one direction upon which the timer will rotate the spindle 18 in the opposite direction. The spindle 18 is provided with a gear wheel 19 with an outer toothing (numeral 20 in Fig. 8). When the configuration element 9 is in the closed position, the gearwheel is engaged with an inner toothing 21 on an inner surface of the configuration element 9, via an additional gear wheel 22. The timer function will be described further with reference to Figs. 7 and 8.

In Fig. 4, the thermostat 1 is illustrated with the handle 4 being moved rearward in the direction of the arrow 11. By the rearward movement of the handle 4, a small area 23 on the outer surface of the handle 4 becomes visible. A dial which indicates the setting of the set-value may be printed at this area, so that the dial is only visible when the handle 4 is in the rearward position, whereas the dial is covered by the configuration element 9, when the handle 4 is in the neutral position.

In Fig. 5, the handle 4 has been rotated while retracted rearward. By this action, the set-value is changed which has caused the thermo sensitive element 5 and the shoulder 7 to move in the forward direction (arrow 10). By use of the thermostat in combination with a traditional valve for radiators in a heating system, the forward movement of the shoulder 7 causes a lower set-value and a corresponding lower release of thermal energy from the thermal system and therefore a lower temperature in the environment.

In Fig. 6, the handle 4 is released whereby it returns to the neutral position under the influence of a spring force from the second biasing means. This prevents rotation of the handle 4 and therefore prevents changing of the set-value.

Fig. 7 illustrates again the thermostat from Fig. 1 , where the handle 4 is pushed in the forward direction (arrow 10). The handle 4 thereby pushes the configuration element 9 in the forward direction, and since the configuration element 9 brings the thermo sensitive element 5 and thus the shoulder 7 forward, the switching function is activated without changing the set-value. The second engaging means is disengaged whereby rotation of the handle 4 relative to the base 2 has no impact on the set-value. In this situation, the first engaging means ensures that rotation of the handle 4 is transferred to the configuration element 9. By the rotation of the configuration element 9, the handle 4 becomes locked in the closed position by the T-groove 8. When the handle 4 is pushed in the forward direction, a small area 24 on an outer surface of the set-value structure becomes visible. A dial indicating a timer setting can be printed on this area.

When the configuration element 9 is in the closed position, the T-shaped groove 8 does not prevent rotation of the configuration element 9, and it may thus rotate when the handle 4 is rotated. Rotation of the configuration element 9 is transferred to the spindle 18 and the timer is activated. When the handle is not rotated anymore, the timer will rotate the spindle 18 in the opposite direction until the T-shaped groove releases the configuration element, which then jumps back from the closed position to an open position. This enables the shoulder 7 to return to the control position.

Fig. 8 illustrates the spindle 18 and the engagement between the gear wheels.

Fig. 9 illustrates the T-shaped groove 8 in which the protrusion 25 is guided. The protrusion 25 forms part of the configuration element 9 and the T-shaped groove 8 is formed in the body 2. In Fig. 9, the protrusion 25 is guided along the vertical part of the T-shaped groove. When the protrusion 25 reaches the horizontal part of the T-shape, further movement of the configuration element 9 relative to the body in the forward direction is prevented. Since the horizontal part of the T-shape forms a circumferential groove on the outer surface of the body 2, the protrusion 25 can be guided in the horizontal part of the T-shaped groove during rotation of the configuration element 9 relative to the body 2. The horizontal part of the T-shape is indicated with numeral 26.

Claims

1. A thermostat (1) comprising a base (2) which is attachable to a valve, a handle (4), a thermo sensitive element (5), a set-value structure (6) for selecting a set-value by movement of the handle (4) relative to the base (2), and a shoulder (7) movable relative to the base (2) to set a flow through the valve, wherein the set-value structure (6) is arranged to position the shoulder (7) in a control position based on a selected set- value, and the thermo sensitive element (5) is arranged to modify the control position based on a sensed temperature, characterized in that the thermostat further comprises a switch function which can be activated to move the shoulder (7) away from the control position without changing the set-value, and which can be deactivated to allow the shoulder (7) to move back to the control position.

2. A thermostat according to claim 1 , comprising first biasing means which biases the shoulder (7) towards the control position.

3. A thermostat according to any of the preceding claims, comprising a configuration element (9) which is slideable relative to the base (2), the configuration element (9) being arranged to move the shoulder (7) away from the control position when the configuration element (9) is moved in a forward direction towards the base and to allow the shoulder (7) to return to the control position when the configuration element (9) is moved in an opposite, rearward, direction away from the base (2).

4. A thermostat according to claim 3, comprising locking means (8, 25) adapted to lock the configuration element (9) in a closed position relative to the base (2) when the shoulder (7) has been moved away from the control position.

5. A thermostat according to claim 4, wherein the locking means (8, 25) provides a forward end-stop limiting movement in the forward direction beyond the closed position and a rearward end-stop limiting movement in the rearward direction beyond an open position of the configuration element (9) relative to the base (2), the locking means (8, 25) being adapted to lock the configuration element (9) in the closed position by rotation of the configuration element (9) relative to the base (2).

6. A thermostat according to claim 4, wherein the locking means (8, 25) is adapted to prevent rotation of the configuration element (9) relative to the base (2) unless the configuration element (9) is in the closed position.

7. A thermostat according to claim 5, wherein the locking means (8, 25) comprises a T-shaped groove (8) cooperating with a protrusion (25), the groove (8) and protrusion (25) being arranged in opposite surfaces of the base (2) and the configuration element (9).

8. A thermostat according to any of claims 3-7, wherein the handle (4) is adapted for translatoric displacement along an axis for moving the configuration element (9) in the forward direction.

9. A thermostat according to claim 8, wherein the handle (4) is adapted for translatoric displacement along the axis from a neutral position in the forward direction towards a front position and from the neutral position in the rearward direction towards a rear position.

10. A thermostat according to claim 9, comprising second biasing means for biasing the handle (4) towards the neutral position.

11. A thermostat according to claims 9 or 10, wherein the handle (4), in the rearward position, engages the set-value structure (6), and rotation of the handle (4) in the rearward position thus changes the set-value.

12. A thermostat according to any of claims 9-11 , wherein the handle (4), by movement from the neutral position to the forward position, moves the configuration element (9) to its closed position, and thus activates the switch function.

13. A thermostat according to any of claims 9-12, comprising first engaging means (12, 13) providing a first coupled state and a first decoupled state by sliding of the handle (4) relative to the configuration element (9), whereby a rotational movement of the handle (4) around the axis is only transferred to the configuration element (9) in the first coupled state.

14. A thermostat according to any of claims 9-13, comprising second engaging means (12, 14) providing a second coupled state and a second decoupled state by sliding of the handle (4) relative to the set-value structure (6), whereby a rotational movement of the handle (4) around the axis is only transferred to the set-value structure (6) in the second coupled state.

15. A thermostat according to claims 13 and 14, wherein both the first and the second coupled states are provided when the handle (4) is in the neutral position.

16. A thermostat according to claim 13 and 14, wherein the first coupled state and the second decoupled state are provided when the handle (4) is in the front position.

17. A thermostat according to claim 13 and 14, wherein the first decoupled state and the second coupled state are provided when the handle (4) is in the rear position.

18. A thermostat according to any of the preceding claims, wherein the switch function comprises a timer (17) arranged to deactivate the switch function after expiry of a period of time.

19. A thermostat according to claim 18, wherein a length of the period of time is selectable by movement of the handle (4) relative to the base.

20. A thermostat according to claim 5 and 18-19, wherein the timer (17) is adapted to unlock the configuration element (9) from the closed position by rotating the configuration element (9) relative to the base (2).

21. A thermostat according to any of claims 18-20, wherein the timer (17) comprises a mechanism which can be winded up by rotation of a spindle

(18) in one rotational direction upon which it rotates in the opposite direction in a period of time, and wherein the configuration element (9) is adapted to rotate the spindle (18).

22. A thermostat according to any of claims 19-21 , comprising a dial indicating the length of the period of time, wherein the handle (4) is movable between a position in which the dial is covered by the handle (4) and a position wherein the dial is uncovered.

23. A thermostat according to any of the preceding claims, wherein the switch function is arranged between the base (2) and the thermo sensitive element (5).