TECHNICAL FIELD The present invention relates to a water heater comprising an outer shell or casing with an insulation positioned inside it and a fluid-tight, elastic container for water interiorly in the insulation.

BACKGROUND ART

Traditionally, water heaters have been manufactured using a stainless steel inner vessel of such high quality that it may, for a lengthy period of time, come into contact with drinking water at elevated temperatures without the drinking water becoming contaminated or discoloured or that the stainless steel sheet or its welds corroding. On the outside of this pressure vessel there is then disposed an insulation which in turn is exteriorly protected by a protective layer.

Water heaters intended for example for pleasure craft and camper vehicles etc. are often subjected to pressure shocks or hammers on opening and closing of faucets and taps, on start and stop of supply pumps or the like. These pressure shocks may be so powerful that fatigue failures may occur in the interior, stainless steel pressure vessel already after quite short periods of time.

Another problem which is relevant in traditional technology is the risk of freezing fractures during winter of a water heater which has not been completely emptied. Further drawbacks may reside in the high cost structure involved in the use of stainless steel in production.

USPS 5,555,997 discloses a water heater with a rigid outer shell and interiorly therein a flexible inner container which comes into contact with the water of the water heater. The inner container may consist of a plurality of layers, of which one insulating layer, and has in its bottom a pressure compensating cushion. The risk of freezing fractures during winter storage of the water heater according to this US Patent Specification is imminent unless it is as good as completely emptied.

In order for this to be possible, on one hand water must be let out and on the other hand air be let in. Further, if the inner container were despite this to contain any water, the inner container must be at a safe distance from the inside of the outer shell, which cannot be guaranteed according to this United States Patent Specification.

PROBLEM STRUCTURE

The present invention has for its object to design the water heater described by way of introduction such that it possesses a superior ability to withstand large pressure oscillations during operation and wholly obviate the risk of frost cracking on winter storage.

SOLUTION

The objects forming the basis of the present invention will be attained if the water heater described by way of introduction is characterised in that the elasticity is so great that, on opening of a faucet in the water system to which the water heater is connected, the volume of the container is reduced by the expulsion of water by at least 8 % compared with a completely filled container.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 is a longitudinal cross section through a water heater according to the present invention; Fig. 2 is a section corresponding to Fig. 1, but in a state where its elastic container has been pressure relieved and has contracted; and

Fig. 3 is a section taken along the section line A-A in Fig. 2.

DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will be described hereinbelow with reference to a water heater which is primarily intended for pleasure craft and camper vehicles, but the same or corresponding technology may be employed within other areas, for example, storage containers for water, accumulator tanks or the like.

The water heater according to the present invention has an outer shell or casing 1 which may be manufactured from a simple and economical material, only if it is dimensioned to withstand the working pressure at which the water heater is intended to work and with a requisite safety margin, as well as in addition such pressure oscillations or peaks as may occur. One usable material may be common, so-called sheet iron or plastic, since it does not come into contact with any water. The wall material need not be completely leakproof, since inside the outer casing there is a thermal insulation 2 and interiorly therein an elastic and completely fluid-tight container 6, which via the insulation transfers the pressure to the outer casing. Even an outer casing of mesh material could fulfil this function.

On the inside of the outer casing 1 there is, as was mentioned above, disposed a thermal insulation 2 which may consist of a foamed material and which covers substantially the whole of the inside of the outer casing 1. Even if the thermal insulation is to some degree protected from the action of pressure oscillations, it should display good mechanical strength, in particular against compression, which is attained if it has a density of at least 100 kg/m ³ , preferably 120 kg/m ³ . As a result, the risk that the insulation 2 be mechanically crumbled is avoided. In Fig. 1, the insulation 2 has been shown as of uniform thickness, but according to the present invention it is possible, for example, to make the thermal insulation thicker in the upper regions of the water heater, since the temperature there may be expected to be higher if the assembly position of the water heater is determined beforehand.

The outer casing 1 has an assembly flange, "manhole" 3, which defines a port 4. The assembly flange 3 serves for securing an assembly plate 5 which, in turn, supports or has connections to the safety and heating components which are to be located interiorly in and exteriorly on the water heater.

Interiorly in the insulation 2, there is disposed in the water heater a fluid-tight container 6 which is intended for the water which is to be found in the water heater. The fluid-tight container 6 is, according to the invention, resilient, preferably elastic and may thereby compensate for pressure oscillations which are caused by starting and stopping of a pump or the opening and closing of a faucet. The container strives, when the pressure is relieved, to reassume its original volume, which is less than the inner volume of the insulation and by such means expels, on winter draining, a sufficient amount of water to compensate for the volume increase of the water in the event of freezing.

Suitably, the fluid-tight container 6 is manufactured as a rubber sack of suitable rubber quality. This rubber sack has a collar 7 which is sealingly clamped between the assembly flange and the mounting plate 5.

In order to achieve as high a level of safety against frost cracking on winter storage, the elasticity in the container 6 is sufficient for at least 8 %, ideally considerably more, of the enclosed water volume to be expelled as soon as any faucet is opened in the water system to which the water heater is connected. Further, the water heater according to the present invention should preferably be mounted recumbent, i.e. with its central longitudinal axis approximately horizontal, since a partly contracted inner container 6 will then lie loosely on the inside of the insulation 2 with expansion room in both the lateral and vertical directions.

Figs. 2 and 3 illustrate the water heater where the elastic container has been pressure- relieved and has contracted. In Fig. 2, the container is shown by broken lines under reference numeral 6', while the container in Fig. 3 is shown by solid lines.

It will be apparent from Fig. 2 that the container 6' has collapsed so that it rests on the upper side of the insulation 2, while on the upper side of the container and at its end there are large free volumes 16 and 17, respectively. This is attained in that the container displays such thickness/stability that its walls will not, under the action of the pressure from enclosed water in the unstretched state, collapse and be forced out into contact with the inside of the insulation 2. It will be apparent from Fig. 3 that the container, in the non-stretched state, is so configurationally stable that free volumes 18 are also to be found on both sides of the container, i.e. far down towards that region which rests on the inside of the insulation 2. The consistency of the insulation 2 is sufficiently hard for the insulation to be able to transfer that pressure which the fluid-tight container 6 exercises, to the outer casing 1.

Interiorly in the container 6 there is a heating loop 8 which is connected for example to the cooling water system of an engine or to solar heating panels. Further, there is an inlet conduit 9, of larger calibre than the outlet conduit so that the speed of flow of incoming water will be low with limited turbulence and which with the aid of a sinker 10 discharges at the bottom of the water heater. Correspondingly, there is an outlet conduit 1 1 which, with the aid of a float 12, is held in the region of the upper wall of the water heater where the water is hottest. Since an elastic inner container 2, on emptying, draws together and contracts to a considerable extent, the inlet conduit 9 and the outlet conduit 1 1 must be manufactured from a flexible material so that they can accompany the movements which the inner container 6 undergoes on pressure release. The same applies to the heating loop 8 unless this is mounted closer to the centre axis of the water heater.

On the outside of the assembly plate 5, there are, for example, mixer faucets, safety valve, pressure guard and water connections as well as connections to an electric traditional heating element 13 or preferably one of Peltier-type.

In the Drawing, there is a minor space 14 drawn between the outside of the container 6 and the inside of the insulation 2. This space may be at atmospheric pressure and thus be in communication with the ambient surroundings, in which event a throttling in this communication may give a damping of the movements which the container 6 may carry out under the action of pressure oscillations. Alternatively, the space may be closed and thus not in communication with the ambient atmosphere, in which event the air which is enclosed there will operate as a gas spring for compensation of pressure oscillations. Possibly, this space 14 may be pressurised via an inlet 15 if this is deemed necessary. As a result of the deformability, preferably elasticity in the container 6, this can move and stretch in response pressure shocks without suffering any damage. Excess pressure in the space 14 may also be used for emptying the water heater before winter storage.

According to the present invention, it is also possible to reduce or wholly eliminate the space 14, on condition that the container 6 consists of the above-mentioned resiliently yieldable material and moreover the insulation 2 is designed as being slightly resilient or compressible.

In particular in the embodiment with the space 14, a water heater designed in the above described manner may be considered as freeze-proof, since there is an expansion space in which can be accommodated the volume increase which occurs in the event of freezing of water interiorly in the container 6.