BACKGROUND OF THE INVENTION A valve of a similar construction is disclosed in US-A,- 4,431,019, EP-A1-0578168 and EP-A1-0085298.

The valve according to the invention is particularly intended to be used in a dialysis machine which, in its liquid-preparation stage, comprises a plurality of valves of this type. These valves are usually solenoid-operated. The valve can be of the one-way or two-way type or any multi-way type of valve.

The valve is provided with a diaphragm which abuts a valve seat in the valve. Wear arises during operation of the valve and abutment of the diaphragm against the valve seats. The function of the valve deteriorates and after a certain time leakage arises. In order to ensure reliable operation of the valves, the diaphragm is thus exchanged once a year. This implies that a service engineer travels out to the machine and disassembles the machine and all of the valves to exchange the diaphragms. The costs for this service are therefore high, particularly the labour costs.

It has been proposed to arrange the diaphragm in some form of cassette which would be simpler to exchange to thereby reduce the precautionary service time.

SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement in a valve which permits simplified procedures during such precautionary services.

A further object of the present invention is to suggest a construction which implies that the diaphragm does not need to be exchanged, whereby the service costs can be radically reduced.

The present invention thus relates to a valve comprising at least one inlet and at least one outlet for a fluid such as a liquid or gas. The inlet and/or the outlet are provided with a valve seat for cooperation with a diaphragm. An operating arrangement causes the diaphragm to abut the valve seat for selective operation of the valve.

According to the invention, the diaphragm has a dimension which is greater than that which is necessary for abutment against the valve seat. Furthermore, an activation arrangement is provided for displacement of the diaphragm so that a new, at least partially unused, region of the diaphragm is exposed to the valve seat.

Preferably, the diaphragm is circular, whereby the activation arrangement rotates the diaphragm about its centre so that a new sector is exposed to the valve seat.

The rotation can take place through an angle of about 10°- 45°, particularly 18°, depending on the desired operating life.

Alternatively, the diaphragm can be displaced linearly and substantially perpendicular to the valve seat.

The diaphragm can be displaced in steps by such an amount that a completely new portion of the diaphragm is exposed to the valve seat.

Alternatively, displacement can take place substantially continuously or in small steps so that the diaphragm is continuously, or substantially continuously, renewed.

Preferably, a locking arrangement is provided which prevents return of a previously exposed portion of the diaphragm to exposure to the valve seat.

The valve is preferably a two-way valve which comprises an inlet and two outlets, these being aligned with each other and whereby each outlet has a valve seat.

The activation arrangement can be powered by a power source such as a solenoid or motor. In this manner, there is no longer any need to dismantle the machine; instead "exchange"of the diaphragm can be initiated electrically, for example by pressing a button or via a micro-computer which may be remote controlled.

BRIEF DESCRIPTION OF THE DRAWINGS Further features, advantages and properties of the two-way valve according to the invention will be apparent from the detailed description of the invention given below and with reference to the drawings.

Fig. 1 is an elevational view of the valve according to the invention partially in cross-section.

Fig. 2 is a perspective view of a diaphragm in the valve according to Fig. 1.

Fig. 3 is an exploded view of the valve according to Fig.

1.

Fig. 4 is a perspective view which shows the valve seats in greater detail.

Fig. 5 is a perspective view similar to Fig. 4 of an alternative embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The valve which is shown in Fig. 1 comprises an outer housing 1 provided with an inner housing 2. The inner housing 2 comprises an inlet 3 which extends perpendicular to the plane of the paper and thereafter bends upwardly 90° and discharges centrally in the upper surface of the inner housing 2, marked at 4. The inner housing 2 further comprises a first outlet 5 and a second outlet 6. The outlets 5 and 6 have openings defined by valve seats 7 and 8 in the upper surface of the inner housing 2.

The upper surface of the inner housing is covered by an elastic diaphragm or a membrane 9 having the general shape as illustrated in Fig. 2. The membrane is symmetrically circular, i. e. round when seen from above in Fig. 2. The membrane 9 is affixed to a circular ring 10 by means of a suitable adhesive 11.

An activator lever 12 is pivotable about an axis 13. The lower end of the lever 12 is provided with a liner 14 having a symmetrically circular cross section generally corresponding to the upper surface of the membrane 9, as shown in Fig. 1 and Fig. 3.

When the lever 12 is rotated about an axis 15 according to the arrow 15, the membrane 9 is pressed against the valve seat 8 as shown in Fig. 1. If the lever 12 is rotated in the other direction, the membrane 9 is instead pressed against the valve seat 7.

The membrane 9 leaves the inlet opening 4 substantially free via a cavity 16 between the upper surface of the inner housing 2 and the membrane 9. Accordingly, liquid can flow from the inlet 3 via the cavity 16 to the open valve seat 7 and out through the outlet 5, as indicated by the arrows 17 and 18. If the lever 12 is pivoted to the left in Fig.

1, the valve seat 8 is opened instead and the liquid flows out through the outlet 6 instead. Actuation of the lever 12 is preferably achieved via a solenoid 23.

The membrane 9 in such a valve is subjected to considerable wear around the region of the valve seats 7 and 8. In order to ensure a reliable functioning of the valve, the membrane is therefore regularly exchanged, for example once a year, as mentioned above.

According to the present invention, an increased working life for the membrane is achieved due to the fact that it is arranged to be rotatable so that new, unused portions of the membrane can be exposed to a valve seat instead of having to exchange the membrane in its entirety.

According to the invention, the membrane 9 is affixed to a ring 10. The ring 10 and the membrane 9 are divided up into ten (or twenty) sectors, each comprising 18° of a circle.

When the membrane is to be exchanged after one year, the engineer simply rotates the ring 10 through 18°, whereby a new, undamaged portion of the membrane 9 is exposed to the valve seats 7 and 8. In this manner, the membrane can be

"exchanged"without having to dismantle the valve. This "exchange"can take place 10 times, whereby the working life of the valve becomes 10 years, assuming that exchange is decreed once a year.

The material of the membrane 9 is preferably silicon rubber (polydimethylsiloxane) of the type WACKER 3003. This membrane material ought to have a possible working life of about 10 years or at least 5 years.

Remaining parts of the valve are made from PEEK, polyetheretherketone, which is a thermoplastic material with good chemical resistance and good flow properties at the operating temperatures in question.

In order to prevent return rotation of the ring 10 and the membrane 9, the ring 10 is provided with teeth 19 which cooperate with a backing pawl 20 arranged in the inner housing 2, see Fig. 4. The teeth are spaced at 18° intervals. Thus, when the ring 10 is rotated one notch, this corresponds to one"exchange"of the membrane 9 since a new, completely unused sector of the membrane is wound forward and exposed to the valve seats.

The ring 10 can be provided with engagements for a tool which provides for rotation of the ring through 18° without having to disengage the tool. By placing the tool in a correct position and rotating it as far as possible, precisely the correct displacement of the membrane is attained.

The ring 10 can be provided with a spring arrangement (not shown) which biases the ring 10 towards the backing pawl so that the teeth engage with the backing pawl as soon as a tooth has ridden over the backing pawl.

The backing pawl can be located on a displaceable carriage 21, as indicated in Fig. 5. The carriage is displaced by a solenoid or motor 22. When the solenoid 22 is activated, the carriage 21 is displaced towards the solenoid and thus passes a tooth 19 in the ring 10 located thereabove, see Fig. 3 in which the backing pawl 21 is partially shown. Thereafter, the carriage 22 is returned to the position shown in Fig. 5 either by spring force or actively via the solenoid 22 and thereby takes with it the ring 10 and the membrane 9.

The actuation of the solenoid takes place electrically and can take place manually by actuating a push-button on or in the machine.

Preferably, the computer in the dialysis machine is, however, pre-programmed to actuate the solenoid after a number of operating hours corresponding to the expected working life for each valve, which of course can be different for different valves.

Alternatively, or complementarily, the actuation can occur via remote control, for example via telephone lines or radio signals for remote service.

The upper surface of the insert 2 having the valve seats 7 and 8 is shown in Fig. 4. These valve seats have an oval form or egg shape in order to permit the largest possible surface without taking up too great a region of the sector- shaped membrane surface. The valve seats thus have an inwardly tapering cross-sectional surface towards the centre.

In addition, the inlet 4 is shown arranged at the centre and with a flow distribution which is designed to avoid formation of regions with stagnating liquid flow.

As is apparent from Fig. 3, the inside of ring 10 is provided with a plurality of projecting ribs. These cooperate with the membrane 9 and serve to ensure that the membrane rotates together with the ring. The liner 14 is affixed to the membrane and also rotates therewith.

The joining of the liner 14, the membrane 9 and the ring 10 can be achieved via a suitable adhesive. A further alternative is to first injection-mould the membrane 9 and thereafter injection-mould the two other components 10 and 14 directly on the membrane 9, whereby adhesion is created already during manufacturing.

In an alternative embodiment of the invention, the membrane is formed during manufacture so that it already comprises segments of 18°. The membrane is thereby provided with ridges which create a suitable division. Naturally, other divisions can be used, for example 30° for a working life of six years, etc.

The membrane 11 and the ring 10 preferably have a circular cross section. The insert 2 and the housing 1 can have an arbitrary cross section and, in a preferred embodiment, are rectangular.

It is possible within the scope of the present invention that other membrane shapes can be used. In particular, the membrane can be rectangular and displaced linearly, substantially perpendicular to the plane of the valve seats.

It is not necessary to displace the membrane so far that a completely unused region of the membrane is exposed to the valve seats. In an alternative embodiment, the membrane is displaced only a short distance of a few millimetres each time, or continuously, so that new material is exposed to the valve seats more or less continuously.

Such small displacements can take place each time the valve is activated. Suitably, however, such displacements do not take place during normal operation, but instead during periods when the machine is not in use. In this manner, execution of functional checks of the machine before the machine is used are facilitated.

The invention has been described above with reference to the embodiment of the invention shown in the drawings. The various components can, however, be combined in different ways within the scope of the invention. The invention is limited only by the appended claims.