The invention relates to a diaphragm-controlled differential-pressure valve, having a valve housing which has an inlet, an outlet and a valve seat co¬ operating with a closure member, and having a diaphragm loaded by a set-point spring, the outer edge of which diaphragm is fixedly clamped between the lower part and the cover of a diaphragm capsule, the centre of which diaphragm capsule is connected by way of a valve rod to the closure member and which separates an inner and an outer pressure chamber from one another.

Such a differential-pressure valve is known, for example, from EP 0 405 339 A2. It has a valve housing having an inlet, outlet and valve seat and, separated therefrom, a diaphragm capsule, the lower part of which has a base for insertion in the valve housing, the base at the same time forming a feed-through for the valve rod joined to the diaphragm and carrying the closure member. The valve rod is of hollow construction. In the region of the feed-through it contains a passage which connects the inner space of the valve housing with the inner pressure chamber and in the region of the diaphragm it is provided with a large cavity in which the set-point spring is arranged. In a central extension of the cover there is provided an adjusting means with which the force of the set-point spring can be changed and the travel of the closure member can be limited or the valve completely closed. This construction is of large overall length and takes up a large amount of space in its installed position.

The invention is based on the problem of providing a differential-pressure valve of the kind described in the introduction which takes up little space.

That problem is solved according to the invention in that the lower part of the diaphragm capsule is constructed in one piece with the valve housing and the cover carries a spring housing accommodating the set- point spring.

In this construction a separate diaphragm capsule and a coupling between the diaphragm capsule and the valve housing are unnecessary. This results not only in a small overall length but also in a considerable reduction in manufacturing and installation costs.

It is advantageous for the diameter of the diaphragm to be only about at most 20% smaller than the length of the valve housing measured between the inlet and the outlet. In that case, virtually the entire length of the valve housing is utilized for the lower part of the diaphragm capsule. Diaphragms of sufficiently large size can therefore be used.

The inner faces of the lower part and the cover advantageously run parallel to one another. In this manner a very flat diaphragm capsule is obtained, which allows a further reduction in the overall height.

In a preferred embodiment, provision is made for the valve seat to be remote from the diaphragm and for the valve rod to pass through the valve seat, to be guided in a bore of the valve housing and to be connected in the diaphragm capsule to the diaphragm. The valve function resulting therefrom is suitable for example,

for a differential-pressure valve to be installed in the feed pipe of a heating system.

It is advantageous in that instance for the valve housing to have on the side remote from the diaphragm a mounting opening serving for the introduction of the closure member and which can be closed by an insert. In this manner a very simple installation of the closure member is provided.

Further advantages are provided by the fact that the part of the valve rod adjacent to the diaphragm passes, sealed, through a bore in the valve housing, the diameter of which is the same as the inner diameter of the valve seat, and the part of the valve rod adjacent to the closure member has a cross-section that is smaller than that of the bore. With such dimensioning a valve relieved of pressure is obtained.

In a further development, it is advisable for the valve housing to have on the side remote from the diaphragm an actuator to be operated manually from outside to limit the travel of the closure member or to close the valve. This actuator does not collide with the diaphragm. It can act directly on the closure member. It can also be combined with the insert closing the mounting opening.

The valve housing preferably has an opening connecting the inner pressure chamber to the inside of the valve. The inner pressure chamber then acts as a self-pressure chamber. No ducts in the valve rod are required for this.

It is also advantageous for the mouth of a pressure line connection to be arranged in the cover so that it

can be closed by the diaphragm. When the outer pressure chamber is opened with the differential- pressure valve installed, for example, in order to exchange a set-point spring, sealing occurs automatically. The clamped diaphragm separates the outer pressure chamber from the inside of the valve and also closes the pressure line connection.

It is advisable for the spring housing to be removable and for the set-point spring bearing against its end face to be exchangeable. This leads to a very simple construction in which new desired values can be achieved simply by exchanging a spring.

It is advantageous in that case for the cover to have a neck portion guiding the set-point spring, to the outside of which neck portion the spring housing is fastened. The neck portion thus has a dual function.

Another advantageous alternative consists in that the spring housing is constructed in one piece with the cover and has an adjusting spindle rotatable from outside with which a supporting element, held so that it does not rotate, for the spring to bear against is axially adjustable. The set-point can here be continuously changed.

The invention is explained in further detail hereinafter with reference to preferred embodiments illustrated in the drawing, in which:

Fig. 1 is a longitudinal section through a first embodiment of a differential-pressure valve according to the invention and

Fig. 2 is a longitudinal section through a modified embodiment.

The differential-pressure valve illustrated in Fig. 1 comprises a valve housing 1 with an inlet 2 and an outlet 3 as well as a valve seat 4. The top side of the valve housing 1 forms the lower part 5 of a diaphragm capsule 6, which extends over virtually the entire axial length of the valve housing 1. A diaphragm 7 is fixedly clamped at its outer edge 8 between the lower part 5 and a cover 9, a crimping edge 10 of the valve housing 1 engaging over the edge of the cover 9. The surfaces of the lower part 5 and the cover 9 facing one another run parallel to one another.

The diaphragm 7 divides the diaphragm capsule 9 into an inner pressure chamber 11, which communicates with the external inner chamber 13 of the valve housing 1 by way of an opening 12 in the housing wall, and an outer pressure chamber 14, which is connected by way of a pressure line connection 15 to a pressure sensor 16. The mouth 17 of the pressure line connection is located in a flat portion of the cover 9 where it can be covered, and thus closed, by the diaphragm 7. A set- point spring 18 bears at one end against the end face 19 of a spring housing 20 and at the other end acts on a diaphragm plate 21. The set-point spring 18 is guided by a neck portion 22, on the outside of which there is provided a thread 23 for screwing on the spring housing 20. In this manner a set-point spring 18 can be exchanged in order to provide a particular desired value.

The centre of the diaphragm 7 is fixedly clamped between the diaphragm plate 21 and a reinforcing plate 24, a screw 25 holding the two plates 21 and 24 facing

against a valve stem 26 which at its opposite end carries a closure member 27 which co-operates with the valve seat 4. The end of the valve rod 26 adjacent to the diaphragm 7 is guided through a bore 28 in the valve housing 1 and is sealed there by a seal 29. The diameter of this bore 28 is the same as the internal diameter of the valve seat 4. The bore 28 and the valve sat 4 can be drilled in one operation. The part 30 of the valve rod 26 adjacent to the closure member 27 has a smaller cross-section than the bore 28. In this manner a valve relieved of pressure is obtained.

On the side of the valve housing lying opposite the diaphragm 7 there is a mounting opening 31 which is closeable by an screw-in insert 32. In the insert there is arranged an actuator 33 which can be screwed in by means of the rotary knob 34 and is thereby axially displaceable. Using this actuator 33 the travel of the closure member 27 can be limited and, if desired, the valve can also be completely closed.

For installation, the diaphragm 7 is put into position with the diaphragm plate 21 and the reinforcing plate 24. The valve rod 26 is then introduced through the mounting opening 31 and joined by the screw 25 to the diaphragm centre. The insert 32 is then screwed into the mounting opening 31 and the cover 9 is put into position and secured by crimping over the crimping edge 10. Once the desired set-point spring 18 has been selected, the spring housing 20 can be screwed on. If desired, the valve rod 26 need not be mounted until the cover 9 has been joined to the lower part 5.

The spring housing 20 can also be removed during operation. The diaphragm 7 prevents water escaping

from inside the valve and by covering the mouth 17 prevents water escaping from the pressure sensor 16.

The embodiment of Fig. 2 differs from that of Fig. 1 only in the construction of the cover 35, which is constructed in one piece with a spring housing 36. The set-point spring 37 bears against a supporting element 38, held so that it does not rotate, which is axially adjustable by means of an adjusting spindle. For that purpose the adjusting spindle 39 has an hexagon socket 40 for rotation and an external thread 41 for axial displacement of the supporting element 38. Such a set-point spring 37 can be adjusted continuously.

In both embodiments the inner pressure chamber 11 forms a self-pressure chamber, which is acted upon by the output pressure of the valve. Such a valve can be installed in particular in the feed pipe of a heating system, the upper pressure chamber 14 being supplied with the return pressure. The basic concept of the invention can also be applied, however to those differential-pressure valves in which the input pressure acts on the inner pressure chamber 11, as is the case, for example, with valves arranged in the return line of a heating system.