Valves and valve actuation – Rotary valves – Ball valve
Reexamination Certificate
2000-01-07
2001-10-30
Shaver, Kevin (Department: 3754)
Valves and valve actuation
Rotary valves
Ball valve
Reexamination Certificate
active
06308933
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a shut-off valve including a housing of thermoplastic plastic material, which has a spindle bush, a spindle, which is movably disposed in the spindle bush and is sealed with respect to the housing, and including a closure body, which is disposed in the housing and is connected to the spindle.
DESCRIPTION OF THE PRIOR ART
In practice, shut-off valves must in some cases withstand considerable internal pressures without leaking. If a shut-off valve is subjected to a high internal pressure, the valve housing expands radially outwardly. Shut-off valves are known whose permissible degree of deformation in operation is up to 6%. With housings of thermoplastic material, the deformation is relatively large in comparison to metallic housings. The temperature also has a major influence on the deformability of thermoplastic plastic materials, which soften at high temperatures.
Practice has shown that shut-off valves with a housing of thermoplastic plastic material tend to become leaky under high internal pressure, namely in the vicinity of the spindle bush, whereby the actuating moment also alters negatively, i.e. the ease of movement decreases. The latter can result in problems when actuating the valve.
It is thus the object of the invention to provide a shut-off valve which is reliably sealed to the exterior, even when subjected to an increased internal pressure, and is easily movably operable.
SUMMARY OF THE INVENTION
This object is solved in accordance with the invention if the housing has a recess which extends around the spindle bush and is open to the interior of the housing.
The invention is based on the recognition that the spindle bush, which is of round cross-section, deforms ovally when the valve housing deforms radially and that this is responsible for the leaks and difficulty of movement which occur.
As a result of the recess, a sleeve-shaped region is formed around the spindle guide, the cross-sectional shape of which remains substantially constant when the housing deforms. The cross-section of the spindle bush also remains correspondingly unaltered when there is an increased internal pressure in the housing. This ensures a reliable seal, even at previously critical internal pressures, on the one hand and on the other hand the spindle remains easily movable and simple to operate notwithstanding the deformation of the valve housing since no stresses occur.
Deformation of the housing could be eliminated with large concentrations of material at the critical positions on the housing. However, as changes in wall thickness become increasingly large, the risk of shrinkage cavity formation increases when manufacturing the housing. Shrinkage cavities occur when manufacturing die cast components if the heat is dissipated at differing speeds during solidification of the die cast component. This is particularly so in the case of a large concentration of material, for instance at large changes in wall thickness. Shrinkage cavities can result in destruction of the valve housing in the event of high internal pressures.
In accordance with the invention, deformation of the housing is permitted but the region of the housing which is crucial for reliably sealing, that is to say the region of the spindle bush, remains of constant shape.
An advantageous exemplary embodiment is characterised in that disposed between the spindle and the spindle bush there is at least one seal and that the recess extends in the axial direction of the spindle to at least the height of the seal.
The seal is thus located in the shape-stable region which is not affected by the deformation of the housing. It has transpired to be an additional advantage that an increased internal pressure prevailing in the recess presses this region against the spindle. As the internal pressure rises, the pressure and thus the sealing action of the seal increase also. The seal can be disposed either in an external groove in the spindle or in an internal groove in the spindle bush.
A particularly simple embodiment is produced if the seal is constructed in the form of an O-ring and if the spindle is rotatably mounted in the spindle bush. A simple, reliable and sturdy seal is thus produced. It is basically possible to construct the spindle in the form of a threaded spindle but a rotatable mounting of the spindle in the spindle bush results in a construction which is more packed and more favourable from the manufacturing point of view.
It is proposed in an important embodiment of the invention that the spindle bush is partially surrounded by a housing projection and that the recess extends into the housing projection. Such a construction has advantages, particularly from the injection moulding point of view.
Further advantageous embodiments are characterised in the dependent claims.
The invention will be described below in more detail with reference to a preferred exemplary embodiment in conjunction with the accompanying drawing.
REFERENCES:
patent: 4813649 (1989-03-01), Takeda et al.
patent: 5090447 (1992-02-01), Lewis et al.
patent: 5553831 (1996-09-01), Ozaki et al.
patent: 5586749 (1996-12-01), Conley et al.
ASV Stubbe GmbH & Co. KG
Blakely & Sokoloff, Taylor & Zafman
Bonderer D. Austin
Shaver Kevin
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