Valves and valve actuation – Valve – Materials
Patent
1996-11-12
1999-12-07
Chambers, A. Michael
Valves and valve actuation
Valve
Materials
25112915, 13762523, F16K 3100
Patent
active
059969687
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a valve having a closure member which co-operates with a valve seat and is movable by an actuating device with a driver element, which driver element is guided in a housing.
U.S. Pat. No. 5,145,148 discloses such a valve, which is used in a brake system to control the flow, or the pressure, of the brake fluid. There, the driver element is in the form of a rod which, on actuation by an armature, which changes its position when current flows through a coil surrounding it, pushes a ball away from a valve seat. The rod is in this particular case surrounded by a nylon bushing which guides the rod in the housing. The rod is relatively thin in order not to disrupt the magnetic circuit. The nylon bushing is correspondingly thick.
In such a construction, malfunctioning of the valve can occasionally be observed, that is, the valve does not open or does not close when desired, but remains in the position it has assumed. This is attributed to the different thermal expansion coefficients of driver element and housing on the one hand and of the nylon bushing on the other hand. If the nylon bushing expands to a relatively great extent, the driver element becomes jammed in the housing. This effect can be partly eliminated by providing a larger clearance between the nylon bushing and the housing, but this clearance leads to imprecise guiding. This measure is also not suitable if it is wished to guide the driver element in the housing with an improved seal, nor if a defined gap between the driver element and the housing is an important factor, the gap being intended to damp the movements of the driver element.
Such a gap also causes accelerated wear of the valve, because as the driver element moves, not only is there purely frictional loading on adjacent surfaces, but as the driver element vibrates in the housing there is also a possibility that impact loading will occur, to the detriment of the plastics material.
SUMMARY OF THE INVENTION
The invention is based on the problem of providing a reliably working valve having a long service life which is able to work with a plurality of fluids.
This problem is solved in a valve of the kind mentioned in the introduction in that between the housing and the driver element there is arranged a high-temperature thermoplast.
The high-temperature thermoplast reduces the friction between the driver element and the housing. Both parts can therefore slide in low-friction engagement on one another. The high-temperature thermoplast moreover has a thermal coefficient which, although it does not correspond exactly to that of the material normally used for the driver element and the housing, normally metal, approximates to this thermal expansion coefficient very closely as regards magnitude. The thermal expansion coefficient of such a high-temperature thermoplast is normally only about double that of metal. Even when expansion does therefore occur when the temperature rises, this is not as critical as when using nylon. Thermoplast, housing and driver element can therefore be matched to one another with negligible tolerances. Moreover, the higher friction force occurring during an expansion, caused chiefly by a higher surface pressure between driver element and housing, is compensated for by the improved frictional behaviour of the high-temperature thermoplast. The lower friction therefore results not only in reduced wear, and thus in longer service life, but also in a more reliable operation of the valve. The fluids can be chemical compounds or simply water on its own.
Polyarylether ketone, especially polyetherether ketone, is preferably used as the high-temperature thermoplast. As a result, a good stability can be achieved even at relatively high temperatures. The said high-temperature thermoplasts at the same time have a comparatively good chemical resistance to a series of chemical compounds, for example, refrigerants. moreover, these thermoplastics are dimensionally very stable.
The high-temperature thermoplast is preferably fibre-rein
REFERENCES:
patent: 4233585 (1980-11-01), Sugimoto et al.
patent: 4635681 (1987-01-01), Boldish
patent: 4838145 (1989-06-01), Slocum et al.
patent: 5145148 (1992-09-01), Laurent
patent: 5464191 (1995-11-01), Shenk
patent: 5518027 (1996-05-01), Saiki et al.
Chambers A. Michael
Danfoss A/S
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