Plate valve for the dosing of liquids

Details Plate valve for the dosing of liquids Plate valve for the dosing of liquids

1999-06-18

2001-01-16

Morris, Lesley D. (Department: 3752)

Fluid sprinkling, spraying, and diffusing

Fluid pressure responsive discharge modifier* or flow...

Fuel injector or burner

C239S533300

Reexamination Certificate

active

06173912

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a plate valve which is sealed by corresponding surfaces on a valve seat of the valve housing and on the plate, which is connected to a valve spindle. A stroke of the valve spindle opens the valve and exposes a seal gap, which is usually radially symmetrically constructed, particularly in the shape of a truncated cone. The geometry of the flow in the seal gap and after exiting the valve decisively determines the continuing state of the liquid.
FIGS. 3 and 4
illustrate a typical plate valve according to the prior art in an axial section. This valve serves to generate a liquid cone spray. The liquid first flows axially in the annular gap
5
between a valve spindle
2
and the valve body
3
downward from above in the direction of the valve plate
3
and is deflected in the direction of a valve seat
4
which is incorporated into the valve body
1
. Given an open valve, the liquid thus exits the valve gap (also referred to as a seal gap) which is located between the valve plate
3
and the valve seat
4
in the shape of a cone spray. This cone spray comprises a cone angle &agr; which is pressed on by valve plate
3
and valve seat
4
.
Previously common cone angles a of the plate seal face and cone angles &bgr; of the valve seat face for generating a liquid-tight union have been selected equally large (&agr;=&bgr;). The problem regularly arises that, given an open valve, the flow cross-section, which is shaped like a truncated cone, in the seal gap
6
grows linearly with the radius (DI<2R<DA, with DI=inner diameter of the seal gap
6
and DA=outer diameter of the seal gap
6
). The formula for the area, or respectively, cross-section A of the flow cross-section, which is shaped like a truncated cone, in the seal gap
6
derives from elementary geometrical considerations:
A=Π·HA·
sin(&agr;/2)·(2
R−
0.5
HA
·sin(&agr;))
with HA=outer height of the gap.
In the prior art, with &agr;=&bgr;, the difference between the outer height HA of the gap
6
and the inner height HI of the gap
6
corresponds to the stroke executed by the valve spindle.
With dimensions that are typical in fuel injection valves, the following applies: inner diameter DI=4 mm; outer diameter DA=4.5 mm.
A relative change derives of the minimal flow cross-section from the inflow of the liquid to the outflow of the liquid in relation to the valve gap, or respectively, seal gap
6
, which can be calculated accordingly:
(
DA−DI
)/(
DI−
0, 5
HA·
sin(&agr;))≈0.5/4=0.125=12.5%.
In the open condition, the cone spray valve thus represents a diffusor. Such a sharp increase of the flow cross-section over such a short distance leads to a heavily delayed flow and to cavitation. Such cavitation has already been experimentally observed in injection valves with a seal face such as is described above. Given the decompression from ca. 200 bar to 1 bar, which corresponds to 2%, the volume increase cannot compensate this geometric expansion of the traversed cross-section by means of the liquid itself, whose compressibility is &kgr;=10
−9
m
2
/N, particularly in fuels,. For this reason, this sharp drop in pressure is associated with vaporization phenomena and cavitation.
SUMMARY OF THE INVENTION
The invention is based on the object of preventing, in a plate valve, flow delays that are associated with cavitation.
The invention is based on the realization that the geometry of the plate valve should be adapted such that the flow cross-section in the seal gap is independent of the radius. This occurs in that, in contrast to the prior art, the face of the valve seat
4
at the valve body the corresponding seal face at the valve plate
3
are not oriented in parallel fashion as previously. The cone angle &agr; of the valve plate is larger than the cone angle &bgr; of the valve seat
4
. The particular advantages resulting from this modification of the valve seat geometry and/or of the valve plate geometry prevent cavitation. Furthermore, the seal of the valve, which now exists as a line seal, requires less closing force for sealing than does a surface seal, such as had to be expended given the parallel construction of the seal faces.
Advantageous developments of the invention provide that the liquid to be dosed flows out from the interior. In addition, the plate valve is advantageously designed as a special steel valve.


REFERENCES:
patent: 2255203 (1941-09-01), Wiegand
patent: 2555803 (1951-06-01), Mashinter et al.
patent: 4958771 (1990-09-01), Klomp
patent: 5685492 (1997-11-01), Davis et al.

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