Fluid handling – Systems – Flow path with serial valves and/or closures
Reexamination Certificate
2000-02-23
2002-02-26
Lee, Kevin (Department: 3753)
Fluid handling
Systems
Flow path with serial valves and/or closures
C137S312000, C137S240000
Reexamination Certificate
active
06349742
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a dual-seat valve that switches in a leak-free manner, including: a valve housing part having at least two openings for two lines for letting fluid in and out, two coaxial valve seats disposed between these openings, two valve closing members that are each guided in the valve housing between an open position and a closing position for the sake of coaxial motion relative to one another and to the corresponding valve seats and which in their closing position effect double sealing between the aforementioned openings, the first closing member being a slide piston with radial sealing means disposed on its end portion, which piston is intended to press, during its opening motion, against the second closing member and during the continued opening motion moving the latter into its open position as well, the first valve seat being cylindrical and in the closing position receiving the slide piston in sealing fashion, and both in the closing position and in the open position a leakage chamber is formed between the closing members, which communicates permanently with the outside of the valve via a drain outlet.
A dual-seat valve of this kind is known from European Patent Disclosure EP 0 174 384. Such valves are used in the foods industry, especially in brewing and milk processing, for separating lines that carry different products at their connection points. The valve must be capable of reliably preventing mixing of the different products and must be capable of functioning perfectly from a hygienic standpoint. The two closing members of the known valve can therefore each execute a cleaning stroke individually for cleaning of the valve seat. During the valve seat cleaning, however, only a single seal separates the two lines. Hence there is the risk that a pressure spike may force the closed closing member out of its valve seat, which would allow the products in the lines to mix together. Such pressure spikes occur above all when the closing members are individually lifted for cleaning, since when the one closing member is opened, the line pressure suddenly acts on the other closing member, reducing its contact pressure against the valve seat. In the known dual-seat valve, a groove is therefore provided on the second valve seat and on the end, toward the first closing member, of the recess of the second closing member. During the cleaning of the valve seat, a flow of cleaning medium can flow into the leakage chamber through the gap formed by the groove between the closing member and the valve seat or the recess.
From German Patent DE 38 35 944 C2, a dual-seat valve of this generic type is also known. To compensate for pressure surges, the second, lower closing member is lengthened toward the underside of the valve to form a compensation piston, which passes in sealed fashion through the lower part of the housing. In the cleaning stroke of the lower closing member, a circular gap is formed both between the lower valve plate and the valve seat and between the outer face of the compensation piston and the wall of the passage in the lower housing part; by way of this gap, cleaning fluid can enter the leakage chamber or the rinsing region for the compensation piston.
A disadvantage of the known dual-seat valve is that the cleaning stroke must be executed with great precision; otherwise, the cleaning gap between the valve seat and the closing member becomes too large, and large quantities of cleaning medium flow into the leakage chamber. This leads to an uncontrolled increase in the pressure in the leakage chamber and thus to stress on the closed closing member. There is accordingly the risk that the closing member will be lifted and cleaning fluid can enter the line carrying a product. Another disadvantage is that when the cleaning gap between the closing member and the valve seat is opened, the pressure in the leakage chamber is suddenly raised, as a result of which the other closing member can also be forced out of its seat.
SUMMARY OF THE INVENTION
The object of the invention is therefore to disclose a dual-seat valve of this generic type in which pressure spikes in the leakage chamber can be reliably avoided during the seat cleaning.
This object is attained in that a cylindrical inside face is provided at the second valve seat, and a cylindrical portion corresponding to it is provided on the second closing member, the diameter of which portion is slightly less than the diameter of the cylindrical inside face of the second valve seat, and the cylindrical faces, both in the cleaning stroke and in the closing and opening motion of the second closing member, form a throttle gap between them, and that a sealing means is provided on the second closing member in such a way that in the closing motion, the throttle gap is formed first, before the sealing means seals off the leakage chamber from the line.
In the cleaning stroke of the valve member, cleaning fluid enters only through the throttle gap formed between the two cylindrical faces. As a result, the pressure buildup in the leakage chamber takes place slowly and uniformly. Both pressure and a volumetric flow of the cleaning fluid flowing into the leakage chamber can easily be controlled. Because of the length of the throttle gap, the pressure and the volumetric flow are also relatively insensitive to fluctuations in the stroke of the closing member, so that precise adjustment and monitoring of the stroke is unnecessary. A pronounced pressure rise in the leakage chamber during the cleaning process is reliably prevented.
Pressure spikes in the cleaning stroke of the slide piston are avoided if in the cleaning position of the slide piston, a cylindrical throttle gap is formed between a cylindrical face of the slide piston and the first valve seat.
The sealing means can be formed as a radial seal on the slide piston and/or on the second closing member. However, it is also possible to embody the sealing means at the second closing member as an axial or conical seal. It is then positioned on the end of the second closing member toward the slide piston.
The guidance of the closing member on moving inward is facilitated if the second valve seat has a conical portion, which extends from the cylindrical portion of the second valve seat to the first valve seat. By means of the conical face, the slide piston is guided in the closing motion of the valve and centered in the valve seat. The radial sealing means of the slide piston are not stressed by the upper edge of the first valve seat and are therefore subjected to less wear.
Guidance and centering of the second closing member in the valve seat is attained if the second valve seat has a conical portion that adjoins the cylindrical portion toward the opening side of the second closing member.
Fast and easy replacement of the sealing means is possible if the closing member is constructed from two parts joined together separably, preferably by means of a screw connection, and the sealing means is provided between the two parts.
In an especially advantageous embodiment, the second closing member, on its end toward the slide piston, has a recess with a substantially cylindrical circumferential wall aligned with the cylindrical valve seat, and the recess is dimensioned so as during the opening motion to sealingly receive the end portion and the radial sealing means of the slide piston, before the second closing member opens. Since in the closing motion of the valve the recess of the second closing member and the cylindrical valve seat of the slide piston are centered by the conical faces of the second valve seat, the recess and the first valve seat are aligned with one another. In the closing motion of the slide piston, this piston is centered by the conical face of the second valve seat, so that virtually no wear from the closing motion is brought about at its radial seals.
REFERENCES:
patent: 4460014 (1984-07-01), Mases et al.
patent: 4605035 (1986-08-01), Rasmussen et al.
patent: 6178986 (2001-01-01), Burmester
Borg Søren
Holmgaard Poul
Alfa Laval LKM A/S
Lee Kevin
Striker Michael J.
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