Fluid handling – With cleaner – lubrication added to fluid or liquid sealing... – Cleaning or steam sterilizing
Reexamination Certificate
1999-07-16
2001-01-30
Walton, George L. (Department: 3753)
Fluid handling
With cleaner, lubrication added to fluid or liquid sealing...
Cleaning or steam sterilizing
C137S312000, C137S614180, C134S16600C
Reexamination Certificate
active
06178986
ABSTRACT:
The invention relates to a double seat valve with cleanable seats with two closure members mounted in series and movable relative to each other, as described in the preamble of claim
1
.
A generic double seat valve is known, for example, from EP-A-0 174 384. This valve presents the disadvantage that in order to clean the seat surface of the closure member in the form of a slide valve, the valve piston, the circumferential groove provided in the other closure member (see
FIGS. 2
a
-
3
d
) or in the cylindrical valve seat (see
FIGS. 4
a
-
4
d
), into which member the sealing agent of the slide valve piston must be brought in an intermediate position in order to effect seat cleaning, must also be passed during each regular opening or closing movement of the double seat valve. As a result, penetration of liquid, which is desirable in the case of seat cleaning but not in the normal alternating movement of the double seat valve, occurs during each of these movements.
DE 38 35 944 A1 discloses another double seat valve whose seats may be cleaned, one in which, in contrast to the generic double seat valve, the slide valve rests only against the other closure member to effect sealing, before the latter is also transferred to the open position. For the purpose of cleaning the seat surface of the slide valve piston, this slide valve piston is transferred to a seat cleaning position by the amount of a partial stroke in the direction of its open position to the width of a gap. With this double seat valve the regular opening and closing movement does remain unaffected by the measures applied for seat cleaning, it is difficult to measure and limit to the absolute minimum necessary for elimination of fouling in the seat area the amount of cleaning means obtained in each instance from the associated valve housing element for cleaning the valve seats by gap-wide actuation of the closure members. But in order nevertheless to ensure economical and environment friendly use of cleaning agents, it is proposed in DE 38 35 944 A1 that the valve disks be actuated in cycles.
In another state-of-the-art cleanable-seat double seat valve (EP-A-0 646 741), the amount of cleaning means to be prepared for cleaning the valve seats is limited by the fact that the slide valve piston element involved rests against a housing stop provided with flushing means apertures when in the pertinent flushing position. Consequently, in this state-of-the-art double seat valve there are areas that cannot be wetted with cleaning means during the flushing process unless this valve as well is cleaned periodically, to be sure because of the disadvantage indicated above.
In the case of the known double seat valves referred to above cleaning means introduced by way of the cleared seat surface from the adjacent valve housing element can impinge on the other valve seat area with more or less high kinetic energy when the latter is in its closed position. This can occasionally result in penetration of the closed sealing area by cleaning means. A particular danger is then caused if the pertinent seal has undergone extensive wear as a result of which the reduced sealing pressure can no longer ensure a sufficient sealing effect because of the action of the kinetic energy of the spray stream.
In addition, there is set for cleanable-seat double seat valves the requirement that cleaning means flowing into the leakage cavity during seat cleaning be drained into the vicinity of the double seat valve free of pressure, that is, with no pressure buildup in the leakage cavity. The double seat valves referred to above (DE 38 35 944 A1 and EP-A-0 174 384) could only with great difficulty meet the requirements set in this connection, since, on the one hand, the possibility of concise measurement of the pertinent amount of cleaning means is not obvious, and, on the other, the discharge cross-sections cannot be suitably adapted to the increased supply of cleaning means.
In the United States of America there is even set for the double seat valves employed in dairy industry installations the requirement that no cleaning means may flow by way of an unsealed valve seat into the adjacent valve housing element in the event of major defects in seals or even absence of such seals. Even if it is possible to measure out the extremely small amount of cleaning means used in seat cleaning, as apparently is the case with the state-of-the art double seat valve disclosed in EP-A-0 646 741, direct spray application in this instance to one of the two seat areas would in the event of a major seal defect or loss of the seal result in penetration of cleaning liquid into the adjacent valve housing element. Such a situation would arise at least on the lower valve seat in flushing of the upper seat area (cf.
FIG. 2
c
of EP-A-0 646 741) if there is a major seal defect or even loss of the seal has occurred here. For this reason use of the cleanable seat double seat valves referred to in the foregoing has been rejected, at least in the dairy industry.
Absolutely pressure-free removal of amounts of liquid from the leakage cavity, leaks due either to sealing defects or amounts of cleaning means used in any type of cleaning of the leakage cavity or seat cleaning, desirable because necessary, is a requirement which has been gaining in importance recently, especially on the United States market or in the American area of influence in use of double seat valves and there especially in dairy technology. What is involved here is compliance with the United States so-called “3A Standard” and the so-called “FDA Regulations,” which state that the leakage space is to be connected to the atmosphere so as to be drainable with a cross-section corresponding to the rated value of the largest pipe connected to the valve.
On the one hand, cleanable-seat double seat valves are increasing in importance because seat areas can thereby be cleaned even if cleaning means is present in only one of the valve housing elements and, if desired, product is still applied to the other, that is, if the valve cannot be fully opened for the purpose of cleaning its seat areas, and, on the other, the safety philosophy of the double seat valve, specifically, that cleaning means and product present under pressure in the valve must not be separated from each other by only one seal, is always inoperative during seat cleaning. Similarly, by the way, the safety philosophy of the double seat valve is always avoided if the leakage cavity is cleaned with the double seat valve in the closed or open position by external delivery of the cleaning means from the vicinity of the double seat valve. Outside the United States' sphere of influence in the case of cleaning a leakage cavity with the valve open or closed and during seat cleaning, the requirements deriving from the double seat valve safety philosophy have thus far not been consistently and stringently complied with because it is assumed that, if the connecting path between the leakage cavity and the vicinity of the double seat valve is properly measured, the cleaning means on the closed valve seat is not under pressure and because, in addition, no other solution of the problem is available.
On the basis of the disadvantages of the state of the art described in the foregoing, the object of this invention is to develop a cleanable-seat double seat valve in which, for the purpose of consistent implementation of the double seat valve safety philosophy, dual sealing secured by a leakage cavity from the valve housing element closed by the other closure member is provided in each instance in the course of seat cleaning of the closure member separated by the width of a gap from its seat surface.
This problem is solved by the features set forth in claim
1
. Advantageous embodiments of the proposed cleanable-seat double seat valve are described in additional subsidiary claims.
The proposal shows how double sealing can be accomplished in a surprisingly simple manner under the conditions described. For this purpose a generic double seat valve at least the essential features of
Shannon John P.
Tuchenhagen GmbH
Venable
Walton George L.
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