Valves and valve actuation – Reciprocating valve – Diaphragm
Reexamination Certificate
2002-02-20
2004-09-07
Bastianelli, John (Department: 3754)
Valves and valve actuation
Reciprocating valve
Diaphragm
C251S335200
Reexamination Certificate
active
06786470
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to diaphragm valves. In particular, the present invention relates to diaphragm valves which allow for free-drainage of a valve body of the valve when the valve is in the open position.
2. Description of Background Art
The demand for higher quality products forces industries to continually reevaluate fundamental and basic elements of their processes in a search to discover new methods and better components that will yield greater uniformity with higher levels of reproducibility in order to achieve the quality desired. Evaluation of inspection results by United States Food and Drug Administration (FDA) inspectors in recent years has caused that agency to push industry to focus on cleaning validation and, of particular relevance to this disclosure, the cleanability of equipment, a large part of which is sanitary valving. Among the concerns are that some equipment in these processes may not be adequately cleanable in place, that in-situ cleaning procedures are not themselves adequate to clean the equipment installed or that the procedures and equipment are appropriately matched, but the procedures are not being properly executed.
Valves are by far the largest category of equipment used in processes. Relative to other existing valve designs, weir-style diaphragm valves are simple, provide good process isolation, cost-effective to install and maintain and because they were thought to be easily and reliably cleanable in place. Unlike several other categories of valve designs, weir diaphragm valves generally offer good drainability with little hold-up of material when properly installed. For these reasons they have, over the last fifty years, become the valve of choice for use in hygienic processes.
In recent years the performance of these valves has been subject to much greater and closer scrutiny, at least in part due to pressure from FDA. While still the preferred choice for some applications, it has become apparent that weir diaphragm valves can pose a significant risk as a source of cross over contamination, particularly if improperly installed, operated and maintained or if clean-in-place and sterilize-in-place procedures are not properly followed. These concerns stem from the basic design of weir diaphragm valves. Referring to
FIG. 10
of the present invention, a typical weir diaphragm valve
101
is illustrated. The weir diaphragm valve
101
includes a valve body
103
, a diaphragm
133
and a bonnet, as well as other typical valve components (all not shown).
In
FIG. 10
, a static perimeter or circumferential seal
136
is formed between the valve body
103
and the bonnet by a perimeter of the diaphragm
133
. Furthermore, a dynamic line seal
137
is formed along a weir
140
. The main problem with the weir diaphragm valve design is that the static circumferential seal
136
is continuous with the line seal
137
made by the diaphragm
133
across the top of the weir
140
. When the center portion of the diaphragm
133
is raised to break the line seal
137
across the weir
144
to allow for flow through the valve, pressure is applied to the inner edge of the diaphragm
133
where it forms the static circumferential seal
136
with the valve body
103
. Accordingly, a portion of the static circumferential seal
136
is also raised. When the line seal
137
is reformed across the weir
140
by lowering the diaphragm
133
, material is trapped between the inner edge of the diaphragm
133
and the valve body
103
, i.e., within the static circumferential seal
136
. This trapped material may migrate back into the internal cavity
113
of the valve body
103
over time. Although this may be less of a problem while a batch of a process is in progress, not completely removing the trapped residual during cleaning procedures between batches is a more serious issue and may be considered very critical between campaigns of different products by the FDA.
In addition to the above, weir valves in the past were typically used in an orientation where the flow through the valve proceeded from the inlet passage to the outlet passage by flowing vertically over the weir
140
. Accordingly, material would be trapped on the upstream side of the internal cavity
113
. This of course causes cross contamination.
Manufacturers today, in an effort to improve drainage through their valves and minimize hold-up, recommend that weir diaphragm valves be cantilevered over onto the side so that fluids can flow passively around the weir and out, rather than vertically over the weir. While this is necessary in order to make weir valves drain, this also places a portion of the circumferential seal
136
at the bottom of the valve, causing it to become a sump where material will tend to collect and where complete drainage will be very difficult to fully achieve. Consequently, a more significant cleaning challenge and possible point source for cross contamination is exacerbated when using a weir valve in this manner. Several articles can be found through the literature on the subject of weir-style valve cleanability. One of the most recent is an article in Pharmaceutical Processing (September, 2001, pg. 80) in which the author, in a comparison study of weir valves and radial diaphragm valves, demonstrates that weir valves frequently do not become fully cleaned. In this study, radial diaphragm valves provided much higher clean-in-place reliability.
Accordingly, the primary alternative valve design to weir valves that has gained favor in many industries is the radial diaphragm valve, similar to the testing in the study mentioned above.
FIG. 11
of the present invention illustrates a typical radial diaphragm valve
101
. As with weir diaphragm valves, radial diaphragm valves include a flexing diaphragm
233
that allows the valve
201
to be opened and closed while segregating the mechanical elements of the valve
201
from the process. Radial diaphragm valves, however, differ from weir diaphragm valves in several important ways. The most important advantage radial diaphragm designs offer is that the static circumferential seal
236
between the valve body
203
in a radial diaphragm valve is not continuous with the dynamic seal
237
, as is the case with weir valves. Since the two seals are not continuous, a radial diaphragm valve can be actuated without the circumferential seal
236
being affected. Accordingly, cross contamination as a result of residual hold-up in the circumferential seal
236
is effectively eliminated when compared to the weir diaphragm valve.
While it would seem that the solution to the cross contamination problems currently plaguing the industry could be resolved by radial diaphragm valves, it is a byproduct of the radial design that makes radial diaphragm valves a less perfect solution to the problem. As mentioned above, radial diaphragm valves are defined by the segregation of the circumferential seal
236
from the flow control or dynamic seal
237
and the passage it seals. A review of the background art will show that in the dynamic seal
237
, the flow control passage
224
and the mating annular dynamic sealing surface
237
immediately about it are positioned at the center of the internal valve cavity. Accordingly, the flexible portion
241
of the diaphragm
233
between the static circumferential seal
236
and the dynamic seal
237
is enough to allow the necessary range of movement of the dynamic sealing tip
235
of the diaphragm
233
to seal the flow control passage
244
, while minimizing stress on the flexible portion
241
of the diaphragm
233
. In view of this, the portion of the diaphragm
233
which mates with the valve body
203
at the circumferential seal
236
is not lifted. Accordingly, material is not trapped in the circumferential seal as in a weir valve.
As can be readily understood, with the arrangement of radial diaphragm valve, an opening into the internal cavity
213
of one flow passage
226
is located radially outward from the centrally placed flow control passage
2
Bastianelli John
Birch & Stewart Kolasch & Birch, LLP
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