Multiple filter case

A multipart filter case for holding at least one cartridge-shaped filter element, particularly for the sterile filtration of fluids, has a bell-shaped case with a top part into which the filter inlet side protrudes. The filter outlet side is held downstream in an intermediate plate and ends in a filtrate space below the intermediate plate. The filtrate space is defined in part by a dish-shaped base plate parallel to the intermediate plate, and has a filtrate outlet therein. The inlet for the medium to be filtered extends through the base plate and intermediate plate into the top part of the case, and comprises a tubular part integral with the intermediate plate and which detachably penetrates the base plate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to filters for sterile filtration of fluids, and 
more particularly, to a filter case construction for such filters in which 
means is provided to prevent leakage of medium to be filtered from an 
inlet into the filtrate chamber. In copending application Ser. No. 
158,790, filed concurrently herewith, leak detecting means is disclosed 
for detecting leakage of non-filtered medium. 
2. Prior Art 
U.S. Pat. No. 3,298,522 is made of record. 
In a known filter case the inlet connection piece for the medium to be 
filtered is undetachably connected with the base plate; it penetrates the 
intermediate plate, and ends in the top part of the case. The filtrate 
space below the intermediate plate is sealed off against the top part of 
the case in the area of the connection piece by at least one O-ring 
packing, arranged on the inside of the perforation in the intermediate 
plate or on the outside of the tubular inlet connection piece. At 
filtration under high pressure, the packings of replaceable structural 
elements or of the filter cartridges sometimes become loose. This is 
partly caused by damage to the packing rings, and partly by a canting of 
the structural elements. In the known case, unfiltered medium flows or 
leaks from the top portion of the case along the packing and the outer 
edge of the inlet connection piece into the filtrate space, the leaky spot 
remaining undeterminable. In sterile filtration, a non-sterile medium thus 
enters the sterile space, whereby the whole filtrate becomes non-sterile. 
SUMMARY OF THE INVENTION 
The principal object of the invention is therefore to improve with simple 
means a filter case of the type discussed above in such a way that 
occurring leaky spots and leakage losses are easily determinable and 
filtrate already sterile does not become non-sterile by contact with 
leakage losses. 
This is achieved according to the invention in that the inlet for the 
medium to be filtered is a tubular connection piece formed as an integral 
part of the intermediate plate and undetachably connected therewith, and 
that the connection piece detachably perforates the base plate, with the 
inclusion of a packing. 
In one development of the invention, the connection piece is sealed in the 
perforation of the base plate by an O-ring packing. In another embodiment, 
the connection piece is provided with a flange which adapts itself to the 
edge of the perforation of the base plate with a packing. 
Due to the arrangement of the perforation in the base plate and the 
absolutely tight structure of the intermediate plate and connection piece, 
no unfiltered medium can penetrate from the top part into the sterile 
space. Should, however, the packing between the connection piece and the 
base plate become loose, no harm is done since the liquid pressure in the 
sterile space is, on the one hand, not so high that larger amounts of 
leakage pass through the packing, but is on the other hand, high enough to 
prevent a secondary contamination from the outside into the sterile space. 
Besides, the leaky spot is sufficiently recognizable so that correction 
can be made.

DETAILED DESCRIPTION OF THE INVENTION 
The multipart case consists essentially of a bell-shaped case top part 1, 
an intermediate plate 9, and a dish-shaped base plate 12, which parts are 
sealably connected on their periphery with the inclusion of packings 16, 
17 by clamping means 14. 
Intermediate plate 9 is provided with a tubular connection piece 11 welded 
to the plate, in each case durably connected therewith in a tight manner 
and which forms an inlet 10 which passes upward through the base late 12 
and ends in case top part 1. 
Base plate 12 is dish-shaped and an associated collar 13 may also be molded 
thereon, extending toward intermediate plate 9 so as to form a filtrate 
space 22. In sterile filtration, this space assumes the function of the 
sterile space, and is provided with an outlet connection piece 19. 
The outside of connection piece 11 is provided, in the area of a 
perforation 23 of the base plate with an O-ring packing 15 and serves, 
besides, as a visible leakage control station. 
In the embodiment of Fig. 2, a flange 20 is provided on the outer surface 
of connection piece 11', which flange 20 adapts itself with a packing 21 
to the upper edge of base plate 12 in the area of perforation 23 and is 
likewise subject to clamping means 14. Filtrate can therefore, if at all, 
pass at this spot from filtrate space 22 without the danger of a secondary 
contamination for the sterile filtrate. 
The cartridge-shaped filter element 2 proper protrudes with its closed end 
capt 5 into the case top part, and with its end cap 4 into a perforation 
of intermediate plate 9 and is provided, in this area, with at least two 
ring packings 5 and 6 which are fixed, with an axial space between them, 
to the outside of the end cap 4 and thus seal the bell-shaped space of the 
case top part 1 against filtrate space 22. 
Usually several of such filter elements 2 are distributed over the 
periphery of intermediate plate 9, whereby the danger of leaky spots at 
the end caps 4 increases. In order to prevent an uncontrolled penetration 
of medium to be filtered along the two ring packings 5 and 6 into filtrate 
space 22, especially in sterile filtration, at least one leakage control 
channel 8 is attached in the area between the two ring packings 5 and 6, 
which channel 8 ends on the case outside of intermediate plate 9 and can 
therefore be inspected. Preferably, in the free space between the two ring 
packings 5 and 6, a ring channel 7 is inserted either in the end cap 4 or, 
as shown, in the wall of the perforation of intermediate plate 9, in which 
ring channel 7 leakage channel 8 ends. 
If, in fact, due to damaged packing 5 or canting of filter element 2, a 
leakage of the medium from case top part 1 in the direction toward 
filtrate space 22 occurs, the medium, usually liquid, is discharged from 
ring channel 7 through leakage control channel 8 toward the outside of the 
casing. 
Due to the pressure drop in ring channel 7, the medium can also no longer 
overcome packing 6 to sterile space 22, so that the filtrate does not 
become non-sterile space 22, so that the filtrate does not become 
non-sterile again. The medium to be filtered is therefore only capable of 
flowing as it is supposed to, i.e. through the filter layers of filter 
element 2 into filtrate space 22. 
When more than two ring packings 5, 6, e.g., three, are provided on the end 
cap 4, the leakage control channel is suitably arranged in a downstream 
direction between the last two ring packings. 
The special advantage of leakage control channel 8 becomes apparent when a 
multiplicity of such filter elements are arranged on the periphery of 
intermediate plate 9 and when by means of the leakage control channel 
associated with each filter element 2 it can be unambiguously determined 
which filter element 2 located in intermediate plate 9 has become untight, 
so that suitable measures can be initiated.