Expressing filter plate for filter press of expression type

An expressing filter plate comprising a base plate and a diaphragm sheet covering the base plate and having a filter surface, with a pressure fluid chamber formed between the base plate and the diaphragm sheet. The diaphragm sheet is formed, in its peripheral portion to be clamped between pressed filter plates, with a fluid passing opening in communication with a fluid passage in the base plate. A covering member having a tubular portion fitting in the opening is made of a material having higher hardness than the diaphragm sheet. The covering member has a flange portion formed with fluid grooves for maintaining the tubular portion in communication with filtrate grooves in the filter surface of the diaphragm sheet.

BACKGROUND OF THE INVENTION 
The present invention relates to an expressing filter plate for filter 
presses of the expression type. 
Various types of expression filter presses are known which include one type 
comprising base plates and diaphragm sheets each covering the base plate 
and having a filter surface formed with filtrate grooves. The grooved 
filter surface of the diaphragm sheet defines at least one side of a 
filter chamber to which a prefilt is fed under pressure. The prefilt is 
filtered by a filter medium covering the diaphragm sheet. Subsequently a 
pressure fluid is supplied to a fluid chamber formed between the diaphragm 
sheet and the base plate, bulging the diaphragm sheet toward the filter 
chamber to press the cake remaining in the filter chamber. The filtrate 
filtered off by the filter medium flows down the filtrate grooves in the 
filter surface. Since a filtrate passage for drawing off the filtrate is 
formed in the base plate, the diaphragm plate is provided in its filter 
surface with a filtrate outlet communicating with the filtrate passage in 
the base plate. 
FIG. 1 shows an expressing filter plate of the type described which 
comprises the combination of a diaphragm sheet A and a base plate C so as 
to effect both filtration and expression. With the illustrated 
construction, the diaphragm sheet A has a filtrate outlet B which is 
merely so formed as to communicate with a filtrate passage D formed in the 
base plate C. Expressing filter plates E are arranged alternately with 
ordinary filter plates G having filter surfaces F, or the same expressing 
filter plates are arranged side by side although unillustrated, with 
filter chambers H provided between adjacent plates for the filtration of 
prefilt and expression of cake. When expressing the cake, a pressure fluid 
is fed to a fluid chamber I between the diaphragm sheet A and the base 
plate C to establish a pressure balance between the chamber I and the 
filter chamber H. Consequently the diaphragm sheet A is usually subjected 
to pressure for example of about 4 to 10 kg/cm.sup.2 from both the 
chambers H and I on its opposite sides, with the result that the sheet 
tends to decrease in thickness and to spread out in a plane, undergoing 
plastic deformation. This deformation is directed concentrically to the 
filtrate outlet portion B where no resistance is encountered. The 
repetition of filtration and expression leads to increased deformation 
with the lapse of time, consequently blocking the filtrate outlet B. The 
filtrate outlet B is provided outside the bulging area of the diaphragm 
sheet A, namely in the portion of the sheet A which is clamped between the 
base plate C and the filter plate G or between the base plates, whereby 
the filtrate outlet portion B is held immediately adjacent to the filtrate 
passage D of the base plate. This construction readily ensures reliable 
communication between the filtrate outlet B and the filtrate passage D. 
However since the expressing filter plate E and filter plate G, or the 
closely fitted filter plates are tightly held together during expressing 
operation without any separation, these plates are pressed against each 
other with pressure greater than the expressing pressure. This produces 
greater deformation in the filtrate outlet portion B of the diaphragm A, 
promoting the blocking of the outlet B. 
When the filtrate outlet B has been constricted or blocked up, the filtrate 
flowing down the grooves K in the filter surface J of the diaphragm sheet 
A is greatly hindered or prevented from flowing into the filtrate passage 
D of the base plate C by way of the outlet B. Discharge of the filtrate is 
impeded or prevented. As a result, abnormal high pressure will build up in 
the filter chamber H and pressure fluid chamber I and further in the 
prefilt feed passage, entailing the hazard of damage to the apparatus. 
A wash liquor inlet, like the filtrate outlet, is further formed in the 
diaphragm sheet in communication with a wash liquor passage in the base 
plate for the reverse washing of the filter medium to remove the cake. 
With the known construction, the wash liquor inlet similarly tends to be 
constricted or blocked, in which event reverse washing can not be 
performed sufficiently or may be prevented, with abnormal high pressure 
created to damage the wash liquor feeding system. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a fluid inlet or outlet opening 
which is serviceable, free of any constriction or blocking, as the 
above-mentioned filtrate outlet or wash liquor inlet to thereby ensure 
smooth discharge or filtrate or smooth inflow of wash liquor without 
entailing abnormal high pressure. 
Another object of this invention is to provide the opening with a very 
simple construction. 
Still another object of this invention is to provide fluid grooves in the 
vicinity of the fluid inlet or outlet opening which grooves are 
serviceable free of any deformation to permit outflow of filtrate or 
inflow of wash liquor without any interference and to thereby ensure 
satisfactory filtration and expression or washing. 
The present invention provides an expressing filter plate comprising a base 
plate, a diaphragm sheet having a filter surface and covering the base 
plate, the diaphragm sheet being formed with at least one fluid passing 
opening in communication with a fluid passage serving as a filtrate 
passage formed in a lower portion of the base plate or as a wash liquor 
passage formed in an upper portion of the base plate, and a covering 
member made of a material having higher hardness than the diaphragm sheet 
and including a tubular portion fitting in the fluid passing opening. The 
tubular portion serves as a fluid inlet or outlet opening of the 
diaphragm. Since it is of higher hardness than the sheet, the inner 
periphery of the tube defining the inlet or outlet opening satisfactorily 
retains its shape without expanding inward toward the center of the 
opening when the sheet is subjected to pressure on its opposite surfaces. 
Thus the fluid inlet and outlet opening will not be constricted or blocked 
due to plastic deformation or will not be so deformed even elastically, 
namely temporarily. Consequently the tubular portion always assures smooth 
outflow of filtrate or smooth inflow of wash liquor, free of abnormal high 
pressure and the possible damage to the apparatus. 
The tubular portion is integral with a flange portion for covering the 
portion of the diaphragm sheet in the vicinity of the fluid passing 
opening, especially the portion adjacent the opening over which the 
filtrate flows into the opening or the wash liquor is fed to the filter 
surface. The flange portion effectively prevents the diaphragm sheet from 
constricting or blocking the opening by being forced over the edge of the 
tubular portion. The flange portion is formed in its surface with fluid 
grooves for maintaining the tubular portion in communication with the 
filtrate grooves in the filter surface of the diaphragm sheet. The fluid 
grooves are provided for the diaphragm sheet at the portion thereof which 
is clamped between the filter plates so as to withstand the clamping 
pressure. Accordingly the fluid grooves assure stable outflow of the 
filtrate or stable inflow of the wash liquor, permitting filtration and 
expression or reverse washing at constant pressure. 
The covering member may be elastically fitted to the fluid passing opening 
of the diaphragm sheet or may be secured by screw or otherwise joined to 
the opening portion. Alternatively, the covering members fitted to the 
diaphragm sheets on the opposite surfaces of the base plate may be 
fastened together by a wire or string to secure the members to the sheets. 
Other features of this invention will become more apparent from the 
following description of an embodiment given with reference to the 
accompanyig drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of this invention will be described below with reference to 
FIGS. 2 to 7. 
An expressing filter plate 1 comprises a base plate 2 and diaphragm sheets 
4 covering the opposite surfaces of the base plate 2 respectively and each 
having a filter surface 3. Usually the diaphragm sheet 4 is joined to the 
base plate 2 at its peripheral portion 41 other than the inner portion 
thereof which defines a pressure fluid chamber 5. As shown in FIG. 2, the 
expressing filter plates 1 are arranged alternately with usual filter 
plates 6 each formed with filter surfaces 61 directly on the opposite 
sides of the plate. The filter surfaces 3 and 61 facing each other define 
a filter chamber 7. For filtration, a prefilt is forced into each of the 
filter chambers 7 from a prefilt inlet 15 as indicated by the arrows X in 
FIG. 2 and is filtered by a filter medium 8 covering the filter surfaces 3 
and 61. After the filtration, a pressure fluid is introduced into each 
pressure fluid chamber 5 from a pressure fluid passage 22 as indicated by 
the arrow Y in FIG. 3, bulging the diaphragm sheet 4 toward the filter 
chamber 7 as indicated in the phantom line in FIG. 2 to express the cake 
accumulating in the filter chamber 7 due to the filtration. The cake 
resulting from the filtration contains a small amount of liquid, which is 
almost completely removed therefrom by the expression. A main filtrate 
discharge passage 9 extending through the base plates 2 and filter plates 
6 is branched into filtrate channels 10 and 11 in the base plates and 
filter plates respectively. The filter channels 10 and 11 are open to the 
filter surfaces 3 and 61 respectively. The filtrate passing through the 
filter medium 8 due to the filtration and expression described above flows 
down filtrate grooves 31 and 62 formed in the filter surfaces 3, 61 and is 
run off through the channels 10, 11 and the main discharge passage 9 as 
indicated by the arrows W in FIGS. 2, 3 and 5. The filtrate channel 11 in 
the usual filter plate 6 is directly open to the filter surface 61, 
whereas the filtrate channel 10 in the base plate 2 is open to the filter 
surface 3 via a filtrate outlet 12 formed in the diaphram sheet 4, since 
the filter surface 3 is formed on the diaphram sheet 4. 
According to this invention, a cover member 13 is made of a material having 
higher hardness than the diaphragm sheet 4 and has a tubular portion 131 
fitting in the filtrate outlet 12 of the sheet 4. The diaphragm sheet 4 is 
molded from vulcanized rubber or the like, while the covering member 13 is 
molded from a material having higher hardness such as hard rubber, 
polyethylene, polypropylene or metal. When the diaphragm sheet 4 is 
subjected to high pressure over the opposite sides thereof during the 
expression of cake, the sheet 4 tends to undergo deformation in the 
directions of a plane, but the tubular portion 131 harder than the sheet 4 
and provided in the filtrate outlet 12 prevents the resulting inward 
expansion of the periphery of the filtrate outlet portion 12, rendering 
the outlet 12 free of any deformation which would constrict or block up 
the outlet. 
At least one of the peripheral portion 41 of the diaphragm sheet 4 having 
the filtrate outlet 12 and the peripheral portion 63 of the filter plate 6 
is projected in the form of a picture frame as illustrated, so that when 
the expressing filter plate 1 and the filter plate 6 are brought into 
pressing contact with each other, the peripheral portion 41 will be 
clamped between the base plate 2 and the filter plate 6. Because of the 
clamping pressure, the portion of the diaphragm sheet 4 where the outlet 
12 is formed is held to the base plate 2 irrespective of whether or not 
the peripheral portion 41 is joined to the base plate 2, even when the 
pressure fluid is fed to the fluid chamber 5 to bulge the diaphragm sheet 
4. The filtrate outlet 12 is therefore hermetically held in communication 
with the filtrate channel 10 in the base plate 2. Moreover, because of the 
above construction which is subjected to the clamping pressure, the 
covering member 13 can be held in position even when the tubular portion 
131 of the covering member 13 is merely fitted in the filtrate outlet 12 
elastically. 
On the other hand, since the expressing filter plate 1 is held under 
pressure greater than the expressing pressure against possible separation 
from the adjoining plate under the action of the expressing pressure, the 
clamped portion undergoes marked deformation, which would constrict or 
block the filter grooves to be so formed in the filter surface as to 
extend to the filtrate outlet portion 12. As experienced with the filtrate 
outlet of the conventional construction, the outflow of the filtrate 
through the grooves would then be impeded, giving rise to abnormal high 
pressure. 
To avoid such objection, the covering member 13 includes a flange portion 
132 integral with one end of the tubular portion 131, the flange portion 
132 being adapted to cover the portion of the diaphragm sheet 4 where an 
extension of the filter surface is to be provided as referred to above. 
The flange portion 132 is formed in its surface with fluid grooves 134 for 
communicating the filtrate outlet 12, namely the opening 133 of the 
tubular portion 131, with the filtrate grooves 31 provided in the usual 
area of the filter surface 3. Accordingly by virtue of the hardness of the 
covering member 13, the fluid grooves 134 in the portion to be clamped 
will not be readily constricted or blocked by the clamping pressure. The 
flange portion also prevents the diaphragm sheet 4 from constricting or 
blocking the filtrate outlet 12 by being forced over the covering member 
13 due to deformation. 
The covering member 13 may be merely fitted to the diaphram sheet 4 or 
secured to the base plate 2 with a screw. Alternatively, the end of the 
tubular portion 131 is so positioned as to oppose the open end of the 
filtrate channel 10 in the base plate 2, with a bridge 135 formed to 
partition the opening 133 centrally thereof, the arrangement being such 
that when the covering members 13 are mounted on the diaphragm sheets 4 on 
the opposite sides of the base plate 2, the bridges 135 are connected 
together by a wire 14, utilizing the opening of the filtrate channel 10 
extending through the plate 2. In place of the wire 14, a string or an 
elastic line may be used, with its opposite ends engaged with the bridges 
to draw them toward each other. 
The covering member 13 is thus very easy to mount and yet is effectively 
retainable in position against dropping. The covering member 13, which is 
mountable in the above manner, is amenable to the planar displacement of 
the sheet 4 due to its expansion or contraction, so that the sheet 4 and 
the covering member 13 are rendered free of an objectionable force and 
made durable. 
Exactly in the same manner as the filtrate outlet 12, the diaphragm sheet 4 
is also formed in its peripheral portion 41 with a wash liquor inlet 16 
for feeding a back or reverse washing liquor to the filter surface 3 as 
indicated in the arrows Z in FIGS. 2 an 3. The wash liquor inlet 16, like 
the filtrate outlet 12, is provided with the same covering member 13 as 
above (see FIG. 3). The covering member 13 ensures satisfactory reverse 
washing by preventing the constriction or blocking of the inlet 16 and of 
the filtrate grooves to be so formed as to extend to the inlet portion, 
whereby the wash liquor feeding system is protected against damage which 
would result when the pressure builds up to an abnormal high level. 
Indicated at 17 is a wash liquor channel in the base plate 2 which channel 
is in communication with the inlet 16 and branched from a main wash liquor 
feed passage 18. 
As shown in the drawings, the filtrate passage 9 is formed in the lower end 
of the base plate 2 to completely drain the filtrate. Only one filtrate 
passage 9 may be provided, but in the illustrated embodiment, the passage 
9 is provided on each of the opposite sides of the plate to promote smooth 
and complete outflow of the filtrate. The wash liquor passage 18 is formed 
in the upper end of the base plate 2. The wash liquor admitted into the 
press can be readily run off through the filtrate passage 9 or prefilt 
inlet 15 which is used temporarily as a drain channel. 
The filtrate passage may be provided at the upper end of the base plate, 
with the wash liquor passage formed at the lower end of the base plate. If 
the cake has a settling property and tends to accumulate on the bottom of 
the filter chamber, the cake can then be expressed efficiently and 
sufficiently while permitting the liquid component to flow away upward. 
Further since the wash liquor will then fill the interior progressively 
upward to run off from the upper portion, especially marked clogging at 
the lower portion of filter medium can be eliminated effectively. 
The diaphragm sheets 4 covering the opposite surfaces of the base plate 2 
are joined together at the prefilt inlet portion 15. To cover the base 
plate with the sheets 4, one of the sheets is folded and then passed 
through the opening 19 in the base plate 2. The joint portion of the 
sheets to be positioned at the prefilt inlet is therefore simple in 
structure and ensures satisfactory air-tightness. The opening 19 is made 
larger than the joint portion 42 of the sheets 4 to render the sheet easy 
to pass through the opening. The resulting clearance is filled up with a 
split ring 20 interposed between the joint portion 42 and the inner 
surface defining the opening 19 to eliminate the displacement of the 
sheets 4. A metal protective ring 21, fitted in the joint portion 42, 
restricts bulging of the sheet joint portion 42 during expressing 
operation to preclude rupture of the sheet.