Improvements in Filters, and in the Manufacture of a Felt or Filtering Medium for use therein.
Year: 1895

page_text: Date of Application, 13th Feb., 1895-Accepted, 27th Apr., 1895
COMPLETE
SPECIFICATION.
Improvements in Filters, and in the Manufacture of a Felt or
Filtering Medium for use therein.
I, EDWARD MARTIN KNIGHT, of 32, Warren Street, New York, United States
of America, Gentleman, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
My invention relates to filters and to the manufacture of an improved felt or
filtering medium for use therein.
The objects of my said invention are, the manufacture of an improved felt or
filtering medium of such a character that it is peculiarly adapted for the removal
of the finest micro-organisms from water; the construction of a filter in such a
manner that it will work rapidly and efficiently and can be very readily taken
entirely to pieces, cleaned and sterilized and put together again; the provision of
improved means whereby leakage of the unfiltered water into the filtered water
will be effectually prevented; the construction and arrangement of the filter-bed
so that my improved felt or filtering medium or other filtering media of delicate
structure can be used without liability to disintegration thereof, and the filter-bed
will not be liable to disturbance by vibration or oscillation in transit; and the
construction of a portable filter the action of which shall be very rapid and
effective and which can be manufactured at a low cost.
My said invention is chiefly designed to improve the construction and increase
the efficiency of filters of that kind or class wherein a fibrous material is used as the
filtering medium in such form and so arranged that it can easily be removed and
replaced or renewed at pleasure; for example, filters such as those described in
the Specifications of the following former Letters Patent granted to me, viz. :-
No. 1509 dated 27th January 1891, No. 1521 dated 27th January 1891, No. 2500
dated 9th February 1892, and No. 6560 dated 28th March 1893.
My said invention comprises an improved felt or filtering medium composed of
fibres or flakes of asbestos massed together and compressed in such a manner that
the mass is of very uniform structure throughout and is well adapted to arrest the
impurities and micro-organisms usually contained in water.
My invention also comprises a novel method or process of preparing my felt or
filtering medium from asbestos.
And my said invention further comprises other improvements hereinafter
described.
In the accompanying drawing
Figure 1 is a vertical central section showing one form of my improved filter
adapted to work with a constant supply of water from a water-main or other
convenient source.
Figure 2 is a vertical central section, and
Figure 3 an underside view, some portions being removed, illustrating details
of construction.
Figure 4 is a transverse section, drawn to an enlarged scale, illustrating another
detail of construction.
Figure 5 is a vertical central section, and
Figure 6 a plan, with the upper half removed, showing another form or
modification of my improved filter showing the same ready for use.

page_text: Figure 7 is a perspective view, drawn to a reduced scale, showing how the said
filter disc and the filtering medium are removed.
Figure 8 is a perspective view also drawn to a reduced scale, showing the said
filter ready for transport.
Figure 9 is a vertical central section illustrating a further modification of my
invention, and
Figure 10 is a vertical central section illustrating a still further modification
thereof.
Like letters iudicate corresponding parts throughout the drawing.
The manufacture of my improved asbestos felt or filtering medium is an important
feature of my said invention. In my said former Specification, No. 6560 of 1893,
I have described a filtering medium consisting of a thin wafer-like film of asbestos,
which is so arranged that it will arrest the impurities contained in the water.
Now, although the thin films of this kind are very efficient for the purpose for
which they are intended, yet I have found in practice that they are so fragile that
they are liable to be broken or damaged in handling or transport so as to permit
leakage of unfiltered water through them; and also that it is very difficult to
make them of even or uniformn thickness, as, by reason of the peculiar nature of
asbestos fibre, a very thin film made by the process I have described in my said
former Specification may appear all right to the eye when dry, but, if wetted and
then held up to a strong light, it will be seen to be uneven in thickness and
extremely thin in some places; it is in these thin places that it is liable to break in
handling, and even if it does not break, fine micro-organisms may soon eat their
way through the thin places. Now it is to correct these imperfections that I have
devised my improved felt or filtering medium, the express purpose of which is to
extract from water the finest micro-organisms and not only to extract them but to
retain them on its surface and prevent them from eating their way through.
To accomplish this result I manufacture my improved felt or filtering medium as
follows, that is to say :-
I take crude asbestos, crush it, and pass it through a carding machine similar to
those used in carding cotton, or through any other machine that will effectually
separate the fibres of the asbestos, and I allow the separated fibres or flakes of
asbestos to fall lightly one above another into a box or other receptacle directly
from the carding or other machine, so that the asbestos is deposited in the box or
other receptacle in very fine flakes like snow, in fact the action is similar to the
falling of snow.
The receptacle for the asbestos fibres or flakes is preferably constructed in the
form of a shallow tray of dimensions varying according to the size and thickness of
the felt required. The bottom of the said tray is perforated and covered with
flannel or similar material, upon which is laid a piece of fine muslin or the like,
to enable the mass of asbestos to be lifted out of the tray. The flannel and
muslin are damped with water and the tray is then placed under the carding
inachine and quickly moved to and fro as the carded asbestos falls into it, this
being done in order to promote the evenness or uniformity of the deposit. When
sufficient asbestes has been deposited in the tray, the latter is withdrawn and
another piece of muslin placed on the top of the mass of asbestos; water is then
sprayed over the said mass until it is thoroughly soaked. A piece of board is
now taken and placed on top of the mass of asbestos. This board should be of
the exact dimensions of the inside of the tray. Pressure is now applied to the
board evenly or uniformly, and the wet asbestos is thus squeezed down into a
small compass and a large proportion of the water forced out through the
perforations in the bottom of the box. The pressure is then relaxed, the loose
board is removed, and the asbestos felt thus formed, with the pieces of muslin on
either side thereof, is lifted out of the tray, and laid on one side till a number of
sheets of felt have been made in a similar manner, the said sheets being laid one
upon another until there is a suitable number of the same in the pile. The pile
of sheets is then taken and put into a press sufficiently powerful to exert a pressure

page_text: of from one to two tons per square inch, more or less, the heavier pressure being
preferable. The sheets of felt are then taken from the press, after which the
pieces of muslin may be removed, and each sheet is laid separately in a hot room
or drying chamber and the remaining moisture evaporated. When dry, the sheets
of felt are laid between sheets of paper or the like and cut into discs, or pieces of
other suitable form. The object of placing them between sheets of paper is that
the felt may be cut much more evenly in this manner.
In the manufacture of my asbestos felt, it is important that the fibres or flakes
of asbestos should be allowed to fall lightly one upon another as above set forth
and that the mass should not be touched or disturbed before being compressed in
the manner described, because if the mass of asbestos were handled or lifted in
handfuls from the box or receptacle and placed in the press, the resulting felt
would be lumpy and of uneven structure. Whereas when the felt is made as
above described it is of very uniform structure throughout.
By the method above described, I am enabled to manufacture a felt for filtering
purposes entirely out of an inorganic substance, i.e., pure asbestos, with no admixture
whatever. Felt made in this way not only possesses all the advantages I claim for
my films in my said former Specification No. 6560, but also others, viz:-It is
more even, compact and solid; it will not break in handling and will not show
imperfections when wet. It will, moreover, whilst effecting the filtration of the
water very rapidly, effectually retain on its surface minute micro-organisms that
might eat through the earlier form of film made as described in the said former
Specification, and it can be produced much more cheaply and rapidly.
In order to efficiently support and utilize the felt manufactured as above described
or other filtering media of a delicate nature, I employ the arrangements hereinafter
described, although it must be understood that my improved asbestos felt may be
employed in any other suitable manner if desired.
In the form of my improved filter shown in Figure 1, A is the vessel or container,
B is the lid or cover thereof; C is the asbestos felt or filtering medium; this felt is
supported between and protected by two layers D of open woven asbestos cloth
mounted on upper and lower frames E, E', the upper of which E is shown detached
in Figures 2 and 3. The asbestos cloth D that covers these frames is not intended
to serve as a filtering medium but only as a support and protection for the felt C,
and in order that the said cloth may in no way retard the flow of the water, it is
made of a very open mesh. This is a matter of importance since the interstices
between the meshes of the ordinary closely woven asbestos cloth, when used in a
filter, gradually close up, not merely because the pores of the material become
clogged with impurities from the water, but from the nature of the asbestos itself,
the result being that, in the course of time, the flow of the water through the filter
is so retarded that the filter becomes useless. To obviate this difficulty, I use
asbestos cloth which is woven very open indeed so as to ensure that it shall
never close up, and thus retard or arrest the flow of the water through the
filter.
By my present improvements 1 reduce the resistance to the flow of water through
the filter to a minimum and thus ensure a rapid filtration of the water without the
aid of a high pressure.
The supporting frames E, E' consist of discs or pieces F of wire cloth surrounded
and bound by metal rings or rims and having sewn upon one side the openly-woven
asbestos cloth D, the said frames being tinned or made of or coated with such metals
or materials as are not liable to be chemically acted upon by the liquid to be
filtered. Each of these frames with its asbestos covering forms one of the filter
discs or diaphragms. The lower frame E¹ rests on an internal flange G or on
projections on the interior of the vessel A. The upper frame E is provided with a
handle H to facilitate its insertion into and removal from the vessel A; and the
passage of unfiltered water between its outer edge and the wall of the vessel A is
prevented by means of an asbestos packing or jointing device made and applied as
shown in Figures 2, 3 and 4. The said jointing device consists of a folded tape or

page_text: band J of asbestos enclosing a piping cord or cure J' of asbestos or other suitable
material, which is secured in position by sewing as shown at a, Figure 4. The
jointing device shown in Figures 1, 2 and 3 is made in the form of a ring which is
secured around the outer edge of the frame E by sewing or otherwise fastening the
free edges of the tape or band J thereto, the fold of the said tape and the enclosed
cord or core surrounding the periphery of the said frame. The projecting part
of the said jointing ring presses tightly against the walls of the container and
adapts itself to inequalities or undulations of the wall of the container, whether the
latter be made of metal, earthenware or other material and thus ensures a tight
joint around the edge of the frame E when the said frame is in its operative
position, whilst permitting ready insertion and removal of the said frame by means
of the handle H. This peculiar asbestos joint will answer equally well in a
cylindrical container as in one which is taper or conical. It is also useful in com-
bination with other kinds of filter discs, for example stoneware or other perforated
discs such as are described in my said former Specification No. 2500.
To retain the frames E, E' and the filtering felt C in position, I provide a bar M
which engages with off-sets N secured to the interior of the vessel A, and through
which extends a screw P fixed to the handle H of the upper frame E, and provided
with a nut Q beneath the said bar. Or other suitable means may be employed for
securely retaining the said frames and felt in place whilst permitting their ready
removal when necessary.
The upper part of the vessel A is provided with a valve K controlled by a ball
or float, whereby water will be admitted as required to the said vessel from a
water-main or other source of supply; taps L are also provided for drawing off the
water when desired from the upper and lower compartiments of the vessel A. The
ball or float lever is so arranged that it can be readily removed to permit the with-
drawal of the filter discs or diaphragms E, E¹, and felt C.
It will be seen that the filter above described is so constructed that the with-
drawal of the felt C, when it becomes fouled by the impurities extracted from the
water, and its replacement can be effected very readily and expeditiously. More-
over both the filter discs or frames E, E' can be easily taken out, put into boiling
water and thoroughly sterilized, and the containing vessel A, being thus left quite
clear of all obstructions, can in like manner be sterilized, and the whole machine
can be fitted up again with a fresh disc of felt without the slightest difficulty in a
few minutes, which is obviously impracticable in the filter described in my former
Specification No. 1509.
By supporting the felt C between the two layers of asbestos cloth D, on the filter
discs or diaphragms, I am, moreover, enabled to protect it against disintegration and
to prevent disturbance of the said felt by vibration or oscillation when the filter is
used on board ship, in railway trains, or in similar situations. It is evident that my
improved filter discs or diaphragms can, if desired, be used with asbestos films such
as are described in my said former Specification No. 6560.
In Figures 5 to 8, I have shown a very effective cheap and portable form or
modification of my improved filter which I term my "Bucket Filter." This filter
comprises a lower bucket-shaped receptacle A for receiving the filtered water and a
smaller similarly shaped receptacle R for the unfiltered water. The receptacle R
is provided with somewhat similar filtering arrangements to those above described
with reference to Figure 1, and it is adapted to be inserted in the bucket A when
the filter is not in use or is to be packed or carried from place to place. The
bucket A is provided with movable or detachable cross-bars S in the upper part
thereof, which serve for supporting the smaller bucket R over the larger bucket A
when the filter is in use, and for retaining it in the bucket A when the filter is not
in use.
These cross-bars, in the arrangement shown, fit into apertures in the wall
of the bucket A, and each bar is provided near one end with a collar d and at the
other end with a screw-thread on which is fitted a nut e, so that the said bars may
be firmly secured in position or may be removed as and when required. The
handle T of the bucket A is secured thereto on the outside thereof in the usual

page_text: manner; the handle T' of the bucket R is, however, secured on the inside thereof,
so that the bucket R may fit closely within the bucket A as shown in Figure 8..
The frame E' may, if desired, rest upon a flange or upon projections on the interior
of the bucket R. To prevent displacement of the frames and felt, however, I
prefer to make the bucket R with a perforated bottom R¹, which may, if desired,
be dished as shown and which is protected by the chine at the lower end of the said
bucket. In this arrangement the felt C and frames E, E' may, if desired, be
held down by means of a cross-bar and screw as above described or by other
convenient means.
In Figure 9 I have shown a further modification of my improved filter adapted
for small sizes. This filter comprises an outer vessel or container A formed with a
downwardly extending neck or nozzle fadapted to be inserted into the mouth of a
bottle or the like. Inside the container I provide a funnel-shaped vessel U having
a nozzle g which passes into the neck f of the container A. The vessel U serves
to support the filtering felt C and frames E, E¹, which may, if desired, be held in
position by means of a cross-bar and screw, substantially as described with reference
to Figure 1 or in any other suitable manner.
9
In Figure 10 I have shown à further modification of my invention in which two
sets of felt discs C and frames E, E' are arranged in an internal cylinder or
chamber W provided with a perforated tube Y. By this arrangement I provide a
much larger area of the filtering medium, the water filtering through each of the
elt discs C into the interior of the cylinder or chamber W, and the filtered water
flowing from the said chamber through the tube Y. This arrangement can be
conveniently employed in a vessel or tank of large size.
It is obvious that the construction of my improved filter may be somewhat
further modified without departing from the nature of my said invention. For
instance I can, if desired use the aforesaid woven wire filter discs or diaphragms
with the jointing device but without the asbestos cloth.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
First. A felt or filtering medium composed of fibres or flakes of asbestos massed
together and compressed, substantially as herein before described.
Second. The manufacture of an asbestos felt or filtering medium, by allowing the
fibres or flakes of asbestos from a carding machine or the like to fall lightly one
upon another until the mass thereof is of suitable thickness and then compressing
the mass by heavy pressure uniformly applied thereto.
Third. The improved method of preparing a felt or filtering medium, consisting
in allowing fibres or flakes of asbestos to fall lightly one upon another until a mass
thereof of the requisite thickness is obtained, moistening the mass and compressing
it by heavy pressure uniformly applied thereto, and then placing paper or the like
at both sides of the sheet of compressed asbestos and cutting pieces of the desired
shape from such sheets, substantially as hereinbefore described.
Fourth. In a filter disc or diaphragm, the use of a sheet of open woven asbestos
cloth, as and for the purposes set forth.
Fifth. The improved filter disc or diaphragm consisting of asbestos cloth so woven
that when saturated it will still be pervious to water, and attached to woven wire
fabric, substantially as and for the purpose above specified.
Sixth. The combination, with a filter disc or diaphragm, of the peculiar self-
adjusting jointing device, substantially as herein before described.
Seventh. A filter comprising a bucket or other receptacle provided with a filter-
bed and adapted to be inserted in another bucket or receptacle which is provided
with movable or detachable supports for sustaining the filtering receptacle above it
when in use, or retaining the same within it when not in use, substantially as
herein before described.

page_text: Eighth. A bucket having a perforated bottom and a filter-bed above the same,
substantially as described.
Ninth. A bucket having the handle attached to the interior thereof so that the said
bucket will fit within another bucket of but slightly larger diameter, for the purpose
above specified.
Tenth. The combination of the filter-bed resting on a projection or projections in
the container, and suitable means for holding the said filter-bed firmly in place,
whilst permitting the ready removal thereof when required, substantially as and for
the purposes above specified.
Eleventh. The improved filter constructed substantially as described with
reference to either of the forms or modifications illustrated in the accompanying
drawing.
Dated the 13th day of February 1895
EDWARD MARTIN KNIGHT.
D. Young & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.