Improvements in the Method of and Apparatus for Forcing Semi-fluids into Filter Presses.
Year: 1891

page_text: Date of Application, 19th Feb., 1891--Accepted, 25th Apr., 1891
Improvements in the Method of and Apparatus for Forcing
Semi-fluids into Filter Presses.
SAMUEL HENRY JOHNSON, of the Engineering Works, Stratford, in the County.
of Essex, and CHRISTOPHER CLARKE HUTCHINSON, of same address, Engineers,
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:-
Hitherto considerable difficulty has been experienced in forcing semi-fluids such
as sewage sludge into filter presses by means of pumps which pump the sludge
directly into the presses. When pumps are made so as to be worked at a fixed
speed during the whole period of pressing, there is inconvenience and considerable
loss of power, because sludge presses require a large quantity of sludge to
be pumped into them at first, and afterwards, as the pressure rises, the quantity
required diminishes considerably till towards the end they are unable to deal with
more than a very small fraction of that required at the commencement of the charge,
the result being, that a relief valve became necessary so that the excess of sludge
pumped might overflow and be pumped continuously to waste until the pressing
was finished, thus losing power; or in some cases, to obviate this loss of power,
direct acting pumps were employed, having the areas of the steam cylinder pistons
so proportioned to the areas of the pump plungers, that the speed of pumping would
gradually become slower when the maximum pressure was approached, the steam
pressure just balancing the required maximum working pressure on the pump ram.
By this means the relief valve above described became unnecessary, the pump
working only at the speed required by the sludge press, which thus became
exceedingly slow towards the end of the operation. When this mode of pumping
is employed and the pump plungers are working slowly, the valves do not open
sufficiently to allow fibrous and other solid matter to pass through, and so the valves
are converted into strainers which soon become obstructed and the pumps cease to
work until the valves are cleared; this inconvenience occasions frequent stoppages
And in
during the progress of the pressing and much delay in consequence.
addition to this. the steam pumps constructed for this purpose, cannot use the
steam expansively as the pressure of the steam must balance that against the
pump ram the whole length of the stroke there is consequently great waste of
steam.
Now it is the object of this invention to show how these difficulties may be
overcome and the kind of apparatus that we apply for that purpose, and with this
object we describe same as follows:-
Instead of pumping continuously during the period of charging the press and
gradually reducing the speed of pumping towards the close of the operation, we
work the pumps at their full working speed until the maximum working pressure is
attained, and then by means of a regulator actuated by the pressure at which the
presses are working, suddenly stop. This period of rest we arrange to continue
until the pressure has fallen sufficiently below the normal maximum working
pressure to allow the regulator to start the engines again full speed and this process
of intermittent working, maintaining the pressure at or near its maximum we
continue until the pressing is completed, the periods of rest becoming longer as the
operation of pressing approaches completion, but the pump always working full
speed when at work.
By working in this way the valves open to their maximum lift at each stroke of

page_text: the pump, and this coupled with the higher velocity carries such obstructions
through the valves as would have obstructed them when working with the low
speed balanced pressure pumps, hitherto employed for the purpose, and so we find in
practice the difficulties hitherto existing are completely overcome.
For economy of steam we also prefer to employ a pair of steam cylinders
provided with cranks at right angles to cach other, the steam being cut off at
rather more than half stroke, so that they shall be self-starting in every position
and without dead point, whilst working with a fair amount of expansion and conse-
quent economy.
We also prefer to use a large air vessel or accumulator into which the sludge is
pumped and stored under pressure in connection with the delivery main of the
pumps, and we use the air compressed into this accumulator for the purpose of actuating
the regulator which controls the starting valve of the pair of engines, it will thus be
seen that the whole arrangement is perfectly automatic in adapting the supply of the
sludge to the requirements of the filter presses.
Having thus described the nature of our said invention, we will now proceed to
describe more particularly an example of a means of carrying same into effect
in accordance with our invention, due reference being made to the drawings and the
letters of reference thereon.
Fig. 1 shows a plan view of a sludge pressing house in which P¹ p¹ pill are three
sludge presses such as are now well known and used for such purpose. E is a pair
of sludge forcing engines having steam cylinders ss" and pump rams p¹p" and
valve boxes vv vv. The hydro-pneumatic regulator is shown at communicating
by means of the pipe with the air vessel A. SR shows the sludge receiver from
which the sludge to be pressed is pumped. S is the sump from which the sludge is
drawn and which communicates by means of the underground passage m with the
sludge receiver.
Fig. 2 shows sectional elevation of the same in which parts similarly lettered
correspond with the plan. W is the tipping waggon for taking away the pressed
cake.
Figs. 3 & 4 show side and cross sections of the hydro-pneumatic regulator in
which V is the stop valve which controls the pair of engines actuated by the screw
and hand wheel as shown. The inlet is at I from the steam main to work the
engines. The outlet is at O to the engines. The regulating valve or sleeve S
works in the casing C which it fits accurately. The casing and the regulating
valve have annular slots cut through them as shown at sssss which correspond with
one another when the valve is open. s is the stuffing box and gland with the
packing in same for the purpose of preventing leakage past the sleeve S into the
steam space. OV is the oil vessel and R the oil reservoir by means of which
the pressure is communicated from the air vessel Fig. 2 A through the pipe a. The
rod attached to the sleeve S passes through the stuffing box where by means of
a washer w and check nuts nn it is actuated by means of the spring sp which is so
adjusted by means of the check nuts n n that the pressure exerted in drawing back
the sleeve S is equal to or a little less than the maximum working pressure at which
it is desired the sludge rams shall work. It is obvious that when this pressure is
reached, that is to say, slightly in excess of that exercised by the spring, the sleeve S
will move forward further compressing the spring until it shuts off the annular
ports sssss.
It is found in practice that as soon as pressure begins to overcome the spring and
gets the sleeve into motion, it moves forward immediately and shuts off the steam
at once. This valve remains closed until the pressure in the air vessel A Fig.
is reduced sufficiently for the sleeve S to start in motion backwards under the
influence of the spring, it is found also that this operation, owing to the very small
range of motion in this form of valve, takes place instantly and full steam again
passes on to the engines. It is obvious that in the drawing the starting valve V is
shown closed, but when at work it must be open.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. The mode of forcing semi-fluids by pumping them direct into filter presses
by means of pumps, such pumps working intermittently at full speed and alter-
nately stopping and starting at or near the maximum pressure substantially as
described.
2. The combination of a pair of engines, a regulator, an air accumulator and one
or more filter presses working together automatically so as to produce the inter-
mittent working of the pumps at full speed at or near the maximum pressure, with
periods of rest according to the requirements of the filter presses, substantially as
described and shown.
Dated this Eighteenth day of February 1891.
SAML. H. JOHNSON.
C. C. HUTCHINSON.