Device for automatic control of pressure filters

A device for automatic control of pressure filters comprises a control assembly connected by a filtrate pipe (2) to at least one pressure filter (1 ), which is essentially a vertically arranged pipe (4) communicated with the filtrate pipe (2) and limited, at the lower end thereof, by a baffle (7) having a calibrated opening (7') and provided with a sensor (3) which is an electro-capacitive element connected via a converter (14) and a switch (15) to a timer unit (8) coupled to a frequency coincidence unit (17) which is connected to a frequency generator (19), and to control units (9) and to the pressure filter control consoles (11). The control unit (9) and the control console (11) of each pressure filter (1) are joined together, while the control output of each control console (11) is connected to an actuating device of a respective pressure filter (1).

TECHNICAL FIELD 
This invention relates to control of suspension filtration processes and, 
in particular, to devices for automatic control of pressure filters. 
BACKGROUND ART 
Known in the art is a method of automatic control of a chamber filter press 
(cf., for example, the USSR Inventor's Certificate No. 442 812, Class B 01 
D 37/04, J 05 D 27/00, published in 1974). The automatic controlling 
device realizing the known method is provided with a unit for 
determination of the termination of the suspension dehydration process 
when the filter cake reaches a specific water content which is 
continuously monitored by means of a sensor extending through the rubber 
membrane and located inside a top control chamber of the horizontal 
chamber filter press. This sensor is connected to an amplifying device 
connected to an actuating device of the filter press. The amplifying 
device is equipped with a sensor in order to set a specific water content 
level of the filter cake and is provided with a scale for visual control. 
Continuous monitoring of the water content level of the filter cake, which 
is the function of the electrical conductivity of the liquid phase in the 
filter cake, is effected by means of the sensor located in the chamber of 
the filter press and the amplifying device. The water content of the 
filter cake is shown on the scale of the amplifier sensor, calibrated to 
read the percentage ratio of the liquid and solid phases. 
When a specific water content of the filter cake is obtained, the amplifier 
sensor generates a signal to indicate termination of the filtering 
process, which is delivered, after amplification, to the actuating device 
of the filter press. 
A gland seal in the membrane is to be provided to install the sensor in the 
filter press chamber. If the membrane is made movable along the sensor, 
the chamber cannot be hermetically sealed. 
The known device is deficient in that the sensor is installed in the upper 
chamber on the filter press whose chambers are arranged horizontally. The 
water content of the cake in the upper chamber can substantially differ 
from that of other chambers and cannot, therefore, be accurately 
controlled. Moreover, the conductivity of the liquid phase of the filter 
cake varies with the amount of coagulating agents and soluble salts used, 
also affecting the accuracy of the water content determination. 
To summarize, the known device cannot be used for accurate determination of 
the average water content of the filter cake in all chambers of the filter 
press. It is certainly not applicable to filter presses having a vertical 
arrangement of chambers. 
Also known in the art is a device for automatic control of the cake water 
content in a horizontal chamber filter press (cf., for example, the USSR 
Inventor's Certificate No. 683 784, Cl. B 01 D 37/04, B 01 D 25/12, 
published in 1979), which comprises a unit for monitoring the water 
content of the filter cake in the chambers of the filter press, a 
measuring vessel for filterate collection, a pipe connecting one of the 
chambers to the measuring vessel, a filtrate level detector comprising an 
electrode vertically movable by a hand drive, a scale calibrated in 
percent of the initial water content, and a locking valve equipped with an 
electromagnetic drive, and an amplifying-converting unit. The 
amplifier-converter comprises a step-down transformer, a resistor, a 
rectifier built around diodes, a semiconductor amplifier, and sound and 
light indicators. 
For effective use of the known device, the content of the solid phase in 
the suspension has to be determined. It is done in a laboratory and the 
process takes more time than the actual dehydration of the suspension. 
Moreover, the water content of the cake is monitored in one chamber only, 
where it can substantially differ from the average water content of the 
cake in other chambers of the filter press. The efficiency of the filter 
press is therefore seriously affected. 
Also known in the art is a method for controlling a chamber filter press 
(cf., for example, the USSR Inventor's Certificate No. 841 650, Cl. B 01 D 
37/04, published in 1981) which can be used to control the water content 
of the filter cake by way of the feed rate and density of the suspension 
delivered to the filter press. The device realizing the known method 
comprises a delivery pipeline on which a suspension density transmitter is 
mounted together with a flowmeter and an actuating device (valve). The 
device also comprises a comparison unit, a multiplier, an averaging unit, 
an integrator, a functional unit, an indication unit, and a computing 
unit. 
The output of the suspension density transmitter is connected to one of the 
inputs of the multiplication unit and an input of the functional unit via 
the averaging unit. The output of the flowmeter is connected to a second 
input of the multiplication unit via the integrating unit. The output of 
the functional unit is connected to a first input of the computing unit, 
while the output of the multiplication unit is connected to a second input 
of the computing unit. The first input of the comparison unit is connected 
to the output of the transmitter, while the second input of the comparison 
unit is connected to the output of the computing unit. The output of the 
comparison unit is connected to an input of the indicating device and to 
the input of the actuating device. 
The known device is deficient in that the flow rate of the suspension and 
its density cannot be determined when the content of the solid phase is 
too high. The termination of the suspension dehydration process is 
therefore impossible to control with acceptable accuracy. 
Also known in the art is a method for automatic control of pressure filters 
(cf., for example, the USSR Inventor's Certificate No. 680 749, Cl. B 01 D 
37/04, published in 1979). The device realizing this method comprises a 
unit for determination of the suspension dehydration process length, which 
is connected to at least one filter press and is equipped with sensor 
capable of determining, in the process of dehydration, the moment the 
solid phase reaches specific parameters. The unit also comprises a timer 
indicating the length of the suspension dehydration process, which is 
connected (electrically) to the sensor, a control console of pressure 
filters, whose control outputs are connected to actuating devices of the 
pressure filters, while the inputs thereof are conencted to an output of a 
computer memory unit connected to a computer and to the timer. 
The control unit is a standard cell through which a specific amount of 
suspension and filtrate passes within a specific time. The timer supplies 
the duration of the period in which the specific amount of filtrate passes 
through the standard cell. This time is fed to the computer and converted 
to filtration constants which are entered to the computer memory. The 
operator then uses conversion tables to find, on the basis of the 
filtration constants, the length of the dehydration process and enters 
this information to the control consoles of the pressure filters. 
This device realizing the known method is deficient in that it relies on 
the conversion tables to find the length of the suspension dehydration 
process, the procedure being unreliable and inaccurate. 
Disclosure of the Invention 
The invention is to provide a device for automatic control of pressure 
filters, whose design and circuitry ensure accurate determination of the 
time required for the suspension dehydration process to be completed so 
that cakes having specific water content can be obtained with varying 
filter-ability of the suspension and varying content of the solid phase 
therein, this time to be used to control the operation of the pressure 
filters. 
The invention consists in that a device for automatic control of pressure 
filters used to dehydrate suspensions, comprising a control assembly 
connected to at least one filter press, which is to determine the duration 
of the suspension dehydration process and is equipped with a sensor to 
determine, in the process of dehydration, the moment when the solid phase 
reaches specific parameters, a timer to count the length of the 
dehydration process, which is electrically connected to the sensor, 
control consoles whose number is equal to the number of press filters, the 
first input of each control console being electrically connected to an 
output of the timer, while a control output of each control console is 
connected to an actuating device of a respective filter press, according 
to the invention, also comprises a frequency generator whose control input 
is united with a first control input of the timer and connected to first 
outputs of the control consoles, a second control input of the timer is 
connected to second outputs of the control consoles, control units whose 
number is equal to the number of filter presses, the first input of each 
control unit is connected to the output of the timer, an output of each 
control unit is connected to the input of a respective control console, 
the control assembly is connected to at least one filter press by means of 
a filtrate pipe, the control assembly being essentially a vertically 
arranged pipe whose cross-section is equal to or larger than the 
cross-section of the filtrate pipe and whose upper end communicates with 
the initial portion of the filtrate pipe, while the lower end thereof is 
closed by a baffle featuring a calibrated opening through which said pipe 
communicates with the final portion of the filtrate carrying pipe, the 
sensor is an electrocapacitance-type element positioned inside the pipe 
throughout its length so that the axis of the electrocapacitance-type 
element is displaced in relation to the axis of the calibrated opening, 
the sensor is electrically connected to the timer via a 
capacitance-to-frequency converter coupled in series with a sensor switch 
and a frequency coincidence unit connected to an output of the frequency 
generator and via suspension dewatering termination switches whose number 
is equal to that of the filter presses and which are connected to the 
input of each control console, which is united with the input of the 
timer, third, fourth and fifth outputs of each control console are 
connected, respectively, to the second, third and fourth inputs of 
respective control units, the sensor switch and the suspension dewatering 
termination switch of a fiter press are joined with a switch of the 
control console of this filter press. 
The control unit of each filter press can comprise a first coincidence 
circuit whose first input should be connected to an output of the timer, a 
second input should be connected to an output of the control console, a 
flip-flop whose input should be connected to an output of the matching 
circuit, an electrical signal generator whose output should be connected 
to an input of the flip-flop and the input thereof to the output of the 
control console, a second matching circuit whose input should be connected 
to an output of the electrical signal generator, while the output thereof 
should be connected to the input of the control console, a frequency 
divider whose output should be connected to the input of the second 
matching circuit, while the input thereof should be joined with the input 
of the electrical signal generator, an AND gate, a generator whose output 
should be connected to an input of the AND gate and to an input of the 
frequency divider, while the input thereof should be connected to the 
output of the control console, the input of the AND gate being connected 
to the output of the flip-flop, while the output thereof is connected to 
the inputs of the matching circuits. 
The invention permits dewatering of suspension by means of pressure filters 
and obtaining a specific final water content irrespective of the filtering 
properties of the suspension and the content of the solid phase therein. 
It also permits automatic determination of the duration of the dewatering 
process with due allowance for varying filtering parameters and control of 
a group of pressure filters on the basis of the time determined by means 
of the control pressure filter during the suspension dewatering. 
The design and circuitry of the device for automatic control of pressure 
filters are such that no monitoring of the suspension filtering 
properties, the solid phase content and water content of the filter cake 
is necessary. 
Since the filter cake has a desired and constant water content, no 
additional treatment of the cake is required to remove the excess water 
therefrom. The device according to the invention permits obtaining better 
quality of filter cakes and make the servicing less labour-intensive.

BEST MODE FOR CARRYING OUT THE INVENTION 
A device for automatic control of pressure filters comprises a control 
assembly connected to at least one pressure filter 1 (FIG. 1), which is a 
reference or monitoring pressure filter, by means of a filtrate pipe 2. 
The control assembly is intended to determine the duration of the 
suspension dewatering process and is equipped with a sensor 3 which 
determines, in the course of the dewatering process, the moment when the 
solid phase of the suspension reaches desired parameters. 
Control assemblies can be installed on several pressure filters so that the 
operation of the filters is not interrupted when the monitored pressure 
filter is stopped for repair and a ready substitute is available. 
A control assembly is essentially a vertically arranged pipe 4 whose 
cross-section is equal to or larger than that of the filtrate pipe 2. The 
upper end of the pipe 4 communicates with an initial portion 5 of the 
filtrate pipe 2, while the lower end thereof is limited by a baffle 7 
having a calibrated opening 7' through which the pipe 4 communicates with 
a final portion 6 of the filtrate pipe 6. The sensor 3 is a 
capacitance-type element and is located inside the pipe 4 throughout its 
length so that the axis of the capacitance-type element is displaced in 
relation to the axis of the calibrated opening 7'. The sensor 3 permits 
monitoring of the water content of the filter cake in all chambers of the 
pressure filter simultaneously, since the filtrate is supplied from all 
chambers to the pipe 2 and passes through the sensor 3. The conductivity 
of the liquid phase of the suspension has no effect on the capacitance of 
the sensor. The monitoring helps to determine an average water content of 
the cake during the dewatering process irrespective of the irregular 
thickness of the cake in the chambers of the pressure filter 1. In 
addition, when the water content of the cake in the chambers of the 
pressure filter 1 is monitored by means of the sensor 3 disposed in the 
pipe 4, there is no need to determine the density and flow rate of the 
suspension. 
The device according to the invention comprises a timing unit 8 which 
measures the duration of the suspension dewatering process. The timer 8 is 
built around a known circuit (cf., for example, V Pomosch Radioliubiteliu, 
collection of articles in Russian, issue 77, Moscow, DOSAAF Publ., 1982, 
pp. 47-49, E. Zeldin, Frequency Dividers Built around Microcircuits; or 
issue 72, ibid., 1981, R. Maizuls, Electronic Watch Built around 
Micropower Integrated Circuits, pp. 60-62, 63 and 64). The device also 
comprises control units 9 whose number is equal to the number of the 
pressure filters 1, first inputs of each filter 1 being connected to an 
output 10 of the timer 8, a control consoles 11 whose number is also equal 
to that of the pressure filters 1. Inputs 12 of the control consoles 11 
are connected to outputs of respective control units 9, while control 
outputs 13 of the control consoles 11 are connected to actuating devices 
(not shown) of the pressure filters 1. 
The sensor 3 is connected to an input of a capacitance-to-frequency 
converter 14 whose output is connected, via a sensor engagement switch 15, 
to an input 16 of a frequency coincidence unit 17 build around a known 
circuit (cf., for example, V Pomosch Radioliubiteliu, collection of 
articles, issue 72, Moscow, DOSAAF Publ., 1981, R. Tomas, Digital 
Synchronizer for Film Sound System, pp. 68, 69-73). An input 18 of the 
coincidence unit 17 is connected to a frequency generator 19 using a known 
circuit (cf., for example, ibid., issue 76, 1982, S. Mindelevich, Pulse 
Generators on Digital Microcircuits, pp. 52-54), while the output thereof 
is connected to an input 20 of the timer unit 8 and, via switches 21, to 
the inputs 12 of the control consoles 11. The switches 15 and 21 of a 
respective pressure filter 1 are mechanically joined with a switch (not 
shown) of the control console 11 of the same pressure filter 1. 
A control input of the frequency generator 19 is joined with a first 
control input of the timer unit 8 and connected to outputs 22 of the 
control consoles 11. A second control input of the timer unit 8 is 
connected to outputs 23 of the control consoles 11. Outputs 24, 25 and 26 
of the control consoles 11 are connected, respectively, to second, third 
and fourth inputs of respective control units 9, a second output of the 
timer unit 8 being connected to an indication unit 27. 
Each control unit 9 comprises a coincidence circuit 28 which is analogous 
to the coincidence unit 17. Inputs 29 and 30 of the coincidence circuit 28 
are connected to the output 10 of the timer unit 8 and to the output 25 of 
the control console 11. Each control unit 9 also comprises a flip-flop 31 
whose input 32 is connected to an output of the coincidence circuit 28, an 
electrical signal generator 33 using a known circuit (cf., for example, 
Radio magazine, No. 1, 1977, DOSAAF Publ., Moscow, V. Milchenko, 
Pulse-Type Units Using Logic Elements, in Russian, pp. 43-44), whose 
output is connected to an input 34 of the flip-flop 31, while an input 35 
is connected to the output 24 of the control console 11. 
The control unit 9 also comprises a coincidence circuit 36 which is 
analogous to the unit 17, whose input 37 is connected to an output of the 
electrical signal generator 33, while the output thereof is connected to 
the input 12 of the control console 11, a frequency divider 38 (cf., for 
example, collection of articles, V Pomosch Radioliubiteliu, issue 77, 
1982, Moscow, DOSAAF Publ., E. Zeldin, Frequency Dividers Built around 
Microcircuits, in Russian, pp. 47-51) whose output is connected to an 
input 39 of the coincidence circuit 36. An input 40 of the frequency 
divider 38 is joined with the input 35 of the generator 33. 
The control unit 9 also comprises an AND gate 41, a pulse generator 42 
which is analogous to the generator 19 and whose output is connected to an 
input 43 of the AND gate 41 and to an input 44 of the frequency divider 
38. An input 45 of the generator 42 is connected to the output 26 of the 
control console 11, an input 46 of the AND gate 41 is connected to the 
output of the flip-flop 31, while the output thereof is connected to 
inputs 47 and 48 of the circuits 28 and 36 respectively. 
The capacitance-to-frequency converter 14 comprises an operational 
amplifier 49 (FIG. 2) whose first input is connected, via a resistor 50, 
to the output thereof connected, via a resistor 51, to the first input of 
an operational amplifier 52 and to the sensor 3. The output of the 
operational amplifier 52 is directly coupled to the second input thereof 
and to a screen connecting the first input of the operational amplifier 52 
and the sensor 3, and, via a resistor 53, to a second input of the 
operational amplifier 49 through which a resistor 54 is coupled to a 
common bus. The output of the operational amplifier 52 is connected, via a 
resistor 55, to a first input of an operational amplifier 56, a second 
input thereof being connected to the common bus, while the output is 
connected to the switch 15 and, via a resistor 57, to its first input, 
and, in addition, via a resistor 58, to the first input of the operational 
amplifier 49. 
The control console 11 comprises coils of relays 59 (FIG. 3), 60, 61 and 
62. Some leads of these relays are coupled to a zero bus. A second lead of 
the relay 59 is the input 12 of the console 11, a second lead of the coil 
of the relay 60 is connected, via make contacts 61" and 59', to the power 
supply bus. A second lead of the coil of the relay 61 is connected to the 
power supply bus via a break contact 63 of a suspension supply valve (not 
shown) and a make contact 64 of a suspension pressure gauge (not shown). A 
second lead of the coil of the relay 62 is connected to the power supply 
bus via a switch 65. The switch 65 is mechanically connected with the 
switches 15 and 21. The power supply bus is coupled via a make contact 66 
of a relay coil (not shown) to an actuating device of the pressure filter 
1 (FIG. 1). 
A dc terminal 67 (FIG. 3) is connected, via make contacts 62' and 61', to 
the integrated control inputs of the units 8 (FIG. 1) and 19 and, via a 
make contact 68 (FIG. 3) of a relay (whose coil is not shown), to the 
second control input of the timer unit 8 (FIG. 1). 
The same terminal 62' (FIG. 3) is connected via a transfer contact 62' and 
the make contact 68, to the inputs 35 (FIG. 1) and 40 of the generator 33 
and the frequency divider 38 respectively. 
The same terminal 67 (FIG. 3) is connected, via the transfer contact 62' 
and the make contacts 61' and 68 coupled parallelly, to the input 45 (FIG. 
1) of the unit 42. 
The terminal 67 (FIG. 3) is connected, via the transfer contact 62', the 
make contact 68, and the series-connected break contacts 61.sub.1 ' and 
61.sub.1 ', to the input 30 (FIG. 1) of the circuit 28. The coil 61.sub.I 
belongs to the control consoles 11 and is not shown. 
The device according to the invention is capable of automatic determination 
of the duration of the suspension dewatering process in the monitored 
pressure filter 1 and thus provide a means to control a group of pressure 
filters engaged in dewatering the same suspension, using the data of the 
monitored pressure filter on the deatering process duration as a guide. 
The proposed device is advantageous in that it eliminates the operations of 
determining the volume of the filtrate and suspension, the content of the 
solid phase in the suspension, and the water content of the cake. This is 
achieved by making use of the kinetics of the flltrate flow from the 
pressure filter 1. The filtrate flow kinetics remains unchanged with a 
specific cake thickness and water content. The time varies depending on 
the solid phase content in the suspension and its fitrability. This time 
is determined from the moment the filtrate starts flowing in the pipe 2. 
The device ensures the desired kinetics and thus the maximum productivity 
of the pressure filter 1, the output cake having a constant specific water 
content. 
The group of pressure filters can be controlled automatically using one of 
the filters as a pilot unit. The control units 9 and control consoles 11 
can control filters automatically without an operator. 
The stack of frames (not shown) of the pilot pressure filter 1 is 
compressed so that the chambers are leak-proof. Each chamber is provided 
with a filtration plate (not shown). The suspension is pumped into 
chambers under pressure and is separated by the filtering plate into 
liquid and solid phases. The liquid phase (filtrate) is removed from the 
chambers of the pressure filter 1 through the pipe 2, while the solid 
phase is retained by the filtering plate and accumulated in the chambers 
of the filter press 1. 
The duration of the dewatering process is controlled using the flow rate of 
the filtrate passing through the filtering plate. The desired parameters 
of the dewatered cake have a corresponding flow rate of the filtrate 
passing through the filtering plate, which means the dewatering process 
has come to an end. A calibrated opening 7' in the baffle 7 having a 
specific size is selected to provide a specific flow rate. 
Initially, during the dewatering process the filtrate passes through the 
filtering plate at a higher rate than the preselected value. All filtrate 
cannot pass through the opening 7' in the baffle 7. The excess filtrate 
passes through the pipe 2 in a continuous flow. 
The capacitance of the sensor 3 remains unchanged and the converter 14 
generates pulses of constant frequency to be supplied to the frequency 
coincidence unit 17. When the filtrate flow through the pipe 2 is 
uninterrupted, the output frequencies of the converter 14 and the 
generator 9 are different, and the output of the unit 17 is zero. 
The start of the suspension dewatering process coincides with the moment 
the timer unit 8 is switched on to count the duration of the deatering 
operation. 
As soon as the flow rate at which the filtrate passes through the filtering 
plate becomes equal to the predetermined rate or, when the flow rate at 
which the filtrate passes through the opening 7' in the baffle 7 exceeds 
the flow rate at which the filtrate exists from the filter press 1, the 
flow of the filtrate in the pipe 2 is interrupted. The electrical 
capacitance of the sensor 3 changes and, consequently, the pulse 
recurrence rate at the output of the converter 14 also changes. The 
generator 19 is adjusted so that the frequency of its output pulses is 
equal to the frequency of the output pulses of the converter 14, when a 
capacitance-type signal arrives to the input of the converter 14 at the 
moment the flow of the filtrate is interrupted. The capacitance of the 
sensor 3 changes and, consequently, so does the output pulse recurrence 
rate of the converter 14. The generator 19 is adjusted so that the 
frequency of its output pulses is equal to the frequency of the output 
pulses of the converter 14 when a capacitance type signal arrives to the 
input of the converter 14 indicating the filtrate flow is interrupted. 
When pulses having the same frequencies are supplied from the outputs of 
the generator 19 and the converter 14 to the inputs of the unit 17, the 
latter produces a signal fed to the unit 8 and to the control console 11. 
This signal makes the timer unit 8 stop counting the duration of the 
suspension dewatering process, and the control console 11 produces a 
command to terminate the suspension dewatering process. After the 
suspension dewatering process is stopped, the information on the duration 
of this process is supplied from the unit 8 to the control units 9 of all 
other pressure filters 1 which are operated on the basis of the duration 
of the dewatering process of the pressure filter 1. 
If the parameters of the suspension fed to the pressure filter 1 during the 
dewatering process change, the duration of the process also changes and 
the relevant information is supplied to the control units 9 of other 
pressure filters 1 which are operated on the basis of the different 
information of the dewatering process duration. 
The device for automatic control of pressure filters operates as follows. 
Prior to the start the operator selects any pressure filter 1 equipped with 
a sensor 3 as a pilot filter and makes contacts of the switches 15, 21 and 
65 (FIG. 3). Power is supplied to all pressure filters 1 (FIG. 1). The 
contact 63 (FIG. 3) of all pressure filters 1 is disconnected. As the 
switch 65 is closed, current flows through the coil 62, the relay is 
actuated and the transfer contact 62' disconnects the control unit 9 (FIG. 
1), preparing control circuits of the units 8 and 17 for operation. 
The first to be operated is the pilot pressure filter 1. To this end its 
filtering plates are compressed and fixed. As the plates are fixed, the 
contact 68 (FIG. 3) is closed and a signal is generated from the terminal 
67 to be fed through the control circuit to the unit 8 (FIG. 1) so that 
the unit 8 is set. 
After the filtering plates are fixed, the contacts 68 (FIG. 3) are opened 
and a command is produced to start the operation of the pilot pressure 
filter 1 (FIG. 1). To this end the chambers of the pressure filter 1 are 
filled with the suspension and an excess pressure is built up therein. As 
soon as the suspension delivery is started, the contact 63 (FIG. 3) of the 
relay is closed and provides a power supply circuit for the relay coil 61. 
When the operational excess pressure is reached in the chambers, the 
contact 64 is closed and the relay coil 61 is energized, the relay is 
actuated. The contact 61' is closed and a signal is fed from the terminal 
67 to the unit 8 (FIG. 1) and to the frequency generator 19 to make them 
operate. The frequency generator 19 starts producing pulses having a 
specific frequency, while the unit 8 starts counting the time indicated by 
the unit 27. 
Since the pipe 2 is filled with the filtrate with a certain delay in 
relation to the moment the operational excess pressure is reached in the 
chambers of the pilot pressure filter 1, the closing time of the contact 
61' (FIG. 3) is selected to be longer than the delay time in order to 
avoid a false response terminating the dewatering process. 
As the pipe 2 and the filtrate pipe 4 are filled, the contact 61" is closed 
and establishes a power supply circuit for the coil 60. 
The information of the sensor 3 (FIG. 1), corresponding to the capacitance 
value and depending on the degree to which the pipes 2 and 4 are filled 
with the filtrate, is supplied to the converter 14. 
Initially, at the beginning of the suspension dewatering period, the 
filtrate flows through the pipe 2 in a continuous stream. The capacitance 
of the sensor 3 is therefore more or less constant, and the recurrence 
rate of output pulses of the converter 14 is also constant and different 
from that of the frequency generator 19. No signal is produced at the 
output of the coincidence circuit 17. 
At the moment, when the flow rate of the filtrate passing through the 
calibrated opening 7' in the baffle 7 exceeds the flow rate of the 
filtrate coming out of the pressure filter 1, the flow of the filtrate in 
the pipe 2 is interrupted. 
As soon as the filtrate flow in the pipe 2 is interrupted, the capacitance 
value of the sensor 3 coincides with the value corresponding to the end of 
the suspension dewatering process and the frequency of the pulses, which 
corresponds to this value, at the output of the converter 14 coincides 
with the assigned frequency of pulses produced by the generator 19. These 
pulses are fed to the unit 17 which produces a signal delivered to the 
unit 8 and to the control console 11 to the coil 59 (FIG. 3). The timer 
stops indicating the end of the suspension dewatering period, the contact 
59' is closed, and current flows through the relay coil 60 of the 
actuating devices of the pilot pressure filter 1 thus terminating the 
supply of suspension to the chambers of this pilot pressure filter 1. 
At the same time, a code signal which corresponds to the duration of the 
suspension dewatering period is fed to the control units 9 (FIG. 1) of 
other pressure filters 1, particularly to the inputs 29 of the circuits 
28. Other pressure filters 1 start operating from this moment on. 
The duration of the suspension dewatering period is determined directly on 
the pilot pressure filter 1, using the timer unit 8, and this information 
is supplied to the units 9 and control consoles 11. This procedure 
eliminates the use of tables and participation of operators in the 
transfer of information from the control console 11 to other control 
consoles 11 of the rest pressure filters 1. 
One of the contacts 61.sub.I ' (FIG. 3) in the control circuit of the 
circuits 28 (FIG. 1) coincidence circuits 28 (FIG. 1) of other pressure 
filters 1 is opened in order to avoid feeding false information to the 
coincidence circuit 36. 
We shall deal with the operation of only one pressure filter 1 since the 
suspension dewatering process is identical in all of them. 
The switch 65 (FIG. 3) of the control console is turned off and all control 
circuits of the control unit 9 are ready for transmission of a control 
signal, since the contact 62' is closed. 
At the moment the filtering plates are fixed, the contacts 68 in the 
control circuits of units 9 are closed. DC voltage is supplied from the 
terminal 67, via the contacts 62' and 68 and via all contacts 61.sub.I ' 
to the input 30 (FIG. 1) of the circuit 28 and resets this circuit 28. 
DC voltage is supplied from the terminal 67 (FIG. 3) via the contacts 62' 
and 68 to the input 35 (FIG. 1) of the generator 33 to reset the flip-flop 
31 and the circuit 36 and to the input 40 of the divider 38 to reset the 
divider 38 and interlock the divider 38. A signal "I" s produced at the 
output of the flip-flop 31 and fed to the input 46 of the AND gate 41. 
Direct voltage is supplied from the terminal 67 (FIG. 3), via the contacts 
62' and the contact 68 coupled in parallel to the contact 61' to the input 
45 (FIG. 1) of the generator 42 and turns it on. 
Output signals of the generator 42 are supplied, as pulses, to the input 43 
of the AND gate 41. Signals are then supplied from the output of the AND 
gate 41 to the inputs 47 and 48 of the circuits 28 and 36 respectively. 
The signals are added in the circuit 28 and correlated with the information 
fed from the pressure filter 1. These signals are stored n the circuit 36. 
When the number of pulses is equal to the number of pulses of the code 
information, a signal is produced at the output of the circuit 28 and 
delivered to the input 32 of the flip-flop 31 and resets it. The "0" 
signal is supplied from the output of the flip-flop 31 to the input 46 of 
the AND gate 41 to close the gate. Delivery of pulses from the generator 
42 is discontinued. The number of pulses in the memory of the circuit 36 
corresponds to the code information. 
After the filtering plates are completely fixed, the contacts 68 (FIG. 3) 
are opened and the unit 38 (FIG. 1) is unlocked. The process of dewatering 
starts in the controlled pressure filter 1. 
When the suspension supply starts, the contact 63 (FIG. 3) is closed and 
prepares the power supply circuit for the relay coil 61. When the 
operational excess pressure is reached in the chambers, the contact 64 
closes and current flows through the relay coil 61 making the relay 
operate. 
Direct voltage is supplied from the terminal 67, via the transfer contact 
62' and the contact 61', to the input 45 (FIG. 1) of the generator 42 and 
from the output thereof pulses are fed to the input 44 (FIG. 1) of the 
frequency divider 38 which produces pulses at certain intervals to be fed 
to the input 39 of the coincidence circuit 36. These pulses are summed up 
in the circuit 36 and compared to a sum of pulses stored therein. If the 
sums are equal, a signal is produced at the output of the circuit 36 and 
supplied to the control console 11 to the relay coil 59 (FIG. 3). The 
contact 59' is closed, current flows through the relay coil 60 belonging 
to the actuating devices of the pilot pressure filter 1, and the supply of 
the suspension is terminated. 
The converter 14 operates as follows. 
There is negative voltage at the output of the converter 14, when it is 
turned in. This negative voltage is supplied via the resistor 58 (FIG. 2) 
to the inverting input of the operational amplifier 49 having a negative 
fedback via the resistor 50 and a positive feedback via the resistor 58. 
The resistor 54 limits the positive feedback degree. A positive potential 
is formed at the output of the operational amplifier 49. The output of the 
operational amplifier 49 is connected to an integrating circuit comprising 
the resistor 51 and sensor 3 which is a capacitance-type electrical 
element whose one plate is coupled to a common zero bus. As the positive 
output voltage of the operational amplifier 49 grows, the sensor 3 is 
being charged by a positive potential via the resistor 51. The operational 
amplifier 52 is a voltage follower and the amplified signal produced at 
the output thereof has a voltage proportional to the voltage across the 
plates of the capacitance-type element. 
The capacitance-type element is charged until a signal is produced at the 
output of the operational amplifier 52. This signal trips the Schmitt 
trigger circuit built around the operational amplifier 56. The output 
signal of the operational amplifier 56 changes cumulatively from negative 
to positive and is supplied, via the resistor 58, to the control input of 
the operational amplifier 49, a negative signal being formed at the output 
thereof. The capacitance-type element starts discharging via the resistor 
51, the voltage therein and at the input of the operational amplifier 52 
reversing from positive to negative value. At the output of the amplifier 
52 the output signal changes the polarity to a negative value, the Schmitt 
trigger circuit switches over, the polarity of the output signal is 
reversed from positive to negative value. The process is repeated further 
on. 
When the capacitance of the capacitance-type element is constant, the 
output signal of the converter 14 has a constant frequency. As the pipe 2 
(FIG. 1) and the vertical pipe 4 are filled with the filtrate, the 
capacitance of the sensor 3 changes, the frequency of the output signal of 
the converter 14 being the function of this capacitance. When the filtrate 
flow is interrupted, the capacitance of the sensor 3 reaches the value 
which corresponds to the frequency of the frequency generator 19. 
A device for automatic control of pressure filters provides a constant 
water content in the discharged cake within specific limits whatever the 
filtering properties and the content of the solid phase in the suspension; 
ensures stability of the technological process of suspension filtering by 
eliminating the discharge of the cake having a water content outside the 
regulation standards, thus substantially improving the quality of the 
filtering cake. The downtime of the equipemnt is drastically reduced by 
elimination of unscheduled clean-ups and failures which are possible when 
the water content of the cake exceeds the admissible level. The constant 
water content of the filtering cake permits organization of a stable and 
reliable technological process for processing the discharged cake and its 
transportation, cutting down the costs for: 
evaporation of water during cake drying; 
transportation of the liquid phase to the storage site; 
storage due to lesser areas occupied. 
A device for automatic control of pressure filters makes the filtering 
equipment used for dewatering of suspension more efficient, simplifies the 
dewatering processes and eliminates the effect of the variable 
filterability of the suspension and the solid phase content therein on the 
output properties of the suspension -the water content of the cake. It 
also makes it possible to control a group of pressure filters without an 
operator. 
Industrial Applicability 
This invention can be used for dewatering the sediments of sewage at 
municipal aeration plants, sediments of industrial sewage in papermaking 
industry, the slime in the circulating water supply systems of gas 
cleaners, sediments of sewage at neutrilization plants and production 
installations in microbiological and petrochemical industries.