VINCENT CP-4 Assembly instructions

Vincent In our ninth decade
CORPORATION
August 16, 2014 OPERATING HINTS
MODEL CP-4
SEE NOMENCLATURE DRAWING AT THE END OF THIS MANUAL
INDEX
START-UP 3
INSTRUMENTATION 3
INVERTER VFD & PLC CONTROL 4
FEEDING 5
BUILDING A PLUG 6
PRE-THICKENING 7
AIR CYLINDER REGULATOR 7
DISCHARGE CONE 8
INTERMITTENT OPERATION 10
DOUBLE PRESSING 10
MOISTURE CONTENT 11
COMPRESSION 12
PRESS SPEED (RPM) 12
CAPACITY MEASUREMENT 13
A-B-C PLATES 13
SCREW LIFE 14
SCREW CONFIGURATION 14
PIE CUTTING 15
JAMMING 17
2810 E. 5
th
Avenue, Tampa, Florida 33605
Phone: [phone] Fax: [phone]
E-mail: [e-mail]

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SCREEN BLINDING 18
CHANNELING 19
PURGING 19
BRIDGING 20
RESISTOR TEETH 20
FLUID INJECTION 20
CORD CUTTER AND STRIPPER 21
VACUUM EFFECT 20
POLYMER 22
NOTCHES 22
WIPERS 23
PRESS AID 23
HYDRATED LIME, GYPSUM, AND ALUM 24
VACUUM EFFECT 24
PRESS LIQUOR 24
SCREEN 25
SCREW-TO-SCREEN CLEARANCE 26
CONE BUSHING 27
WING FEEDERS 28
CLEANING 28
SHAFT SEAL 29
SCREW REMOVAL 30
SCREW REPLACEMENT 32
GEARBOX BASICS 33
PRESS LUBRICATION 33
REPLACEMENT PARTS 34
SAFETY 35
NOMENCLATURE 36

3
OPERATING HINTS
SERIES CP-4 PRESS
START-UP
The CP-4 press runs on single phase current, 110 volts. It is provided with a
reversing switch so that the direction of rotation can be selected. The screw of the
press turns in a counterclockwise direction, when viewed from the drive end of the
press.
Alternatively, the press can be supplied with motor options such as 208-220 volt
single phase, three phase, 380-580 volt, explosion proof. Extended length inlet
hoppers and 316 stainless steel construction are available.
To suit individual situations, the press can be installed tilted upwards. Also, the
gearbox can be rotated 90oor 180o. Consult the factory in these situations as the
oil level in the gearbox may have to be adjusted.
Before putting power to the screw press it is advisable to bump the motor or even
rotate the screw by hand. This will prevent damage to the press in case the screw
has shifted so as to hit the screen. Also, the presence of tramp material in the
press will be revealed. To turn the screw by hand, remove the fan guard on the
motor and turn the fan blades.
INSTRUMENTATION
The most useful instrument to have when testing a press is an ammeter. The load
drawn by the drive motor of the press is indicative of how much work the press is
doing. The higher the amps, the better the dewatering. Also, the higher the amps,
the closer the press is to jamming, and the greater is the abrasive wear. Very low
amps indicate little dewatering is being done; the screen is blinded; low
compression is taking place; or the flow into the press has stopped.
A moisture balance is valuable for measuring the moisture content of the inbound
material and of the press cake. If an oven is used to dry samples, be sure it is set
at 160oF or less if there are sugars in the sample. Samples should be left in the
oven overnight. The tare weight of the pan should be much less than the weight of
the sample which is being dried.
Although it is unusual for a CP-4, level controls can be useful in operating a press.
With a signal providing the depth of material in the inlet hopper, the speed of the
press can be varied to match the flow going into the press. With egg shells, a
simpler level control is used to only signal when a high level is reached; its signal

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will increase the screw speed. In special cases the press can be turned off when a
low level is reached and re-started when a higher level is reached.
In the case of pressing liquids that contain dissolved sugars, a refractometer is
valuable for assessing press performance. The Brix of the inbound flow, the press
cake, and the press liquor will all be the same figure. The higher the Brix, the
higher will be the solids content of the press cake.
If dissolved (soluble) solids are present, the suspended (insoluble) solids (fiber) in
the press liquor are generally measured by filtering and washing a sample and
drying the filter paper in an oven. Dissolved solids will be washed from the sample
during the washing process.
INVERTER VFD & PLC CONTROL
While it is not necessary for a CP-4 press, it can be handy to have an inverter VFD
to start, protect, and operate the screw press. (A three phase motor is required if a
VFD is used, although the power supply can be single phase; have someone at the
factory explain this to you.) With a VFD it is possible to establish the optimal
combination of screw speed and discharge cone air pressure. The VFD also can
be used to reverse the press in case of a jam or to slow it down during upset
conditions.
Nine presses out of ten will operate unattended, indefinitely, and just fine at line
frequency of 50 or 60 Hertz. However, there are exceptions, especially with larger
screw presses:
In some cases the press will tend to jam, overload, and trip out on high amps. In
this situation it may be necessary to program the controls so that the cone
automatically goes open on high amps, re-closing at a lower set point. This
arrangement requires a solenoid operated 4-way air valve, replacing the manual
valve which is provided with the press.
In other cases of jamming, a simpler arrangement is to install a Cone Timer. A
timer is used to periodically open the cone. The closed period is determined by the
amount of time required for press cake to accumulate in the press. The duration of
the "cone open" period is long enough to dump most of the press cake that has
formed. This type of operation may be used if the press periodically experiences
jamming or overload due to fluctuations in the amount of material being fed into the
press. Alternatively, it may be used with slippery or slimy press cake that cannot
be dewatered to sufficient firmness to force the cone open. Cone Timer panels are
available from Vincent at no charge.

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Some applications require the use of a specially programmed variable frequency
drive. In this case the VFD is not used to change the speed of the press, but,
rather to set it for auto-reversing operation. By having the screw run backwards for
three or four turns every few minutes, some difficult-to-dewater materials can be
pressed much more effectively. This operation can help a great deal with material
which tends to blind (cover over) the openings in the screen. Vincent has loaner
VFD's if you want to give it a try. The technique works well on bar screens; care
must be taken with perf screens so that the screw does not snag the screen during
the reverse cycle.
In some applications a press is sized for handling upset conditions of large flow,
while the normal flow is quite small. In these cases a level control is used, and the
PLC can be programmed to turn off the press when a low level is reached in the
inlet hopper, and the press re-started when a higher level is signaled.
Once through start-up, the cone is almost always permanently left in the closed
position at whatever air pressure has been found to be effective. A plug of cake
will be left around the cone whenever the press is turned off; this will clear on its
own accord on restarting the press.
However, some materials may set up and become hard or freeze within the press
when the press in turned off. This is especially true in the case of pressing wet
coffee grounds or outdoor installatons. For these applications it is advisable to
open the cone for a period of one minute before turning off the press. This allows
the press to partially empty itself, fluffing the material left in the press. Vincent can
provide information for automating this procedure.
FEEDING
Material can be fed into the press many ways. Pouring from a 5-gallon pail is most
common for the CP-4 press. In pilot or production runs, screw conveyors, pumps,
transition chutes, or cyclone separators are used. Consider making provision for
overflow return of material in the event that more is fed to the press than it can
take. Spill containment is a consideration.
Sometimes either a static (sidehill or parabolic) screen or a rotary drum screen
(RDS) is mounted over the inlet hopper to prethicken the flow ahead of the press;
the tailings (solids) from the screen are funneled into the press. This arrangement
is desirable when the feed to the press is dilute.
Also, material can be dropped from a shredder or cyclone separator into the press.
A shredder is used to increase capacity and dewatering in the case of low bulk
density materials like lettuce leaves, alfalfa, onion peel, and cornhusk, or to prevent
blockage.

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Most commonly, the best screw press performance is achieved if the material in the
inlet hopper stays just over the top edge of the screw. Usually presses work the
best with only atmospheric pressure in the inlet hopper. In order to minimize static
head, press headboxes are kept short, and level controls are used to minimize the
depth.
When a pump is used to feed a press, the system can be either open or closed.
We recommend the open system where little or no pressure exists in the inlet
hopper, thus preventing the press from being force-fed. In this arrangement either
there is an open return line allowing flow back to the source feeding the press, or
level is controlled in the inlet hopper. It is best to have a line that allows material to
recirculate past the press inlet. This will prevent pressurizing the inlet of the press,
which can cause both blinding of the screen and purging from the cake discharge.
A port on the side of the inlet hopper is frequently provided on larger Vincent
presses. It is used to view the level of material over the screw. It has a bolted
cover because it is rarely used.
If a fluid flow is piped through a sealed cover which is bolted to the inlet hopper,
force-feeding is possible. A by-pass tee should be provided so that the pressure in
the inlet hopper is minimized. In addition, a 2" vent line, open to the atmosphere,
must be provided to prevent siphoning material in the inlet hopper out through the
recirculation line.
Inlet hopper pressure over one to four psi can force fibrous material against the
screen so as to blind off the screen, resulting in unsatisfactory performance.
At pressures above 10 to 15 psi in the inlet hopper, it is possible to blow the "plug"
of press cake that forms at the discharge of the press. Unscreened liquid will purge
from the cake discharge. Exercise caution if either hot or hazardous material is
being pumped into a press.
At inlet hopper pressures of 40 psi and above, the shaft seals will be blown out of
their housing. At pressures around 60 psi the screen will start to separate from its
support plates, resulting in bypassing of feed material directly into the press liquor
flow.
BUILDING A PLUG
In order for the press to work, a plug of cake must form between the cake
discharge opening and the pressure cone. The press will almost always do this on
its own accord as material is fed into the press.

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In the case of sloppy materials like manure and DAF sludge, it may be advisable to
start off by first packing the discharge of the press with any available fibrous
material.
Alternatively, the press can be turned on and the feed pump allowed to run just
long enough to fill the feed line and the press. Then shut off the pump, leaving the
press running, and wait until no more liquid drains from the screen of the press.
Repeat this process until a plug of cake starts to open the cone.
PRE-THICKENING
Almost always, the thicker a flow going into a press, the better it will work.
If the flow into a screw press is too dilute, the high volume of liquid going through
the press screen can cause either of two problems. The flow may either flush most
of the solids through the screen, or it may plaster solids against the screen, thus
blinding (covering over) the screen.
To prevent these things from occurring, it may be necessary to pre-thicken the flow
ahead of the screw press. This is commonly done with a static screen (sidehill or
parabolic) or a rotary drum screen (RDS). In the case of very dilute feed to the
press, a Vincent Fiber Filter can be used.
AIR CYLINDER REGULATOR
To regulate the air pressure of the discharge air cylinder, presses are supplied with
an air pressure regulator along with a Parker four-way reversing valve. These
should be installed near the cone end of the press. (Until recently FRL (Filter,
Regulator, Lubricator) sets were provided to regulate air pressure. Most air
cylinder manufacturers now recommend against the use of lubricators.)
The Parker valve allows manual selection of the shut, open, or "neutral" position.
This valve connects air supply from the regulator to one end of the air cylinder,
while simultaneously opening the other end to atmosphere. The vent line on the 4-
way valve allows air to escape when pressure is switched from one end of the air
cylinder to the other.
Continuous air flow from the Parker vent line indicates a leak inside the air cylinder,
or possibly a faulty 4-way valve.
Once material is going through the press, set the 4-way valve so that the discharge
cone goes shut in the "in" or closed position. Start with a low air pressure, working
your way up until the desired performance is obtained.

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The neutral position of the Parker valve is used only in testing. If left in the neutral
position, the cone will not move unless it is pushed open by press cake. If, later,
the flow of press cake is diminished, the cone will remain in the position to which it
was pushed, and purging can occur.
FRL AIR REGULATOR WITH 4-WAY REVERSING VALVE
DISCHARGE CONE
The principal adjustment of the press is made with the discharge cone. The cone
is the component at the cake discharge end of the press that acts as a door or
stopper plug to restrict material from leaving the press. The more pressure exerted
by the discharge cone, the drier the cake material will be leaving the press. Also,
the motor amps can be expected to increase with added pressure, and throughput
may decrease.
In the small CP-4 press, the cone is usually actuated by an air cylinder, although
lever arm actuated models used to be available.
Presses are generally started up with the cone in the withdrawn position. Once
material is going through the press, the cone is set to the closed position. With
many materials it is satisfactory to start the press with the cone in the closed
position. However, with materials that are dry to begin with, such as swarf or
plastic wash tank sludge, it becomes more important to start with the cone in the
open position in order to prevent an unnecessary jam. Alternatively, very thin or
soupy materials, like pumped pig manure or clarifier underflow, might tend to purge

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right through the press if the press is started with the cone in the open position;
with these materials it is frequently better to start up with the cone nudged into the
closed position.
As the pressure on the cone is increased, not only will the cake become drier, but
the flow through the press may also be reduced. With very slimy inbound material
it may be possible to apply enough cone pressure to stop the flow altogether.
High cone pressures can result in increased quantities of suspended solids in the
press liquor.
Typical air cylinder pressures to actuate the discharge cone are in the range of 30
to 60 psi. Some materials will press only in a low range, say 10 to 20 psi. Other
materials may press best with a pressure of 60 to 100 psi. Air consumption is
minimal in all models, 1 to 2 cfm.
On models without an air cylinder, typical weights used actuate the discharge cone
vary considerably. When juicing fruit there may be a need to minimize the amount
of solids being forced through the screen. At the other end of the scale, sometime
applications require an extension arm with a very heavy weight.
It is acceptable to open the discharge cone, in most cases, during normal operating
conditions. This allows inspection, while in operation, of the discharge end of the
screw and screen. This will give the operator a chance to observe operation with
minimum dewatering and maximum throughput. It is also a good technique for
purging bad material i.e., either jammed or spoiled material, from the press. (Do
not try this trick if you are pressing hot or chemically aggressive materials.)
With some feed materials, the press can be operated with the cone in the
withdrawn position. The screw itself will do enough compressing and dewatering to
produce a cake at the discharge. If the material being pressed dewaters very
readily, the press can jam even with the cone in the withdrawn position. If this
happens, a lower compression screw is called for.
An unusual technique is to set the air pressure so that the cone normally stays
completely shut. A timer is used to periodically open the cone. The closed period
is determined by the amount to time required for press cake to accumulate in the
press. This type of operation is used with slippery or slimy press cake that cannot
be dewatered to sufficient firmness to force the cone to open. The duration of the
"cone open" period is long enough to dump the press cake that has been formed.
Cone Timer panels are available from Vincent at no charge.
Care must be taken if a press is to be left running at a very low pressure like 10 psi.
If some fiber enters between the cone bushing and the screw shaft, it will take more
than that much air pressure to close a cone which has have been pushed open by

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a heavy flow of cake. The result will be either high moisture content in the cake or,
worse, purging.
Where very low air pressures are required for proper operation, it may be practical
to put the 4-way valve in a neutral position, half way between open and closed.
(Keep in mind that a slug of cake will push the cone open, and it will not re-close on
its own afterwards.)
Once through start-up, the cone is almost always left in the closed position at
whatever air pressure had been found to be effective. A plug of cake will be left
around the cone whenever the press is turned off; this will clear on its own accord
on restarting the press.
There are a few applications where the air cylinders are removed and replaced with
a jacking bolt. This is used if the cone pushes completely closed even with the
lowest air pressure. It results in operating the press with a fixed discharge annulus.
Air cylinders with linear actuators are available.
INTERMITTENT OPERATION
In the case of intermittent operation, it is recommended that the control panel for
the feed pump or conveyor which feeds the press should have a timer. This timer
should be set to have the press run for three minutes after the feed pump (or
conveyor) shuts off. This will partially clear the press so that it will not trip out on
overload when it is re-started. (This applies in high torque applications or in
installations where the material in the press dries out or freezes.)
An extreme case occurs when pressing spent coffee grounds and some paper mill
fibers. Each time the press is turned off, the cone must first be opened for a
minute. If this precaution is not taken, nasty damage to the screw or screen can
occur when the press is re-started.
(See the previous section, INVERTER VFD & PLC CONTROL.)
Minimize the time that the screw press is run with no material being fed into it. The
last material admitted to the press will dry to powder, and it can cause severe
accelerated abrasive wear.
Initially the press will likely be run empty in order to check rotation. Even though
some rubbing may be heard, negligible wear will occur so long that this period is
kept to a minimum. Also, since the screw is supported to some extent by the
material inside the press, running dry may allow the screw to rub the screen.

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DOUBLE PRESSING
Some processes benefit from what is called double pressing. This means that the
cake coming from the press is run through the press a second time (or through a
second press). If little moisture is removed in the second (double) pressing, then it
is known that the liquid removed in the first pressing is all of the free liquid that
there is to be pressed out.
Sometimes water is added to the cake in between the first pressing and second
pressing. This is done to enhance the recovery of dissolved sugars in the original
press cake.
Molasses can be added to press cake between the first and second pressing. This
is used to infuse dissolved sugar into the cake, increasing the solids content of the
final press cake.
Capital-effective double pressing can be achieved by using an inexpensive Soft
Squeeze Series KP screw press for the first pressing, following with a tighter-
pressing Series CP or VP in the second position.
MOISTURE CONTENT
A screw press separates free water. This will leave organic water in the press
cake. The organic water is either bound to, or part of, the animal or vegetable
molecules. Mechanical pressure alone will not remove organic water; it takes heat
or chemistry. Frictional heat from the press can remove organic water, but this
obviously should be avoided. For chemistry, see the Hydrated Lime, Gypsum and
Alum section. For heat, see the Fluid Injection section.
To determine the moisture content of a material (feed to the press, press cake, or
press liquor), a sample should be weighed and dried overnight at a temperature
slightly less than 100oC. (If sugars are present use less than 70º C to prevent
caramelizing.) The sample should weigh six or more times the tare weight of the
sample tray or cup.
The moisture content of press cake varies considerably. Tomato press cake will be
90% moisture. Orange peel will be 80%, unless it is reacted with hydrated lime, in
which case it will go down to 72% moisture; add molasses and it will go to 65%.
Dairy and hog manure will come out at 70% moisture, unless there is sand or
sawdust in the sample, which will reduce the moisture content. Cellulose fiber from
a paper mill (knots, screen rejects, primary clarifier underflow) will come out about
50%. However, if secondary (biological) sludge is added, then the moisture
content of the cake will go up considerably. With high ash content in paper mill
samples, moisture may go down to 40%. Moisture contents of only 25% can be
achieved pressing things like eggshell, glass, sand, and plastic chips.

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The heat from steam injection can change the chemistry of the material being
pressed so that cake with lower moisture content is produced. This blanching or
parboiling effect works with fish and orange peel, for example.
A quick approximation of what to expect from a screw press is to squeeze as much
water out with your fist, and figure that the press will do a little bit better. A better
way is to twist a ball of the material in a cotton cloth.
COMPRESSION
A screw press achieves compression using several methods: (1) The discharge
cone of the press causes back-pressure on the material being dewatered. The
higher the cone pressure, the greater the liquid removal. (2) The pitch of the flights
of the screw tightens as the material is conveyed through the press. This forces
liquid to go through the screen. (3) The diameter of the shaft of the screw may be
increased progressively, forcing material outward, against the screen. This is a
tapered shaft design.
SCREW WITH TAPERED SHAFT (Note tightening pitch)
Force-feeding (supercharging) the press and applying a vacuum to the outside of
the screen are two additional methods which may achieve compression. These
two are used infrequently because the performance results are uncertain.
PRESS SPEED (RPM)
In general, the slower the screw speed, the greater the dewatering. Longer
residence time in the screened area results from lower screw speed, which allows
time for more thorough dewatering. Unfortunately, it also goes with reduced
throughput capacity.

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Screw press speed (rpm) can be changed by using a Variable Frequency Drive
(VFD). Alternatively, the drive motor can be switched to a different pole motor
(900, 1200, or 3600 versus the standard 1800 rpm). Most modern motors are good
for permanent 120 Hertz operation; they are always good for a test at this high
speed.
The smaller Nord gearboxes are all rated for 4,000 rpm input, which makes it easy
to switch to a 3000/3600 rpm motor. It is best to switch to synthetic lubricant if this
change is permanent. With other gearboxes, the higher speed can result in
premature gearbox failure. Consult the factory for assistance.
Low screw speeds are used for cooker crumb, potato peel, many sludges, and low
freeness materials in general.
It has become normal for a variable speed drive (frequency inverter VFD) to be
used with Vincent presses.
A small change in screw speed, like 20%, will generally not result in a measurable
change in performance of the press.
CAPACITY MEASUREMENT
The best way to measure capacity of a press is to collect timed samples of press
cake and of press liquor. This should be done during a period of sustained, stable
operation, rather than by timing a batch through the press.
Press cake is generally captured in a tarpaulin, and press liquor in a 5-gallon pail or
55-gallon drum. When the drain is at floor level, a 3-mil plastic bag can be used to
catch press liquor. If the press liquor goes to a pit or tank, the change in depth can
be timed.
Sometimes it is possible to collect only one flow, either press cake or press liquor.
In these cases it is possible to estimate the press throughput if the solids content of
the inbound material and press cake are measured. It is assumed that there are
zero suspended solids in the press liquor, although this is never really the case.
A-B-C PLATES
There are four vertical plates making up the frame of the press. Starting from the
drive end of the press, the first one is the Adaptor Plate. The gearbox is bolted to
the adaptor plate. Through four spacers, the adaptor plate is welded to the A Plate.
This A Plate forms one wall of the inlet hopper; the shaft seal housing is bolted to
the A Plate.

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The next plate is the B Plate. It forms the downstream wall of the inlet hopper. The
screen starts at the B Plate. There is a notch, called a Cord Cutter, in the B plate.
Also, there may be a bar called Brian's Stripper welded to the B Plate, inside the
inlet hopper; it is in a position to kiss the edge of the screw flight as it passes.
These two features prevent long fiber pieces from balling up at the exit of the inlet
hopper. See the section ahead on Cord Cutters.
The final plate, the C Plate, supports the discharge end of the screen. The cone
lightly touches the C Plate when in the closed position. These plates are detailed
in the Nomenclature schematic at the end of this manual.
SCREW LIFE
If a press loses its previous throughput capacity, or if cake moisture content
increases, it can be a sign of a worn screw.
A screw can last anywhere from six months to twenty years. It depends on the
material being pressed and how hard it is being pressed.
Premature screw failure can arise from several causes. The two main ones are:
(a) If a press is allowed to run continuously even when no material is being fed into
it, the screw can wear out in one or two months. The same can happen if a very
low flow is consistently fed into the press.
(b) If abrasive material is dewatered with high cone air pressure, rapid wear will
occur. This condition is avoided if a few drops of water can always be squeezed
from a fistful of press cake.
Two effective ways to extend screw life are:
(a) Various grades of hardsurfacing rod can be used to protect the flights of a
screw. The best hardsurfacing will have Tungsten Carbide impregnated in it.
(b) Using a VFD or lower speed motor to reduce the screw rpm will extend screw
life
If a worn screw is suspected, the thing to do is to shut down the press, open the
cone, and dig out the cake until the tips of the last two flights can be seen or felt.
Check how badly the tips are worn. If the there is 3/8” between the tips and the
screen, wear is evident. It is also an indication that the sharp edges of the flights
throughout the press may have worn, becoming rounded. This can cause the
flights to act like a putty knife, plastering solids against the screen, preventing water
from coming through.
Worn screws are either restored locally or returned to Vincent for rebuilding. The
maximum cost of a screw rebuild is around one third the cost of a new screw.

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SCREW CONFIGURATION
Almost all Vincent screw presses use the Interrupted Screw Flight design. The
interruptions leave room for four stationary resistor teeth that are mounted outside
of the screen. These teeth go through the screen and reach almost to the shaft of
the screw. This design of screw press stands in contrast to a Continuous Screw
design. The main advantage of the interrupted design is that solid material must
accumulate in the interruptions until sufficient consistency is reached for the solids
to be pushed toward the cake discharge. There is a reduced tendency for the
material being pressed to co-rotate with the screw. Also, there is more agitation
within the press and, consequently, quicker and more thorough dewatering.
The screw starts with a feeder section of continuous flight. This picks up material
in the inlet hopper and pushes it into the screen section. The feeder section ends
at the first resistor tooth. The feeder section of the screw is followed by
compression stages where the flights have reduced pitch. The reduction in pitch of
the flights results in compression of the material going through the press. CP-4
presses are made with four stages of compression.
A screw configuration referred to as Sterile Butterfly is available. There are a
reduced number of flights on this screw, and the flights do not wrap as far around
the shaft as is normal. This design screw is good for high throughput of materials
that are easily dewatered. Glass and sand are examples. This configuration is
rarely used in the CP-4 press.
INTERRUPTED FLIGHTS, RESISTOR BARS, and RESISTOR TEETH
LARGER PRESS CP-4 PRESS
PIE CUTTING
Sometimes the compression of a screw is reduced, in the field, in an operation
called "pie cutting". This involves cutting pie-shaped segments from certain flights
of the screw, leaving a butterfly (end view) configuration. This modification is done

16
to avoid excessive compression and jamming. The "sterile cut" is more dramatic.
Consult the factory for assistance before making this modification.
4" PIE CUT PIE CUT
NOT PIE CUT BUTTERFLY CUT

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JAMMING
Should a press trip out on overload because it has become jammed, a series of
steps can be taken to un-jam the press. Generally the easiest thing to do is to
reverse the direction of rotation. This will cause the screw to feed material
backward into the inlet hopper.
Generally jamming is caused by over-pressing excessively dry material. Running
the press backwards will break up this material. If the jamming was caused by
tramp material, hopefully this can be found and retrieved from the inlet hopper
following operation in the reverse direction.
Having a reversing starter greatly facilitates this operation. These cost little more
than a standard starter; they come with a forward-reverse switch. (Having a VFD
with a reverse button can be even handier.)
If a press has had extensive use in an abrasive application, the flights can be worn
away at the discharge of the press. Radial wear of 1" to 4" in larger presses will
lead to serious jamming and, possibly, a burst screen.

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When a press is operated in the reverse direction it is possible that solid material in
the press will be forced against the A Plate. This can damage the shaft seal. For
this reason, care should be taken when running the press backwards.
Usually three or four revolutions of the screw are sufficient to clear a press. If
running the press backwards does not clear the jam, the screen should be removed
so that the cause of the jam can be determined. Look for a bent flight. Before
going to the trouble of removing the screen, shut down the press and try clearing
the end of the press with a long screwdriver.
Sometimes when a press is jammed, a flight on the shaft of the screw will fold.
This can happen if the press overloads on dry cake or if tramp metal is caught
between a flight and a resistor tooth. The weld at the shaft may tear. When this
happens flow through the press is greatly impeded.
FOLDED FLIGHTS
SCREEN BLINDING
A common problem is for the screen of the press to become blinded (covered
over). When this occurs, the flow of press liquor coming through the screen
diminishes. The level in the inlet hopper will fill up to where it overflows.
In some cases, the screen can be cleared by periodically reversing the direction of
rotation of the screw. This can be programmed with many VFD’s, so that the press
runs forward for a given period and then reverses direction briefly for three or four
turns when the screen starts to blind. This is one of the easiest possible solutions
to test. Sometimes it is the only one that is effective.
Many other methods are used to address blinding: (1) Adding notches to the
screw, (2) Reducing or eliminating the pressure in the inlet hopper, (3) Adding
press aid to the flow, (4) Changing to a different screen selection, (5) Reducing the

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screw-to-screen clearance, and/or (6) Employing a screen flush with caustic
solution, acid, or high pressure spray.
If blinding occurs after an extended period of satisfactory operation, it is usually due
to wear of the screw. Rounded edges of the flights will contribute to blinding.
CHANNELING
A condition somewhat similar to purging can occur with slimy materials, like
concord grapes, pineapple pulp, or spent brewer’s grain. These may tend to
channel or squirt out from one side of the cone. Two ways to eliminate channeling
are to lower the air pressure on the discharge cone and to slow down the speed of
the press. Channeling can also be reduced by adding press aid to the material
being dewatered, or by reducing the inbound flow to the press.
An option NOT available with the CP-4 press is called the Rotating Cone. A
tendency for material to channel can be reduced with this option. The cone is
caused to rotate so that the relative motion between it and the (stationary) screen
breaks the channeling.
To break up channeling, pieces called wing feeders can be welded to the end tips
of the last two flights of the screw. See the Wing Feeder section of this manual.
PURGING
An undesirable condition can occur when the material being admitted to the press
purges, without liquid-solid separation, from the cake discharge. This can occur
especially if pressure exists in the inlet hopper.
Mechanically, purging occurs when a dry lump of press cake holds open the
discharge cone. Un-pressed material will flow around this partial plug.
Purging may occur when there is a much reduced, small flow of cake coming from
the press. Usually this is a sign of blinded (covered over) screens. This can be
caused by a worn screw. Liquid from the inlet hopper will wick into the press cake,
making it soft enough to blow out. Sometimes this condition is avoided by
mounting the press inclined at about 5oabove horizontal; the simplest way to do
this is to place a block under the cone end of the press.
A drop in operating amps can be an indicator that a purging condition has begun.
An ammeter circuit can be installed to alarm or trip the system when a reduction in
motor amps occurs. This is rarely done.

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Purging is prevented with the rotating cone option. This option is very unusual in
the Series CP presses, and it may not be available.
BRIDGING
Sometimes bridging will occur at the inlet hopper, stopping the flow of material into
the press. This is a common problem with CP-4 presses because the inlet hopper
narrows down from the 8" inlet to the 4" screw. Poking with a paint-stir or broom
stick is the easiest way to solve this during a simple test.
If a surge hopper is mounted over the inlet to the press, it should have at least one,
preferably two or three, vertical walls. This will minimize bridging.
Bonding Teflon sheets to the inlet hopper of the press is a remedy that has been
used to reduce bridging of bulky materials which allow free-draining of water.
Another way of overcoming bridging is to direct a stream of water or press liquor
into the inlet hopper so as to break the bridge. The nature of the screw press is
that essentially all of this added liquid will be removed in the pressing operation.
This is rarely done.
A vibrator, mounted on the side of a feed hopper, may also alleviate bridging.
RESISTOR TEETH
The interrupted screw design press has stationary teeth that protrude into the flow
of material as it passes through the press. These fit into the gaps of the screw
where there is no flighting. They stop just short of the shaft of the screw.
Not infrequently the resistor teeth are drilled so that fluid can be injected into the
press during operation. See the next section.
Rarely the resistor teeth are shortened, usually by half, to increase the capacity of
the press. Removing the teeth altogether will result in co-rotation and jamming.
FLUID INJECTION
Resistor teeth can be drilled so to permit injection of steam, solvent or water while
the press is in operation. Also, these modified resistor teeth can be used for CIP
cleaning, without the need of removing the screen from the press.