VINCENT KP Series Manual

Operation & Maintenance Manual
KP-6 – KP-16
(Including KP-10L – KP-16L)
Screw Press
Vincent Corporation
2810 East 5th Avenue
Tampa, FL 33605-5638
www.vincentcorp.com
[email protected]

This page intentionally left blank.
2

Contents
Overview..........................................................................................................................5
Safety.....................................................................................................................5
Rigging............................................................................................................................6
Installation........................................................................................................................6
Press Components…………………………………………………………………………7
A/B/C-plates……………………………………………………………………….7
Air Regulator………………………………………………………………………7
Discharge Cone……………………………………………………………………8
Rotating Cone Option…………………………………………………………… 10
Cone Bushing…………………………………………………………………….10
Four-Bar Mechanism……………………………………………………………. 11
Discharge Spout / Spin Stop…………………………………………………….. 11
Screw / Screw Configurations……………………………………………………12
Wing Feeders……………………………………………………………………. 13
Notches………………………………………………………………………….. 14
Resistor Teeth…………………………………………………………………… 14
Screens…………………………………………………………………………... 15
Cord Cutter and Stripper Pins……………………………………………………16
Motor / Gearbox………………………………………………………………….17
A-plate Shaft Seal……………………………………………………………….. 17
Variable Frequency Drives (VFDs)……………………………………………... 18
Vincent Cone Timers (VCTs)……………………………………………………18
Start Up..........................................................................................................................19
Screw Speed (RPM) ......................................................................................................19
Feeding the Press / Pre-Thickening.................................................................................20
Building a Plug...............................................................................................................21
Additional Hints.............................................................................................................21
Vacuum Effect…………………………………………………………………... 21
3

Instruments……………………………………………………………………….21
Stopping the Press………………………………………………………………..22
Double Pressing…………………………………………………………………. 22
Moisture Content………………………………………………………………... 22
Compression…………………………………………………………………….. 23
Measuring Throughput………………………………………………………….. 23
Screw Life………………………………………………………………………..24
Pie Cutting………………………………………………………………………. 24
Jamming / Plugging……………………………………………………………... 26
Screen Blinding…………………………………………………………………. 26
Channeling………………………………………………………………………. 27
Purging………………………………………………………………………….. 27
Bridging…………………………………………………………………………. 28
Fluid Injection……………………………………………………………………28
Polymer Usage…………………………………………………………………...29
Press Aid………………………………………………………………………… 29
Hydrated Lime, Gypsum, and Alum…………………………………………….. 29
Cleaning…………………………………………………………………………. 29
Maintenance...................................................................................................................30
Checking Screw-to-Screen Clearance……………………………………………30
Screen Removal and Replacement……………………………………………….31
Screw Removal and Replacement………………………………………………. 32
Lubrication……………………………………………………………………….33
Maintenance Checklist...................................................................................................35
Nomenclature Drawing...................................................................................................36
Drawing for Mounting KP-6 on Stand............................................................................37
Parts List........................................................................................................................38
General Dimension Drawing..........................................................................................39
Manuals for Purchased Items........................................................................................40+
4

Overview
The Vincent KP Press consists of a screw rotating within a screen housing, a flanged inlet
hopper, and a discharge opening. At the discharge end, the mouth of the screen housing is
closed by a pneumatically actuated cone which moves back and forth on the screw shaft in
proportion to the internal pressure in the screen frame. This motion is opposed by the cone
cylinder thrust, thereby regulating the discharge of solids. An air regulator is provided to adjust
the pressure on the cone. The liquids, which are squeezed from the wet product, escape through
the screen housing and are caught in a built-in pan under the screen.
The screw is driven by a fixed speed electric motor that is C-face mounted to a gearbox. The
gearbox reduces the RPM from the typical 1750 RPM output of the motor to an appropriate
speed for the application, 5 - 50 RPM. The hollow bore gearbox mounts directly on the screw
shaft and is flange mounted to the machine.
The numbers in the model designation stand for the nominal diameter of the screw in inches.
As the press has been adapted to many different applications, options have been added to the
press. These include interrupted or continuous flighted screws, conical screws where the shaft
increases in diameter, different shape inlet hoppers, different style cones, etc. As a result, not all
the information contained in this manual will apply to your press.
Safety
A screw press, like any screw conveyor, is totally unforgiving. If clothing or a limb gets
caught in a rotating screw, the screw will not stop.
Observe the following safety precautions:
Wear safety glasses around the press.
Avoid loose-fitting jewelry or clothing, including high-visibility safety vests. If vests
are required, the Velcro, tear-away type are recommended.
Always lock out electric and compressed air before working on the press.
Dewatering presses squirt liquid out, particularly if screen covers are removed. If
material is hot, acidic, or caustic, do not remove screen covers while operating.
Wear gloves when performing maintenance.
When removing the tailstock and discharge mechanism, watch for pinch points and
hinged assemblies. Be careful when removing or installing the screw and screen
when they are fed through the C-plate as this is a particular pinch point.
Never stand near a press being suspended during installation.
Provide an E-stop button near the press.
Keep hands out of the press inlet and press cake discharge area.
5

Rigging
Be sure to properly support the press when lifting it from the truck. Usually a sling
positioned under the inlet hopper, on the side closest to the gearbox, finds the center of
gravity. On bigger presses, do not lift just one corner of the press, as it is possible for the
frame to deflect, shifting the screw within the press.
Installation
These presses are typically called horizontal screw presses. This doesn't mean that the
presses must be installed exactly level from inlet to discharge. Presses are occasionally
installed at an upward angle. Consult the factory if you need to install the press at an angle
above 15° as an adjustment to the gearbox may be required.
Be careful not to rack the press when tightening the mounting bolts. In the case of large
presses, do not just bolt or weld the press down to a level foundation! Instead, first place the
press where it is to be installed. Next, place shims between the press frame and the steelwork
(or floor, concrete pedestal or foundation) to fill any gap where the press is to be anchored.
Only after shimming (or grouting) should the press be pulled down tight. Doing otherwise
can rack the frame of the press, and this can cause screw-to-screen interference.
A large press must be mounted solidly, preferably to a foundation or structural steel. If a
press draws its full rated horsepower without the press being anchored to the floor, the frame
of the press can twist.
For maintenance, the screw is removed through the cake discharge end of the press. Allow
the space required for such maintenance.
To suit individual conditions, a hollow bore gearbox can be rotated 180o, 90o either way.
Consult the gearbox manual or Vincent factory in these situations as it is likely that the oil
level in the gearbox will have to be adjusted.
Material can be fed into the press many ways. You may need to allow for return of overflow
material if more is fed to the press than it can take. When material is piped to a press in a
closed piping system, it is important to have a 2" vent line open to the atmosphere, along
with an overflow return line. The vent is necessary to prevent a siphon effect which can
induce a vacuum in the inlet hopper and reduce press capacity. The return line should empty
above the surface of the return pit. The overflow should fill less than half of the cross section
of the return line.
Spill containment is a consideration which should be considered, because it may be possible
for un-pressed material to purge from the cake discharge of a press.
We recommend that a manual disconnect, for killing power to the motor, be installed close to
the press.
6

A variable frequency drive (VFD) programmed for either variable speed or auto-reversing
may be required, depending on the application. If not, the use of a reversing starter switch is
recommended; they cost only a little extra. Such a switch is handy for clearing a jammed
press.
Press Components
A/B/C-plates
There are four vertical plates making up the frame of the press, called out in the
Nomenclature drawing at the end of this manual. Starting from the drive end of a press, the
first one is the Adapter Plate. The gearbox is bolted to the Adapter Plate. Through four
spacers, the Adapter 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.
The next plate is the B-plate. It forms the downstream wall of the inlet hopper. The screen
starts at the B-plate. There may be a notch (or pair of notches), called a Cord Cutter, in the
B-plate. Also, there may be a bar called Brian's Stripper welded to the bottom of the B-plate,
inside the inlet hopper; it is designed 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
“Cord Cutter and Stripper Pins” section ahead.
The final plate, the C-plate, supports the discharge end of the screen. The cake discharge
spout is bolted to the C-plate. The discharge cone touches the spout when the cone is in the
closed position.
Air Regulator
To regulate the air pressure of the discharge air cylinder, presses are supplied with an air
pressure regulator along with a 4-way cone positioning valve. These are typically 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 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 4-way valve’s vent line indicates a leak inside the air cylinder,
or possibly a faulty valve.
The neutral position of the 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.
7

Regulator 4-way 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.
The discharge cone is moved in (actuated) either by an air cylinder or, rarely, by weights.
Typical air cylinder pressures 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.
During initial, first-time start up, presses with air cylinder actuators are generally started up
with the discharge cone in the withdrawn position. This will avoid an unnecessary jam.
With the air cylinder models, the discharge cone mechanism can readily be positioned in the
"open" (or withdrawn/"out") position.
Note that with many materials it is necessary to start the press with the discharge cone in the
closed position at low air pressure. Thin or soupy materials, like pumped manure or clarifier
underflow, can tend to purge right through the press if the press is operated with the
discharge cone open [in the withdrawn ("out") position]. However, with materials that are
dry to begin with, such as sawdust or plastic wash tank sludge, it becomes more important to
start with the discharge cone in the open position. This is because these materials may tend
to jam or overload the press. Similarly, high freeness materials, from which the water falls
away freely, will tend to jam in a press. Start the press with the cone open, then close it with
low air pressure initially, when running such materials for the first time.
8
Air to cylinder
Air
Supply
Vent

Once you are through the initial startup, it will be unlikely that your press should have the
cone opened before starting. Most operators rarely open or shut the cone once it is set.
As the pressure on the discharge cone is increased, not only will the cake become drier, but
the flow through the press may also be reduced. With very slippery or slimy feed material it
may be possible to apply enough discharge cone pressure to stop the flow altogether.
High discharge cone pressures can result in increased quantities of suspended solids in the
press liquor.
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
pressure to close a cone which has been pushed open by a heavy flow of cake. The result
will be either high moisture content in the cake or, worse, purging.
On models without air cylinders, weights used to actuate the discharge cone vary
considerably. When dewatering food waste there may be a need to minimize the amount of
solids being forced through the screen. At the other end of the scale, some KP-10s used on
dairy manure may use a 5' extension arm with a hundred pounds of weight.
With some feed materials, the press can be operated with the discharge cone in the
withdrawn position. The screw alone may do enough compressing and dewatering to
produce a cake at the discharge.
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.)
Where very low air pressure is required for proper operation, it may be practical to put the
cone positioning valve in a neutral position, halfway between open and closed. A press
cannot be left permanently in this condition: keep in mind that a slug of cake will push the
cone open, and it will not re-close on its own afterwards.
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 of 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 open. The duration of the "cone open" period is long enough to dump much
of the press cake that has been formed. Vincent Cone Timer panels are available at a
minimal cost.
Once through start-up, the cone is almost always 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
9

whenever the press is turned off; this will normally clear on its own accord on restarting the
press. To prevent a potential jam upon restarting, it is a good idea to open the cone for a few
minutes prior to shutting down the press, after flow to the press has been stopped. Although
there will be solids left in the press, they won't be highly compacted.
There are a few applications where the air cylinder is removed and replaced with a jacking
bolt. There is also a cone rocker arm set screw that can be used instead. 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, or air cylinders with linear actuators are available.
Rotating Cone Option
Most KP screw presses come with an optional feature which makes the cone rotate and strip
away the press cake. The rotation is driven by two large pins mounted on the back of the
cone. These pins engage with a collar which is clamped onto the screw shaft. Press cake is
stripped away by studs on the face of the cone. These studs are in an axial position parallel
to the screw shaft. If the cake comes out too wet, shorten the length of the studs.
The rotating cone can serve multiple functions. By stripping the cake away, it can prevent
either jamming or purging. Its use generally results in wetter press cake and lower motor
amps. Most commonly it is used when all the press cake tends to channel out past one side
of the cone. It is invaluable in situations where press cake props open the cone and allows
un-pressed material to purge.
The cake will tend to co-rotate with the screw when the cone is rotating. A spin-stop bar,
welded to the inside-bottom of the cake discharge spout, prevents this. See the “Discharge
Spout/Spin Stop” section later in this manual.
Positioning the drive collar limits the maximum opening of the cone. Or, if a large amount
of cake comes from the press, the cone can run into the drive collar and force it to slip along
the screw shaft.
Disconnect the rotating cone by removing the drive pins and/or drive collar.
Cone Bushing
The cone rides on the shaft of the screw. "Cone Sleeve" is the name given to the portion of
the screw on which the cone rides. There may be a bushing in the cone to support and guide
10

it, and to protect the Cone Sleeve journal surface of the screw shaft. Sometimes the bushing
is lubricated with liquid from the material being pressed, such as the juice from apples or
water from pectin peel. Sometimes there is a grease fitting provided for lubricating the
bushing or to minimize leakage of press liquor through the cone bushing.
Bushing lubrication is extremely important when materials that are dry (like paper mill
screen rejects) are being pressed. By the time such materials reach the discharge of the press,
they do not have enough free moisture left in them to adequately lubricate the cone bushings.
Similarly, in some applications the cone is relatively stationary, rarely moving in or out. In
these applications the operator should, at the start of each shift, pump grease in until it comes
out between the cone bushing and the screw shaft. Then he should open and shut the cone
three times in order to spread the grease over the cone sleeve.
Rarely, presses are supplied with additional lubrication fittings so that water, in addition to
grease, can be metered to the bushings as a lubricant.
Automatic grease systems are available but only usable for fixed cones, a rarity for the KP-6
- KP-16 presses. These should be the high pressure (900 psi) electric or battery variety.
Vincent provides these for critical applications, especially pulp & paper.
Liquid leaking past the cone bushings drains out the back of the cone (at the air cylinder end
of the press). Almost always it is minimal compared to the flow of press cake.
Four-Bar Mechanism
Recently, a new discharge mechanism has been added. Its design eliminates the cone
bushing. This is typically used for applications where the material fed to the press is fairly
dry. With abrasive materials that sometimes get between the cone bushing and screw shaft,
causing issues, the four-bar mechanism has proven very effective.
Discharge Spout / Spin Stop
The press cake emerges from the end of the screen through a discharge spout, bolted to the
C-plate. If a press tends to jam, it may be necessary to shorten this spout. There is usually a
bar, called a Spin Stop, welded inside this spout. This will prevent cake from co-rotating
with the screw. There is a tendency for this to happen when the rotating cone feature is in
11

service. In some cases, performance with materials like corn silage is improved by removing
this spin-stop.
Spin Stop in Spout
Screw / Screw Configurations
Most Vincent screw presses use the Interrupted Flight Screw design. The interruptions leave
room for 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 solids 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. Pushing the
material through the compression zones past the resistor teeth will also shred the material a
bit.
Interrupted Flight Screw with Resistor Bar
For applications where tramp material is more likely to enter the press, a continuous-flighted
screw is often used. Typically, if maximizing dryness is a priority, the screw shaft is tapered
to provide increased compression.
12

Screw with Tapered (Conical) Shaft
All screws start with a feeder section of continuous flights. This picks up material in the inlet
hopper and pushes it into the screen section. The feeder section ends at the first resistor
tooth. This 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.
A screw configuration referred to as Sterile Butterfly is occasionally used. Sterile is a
reference to a company, not cleanliness. 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 screw design is good
for high throughput of materials which are easily dewatered and might jam the press.
Wing Feeders
Sometimes there are blades welded to the outside tips of the last two flights of the screw.
Called "Wing Feeders", these are mounted parallel to the discharge screen surface. If you
install your own, care must be taken that wing feeders are not made so long that they hit the
face of the cone when the cone is in the closed position.
Long Wing Feeder Knobby Wing Feeder
Wing feeders can serve two purposes: (1) In the case of materials that want to channel out the
discharge of the press, like pineapple and spent brewer's grains, long wing feeders break
up the channeling flow and (2) For abrasive applications, short knobby wing feeders are
provided as sacrificial wear elements.
When certain materials are fed through a screw press, clumps of dry material may
13

accumulate between the wing feeders and the screen. This buildup can cause wear of the
screen. Should the problem occur, grind off the wing feeders.
Notches
Sometimes it is necessary, during press operation, to have the screw wipe the screens clear of
blinding material. This is best achieved by having notches in the outer edge of the screw.
Fibrous material accumulates in the notches and brushes away slimy material which may be
blinding the screens. Shallow notches (1/16" wide by 1/16" deep, 1-1/2" apart) in the outer
edge of the screw flights work well. Notching is easy to do while in the field, using a grinder
with cutting wheel or a portable band saw. Typically, notching is done from the B-plate to
the second resistor tooth. Many Vincent presses are supplied with notches.
Grinding Notches on Screw Flights
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.
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.
Occasionally, the teeth are drilled so that fluid can be injected into the press during operation.
Fluids include caustic solution, solvent, hot water, and steam.
KP Resistor Bar with Three Teeth
14

Sometimes resistor teeth are bent by tramp material so that they are hit by the screw flights.
Grinding a little off such a tooth with an angle grinder is an acceptable alternative to trying to
straighten a bent tooth.
Screens
The screen of the press is made either of wedgewire or profile bar (slotted screen) or
perforated stainless sheet (round holes).
Perforated Screen Assembly
Profile Bar / Wedgewire Screens
Screens made of wedgewire come standard with 0.015" to 0.020" slot width; they are also
available with slots that are 0.006" to 0.060" wide. With slot widths less than 0.012" there is
a tendency for the screen to blind (be covered over) with the material being pressed.
However, they work well in alcohol and oil separation. Changing the slot width generally
has little impact on the clarity of the press liquor or the dewatering capacity of the press.
These screens are reversible as most wear will occur at the discharge end. This doubles the
life of the screen. When worn, the screen may be patched or the entire wedgewire assembly
must be replaced.
Perforated metal screens are usually a simple sleeve made from rolled perforated plate which
is held in the screen assembly. These are less durable but usually only the inner screen, the
screen insert, must be replaced, reducing cost.
15

The most common damage to a wedgewire screen is for part of the surface to be smeared
over from being rubbed by the screw. This rarely is bad enough to affect press performance.
Profile bar screens generally work satisfactorily with 30% or even more of their surface
smeared over. Smeared screens can be remedied by running a die grinder blade through the
slots. Small holes can just be patched with sheet metal to extend life. In cases of severe
wear or damage, it is common to patch a screen. Stainless sheet metal is used for this. The
reduction in drainage surface is of little consequence as the screens have ample open area.
Standard perforated screens have a hole size of 0.094" diameter, although material with
0.050", 0.033", down to 0.023" holes can be supplied. Surprisingly, usually there is little
difference in the degree of filtration achieved by either changing hole size or going to a
slotted profile bar screen.
Frequently, increased press capacity can be achieved by changing a perforated screen to one
with smaller holes. This unexpected result arises from a combination of factors: (1) smaller
hole screens are made of thinner sheet metal, so the press liquor has a shorter distance to
travel before it falls free from the screen, reducing the chance of blinding and (2) particles
which fall into and plug a larger hole will roll over a smaller hole.
Minor rubbing between the screw and screen is normal, although, obviously, hard rubbing
will cause wear and premature failure of the screen. With a clearance greater than 3/16", the
dewatering performance of the press can start to deteriorate; this depends a lot on the nature
of the material being dewatered.
The most common cause of screen failure ties to failure of the outboard support bushing. If
the bushing holding the end of the screw wears out, it can let the screw move enough to rub
against the screen.
Cord Cutter and Stripper Pins
Sometimes long stringy material will be pinched where the feeder portion of the screw goes
through the hole in the B-plate. This material will co-rotate with the screw and build into a
bundle which reduces flow through the press.
A groove, like a 3/8" deep keyway, is cut halfway through the hole in the B-plate. We call
this a Cord Cutter. Material trapped between the flight and the hole in the B-plate will pop
up slightly as it passes the Cord Cutter. The result is that the material is sheared loose.
A part called Brian's Stripper may be welded to the bottom of the B-plate, inside the inlet
hopper. It goes in a position so that the flight lightly kisses the stripper as it goes past. This
strips the material away. Strippers are made of square bar.
16

Motor / Gearbox
Vincent presses are supplied complete with a motor. Standard motors are 60 Hz, Inverter
Duty, TEFC, 230/460 V. We will supply whatever motor is called for where the press is
headed, 575 V, 50 Hz, IEC, whatever. Motors used are standard, off the shelf motors, easily
replaced if needed from your local motor distributor.
Specialty motors are available upon request, including stainless, washdown duty, explosion-
proof, etc.
Standard gearboxes supplied are NORD shaft mounted. Gearboxes are supplied with the oil
at the right level for horizontal mounting. If the press is mounted off horizontal, a change
could be required in oil level. Sometimes, to increase capacity, the press is sped up to 120
Hz or a 3600 RPM motor is installed. If your press is going to be run at high speeds, NORD
recommends changing the oil to synthetic.
Both a motor manual and a gearbox manual are supplied toward the end of this manual.
A-plate Shaft Seal
Consult the Parts List contained in this manual to determine what type of seal plate assembly
you have. The Seal Plate is bolted to the A-plate. This housing may be solid UHMW (ultra-
high molecular weight polypropylene or polyethylene) and it may contain one or two Johns
Manville (JM Clipper) lip shaft seals. There may be a grease fitting on this plate; the grease
is used to reduce leakage and to help prevent fibrous material from entering and damaging
the screw shaft.
Generally, seals are allowed to drip once they start leaking. They are replaced only in
conjunction with major maintenance, as when the screw is removed from the press.
In some cases, we have found that leakage from a shaft seal can be stopped by simply
selectively loosening or tightening the four bolts holding the seal housing to the A-plate.
17
Cord Cutter

A-Plate Seal Assemblies
Variable Frequency Drives (VFDs)
In this era of dropping costs, Vincent recommends the use of an inverter VFD to start,
protect, and operate the screw press. 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 or speed it up during upset conditions.
VFDs can be programmed to automatically stop and reverse the screw at set intervals. This
is a good feature when the material tends to blind the screen. Reversing the screw will wipe
the screen clear and liquid draining will return to normal. The auto-reverse function is also
useful for applications where long stringy material wraps itself around the screw. The
reversing action will knock free (untie) the stringy material.
Vincent is also more frequently using level controls, particularly in those applications where
the flow to the press can vary substantially. The level controls can be tied to the VFD or a
control system to speed up the press when it reaches a certain level or to gradually increase
screw speed or decrease backpressure to increase press throughput.
Vincent Cone Timers (VCTs)
For some applications a timer is used to periodically open the cone. There are two timer
settings on the cone timer. Timer 1 determines the interval between cone openings. Timer 2
determines how long the cone remains open. Both are set by trial and error, manually
opening and closing the cone using the cone positioning valve and then setting the timers
accordingly to make it automatic.
Cone timers are most frequently used when there is no level sensor. With abrasive materials,
low flow to a press maintained under compression will prematurely wear the screw and
screen at the discharge. As an example, we had a location where flow to the press would
stop for hours and the wood waste material would get completely dry, creating a "Presto
Log". When the flow started again, the presto log would not move, blowing out the screens
and bending back screw flights.
18

Alternatively, the cone timer is 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 for a minimal cost.
Start Up
Check the inlet hopper first. Sometimes debris (or this owner's manual) ends up in the inlet
hopper. 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 tramp material has
been left in the press. Also, the screw may have shifted so as to hit the screen. (Minor
rubbing is normal; it will go away once there is material in the press.) To turn the screw by
hand, remove the fan guard on the motor and turn the fan blades. The screw of the press
turns in a counterclockwise direction, when viewed from the drive end of the press.
Check to make sure that compressed air is being supplied to the regulator and that the cone
can be opened and closed. Set the backpressure at a low level and/or start with the cone
open.
Start the press. Minor screw-to-screen rubbing is normal and will go away when
material is fed to the press.
Begin feeding material to the press. It's helpful to have someone watching the level
in the inlet hopper to ensure that the press isn't overloaded.
When material starts appearing at the discharge end, close the cone if it is open.
Increase backpressure on the cone until the moisture level in the press cake appears to
be as dry as you'd like. Continue monitoring the level in the inlet hopper as
increasing backpressure will influence throughput. You may need to increase screw
speed in tandem with increasing backpressure to get desired dryness and adequate
throughput. See the next section on screw speed.
Screw 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 means reduced throughput capacity.
A small change in screw speed, like 15%, will generally not result in a measurable change in
performance of the press. This is particularly true for the interrupted flight screws.
Continuous flighted screws show more reaction to changes in screw speed. In any case, it's
not going to be a linear relationship. That is, doubling the screw speed will not double the
throughput. And you do reach a point of diminishing returns.
19

Feeding the Press / Pre-Thickening
Material can be fed into the press many ways. Commonly, screw conveyors, pumps,
transition chutes, pre-thickener screens or cyclone separators are used. Consider making
provision for return of overflow material if more is fed to the press than it can take. Spill
containment should be considered.
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 corn husk, or to prevent blockage.
Level in the Inlet Hopper: Most commonly, the best screw press performance is achieved if
the material in the inlet hopper stays just at the top edge of the screw. Usually presses work
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 re-circulate 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 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 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. Un-screened 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.
Pre-Thickening: Sometimes either a static (sidehill or parabolic) or rotary drum screen
(RDS) must be mounted over the inlet hopper to pre-thicken the flow ahead of the press; the
20