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, and stainless steel. Check to be sure you got what you ordered.

To suit individual situations, the press can be installed tilted upwards. Also, the gearbox can be rotated 90° or 180 o. 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 rotate the screw by hand or at least to bump the motor. 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 cooling fan blades.

The screw of the press turns in a counterclockwise direction, when viewed from the drive end of the press.

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. Very low amps indicate little dewatering is being done; the screen is blinded; or low compression is taking place.

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 200° F or less.

Suspended solids in the press liquor are generally measured by filtering a sample and drying the filter paper in an oven. Samples containing dissolved solids must be washed during the measuring process.

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. The higher the Brix, the lower the moisture content of the press cake.

COMPRESSION
A screw press achieves compressing 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 is tightened 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, forcing material outward, against the screen. (4) Force-feeding the press and applying a vacuum to the outside of the screen are two additional ways of achieving compressing. These are used infrequently because the performance results are uncertain.

CAPACITY MEASUREMENT
The best way to measure throughput capacity is to run it continuously and collect timed samples of press cake and press liquor. Alternatively, the time required to press a weighed sample of material can be measured. The press should be run on material ahead of the test in order to fill the screen and screw area.

Press cake is generally captured in a pan or a tarpaulin, and press liquor in a 5-gallon pail. When the press liquor drain is at floor level, a 3-mill plastic bag can be used.

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 chute, or cyclone separators are used. Always allow for return feed of overflow material in the event that more is fed to the press than it can take. Spill containment is a consideration.

Sometimes a rotary drum screen or static (sidehill) screen is mounted over the inlet hopper to prethicken the flow ahead of the press; the tailings (solids) from the screen can be funneled into the press.

Usually presses work the best with only atmospheric pressure in the inlet hopper. Nevertheless, there are ways to force-feed a press, either with a head box over the inlet or by pumping the inbound flow directly into the press. We are generally seeking a pressure of zero to no more than four psi in the inlet hopper, so head boxes are made from two to six feet tall. Force-feeding may increase both the dewatering and throughput capacity of the press; it is more likely to cause the screen to blind, reducing capacity.

Material can be pumped to a press with either an open or a closed system. With the open system, no pressure exists in the inlet hopper so the press will never be force-fed. If the piping is piped through a cover bolted to the screen, force-feeding is possible. Pressure in the inlet hopper is controlled either by pumping with a variable speed pump or by providing a recirculation line which allows material to by-pass the press. At higher inlet hopper pressures (over five psi), solid material can be forced against the screen so as to blind the screen, resulting in poor performance. At pressures of 40 psi and above the shaft seals can be blown out of their housing, necessitating replacement. At pressures above 60 psi the screen frames will start to separate from their mountings, resulting in bypassing of unpressed material into the press liquor flow.

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 solids discharge of the press. Liquid will erupt from the cake discharge. Exercise caution if hazardous or hot material is being pumped into a press.

AUTO-REVERSING VFD
Many applications require the use of a variable frequency drive (VFD). This is used not to change the speed of the press, but, rather to set it for auto-reversing operation. By having the press run backwards for half a dozen turns every 30 seconds or so, many difficult-to-dewater materials can be pressed much more effectively. This operation is indispensable for tomato waste, and it helps a great deal with any other material that tends to blind (cover over) the openings in the screen. Vincent has loaner VFD's if you need to give it a try.

VACUUM EFFECT
In some applications, increased screw press capacity can be obtained if the area outside of the screen is under a vacuum. This can be achieved by mounting the press at a high elevation, with the press liquor drain line dropping below the surface of a drain tank or pit.

That is, the drain line from the press should go below the surface of the pit or pond into which it drains. If this line is relatively small in diameter and has a steady downward slope, a vacuum will be induced around the screen of the screw press. The mass and velocity of press liquor flowing through the drain line create this vacuum. To draw air bubbles downwards with the press liquor, the velocity of the fluid must be greater than 5 fps.

The cover over the screen of the press will have to be sealed, usually with Silicone.

The amount of vacuum is a function of the elevation between the press and the drain pond. For good results, the press should be mounted on a stand that is 20' or higher.

INTERMITTENT OPERATION
In the case of intermittent operation, the control panel for the feed pump or conveyor, and 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.

Minimize the time that the screw press is run with no material being fed into it. Since the screw is supported to some extent by the material inside the press, running dry might allow the screw to rub the screen. The last material admitted to the press will dry to powder, and. as such, it will not provide the lubrication required to prevent abrasive wear. (Initially the press will likely be run dry in order to check rotation; negligible wear will occur so long that this period is kept to a minimum.)

BRIDGING
Sometimes bridging will occur in the inlet hopper, stopping the flow of material into the press. Poking with a broom stick is the easiest way to solve this during a simple test. A more permanent way to overcome bridging is to direct a stream of water 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.

Sometimes it is convenient to pump a jet of the press liquor into the inlet hopper so as to break the bridging.

If a surge hopper is mounted over the inlet to the press, it should have at least one, preferably two, vertical walls. This will minimize bridging.

Coating the inlet hopper of the press with Teflon sheet is a remedy that has been used to reduce bridging of sticky materials.

AIR CYLINDER REGULATOR
Presses with an air cylinders are supplied with an FRL set (filter, regulator, lubricator), along with a Parker four-way reversing valve. These should be installed near the cone end of the press. (Filling the lubricator jar with light oil will assure long air cylinder life.)

The Parker valve allows manual selection of the shut, open, or "neutral" position. This valve connects one side of the air cylinder to the regulator while simultaneously opening the other side to atmosphere. The vent line on the 4-way valve allows air to escape when pressure is switched from one end to the other of the air cylinder; continuous air flow from this line indicates a leak inside the air cylinder.

Once material is going through the press, the 4-way valve is set 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.

DISCHARGE CONE
The principal adjustment of the press is made with the cone. The cone is the component at the cake discharge end of the press that acts as a stopper plug to prevent material from leaving the press. The more pressure exerted by the cone, the dryer the cake material will be leaving the press and the higher will be the motor amps.

In the small CP-4 press, the cone is usually actuated by either a weight arm or an air cylinder.

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 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 as the press may tend to jam and overload with these materials. Also, very thin or soupy materials, like pumped pig manure or clarifier underflow, might tend to purge 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 dryer, but the flow through the press can also be reduced. With very slimy inbound material it is sometimes possible to apply enough cone pressure to stop the flow altogether. High cone pressures will 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 3 to 20 psi. Other materials may press best with a pressure of 60 to 100 psi.

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 very heavy weight.

It is generally quite acceptable to open the cone while the press is in operation. This will give the operator a chance to observe operation with minimum dewatering and maximum throughput. It allows inspection, while in operation, of the discharge end of the screw and screens. It is also a good technique for purging bad material (generally, fermented or spoiled) from the press. (Do not try this trick if you are pressing hot or chemically aggressive materials.)

Generally speaking, 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.

The cone, which rides on the shaft of the screw, is made of bronze or UHMW to protect the journal surface of the screw shaft. Normally the journal area is lubricated with liquid from the material being pressed, such as the juice from apples. A grease fitting may be provided; this is useful for sealing the journal area in the case that press liquor drains through the cone into the press cake.

The grease fitting provided is also used for lubricating the cone/bushing when materials that are quite dry (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 journal.

Automatic grease systems are available. These can be spring, battery, or 110-volt powered. Vincent provides these for critical applications, such as pulp & paper and alcohol extraction

One 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 open. The duration of the "cone open" period is long enough to dump the press cake that has been formed.

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.)

CHANNELING
Very slimy materials, like concord grapes or waste dog food, will tend to channel or squirt out of the discharge of the press. The ways to reduce this channeling are to reduce the cone pressure; to slow the speed of the press; or to reduce the feed into the press. This will allow greater dewatering. It also reduces the throughput capacity of 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 can be caused to rotate so that the relative motion between it and the (stationary) main screens breaks the channeling.

PRESS SPEED (RPM)
Generally, screw press speed (rpm) is changed by switching to a different rpm drive motor (900, 1200, or 3600 versus the standard 1800 rpm). Consult the factory before making drastic reductions in speed to be sure the torque rating of gearbox is not surpassed. Extended operation with a 3600 rpm motor will possibly reduce gearbox bearing life; a lower ratio gearbox is preferred. Be sure to put synthetic oil in the gearbox if a 3600 rpm motor is used.

A small change in screw speed, 20% or less, will generally not result in a measurable change in performance of the press.

It is rare for a variable speed drive to be used with a Vincent single-screw press, except when testing to determine optimum speed.

SCREEN
The screen of the CP-4 press is made of stainless wedgewire. Wedgewire screens are one piece weldments that must be replaced when excessive wear has occurred. The standard screen used in the CP-4 has a slot width of .015" to .020". With the advent of recovering cooking oil from cooking crumb, a 0.008" screen has been introduced.

Perforated stainless steel sheet screens are NOT available for the CP-4 press. In other Vincent presses, perforated screens with hole sizes ranging from .020" to .095" are common. Surprisingly, there is little difference in the degree of filtration achieved by changing hole size. Where the holes are smaller than .050", the screen material is so thin that a reinforcing back-up layer of thicker screen is employed. This back-up material generally has 3/8" holes.

Generally the clearance between the screw and the screen is 1/32", plus or minus 1/32". The screw should not touch the screen, as it will cause wear and premature failure of the screen. With a clearance greater than 5/32" the dewatering performance of the press will start to deteriorate; this depends a lot on the type of material being dewatered.

To measure the screw-to-screen clearance, a feeler gauge can be slipped through and along a slot until it hits the edge of the screw. Subtract the thickness of the wedgewire (0.156") from the measured depth.

SCREEN BLINDING
It is not uncommon, especially when dewatering slimy materials, for the screen of the press to become blinded (covered over). When this occurs, the flow of press liquor coming through the screen diminishes. In some cases, the screen can be cleared by continuously 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 when the screen starts to blind. This is one of the easiest possible solutions to test. Often it is the only one that is effective. (Note: the used of a VFD requires a three phase motor.)

Many other methods are used to prevent blinding: (1) Adding press aid to the flow. (2) Adding notches to the screw. (3) Reducing or eliminating the pressure in the inlet hopper. (4) Changing to a screen with a different opening. (5) Reducing the screw-to-screen clearance. (6) Employing a back-flush with caustic solution, acid, or high pressure spray.

SCREW CONFIGURATION
All Vincent Screw Presses use the interrupted screw design. The interruptions leave room for four stationary resistor teeth, which 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 of the material being pressed to co-rotate with the screw. Also, there is more agitation within the press and, consequently, quicker 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 fairly common. 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. Produce waste, dairy manure, and knots are typical examples. This configuration is rarely used in the CP-4 press.

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. It is useful in modifying a press so that excessive compression and jamming are avoided.

Worn screws are returned to Vincent for rebuilding. The cost of a screw rebuild is one third the cost, or less, of a new screw.

NOTCHES
Sometimes it is necessary during press operation to have the screw wipe the screen clear of blinding material. Cutting shallow notches (1/8" by 1/8") in the outer edge of the screw flights best achieves this. Notching is done from just inside the B plate to the second resistor tooth. Fibrous material accumulates in the notches and wipes away slimy material that may be blinding the screen.

In larger presses, UHMW wipers can be mounted to the outer perimeter of the screw flights. If at all possible we advise against the use of such wipers because (a) they tend to cause material to co-rotate and jam in the press, (b) they are difficult to replace, and (c) they may wear out faster than the screw, resulting in unacceptably frequent shutdowns for replacement. These wipers are never used in CP-4 presses because they obstruct the flow of material.

RESISTOR TEETH
The interrupted screw design press has teeth that protrude into the flow of material as it passes through the press. These teeth reach, between flights, almost all of the way to the shaft of the screw.

Sometimes the resistor teeth can be shortened, usually by half, to increase the capacity of the press. Removing the teeth altogether can result in co-rotation and jamming.

DOUBLE PRESSING
Many processes benefit from what is called double pressing. This means that the cake coming from the press is run again 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 diffuse dissolved sugar into the cake, reducing the final press cake moisture content.

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.

PRESS AID
Some materials press much better if a press aid is mixed into the material to be pressed.

If apples are run in a press, apple sauce will come through the screen. However, if a press aid is added to the apples, then apple juice will come through the screen. Press aids include cottonseed hulls, rice hulls, and paper fiber. These are most commonly used in producing juice from deciduous fruit. The press aid gives the press something to get a bite on. Press aids also tend to hold back suspended solids (short fibers) and prevent them from going through the screen with the press liquor.

Typically, the amount of press aid used is only 1% to 3% by weight of the flow going through the press. This will look like more than such a small percentage because press aids have a much lower bulk density than the wet materials that are pressed.

HYDRATED LIME
Lime (calcium hydroxide) must be added to citrus peel before it can be pressed effectively. The lime breaks down the pectins or cell walls so that the press can remove moisture. Less than 1% by weight is used. A reaction time of several minutes must be allowed prior to pressing. Lime has been used successfully in the same manner with potato, carrot and pineapple waste. It works well on acid materials such as onions, strawberries, and coffee bean pulp. Vincent offers liming systems.

POLYMER
The addition of polymer can be indispensable in achieving adequate screw press performance. The long chain molecules of the polymer will agglomerate suspended solids in the flow going to the press. Polymers are added to dilute waste streams, especially to those containing very small size suspended solids. The polymer will flocculate the solids, agglomerating them to the point where they can be pressed. Under the right conditions drastic improvement can be observed in press throughput, press cake moisture, and pressate clarity. Low speed operation of the press is usually required in order to achieve good performance.

FLUID INJECTION
It is possible to inject either steam or water into the press. This is done by drilling holes through the resistor teeth, and piping these holes to a manifold outside of the press screen. This arrangement is used in dewatering raw fish, citrus and pineapple waste (applications where the steam partially cooks the waste), as well as in pressing materials that need to be washed as they go through the press.

The moisture reduction that comes from adding steam is related to a chemical change that comes with blanching or parboiling a material. Tests run with steam injection in a Vincent Twin Screw press at Anheuser-Busch showed little benefit. The material being pressed, spent grain, had already been "cooked" before steam was added in an effort to squeeze out more moisture.

Photos and drawings are available from the factory. Vincent does not charge for providing a drilled resistor bar.

PRESS LIQUOR
A Screw Press produces relatively "dirty" press liquor as compared to a Filter Press. Suspended solids will pass through the screen of the screw press along with the liquid being expressed from the inbound material.

If suspended solids are to be removed from the press liquor, the most common method is to pump the press liquor through a rotary drum screen or over a static (sidehill) screen. Generally the screen tailings (solids) are fed back into the press along with the flow of inbound material. Most of these solids will be captured with the solids of the inbound material and end up in the press cake. Although some of these tailings will once again go through the press screen with the press liquor, equilibrium is reached and stable pressing operations are realized.

If the press liquor is to be concentrated in an evaporator, better screening than can be achieved with a static screen may be required. Decanters and centrifuges can be effective. Another Vincent machine, the Fiber Filter, offers premium performance.

PRE-THICKENING
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 flush most of the solids along with it, or it may plaster solids against the screen, thus blinding 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 static screens (sidehills) or a rotary drum screen. The Vincent Fiber Filter offers premium performance for pre-thickening dilute flows.

WING FEEDERS
Frequently 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. 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.

Wing feeders can serve three purposes. (1) In the case of materials that want to channel out the discharge of the press, like pineapple and spent brewer's grains, the wing feeders break up the channeling flow. (2) For abrasive applications, short knobby wing feeders are provided as sacrificial wear elements. (3) In the case of press cake that is very hard and which tends to jam at the discharge, the wing feeders can break up the cake to encourage a discharge flow.

Clumps of dry material can accumulate between a wing feeder and the shaft of the screw. This in turn reduces screw press capacity. The problem is most apt to occur with small size presses (10" and under). Should the problem occur, either grind off or at least shorten the wing feeders by half.

Dry material can also pack between a wing feeder and the screen. This will wear out the screen in the area where the wing feeders are located. Removal of the wing feeders is recommended.

In abrasive applications, the thickness of the flights at the discharge should be monitored. When the flights wear very thin, it is easy for the wing feeders to break loose.

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.

The second plate is the B Plate. It forms the other wall of the inlet hopper. The screen starts at the B Plate. There is a part called a Stripper welded to the B plate, inside the inlet hopper, in a position to kiss the screw as it goes past.

The final plate, the C Plate, supports the discharge end of the screen and the cone actuator mechanism. The cone lightly touches the C Plate when in the closed position.

CORD CUTTERS AND STRIPPERS
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 that reduces the flow through the press.

A groove, like a keyway that is 1" wide and 3/8" deep, is cut 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.

Alternatively, a part called a "Stripper" can be welded to the B Plate, inside the inlet hopper. It is welded in a position so that the flight lightly kisses the stripper as it goes past. This strips the material away. Strippers are made of key stock.

JAMMING
Should a press 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. The press should be run backwards for about ten seconds to half a minute.

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.

If a press has had extensive use in an abrasive application, the flights can be worn away at the discharge of the press. This will lead to serious jamming which can even result in a burst screen.

If 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 deform the inlet hopper or cause a failure of the shaft seal. For these reasons care must be taken when running the press backwards.

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.

CLEANING
Material will leave a press only if there is inbound material forcing it out. This makes it difficult to clear material from a press without removing the screen. One technique used successfully is to feed crushed ice into the press. Water must be fed along with the ice to prevent jamming. When the ice melts, the press will be relatively clean inside.

Commonly material is cleared from a press by stopping the inbound flow, setting the cone in the withdrawn position, and running the press for several minutes until no further material is discharged. This will leave some material inside the press, but this is generally insufficient to cause jamming on subsequent start-up of the press.

There are applications in which the press must be cleaned very frequently, such as once a shift, in order to meet sanitary regulations. At these installations, the screen is removed from the press in order to remove residual material.

In laboratory applications, the press may be disassembled for cleaning. The various components can be dipped in an appropriate solution or placed in an autoclave.

SHAFT SEAL
The Seal Housing is bolted to the A Plate. This housing may contain a Johns Manville (JM Clipper) c-cup shaft seal. There may be a grease fitting on this housing. Grease is used to help prevent trash material from entering the seal 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.

SCREW REMOVAL
The screw is removed through the hole in the C Plate, at the cake discharge end of the press. The operation can be difficult the first time, so we recommend consulting with the factory before getting started.

Start by removing the four bolts holding the shaft seal housing to the A Plate. This will prevent damage once the screw is loose.

The resistor bar must be removed before the screw can be removed.

Series CP screw presses use a key and keyway to couple the screw inside the hollow bore of the gearbox. It is common that a great deal of force may be required in removing a screw.

The basic procedure is to push or pull the screw out of the gearbox. This can be done in three ways: (1) pry the screw using the B plate as a lever point, (2) construct a gear puller, using a hydraulic cylinder, combined with a cross bar and two long shafts threaded into the gearbox housing (metric), or (3) use a heavy fine-threaded rod to push the screw out of the gearbox. This rod in threaded through a heavy nut provided inside the hollow bore of the gearbox. This nut has a lug that fits in the keyway, to prevent the nut from turning. The nut backs up against an internal snap ring in the hollow bore of the gearbox. The result is that the rod pushes against the end of the screw. Loaner tool kits are available in Tampa; see Screw Change Kit Drawing B-92839-B.

SCREW REPLACEMENT
In the case of the Series CP hollow shaft gearboxes, when pulling a screw into the press, it may be necessary to use a long allthread rod (English threads). This rod is screwed into the threaded hole on the end of the screw. The screw is slid into the press far enough that the allthread rod goes through the hollow bore of the gearbox. A large washer is slid along the allthread rod to form a brace against the gearbox. Running a nut on the rod, against this large washer, will pull the screw into the gearbox.

When reinstalling a screw, the screw must be pulled in until the step in the shaft seats against the thrust bearing of the gearbox. This will position the flights of the screw so as not to be hit by the resistor teeth. Be careful when guiding this step in the shaft through the shaft seals.

During re-assembly of a keyed shaft, be sure to apply Never Seize or Anti Seize to the portion of the screw shaft that goes into the gearbox.

If the fit is unusually tight, it will help to lubricate (wipe) the inside of the screen with STP Oil Treatment when reinstalling a screw.

Excessive rubbing between a screw and the screen can be corrected by grinding the interference off the edge of the screw. Prussian blue, applied to either the screw or the screen, can be useful.

GEARBOX BASICS
Model CP-4 presses use hollow-shaft gearboxes, with C-face mounted motors.

Gearboxes are rated, and sold, by torque. The manufacturers generally offer their designs in progressively larger sized castings, or boxes. The larger the box, the larger the torque rating. Each box size will be available with different gear ratios. In order to keep the torque fairly constant, larger horsepower motors are used with the high speed boxes. Similarly, smaller horsepower motors must be used when a low output speed is selected.

Some times screw presses are designed around the size of the gearbox that is selected.

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 Hydrated Lime above.

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 100° C. 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 95% 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. Moisture contents of only 25% can be achieved pressing things like glass and plastic chips.

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.

REPLACEMENT PARTS
Most replacement parts are standard OEM components that can be purchased from their original manufacturer. The specification of these items is included in the O&M Manual. Only shaft seals are apt to ever require replacement.

The most common wear parts in the Vincent CP-4 Press are the screens, the screw, and cone. Vincent stocks these. Screws are generally rebuilt at the Vincent factory. Be sure to specify the Serial Number of your press when ordering replacement parts or repairs. If work is required on the screw, it is usually more convenient to obtain a loaner press and return your machine to the factory.

SAFETY
These Operating Hints have left unstated the obvious safety hazard: 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. Vincent Corporation has heard of only one injury of this nature with a screw press; do no let yourself become the second. The use of common sense is all that is required.