National Clothesline

Part 3

Centrigual (spin) disc

This is my third article, since July 1987, on the subject of centrifugal spin disc filters. Since that time these filters have not changed in design or mechanical structure, but there have been many changes in their usage, including the demise of pre-coating with filter powder.

As I wrote before, my first experience with centrifugal disc filters was in South Africa while on two separate consulting and training assignments, one in 1981 for three weeks and the other in 1982 for nine weeks.

While the U.S. drycleaners were converting from filter powder to cartridges, the South Africans were converting from regenerative (bumping tubular) powder filters to the centrifugal disc filters with filter powder and powdered carbon.

These filters had openings of 60 microns to 90 microns, depending upon the manufacturer. Mixing powdered carbon with filter powder produced a very good pre-coat; but due to misuse in operating the filters, and the filter pump with a steep performance curve, many problems were encountered with the pre-coat falling when the filter pump was not producing pressure against the discs. The result was severe cases of redeposition of soil.

Since I know of very few current operations with powder-type centrifugal spin disc filters, I will confine this article to the 30 micron, no-powder centrifugal spin disc filter in popular use today.

As I see it, current drycleaning machines are equipped with a centrifugal spin disc filter housing and a small canister tower of all-carbon cartridges (using two standard size cartridges averaging a total of 16 pounds of activated carbon) for cleaning dark colors in one complete filter circuit, and the second filter circuit consisting of several carbon core cartridges in one housing for whites and light colors.

I cannot understand why the two filter systems are different and what the difference in colors has to do with the type of filtration.

Most manufacturers recommend operating the centrifugal spin disc filter until 1.5 bar (about 22 psi) of filter pressure is reached before its insoluble soil accumulation is spun off. This pressure reading is from the pressure gauge installed at the top of the filter housing.

This is the first error that I observe, that there should be two pressure gauges installed: one in front of the housing to read pressure resistance, and the other installed just after the housing to read the pressure drop.

An after gauge reading of less than 7 psi is unsatisfactory since it indicates a serious drop in solvent flow rate. Also, a pressure drop of more than 12 psi to 15 psi (subtracting the after gauge reading from the before gauge reading) would indicate a spent filter and too low of a solvent flow rate.

The two all-carbon cartridges are good for about 3,200 pounds of cleaning for effective dye removal. These figures can be adjusted up or down according to the amount of fugitive dye removal and the amount of distillation performed.

The old basis of carbon life was computed at 300+ pounds of cleaning per pound of carbon, but today’s inferior and excess dyes on garments have reduced the basis considerably. However, the length of time that the solvent has residency within the carbon bed has a bearing on the quantity of dye removal. If the flow rate is too great, then the residency will be too short. In this regard, a pump with a steep performance curve is not recommended for use with the centrifugal spin disc filter as it is with the cartridge filter.

However, the danger involved is when the discs collapse under severe build-up of insoluble soil within the outer walls and in the perimeter area around the binder tape. Unlike the pleated paper of the cartridge filter, the outer surface of the disc is smooth and cannot entrap the insoluble soil particles as completely as with the pleats, and the high flow rate of the steep performance curve filter pump will cause the collapse by forcing the soil through the surface and lodging within the inner chamber.

The pump with the steep performance curve is ideal for a cartridge filter with pleated paper, but it is not as advantageous for the centrifugal spin disc filter.

In that regard, it would be advantageous to have a throttling valve ahead of the centrifugal spin disc filter housing in order to slow the flow rate down a little in order to build some insoluble soil on the outer surface of the disc. This would help to alleviate the problem of soil pass-through and maximize Vander Waals action (January 2003 article). After two pounds of inlet filter pressure increase, the throttling valve could be opened for maximum flow.

Placing the carbon tower of all-carbon cartridges (without pleated paper) behind the centrifugal spin disc filters will result in pass-through of insoluble soil from the base disc filter unit into the paperless all-carbon cartridges. This will eventually clog the tiny interstices (spaces) between the carbon pellets and create a high pressure build-up within the cartridge resulting in possible rupture of the outer casing of the cartridge to send carbon into the entire solvent system.

If you haven’t experienced carbon deposition in a load of garments then you haven’t experienced the ultimate horror of a damaged load of light colors. Even if the cartridge shell does not rupture, the high slow-down in solvent flow rate would result in very poor soil removal. Always use carbon cartridges with pleated paper as an insurance policy against insoluble soil migration beyond the disc filters.

One experience I had in the middle 1980s with the centrifugal spin disc filters was when we had to open the housing and remove the discs for hand cleaning. The coating was caked so hard on the outer surface and inner surface that we could not remove it satisfactorily by hand even after soaking the discs in oily-type paint remover and solvent.

Also, I experienced bearing failure due to the sleeve-type bearing rather than the ball-type bearing at the ends of the center shaft. However, I assume that the later models have ball bearings at the ends of the shaft.

With the popularity of the cationic injection detergent, there can be much more trouble with hard build-up onto the surface of the disc since that detergent is substantive and will adhere to any fabric including a polyester or nylon disc.

In that regard, it is critical that the batch bath (no filter) be for a total of three minutes, no less, after the detergent is injected. This will ensure that all of the detergent will be deposited on the garments and not the filters, especially if the second filter circulation bath does not follow a drain and extraction to the still. Even after a drain and extraction to the still, the suspended soil particles with the cationic detergent removed in the filter circulation run will clog the surface of the discs. This is one of the reasons for recommending the use of an anionic charge detergent to be dissolved into the solvent, not floating in it.

To help alleviate some of the problems, it is better to spin-off the discs before the inlet pressure reaches 1.5 bar (22 psi), say no more than 1 bar (l4.7 psi) or at the end of the day, whichever comes first.

Another problem lies with maintaining the surface layer of insoluble soil when the pump is turned off during drain, extraction, drying-reclamation, cool-down, loading and unloading during the day. Just like we used to do with the powder constant running filter: keep the pump running as long as we are cleaning clothes.

The claim that there is pressure in the housing after the pump is turned off due to the inlet check valve and the closed outlet electric valve is false.

The pressure within the housing is static and ineffective to hold the insoluble soil to the surface of the discs. The solution lies with either keeping the pump running all the time (cylinder by-pass when not in filter circulation), or by installing a separate pump to be actuated to the filters while the machine is not in the filter circulation cycle.

Unlike the cartridge filters, the centrifugal spin disc filters must have pressure against them to keep the soil from slipping off and returning to the cylinder during the filter circulation run.

Comparing the surface area of the cartridge to the surface area
of the centrifugal spin disc filter unit

For example, a 50-pound cleaning machine’s centrifugal spin disc filter unit contains about 86 square feet of filter surface area, and the standard size carbon core cartridge filter contains about 39 square feet of filter surface area. The carbon core cartridge will admit 3 gallons of perchloroethylene solvent per minute and 4 gallons of hydrocarbon solvent per minute.

For use with perchloroethylene solvent, the 36 discs in the 86 square foot surface area would permit only about a 6.63 gallons per minute solvent flow rate.

Whereas the effective flow rate of one gallon of solvent per pound of garments per minute (1-1-1) would require a centrifugal spin disc filter of about 602 square feet of filter surface area (seven 36-disc filter housings), compared to 16 carbon core cartridges of about 624 square feet of filter surface area. Also, the spin disc unit is considered without carbon.

Regenerating the centrifugal spin disc filters

The main advantage of the centrifugal spin disc filter unit is the removal of accumulated insoluble soil that has lodged upon the surface of the disc. As aforementioned, do not wait until the inlet pressure has climbed to the 22 psi (1.5 bar) recommended by most manufacturers.

Since the disc does not need to be replaced, or removed from its housing, after undesirable pressure has occurred, the entire housing of solvent can be dropped into the still along with most of the insoluble soil from the surface of the discs.

However, if spinning off the soil does not greatly decrease the filter inlet pressure then the only other alternative is to open the housing, remove the discs, inspect them for damage and hand clean them the best you can.

Also, spin the shaft to see whether the shaft or its bearings have been damaged. If the spin unit is belt-driven check the lash of the belt; it should dip from side-to-side only slightly.

The spinning cycle should be accomplished as follows:

1. Turn filter pump off.

2. Make sure the still has somewhat cooled.

3. Spin discs for eight seconds with drain valve closed.

4. Drop solvent until a level is visible in sight glass and close drain valve.

5. Spin discs for eight seconds with drain valve closed.

6. Open drain valve while discs are spinning.

7. When housing is empty, stop spinning and close drain valve.

8. After every other cycle: fill housing with clean solvent to sight glass level. Perform (5), (6) and (7).

Note: It is critical that the drain valve to the filter housing be closed while the still is operating. One of my clients has experienced severe warping and damage to the discs from migrated heat from the still into the filter housing.

Note: My spotting video, “The Caplan Method of Stain Removal,” which includes my comprehensive text and the handy spotting board reference, is available in English, Spanish and Korean (video only in Korean) from the Golomb Group, c/o Dennis McCrory, 7664 Plaza Court, Willowbrook, IL 60521, phone (800) 679-5856. A lecture and demonstration are presented similar to my classes over the years at IFI and SDA. This video and text are ideal for training inexperienced spotters as well as a good review for experienced spotters. Digesting with enzymes, bleaching, oxidized oil stains and caramelized sugar stains are discussed and demonstrated. An article on “Removing Spots in the Cleaning Machine” and an article on “How to Increase Production in the Spotting Department” are included in the comprehensive text book.

Also available from the Golomb Group, in English and Spanish, is my video on step-by-step shirt finishing which includes my comprehensive text in loose-leaf form outlining each procedure for a single-operator and two-operator cabinet shirt unit using a cabinet sleever. Proper forming of the collar using heated collar formers is demonstrated. Each lay is demonstrated for top quality with very little effort by the operators. Attractive detailing and packaging of the hangered shirt, padding, steam pressures and timing are all discussed. A unique wash formula for whiter whites, brighter colors and removal of grease and body oils is included in the loose-leaf text book.

My experience with shirts spans over 55 years with the US Army as a principal laundry and drycleaning concessionaire at Ft. Meade, MD where average shirt volume was approximately 10,000 per day. We were constantly “sampled” for excellent quality in both finishing and washing in laundry and for drycleaning, spotting, finishing and tailoring. We operated our own 40,000 square foot plant for over 35 years.

Note: My spotting video, “The Caplan Method of Stain Removal,” which includes my comprehensive text and the handy spotting board reference, is available in English, Korean (video only) and Spanish (video only) from the Golomb Group, c/o Dennis McCrory, 7664 Plaza Court, Willowbrook, IL 60521, phone (800) 679-5856. A lecture and demonstration are presented similar to my classes over the years at IFI and SDA. This video and text are ideal for training inexperienced spotters as well as a good review for experienced spotters.

Also available from the Golomb Group, in English and Spanish, is my video on step-by-step shirt finishing which includes my comprehensive text in loose-leaf form (English only) outlining each procedure for a single-operator and two-operator cabinet shirt unit using a cabinet sleever. Proper forming of the collar using heated collar formers is demonstrated. Each lay is demonstrated for top quality with very little effort by the operators. Attractive detailing and packaging of the hangered shirt, padding, steam pressures and timing are all discussed. A unique wash formula to give whiter whites, brighter colors and total removal of grease and body oils is included in the loose-leaf note book.

Stan Caplan has over 35 years experience in his own high volume dry-cleaning, laundry and tailoring plant and two package plants with adjoining coin-operated laundry and drycleaning. Stan is the former chief instructor at the International Fabricare Institute, the Southwest Drycleaners Association and various other trade association-sponsored schools throughout the US and courses in Canada, Mexico, South Africa, Singapore and Hong Kong. Stan offers consulting, training and engineering services in all areas from customer service area to the boiler room since 1981. His complete system withtotal quality management will produce maximum efficiency, economy and product excellent quality. Stan can be reached at 7341 Amberly Lane, Suite 310, Delray Beach, FL 33446, phone/fax (561) 496-2548. His e-mail address is stancap100@aol.com.