Keeping the tunnel line running smoothly

1 May 2014



Richard Neale says laundries can minimise downtime in the tunnel washer line by identifying possible causes. He shows how these can be cured, stressing the importance of having right spares in stock


Laundry and textile rental plants often rely on two or three tunnel washer lines to process most of their work. Prolonged downtime in one or more of these lines, could potentially reduce production and eventually affect the laundry's ability to deliver work on time to the customer.
To avoid severe disruptions, successful rental plants often work on pool stock and try to keep a minimum of four hours work in the despatch area. Many plants now manage to keep eight hours ahead, with many now managing to keep eight hours ahead.
In such cases, the engineering team knows that if there is a problem in the main tunnel washer line, it has four to eight hours to cure this and get the line back up and working again.
Of course this does not work for those rental operators that offer a dedicated rental service with marked stock. This demands a substantial premium, because the laundry needs to keep some redundant capacity or have strong contingency plans in place so it can still deliver work on time should a problem occur in the relevant line..
Four to eight hours is usually enough to get the plant running again, provided the engineering team has ordered the right spares and these are in stock. Otherwise the plant is dependent on the manufacturer having the right spare in stock and flying it in quickly.
Good maintenance requires a knowledge of the different causes of tunnel washer downtime and planning spares and cures for each one.

Checking the mnemonic
The modern tunnel washer has excellent diagnostics and a mnemonic board or screen that shows the condition of every key component, including tanks, valves and pumps.
A check on this screen combined with a regular walk-round, gives both the engineer and operator an early warning that problems are developing, and in particular that valves could become blocked, pumps could fail and tanks could overflow.
This is vital if the laundry is to avoid an interruption of the water flow, which is often caused by a blockage in the main tunnel washer.
The water acts as a lubricant to ensure that textiles transfer safely and efficiently from compartment to compartment. If the lubricant suddenly runs dry this will quickly cause a jam.
It is also important to check the cleanliness of the main variable area flow-meters on the tunnel. These must work very precisely under difficult conditions. Every operator is striving to maintain the optimum water flow that will keep to agreed operating costs without risking blockages or compromising the rinse quality.
To achieve this, the variable area flow-meters must be kept clean around the inside of the transparent tubes and over the moving floats. Once these become scaled up with detergent or other deposits, the flow indications rapidly become meaningless.

Essential spares holding
The drive motors are the prime movers on any tunnel and many plants will keep one in the spares stock.
Some machines rely on a single motor, so a spare is vital here. Others have several and can often be run for short periods with one motor down (provided this does not place the remaining motors under undue stress from over-loading or unnecessarily high weir settings).
Similarly, the steam inlet valves used to control the pulses of steam into the hot wash compartments are essential for achieving the implied thermal disinfection that is required for healthcare work and increasingly for hospitality work.
If one of the steam inlets does not work, the linen will still be clean but it will not be disinfected so keeping a spare valve is a prudent and inexpensive option.
The printed circuit boards for the tunnel's main computer controller are more problematic and expensive to replace. There are usually several boards and they are subject to high levels of humidity, temperature and vibration, straining the reliability of even the very best. It is often not practical to hold a spare of each board, but the engineer should know where a spare can be obtained quickly. In addition, the maker normally keeps records showing which board is most likely to go down. If this data is available, then keeping a spare for this board is a wise move.

Membrane press problems
Membrane press failures are just as disruptive as a problem with the main tunnel washer. The press should be inspected frequently, looking for signs of corroding pillars or that the press is beginning to leak hydraulic oil or water.
One or two spare membranes should always be kept in stock. Membrane life can vary from 600 to over 8,000 hours depending on how successful the laundry is in preventing sharps getting into the load and how carefully it looks after the membrane.
The best engineering teams will include polishing the inside of the press basket in regular maintenance schedules and will sometimes even apply wax polish to the edges of the membrane.
Some enterprising engineers have even managed to repair a rubber press membrane successfully.
It is also vital to react to early warnings of serious jams, caused by failure to discharge one load before the next enters the basket.
Sometimes this occurs because the "cheese" of de-watered textiles sticks to the underside of the ram, so that when the ram lifts the "cheese" does not slide on to the discharge conveyor.
This is not usually caused by "sticky" chemicals, even though the detergent supplier may sometimes have paid for the press overhaul and basket repair.
Jams of this kind are more commonly caused by a small amount of air in the membrane. So a membrane that is normally incompressible will compress slightly and become liable to "stick".
The cure is to re-configure the membrane profile, remembering to replace the copper washer on the final bleed nipple if the manual calls for this.
Simply increasing the dose of softener in the final compartment is not the best solution because it will only prevent 50% of jams and the plant will stall have to face the cost and intervenience and repairing the press basket.
If short random oil marks start to appear on work from the press, this is a warning that the membrane edge is suffering abrasion marks.
The black marks look like tiny worms and are caused by a sharp protrusion on the basked surface. These can result from a build-up of calcium salts, particularly calcium metasilicate, which forms exceptionally hard and very sharp deposits.
The calcium usually comes from the moisture in hotel towels and can affect even plants with perfect water softening because hotels rarely soften the water in their guest rooms.
The sharp edges can also arise from a metal object in the load damaging the basket.
The first check is to inspect the sides of the membrane that are in contact with the basket and look for any grooves or similar signs of damage.
The oil marks themselves are a mixture of the oil from the membrane rubber and carbon black used to give the rubber strength.
Once a membrane press has suffered a jam, there is a risk that the press basket will have become distorted and this distortion increases the risk of future jams.
To check the basket's "roundness" put the press controller into "service mode" and put the safety beams in place beneath the membrane. The ram and basket should be in the raised position.
Then look up onto the underside of the ram. If the tiny annular gap between ram and basket is uniform all the way round then the basket is still round and undamaged. If the gap varies and has bits of textile caught in it, then the basket is probably damaged and should be replaced.
Sheets and duvet covers with curved rips are another indication that the basket has been damaged, as these will get trapped when the ram is lowered.

Snake-bite marks
Throughout the industry, laundries are noticing that work will have tiny black marks, commonly referred to as "snake bite" marks as there are two tiny dots a few mm apart.
These marks will appear on one or two sheets, duvet covers or pillowcases in every batch so that within a few weeks each piece in the circulating stock has become marked.
Work to identify the cause these marks is ongoing but it looks as though they may result from operating the tunnel washer at below 7.0pH leading to premature failure of the rubber seal.
This usually starts to degrade and causes sticky black mark-off in the ultimate and penultimate compartments of tunnel.
It can be cured either by changing all the seals or just those that have been affected.
The problem may be the result of the modern trend for souring in the final compartment, rather than relying on rinsing alone. Poor control of the sour dose makes the problem much worse.

UNBLOCKING THE TUNNEL: Preparing to remove the block

 



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