In the modern laundry, the engineer’s job has wide responsibilities, far beyond the quick-fix to machine breakdowns. Astute engineering contributes to the health and safety of the operation as well as to achieving required levels of machine productivity without repeated complaints from the customer.

The cost of complaints continues to increase, especially in the rental sector where damage to circulating stock causes additional costs out of all proportion to any savings from skimping maintenance. Indeed, proper maintenance is vital in preventing problems such as out-of-balance washer-extractors and tumble-dryer problems.

What causes a washer-extractor to go out of balance? A washer-extractor is a high-speed centrifuge designed to run smoothly and sweetly with minimum vibration. Under these conditions it is the cheapest and most effective means of de-watering batches of textiles prior to final finishing with tumble dryer, tumble finisher or calender. But if the load in the washer-extractor is not correctly distributed, it starts to wobble and the resulting stresses can tear the rotating cage from its mountings, causing a ton or so of metal to hurtle across the laundry demolishing everything in its path. The risk of this occurring is sufficiently serious to merit built-in safeguards at several levels and it is because of this high degree of protection that this type of accident is relatively unusual.


The first safeguard lies in the machine controls. Modern microprocessor controls block any attempt by the user to programme high-speed extracts without preceding this by an adequate drain.

Then, before the machine runs up to high speed, the cage rotates for a period to distribute the load evenly, achieving the desired level of balance. On some machine designs water is pumped into the hollow lifters or other pockets near the cage circumference so as to compensate for any minor imbalance. These systems work best, and the risk of imbalance is least, if the cage is properly loaded with its design weight of cotton goods or 80% of this weight in polycottons.

With two pocket or three pocket machines it is vital that the load in each is balanced to within a couple of kilograms. Unless the machine operator does this, there is no point in sending for the engineer when the repeated heavy vibration finally shatters the bearings.

If a machine does become unbalanced, the current to the motor will surge as the load varies. Some safety systems detect these surges and when they exceed the prescribed limits, the controller automatically trips the extractor motor. This is so important on some designs that the manual provides for a simple method of verification that these trip circuits are working correctly, usually by deliberately loading pockets with the wrong weights and observing that the motor trip occurs.

By far the most common safety feature on an out-of-balance washer-extractor is the probe which rides in a hole in a metal plate bolted to the machine frame. As the cage housing moves, so does the probe and if it comes into contact with the fixed metal plate, it is this which then trips the motor before the machine becomes so unstable as to cause damage. It makes sound sense to ensure that the probe does perform its function correctly by ensuring that this verificat- ion technique features on every planned preventative maintenance chart. It is surprising how many routine checks fail to cover this, but it is a task that can be done by the wash-house supervisor very easily during the average working day.

Finally there is one ultimate safeguard which was probably not designed as such in the first place but which, nevertheless, has saved one or two laundries from disaster already. The spring mountings on a modern washer-extractor have a tension bar down the centre and if all else fails and probe contact is not quick enough, then the tension bar snaps. The accompanying sound will usually wake the doziest operator and draw everyone’s attention. If this does happen, not only should the tension bar be replaced, the engineer should also find out why all the other levels of protection failed in this.

Spate of problems.

There have been a spate of tumble dryer problems over the last few years, not least of which has been an increase in incidents of spontaneous combustion. If work is not washed so as to remove all protein and oxidisable oils from the fabric surface, then there is a risk that these will start to oxidise by chemical reaction with the oxygen in the air. This reaction will first generate a warm spot, then a hot spot, then finally (often in the middle of the night) create a source of ignition sufficient to set the whole batch ablaze. Depending on how the work is stored in the drying area this can then set the whole laundry alight. Indeed such incidents are believed to be behind many recent laundry fires.

This is best avoided by ensuring that every drying cycle for fully dried goods concludes with a proper cooldown that cannot be overridden. Time pressures on modern laundries are so great that this is only feasible if the tumble dryer is working perfectly in the first place, proving the value of correct engineering maintenance.

Simply raising the temperature of the drying airstream to the cage (very easy with direct gas-fired units) will not compensate for extended drying times because the result is as likely to be singeing and yellowing of the edges of the terry towels. This is usually accompanied by over-drying which leads to greying of cotton and sticking of polycotton or polyester to the hot metal surface of the tumble dryer cage. Those polyester or polyester cotton goods that do survive tend to develop an uncharacteristic limpness with soft, tired creases that cannot be pressed out.

To maintain the effectiveness of a tumble dryer it is essential to ensure the design airflow through the unit. This requires lint screens that are perfectly clean on both sides and unblocked heater batteries (in steam-heated units). It also requires good seals at the cage and lint-free fans and outflow ductwork.

Once the engineer has got the airflow right, then attention can be turned to achieving the design temperature which needs dry steam at the correct pressure, proper air venting at the heater batteries and effective trapping which discharges air and condensate as rapidly as possible whilst holding back the steam without leakage.


Every tunnel-washer operator complains that the supplier has delivered a washing machine with one too few tumble dryers, but the cause of the problem usually lies elsewhere. Modern tumblers are designed to dry goods with 54% moisture retention (for cotton) and if the press is not giving this, there is little point in blaming the tumbler. The cure is to sort out the press first, not to eliminate the cooldown cycle because you no longer have time for it.

Tuning your tumble dryer to give an effective, efficient and fault-free operation calls for much thought and ingenuity on the part of the laundry engineer, but it is the only way to maintain a safe and productive laundry environment. Those companies that have achieved this generally produce somewhere near the design output from the continuous washer line. Those companies that fail to recognise the warning signs struggle with production output, which is often below 80% of design, without ever understanding the real reasons for this. When capital is limited and prices are under pressure, the value of astute laundry engineering becomes starkly apparent.