The difference between a good laundry engineer and an average one is the attention to detail he pays to the laundry’s water supply. Washing requires a consistent feed of high quality water at the correct pressure, delivered through well-sized pipes and available on demand.
Engineers face a number of water quality problems and the major one is hardness caused by dissolved calcium and magnesium ions. Good laundering calls for water softened down to zero degrees hardness, otherwise detergent costs can double or treble.
The next major problem is the amount of alkali in the raw water. Alkali salts are not removed by the water softener, and while alkali is needed in the main wash, it must be thoroughly removed in rinsing to avoid yellowing (galling). In extreme cases, an acid sour will be needed in the final rinse to neutralise any remaining alkali traces.
Iron and manganese salts also cause problems, and if iron levels rise above 0.1ppm, a special treatment stage may be needed to avoid greying. Reversing the greying caused by high iron levels will require oxalic acid treatment.
There are usually some bacteria present in raw water and allowing a build-up in the holding tanks may lead to odours in the finished work. It may also pose a health risk.
Bacteria can come from natural sources, such as cattle grazing near the borehole catchment zone. Peaty soil can cause traces of colour. Where water has been affected by both, the bacteria and colour can be removed by very low doses of sodium hypochlorite.
Even water which looks pure and clean may, in fact, be contaminated by dissolved solids. Controlling the level of total dissolved solids is usually undertaken by the water company and if the level is very high, the solids will give rise to harshness in sheets and towels. The tumble drier and the calender can only evaporate pure water, leaving the dissolved solids contaminants behind in the work. A water softener is unlikely to help and the best solution is probably to improve hydro-extraction by extending the final spin, or raising membrane press pressure.
Water storage
Water is the laundry’s lifeblood, and many operate with up to one day’s supply of raw water in intermediate storage. An advantage of this is that the supply can be topped up continuously with a steady flow of water softener delivered through the mains. Generally, a softener works better with a continuous flow than with the short sharp changes in demand posed by a bank of washer-extractors.
Water softening is, therefore, best carried out prior to the storage tank. It should ideally use a duplex arrangement, with one softener on regeneration and the other in operation. This should be continuously checked by monitoring the water’s hardness immediately before the switchover point, as this is when hard water is most likely to pass through in error.
A continuous batch washer works best with a gravity water feed; this requires a steady continuous flow of water which can be achieved economically through a properly-sized overhead pipe.
However, washer-extractors really need to be able to make a rinse dip in less than one minute each—no mean feat if four or five extractors call for a rinse simultaneously. In this situation, installing a pumped supply can trim vital seconds off every cycle.
Whether the supply is gravity-fed or pumped, piping must be correctly sized. Undersized pipes will increase cycle time and oversized pipes waste capital.
Pipework is always vulnerable to freezing-up in winter. Either design the supply pipework from the tank to the washer-extractors so that it can be drained if a deep frost is anticipated or insulate the pipework. The latter may be more expensive but it is more reliable.
Most modern flatwork rental plants rely on continuous batch washers and here there is no advantage in using a hot or even warm supply—increasing prewash temperatures can, in fact, bring problems by causing stains to set.
For washer-extractors the picture is totally different. A well engineered hot water system provides an ideal heat sink for recycling waste heat from hot effluent and flash steam. This can easily reduce fuel bills by 20%.
It will also reduce cycle length by cutting warm-up times and so increase productivity. However, the main benefit of using hot water to supply washer-extractors is that it allows an old boiler to support more plants. It is frequently more cost effective to provide hot water than to invest in a new boiler.
The keenest, most price competitive laundries in the UK use borehole water wherever possible. The key problems to counter with water from this source are water quality and consistency and once these have been established by trial bores, then an extract licence can be applied for.
After the set-up costs have been correctly depreciated, the laundry can enjoy significant long term financial benefits.
Most of the advice given here is basic and every laundry can improve quality and productivity by paying attention to detail. It is important to remember that the basic principles of water engineering must be examined before expensive investment in water recycling is even contemplated.
