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depending on the extent of the reduction in the capacity of the
filters which in turn depends on the use that is "being made of
the bath. The "back-washing" is carried out with water from the
bath which then runs to waste and this may use up to 10,000
gallons of water, the level of the bath "being made up with fresh
water from the Metropolitan Water Board. The whole bath is
emptied for cleaning every 12 to 18 months but it will, of course,
be realised that the constant use of water for cleaning the
filters and the "topping up" with fresh water provides for
renewal of the water at much more frequent intervals.
The Goldhurst Pool and the Fairfax Pool use the same
filters and during the summer season when the Goldhurst Pool is
in use the water is mixed and filtered at the same time, although
there is a difference of 9 inches in the level of the water in
the two baths. The present filters were brought into use in
1951. There are three pumps and with two of them in use the
total capacity of the baths can be dealt with in 4 hours. With
the use of the third pump the period can be reduced to three
hours. Each pump has a capacity of 23,000 to 26,000 gallons
per hour but the total capacity of the three pumps together is
only 62,000 gallons per hour. The "back-washing" of the filters
is carried out about twice a week in the summer and once a week
during the winter depending on the use which is being made of
the baths. The quantity of water used each time is between 10,000
and 15,000 gallons which, as with the Youth Pool, goes to waste
and is replaced by water from the Metropolitan Water Board. The
Goldhurst Pool is emptied each September for the winter and the
Fairfax Pool is emptied for cleaning every 12 to 18 months.
In all the filters after cleansing by "back-washing"
it is necessary to form a new "bed" in the filter and for this
purpose alum and soda are added to the water. The modern practice
is to add the full amount of alum (about 15-20 lbs. for the big
baths, and 5-6 lbs. for the Youth Pool) at one time and to add
the soda intermittently over the period, the object being to
maintain the chemical reaction of the water at a pH value of
7.6 to 7.8.
Apart from treatment of the water by filtration the
bacterial content of the water is controlled by the injection
of chlorine. This is used in the form of chlorine gas which is
supplied in cylinders under such pressure as to render the
chlorine liquid. The injectors are Paterson Chloronames of
1930 pattern made by the Paterson Engineering Co.Ltd., which
although old are very satisfactory in operation. One of the
injectors is used for the Youth Pool and up to five injectors
can be used for the two large baths. The concentration of