Filter House.
The filter house will be inaccessible to the public this year
(2006) due to redevelopment work being carried out, this is to make room for
the filters when they arrive later this year.
The Trust apologises for any inconvenience
this may cause to you.
Lime Cylinders.
From the lime mixing room, the "milk of lime" was piped to the
filter house, here it entered one of seven large cylindrical tanks and even
more water was added to it, producing the saturated solution of "slaked" lime
in water, the well known 'lime water' from the school chemistry laboratory.
From the top of the lime cylinders the lime water flowed through pipes into
a cast iron trough which carried it through the wall to the large water softening
tank.
Filters.
There were a total of thirteen filters installed in the
filter house, but like the lime cylinders they were removed and scrapped before
the Trust took over.
The filters were inside tanks kept full of water from the softening tank next
door, each filter had a bank of elements which consisted of two perforated
metal sheets on end, the faces of the sheets held just a small distance apart,
inside a fine-weave cloth bag, water passed through the filter cloths, between
the metal sheets and so to another pipe at the bottom which led the water
out into the clear water tank.
In passing through the filter cloth, the precipitates
from the water softening were removed and stayed in the tank, thus each filter
tank regularly had to be cleaned of the sludge formed by the precipitates,
in addition the filter cloth bags had occasionally to be cleaned and sterilized
with steam from the boilers.
Clear Water Tank
This was used to collect the water from the thirteen filters, the clear water tank consisted of the lower part of the filter house, below floor level, and two adjacent covered tanks. From the clear water tank, the now softened water was then pumped by steam, diesel or electricity, at different times, up to the service reservoirs, on the downs to the south of Twyford or to Yew Hill, and so on to the customer.
Ending of Water Softening
The water softening treatment was suspended during the two
World Wars. A shortage of manpower caused the cessation in 1917, then being
restarted in 1922.
In 1939, at the start of World War II it was considered that the glow
from the lime kilns could have served as a guide to enemy aircraft, trial screens
over the kiln chimneys not being successful, during times of suspension of
softening, hard water then passed directly into the water mains. There were
also times when the lime kilns and softening plant could not fully cope with
demand and on these occasions only partly softened water passed into the mains.
In 1946 softening was resumed but the lime was obtained from Derbyshire
and the Twyford kilns remained disused. In 1969 water softening at Twyford
finally stopped because with the replacement of traditional soaps by synthetic
detergents, it was considered that the expense of softening the public
water supply was no longer justified.
