Lime Mixer.
Lime Mixing Room
Only lumps of quick lime were used in water softening, lumps that were underburnt
or overburnt, together with any clinker from the fuel, were removed, powder
and small pieces were waste. The lime was stored in the adjacent lime store
until it was needed.
A weighing machine was provided so that the lime could
be weighed to get the correct amount to put in the mixing tank. In practice
however, the quantities were reckoned by the barrow load.
The lime mixing
tank (lime mill) was nearly filled with water and then quick lime from the
store was put into the rotating basket, the action of mixing water and quick
lime is to make the lumps of lime swell and disintegrate, at the same time
producing a lot of heat, so that the tank became quite hot, (although the
term 'mill' was used, there was no crushing or grinding involved). Adding
water to quick lime is known as slaking. Rotating the basket ensured thorough
mixing and prevented lime settling in the bottom of the tank.
From the lime
mill, the liquid, called "cream of lime" from the colour and consistency,
was run through a sieve into the adjoining lime tank. Here more water was added
and the liquid held until needed. The liquid in the tank now had the consistency
of milk, and was known as "milk of lime".
When required in the filter house,
it was let out of the hole at the bottom of the tank through a simple flap
valve. Originally the lime holding tank also had a rotating agitator driven
by a belt from a pulley on the line shafting on the wall. Both line shafting
and hydraulic motor are original from 1903.
The head of water from Twyford Reservoir provided enough pressure to drive
the hydraulic engine, the three cylinders of the engine oscillate under the
action of the crankshaft, pivoting on the pipe at the bottom. This pipe has
a central division with water pressure on one side and on the other side
spent water drains away. Ports on the top of the pipe are covered and uncovered
as the cylinders rock to and fro, so that alternately water under pressure is
admitted to power the cylinders and then exhausted, the spent water flows
into the water softening tank.
The carbon plant in the corner of the mixing
room was added when the diesel pumps were installed in the 1930's, to remove
any possible contamination by diesel fuel. The plant is operated by a pelton
wheel, driven by mains water pressure and it measured out a small quantity
of carbon which the spent water from the pelton wheel washed through pipes,
into the water softening tank. Here the carbon floated on the water and absorbed
any oil present on the surface. The carbon was removed in the filters.
