I3 8 MODERN PAPER-MAKING
the bottom again. It Is very Important that, where esparto fibre Is used, the
agitators should be run slowly, otherwise the fibre will be rolled into little
knots or balls. As efficient stirring is absolutely essential for the mixing of
colour, loading, etc., it may be necessary to have two additional wings or
blades half-way up the centre shaft to keep a full chest properly mixed. The
top of the chests should be covered and made water-tight, leaving only a
manhole with a properly fitted lid or cover. Generally, the agitator shaft is
driven by bevel wheels on the top, and proper precautions must be taken
to prevent grease, oil or dirty water from finding their way down the shaft
or through the opening left for the shaft. This may be accomplished by having
a disc of metal running over the opening. Another, shaped like an inverted
umbrella, may be bolted on the shaft close inside the top and cleaned out every
time an opportunity occurs. Though a rinse out with the hose-pipe is sufficient
in washing out a chest on most occasions, all chests should be thoroughly
cleaned and brushed at every opportunity.
On a change from blues or colours to white, this Is compulsory. Where
the water Is hard, It will be found that limy 'scale' will form on the side
walls and blades of the agitators. Soft water is productive of 'slime'. The
machineman should always satisfy himself that his assistant has cleaned the
chest properly before allowing the stuff to be emptied into it. The beaterman
should see that the waste valve has been replaced, and when a chest is to be
cleaned he may take the opportunity of flushing out his stuff pipes with a
copious rush of water. Complete co-operation between the machineman and
the beaterman is essential, if mistakes are to be avoided, in the matter of waste
valves, changing pump from one chest to another and having the overflow
running into the correct chest.
Portable lights should be provided for covered chests, to allow of proper
observation of the quantity of stuff and for efficient cleaning.
The Stuff Pump (Fig, 38).—There are two kinds of stuff pumps in use—the
ordinary plunger pump with lifting valves, and the centrifugal purnp. A badly
fitting or dry plunger or barrel will roll up the fibres, and for this reason it is
necessary to have a jet of water constantly playing on the barrel and washing off
the little bits of fibre that may come up with each lift.
The centrifugal pump has none of these faults. Indeed, the action of the
swifdy moving blades has a certain 'clearing' effect on knotty or badly
cleared stuff. There are no leather or other moving valves to get out of order.
By regulating the chest pipe-gate, it may be made to supply more or less as
desired, and to keep a good level in the stuff box as the level of the stuff in the
chest goes down. Driven by one belt, it occupies very little space, and its
simple construction ensures cleanliness and few breakdowns.. A glance at the