is only
partially adopted; the lower face is considerably larger in diameter than
the upper face, and the difference constitutes an annulus of pressure,
which will cause the valve to open or shut with the same force as a spindle
valve of the area of the annulus. To deaden the shock still more
effectually, the lower face of the valve is made to strike upon end wood
driven into an annular recess in the pump bucket; and valves thus
constructed work with very little noise or tremor; but it is found in
practice, that the use of Harvey and West's valve, or any contrivance of a
similar kind, adds materially to the load upon the pump, especially in low
lifts where the addition of a load, to the valve makes a material addition
to the total resistance which the engine has to overcome. Instead of end
wood driven into a recess for the valve to strike upon, a mixture of tin
and lead cast in a recess is now frequently used, and is found to be
preferable to the wood.

430. _Q._--Is there any other kind of pump valve which is free from the
shocks incidental to the working of common valves?

_A._--In some cases canvass valves are used for pumps, with the effect of
materially mitigating the shock; but they require frequent renewal, and are
of inferior eligibility in their action to the slide valve, which might in
many cases be applied to pumps without inconvenience.

431. _Q._--Could not a form of pump be devised capable of working without
valves at all?

_A._.--It appears probable, that by working a common reciprocating pump at
a high speed, a continuous flow of water might be maintained through the
pipes in such a way as to render the existence of any valves superfluous
after once the action was begun, the momentum of the moving water acting in
fact as valves. The centrifugal pump, however, threatens to supersede pumps
of every other kind; and if the centrifugal pump be employed there will be
no necessity for pump valves at all. There is less loss of effect by the
centrifugal pump than by the common pump.

432. _Q._--What is the best form of the centrifugal pump?

_A._--There are two forms in which the centrifugal pump may be applied to
mines;--that in which the arms diverge from the bottom, like the letter V;
and that in which revolving arms are set in a tight case near the bottom of
the mine, and are turned by a shaft from the surface. Such pumps both draw
and force; and either by arranging them in a succession of lifts in the