For checking the impact of a blow, or more generally the momentum of a
heavy moving part of a machine. The devices in use comprise (_a_)
springs, see Section 80; (_b_) air cylinder, see No. 1480; (_c_) pistons
driven by _elastic_ fluids, such as steam and air, can be cushioned by
imprisoning a portion of the fluid at each end of the cylinder; (_d_)
brakes of various kinds, see Section 5.
=519. Hydraulic cushion.= The descending ram, by its tapered end, closes
gradually the discharge outlet for the water.
Hydraulic buffer stops are constructed on this principle.
=520. Cushioning device,= at the upper end of a steam-hammer cylinder.
Should the piston pass the exhaust holes, the steam above is imprisoned,
and checks the piston without shock.