Retaining valves, or non-return valves, are employed to confine any sudden shocks from hydraulic machines or from breakages, to local pipes.
Relief valves are applied to all hydraulic pressure systems to obviate the effects of shock.
An extra wire rope is frequently employed on suspended lifts to act as a safety rope.
[2490]. Safety centrifugal hooks to arrest a revolving shaft when the speed becomes excessive. The hooks fly out and engage with pins on a fixed disc.
Rope guards boards, screens, guard rails, &c., are necessary to protect persons from running ropes in hoisting and rope-driving gears.
[2491]. Collar and set screw, to prevent a key from working out. A set screw only—tapped into the shaft—is sometimes employed for this service.
Section 82.—STEAM TRAPS.
(See also [p. 184].)
[2492]. Steam trap, operated by expansion of a bent bar, which closes the inlet valve.