Trip valve mechanisms are a class of steam engine

Steam engine

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

 valve gear

Valve gear

The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...

 developed to improve efficiency

Thermal efficiency

In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

. The trip mechanism allows the inlet valve to be closed rapidly, giving a short, sharp cut-off

Cut-off

A cut-off, also known as a kutte or "battle jacket" in heavy metal subcultures, is a type of vest or jacket which originated in the biker subculture and has now found popularity in the punk and various heavy metal subcultures...

. The valve itself can be a drop valve

Double beat valve

The double-beat valve, drop valve or equilibrium valve is a type of poppet valve arranged to allow it to be opened against a high pressure with a minimum of force....

 or a Corliss valve.

Trip valve gear was applied to larger stationary engines

Stationary steam engine

Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars , agricultural engines used for ploughing or...

. It was not used in transport applications,An exception was the very early London Steam Carriage

London Steam Carriage

The London Steam Carriage was an early steam-powered road vehicle constructed by Richard Trevithick in 1803 and the world's first self-propelled passenger-carrying vehicle...

 (1803) which had a form of trip gear. as it was not suitable for high speed.

The trip point of the valve mechanism, and therefore the cut-off, would be adjusted either manually or automatically by the governor

Centrifugal governor

A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions...

. The valve is opened by the mechanical valve gear mechanism, and when the trip gear trigger releases the mechanism the valve is snapped closed, usually by a spring acting against a dashpot

Dashpot

A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring...

.