What is "safety valve"

Safety chain \Safety chain\

1. (Railroads) A normally slack chain for preventing excessive movement between a truck and a car body in sluing.

2. An auxiliary watch chain, secured to the clothes, usually out of sight, to prevent stealing of the watch.

3. A chain of sheet metal links with an elongated hole through each broad end, made up by doubling the first link on itself, slipping the next link through and doubling, and so on.

   Safety arch (Arch.), a discharging arch. See under Discharge, v. t.

   Safety belt, a belt made of some buoyant material, or which is capable of being inflated, so as to enable a person to float in water; a life preserver.

   Safety buoy, a buoy to enable a person to float in water; a safety belt.

   Safety cage (Mach.), a cage for an elevator or mine lift, having appliances to prevent it from dropping if the lifting rope should break.

   Safety lamp. (Mining) See under Lamp.

   Safety match, a match which can be ignited only on a surface specially prepared for the purpose.

   Safety pin, a pin made in the form of a clasp, with a guard covering its point so that it will not prick the wearer.

   Safety plug. See Fusible plug, under Fusible.

   Safety switch. See Switch.

   Safety touchdown (Football), the act or result of a player's touching to the ground behind his own goal line a ball which received its last impulse from a man on his own side; -- distinguished from touchback. See Touchdown. Same as safety

   Safety tube (Chem.), a tube to prevent explosion, or to control delivery of gases by an automatic valvular connection with the outer air; especially, a bent funnel tube with bulbs for adding those reagents which produce unpleasant fumes or violent effervescence.

   Safety valve, a valve which is held shut by a spring or weight and opens automatically to permit the escape of steam, or confined gas, water, etc., from a boiler, or other vessel, when the pressure becomes too great for safety; also, sometimes, a similar valve opening inward to admit air to a vessel in which the pressure is less than that of the atmosphere, to prevent collapse.

n. A relief valve set to open at a pressure below that at which a container (such as a boiler) would burst

n. a valve in a container in which pressure can build up (as a steam boiler); it opens automatically when the pressure reaches a dangerous level [syn: relief valve, escape valve, escape cock, escape]

A safety valve is a valve that acts as a fail-safe in a thermal-hydraulics plant. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits. Pilot-operated relief valves are a specialized type of pressure safety valve.

Safety valves were first developed for use on steam boilers during the Industrial Revolution. Early boilers operating without them were prone to explosion.

Vacuum safety valves (or combined pressure/vacuum safety valves) are used to prevent a tank from collapsing while it is being emptied, or when cold rinse water is used after hot CIP (clean-in-place) or SIP (sterilization-in-place) procedures. When sizing a vacuum safety valve, the calculation method is not defined in any norm, particularly in the hot CIP / cold water scenario, but some manufacturers have developed sizing simulations.

The safety valve is a provision in the Sentencing Reform Act and the United States Federal Sentencing Guidelines that authorizes a sentence below the statutory minimum for certain nonviolent, non-managerial drug offenders with little or no criminal history.

A safety valve is a mechanism for the release of a substance from a pressurized vessel when the pressure or temperature exceeds preset limits.

Safety valve may also refer to:

• Safety valve (law), a provision in the United States Federal Sentencing Guidelines
• Safety valve theory, relating unemployment and the Homestead Act of 1862
• Safety Valve (Biscayne Bay), a structure of sand flats and tidal channels separating Biscayne Bay in Florida from the Atlantic Ocean
• Traditional Safety Valves, balances between the public's interest in open access with the property interest of copyright owners
• Safety valve, a method for managing Emissions trading
• Safety shutoff valve, a device to close a line and stop the flow of material
• Downhole safety valve, a shutoff device in a gas or oil well