The Dead Weight safety valve consists of a valve V which is made of gun metal to prevent rusting. It rests on the gun metal seat S and is fixed to the top of a vertical steam pipe P. The pipe has a flange F at the bottom for fixing at the top of the boiler shell.

A weight carrier C is suspended from the top of the boiler. It carries cast iron rings (i.e., weight W). the total weight must be sufficient to the keep the valve on its seat against the normal working pressure.

Working of Dead Weight safety valve:

When the steam pressure in the boiler exceeds the normal working pressure, it lifts the valve with its weight. The excess steam therefore escapes through the pipe to the atmosphere, until the pressure reaches its normal value.

It is the simplest type of safety valve; it is suitable for stationary boilers only, because it cannot withstand the jerks and vibration of mobile (marine) boilers. Another disadvantage of this valve is the heavy weight required to balance the steam pressure. Hence, it is not suitable for high pressure boilers.