Safety Valve ~ Boiler Mountings

Functions of a Safety Valves:

            Safety valve is used to guard the boiler against the excessive high pressure of steam inside the drum. If the pressure of steam in the boiler drum exceeds the working pressure then the safety valve allows blow-off the excess quantity of steam to atmosphere. Thus the pressure of steam in the drum falls. The escape of steam makes a audio noise to warm the boiler attendant.

Positions of a safety valve in Boiler:

             ☑ Safety valves are located on the top of the boiler. 

⤇ Types of Safety Valves:

There are four types of safety valve:

        ☑ Dead weight safety valve.
        ☑ Spring loaded safety valve
        ☑ Lever loaded safety valve
        ☑ High steam and low water safety valve

Most Commonly used Safety Valve:

The most commonly used safety valve is spring loaded safety valve. Below shows the constructions and working principle of a spring loaded safety valve.

Constructions of a spring loaded safety valve:

    → It consists of a cast iron body having two branch pipes. 
    → Two separate valves are placed over the valve seat.
    → A lever is placed over the valve by means of two pivots. 
    → The lever is held tight at its proper position by means of a spring. 
    → One end of spring is connected with the lever while other end with the body of the valve. 
    → The valve is kept on it seats with help of spring force.

Working Principle:

    → In the normal condition, the downward force due to spring is higher than upward force applied by steam. 
    → The valve is closed due to spring force. 
    → When steam pressure exceeds the normal limit, upward force due to steam pressure is become higher than downward force due to spring. 
    → Thus the valves are lifted from their seats opening the passages for steam to release out of boiler.