High Steam Low Water Safety Valve

Following are the functions of high steam and low water safety valve:

• To blow out steam if steam pressure becomes higher than working pressure
• To blow out steam when the water level in the boiler comes down

The constructional details of the high pressure low water safety valve are shown in Figure 4.17. The arrangement for the outer valve is similar to that of lever loaded valve. The balance or counter weight can be fixed at any position along the arm by a set screw. The arrangement of inner valve and dead weight acts as dead weight safety valve. But, the load on the outer valve is both due to dead weight and strut thrust. If the steam pressure exceeds the limit, valve lifts, and steam escapes to waste.

Figure 4.17 High Steam Low Water Safety Valve

The second lever is attached with a float at one end and a balance weight at other end. When float is submerged in water, the lever is balanced about fulcrum. As soon as the float is uncovered, it gets unbalanced, and tilts the lever towards right. Due to tilting, it pushes the collar of spindle in upward direction, and raising the valve from its seat. Thus, steam starts escaping through the waste pipe. A drain pipe is provided to drain out the condensed steam.