TYPES OF VALVES
The disk lifts off of the seat to open the valve. The airfoil design of the disk allows it to "float"
on the flow. Disk stops built into the body position the disk for optimum flow characteristics.
A large body cavity helps minimize flow restriction. As flow decreases, the disk starts closing
and seals before reverse flow occurs. Backpressure against the disk moves it across the soft seal
into the metal seat for tight shutoff without slamming. If the reverse flow pressure is insufficient
to cause a tight seal, the valve may be fitted with an external lever and weight.
These valves are available with a soft seal ring, metal seat seal, or a metal-to-metal seal. The
latter is recommended for high temperature operation. The soft seal rings are replaceable, but
the valve must be removed from the line to make the replacement.
Lift Check Valves
A lift check valve, illustrated in Figure 24, is commonly used in piping systems in which globe
valves are being used as a flow control valve. They have similar seating arrangements as globe
Lift check valves are suitable for installation in horizontal or vertical lines with upward flow.
They are recommended for use with steam, air, gas, water, and on vapor lines with high flow
velocities. These valves are available in three body patterns: horizontal, angle, and vertical.
Figure 24 Lift Check Valve