TYPES OF VALVES
Gate Valve Stem Design
Gate valves are classified as either rising stem or nonrising stem valves. For the nonrising stem
gate valve, the stem is threaded on the lower end into the gate. As the hand wheel on the stem
is rotated, the gate travels up or down the stem on the threads while the stem remains vertically
stationary. This type valve will almost always have a pointer-type indicator threaded onto the
upper end of the stem to indicate valve position. Figures 2 and 3 illustrate rising-stem gate
valves and nonrising stem gate valves.
The nonrising stem configuration places the stem threads within the boundary established by the
valve packing out of contact with the environment. This configuration assures that the stem
merely rotates in the packing without much danger of carrying dirt into the packing from outside
Rising stem gate valves are designed so that the stem is raised out of the flowpath when the
valve is open. Rising stem gate valves come in two basic designs. Some have a stem that rises
through the handwheel while others have a stem that is threaded to the bonnet.
Gate Valve Seat Design
Seats for gate valves are either provided integral with the valve body or in a seat ring type of
construction. Seat ring construction provides seats which are either threaded into position or are
pressed into position and seal welded to the valve body. The latter form of construction is
recommended for higher temperature service.
Integral seats provide a seat of the same material of construction as the valve body while the
pressed-in or threaded-in seats permit variation. Rings with hard facings may be supplied for
the application where they are required.
Small, forged steel, gate valves may have hard faced seats pressed into the body. In some
series, this type of valve in sizes from 1/2 to 2 inches is rated for 2500 psig steam service. In
large gate valves, disks are often of the solid wedge type with seat rings threaded in, welded in,
or pressed in. Screwed in seat rings are considered replaceable since they may be removed and
new seat rings installed.