TYPES OF VALVES
On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect
to percent of opening. This means that flow rate does not change evenly with stem travel.
Also, a partially open gate disk tends to vibrate from the fluid flow. Most of the flow change
occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual
leakage if used to regulate flow. For these reasons, gate valves are not used to regulate or
A gate valve can be used for a wide variety of fluids and provides a tight seal when closed. The
major disadvantages to the use of a gate valve are:
It is not suitable for throttling applications.
It is prone to vibration in the partially open state.
It is more subject to seat and disk wear than a globe valve.
Repairs, such as lapping and grinding, are generally more difficult to accomplish.
Gate Valve Disk Design
Gate valves are available with a variety of disks. Classification of gate valves is usually made
by the type disk used: solid wedge, flexible wedge, split wedge, or parallel disk.
Solid wedges, flexible wedges, and split wedges are used in valves having inclined seats. Parallel
disks are used in valves having parallel seats.
Regardless of the style of wedge or disk used, the disk is usually replaceable. In services where
solids or high velocity may cause rapid erosion of the seat or disk, these components should
have a high surface hardness and should have replacement seats as well as disks. If the seats
are not replaceable, seat damage requires removal of the valve from the line for refacing of the
seat, or refacing of the seat in place. Valves being used in corrosion service should normally
be specified with replaceable seats.