Isolation Valves

·         Gate Valve

·         Plug Valve

·         Ball Valve

These valves are used to Start or Stop Flow of Fluids. Functionally isolation type of valves are kept either fully opened or fully closed. Isolation valves offer minimum resistance and thereby gives very low pressure drop to flow in its fully open position.

The velocity of flow against a partially opened valve can  cause:

Ø  Vibration - This may result in damage to the valve & piping.

Ø  Hammering - This may result in instantaneous jerk on piping system.

Ø  Hydraulic turbulences – This may result in erosion of the valve Gate & Seat.

The seat is the base on which the disc of the valve fits tightly. When the seat or gate is damaged, the valve will pass even in fully closed condition.

GATE VALVE

The maximum opening of the gate valve is the same size as the inside diameter of the pipe in which it is installed. Fluid flow is straight through the valve.

Gate Valves should be kept either fully Open or fully Closed

Ø  Straight-through flow

Ø  No Direction of flow

Ø  Small pressure drop

There Are Two Types of Gate Valves

Rising Stem

In the rising stem gate valve, the stem is threaded and rises when the valve is opened. Since the stem is exposed to outside atmosphere, it should be kept clean of point, dust, and dirt.

Non-Rising Stem

In the non-rising stem type, the bottom of the stem is threaded and dose not rise when the hand wheel is rotated to open the gate valve

Fluids may corrode the threads on the Non—rising stem gate valve.

Non-Rising stem gate valves are used where there is very little space.

Valve Parts

HAND WHEEL: To keep easy the rotation of the stem

BOX NUT: The threaded end of the stem, pass through the Nut. Rotation of Nut by hand wheel causes                      the stem raising or lowering the stem.

BONNET: Part of the valve mounted on the top of the body to form a tight enclosure.

BODY: Main part of the valve directly attached to the pipe

GATE: Is the part of the valve that controls the opening

YOKE: Part of the valve to support the hand wheel and bushing

GLAND: After the packing is installed the gland compresses the packing, the gland also serves as the                    stuffing box covers

STEM: Solidly connected to the gate, the rotation of the stem raise or lowers the gate

SEAT RINGS: When the gate is lowered, the seat rings fit with the gate to stop all flow

PLUG VALVE 

Plug valves are used as open-close valves. Plug valves have wedge-shaped ports.

The flow of liquid can be started or stopped by turning the plug handle only 90 ^o.

Most plug valves must be lubricated to keep them in good operating condition and make them easy to turn.

The lubricant also makes a seal around the valve to prevent leaking.

The plug valve does not have a long bonnet or exposed threads. The plug fits the body of the valve, and either its open port or its solid faces the fluid. A quarter turn is all that is needed to change from one position to the other.

Ø  Straight-through flow

Ø  Non Directional

Ø  Small Pressure drop

Ø  Multiple-way possible depending on plug

Ø  Fast Operation 

BALL VALVE

Ball Valves are also open-close valves and operate just like plug valves.

The Ball-Shaped port has a hole through it that blocks fluid flow through the valve.

When the hole is aligned with the pipe, flow is allowed.

When the ball is turned a quarter turn, the solid side of the ball blocks fluid flow.

These valves are not normally lubricated. Two rings, made of a material such as Teflon, From the seals around the ball.