Throttling valves

Throttling or regulating valves are used to control the amount of flow They can only receive flow from one side. (Except the butterfly valves)

There are three main types of throttling valves that are used in the petroleum industry.

· Globe Valves.

· Needle Valves.

· Butterfly Valves.

GLOBE VALVES

A globe valve is used to control the amount of flow. The valve can be operated in any position from the fully closed position to the fully open position. The valve disc is globe shaped (circular). The valve operates by raising and lowering the valve disc into a circular seat. There is no contact between the seat and disc ends when the flow through the valve starts. Only a few turns of the handwheel are needed to fully open or close the valve. (The gate valve needs many turns to open or close it.) There are partitions inside a globe valve. The fluid flowing through the valve must make two 90 degree turns. The flow is "under and over" to prevent wear to the seat. Therefore, there is a high pressure drop in the valve. It is easier to control this kind of flow. Globe valves are usually smaller if they are hand controlled and need to be opened and closed often. The direction of the fluid flow through the valve keeps the seat and disc clean.

NEEDLE VALVES

The needle valve is similar to the globe valve. It has a needle shaped plug and seat instead of globe shaped ones.When the valve is fully open the needle valve does not allow a full flow. This is because the hole in the seat is much smaller than the pipe flow area.. The threads on the stem of a needle valve are very close together. This allows very exact control of the flow because the needle can be adjusted very precisely. Needle valves are used in small sizes, only up to 1 ". They are mainly used on instrumentation systems.

BUTTERFLY VALVES

Modern butterfly valves usually have rubber or elastomeric seats. These provide a tight shut off like any other valve. This valve design is very good for installations where space considerations are important. This type of valve is good for large piping systems since they can be made at almost any size. Basically, the valve consists of the valve body, shaft and butterfly disc, sealing gland and valve actuator. Because the design is simple, this valve works equally well in three different valve bodies; flanged butterfly valve, the lug wafer butterfly valve and the wafer type butterfly valve. The butterfly valve moves from fully open to fully closed. in a quarter turn of the valve handle. These valves are used to control the amount of flow. The sealing mechanism is a circular disc made of rubber or metal. It is difficult to shut off the flow if the sealing mechanism is made of metal; rubber gives a better seal. Butterfly valves usually have some kind of automatic actuator because they are fairly hard to close manually. Butterfly valves can be used for fluid flow in either direction. The valve disc in a butterfly valve is a flat disc. The disc rotates around a central pivot. When fully closed the flat disc fills the entire area of the valve body. The butterfly valve offers very little resistance to flow when it is fully open. Butterfly valves are used as low pressure control valves in gas and liquid pipelines.