What
is a Needle Valve
A
needle valve is linear motion valve used to make relatively fine adjustments in the amount of fluid
flow.
The distinguishing characteristic of a needle valve is the long, tapered,
needle like point on the end of the valve stem. This "needle" acts as
a disk. The longer part of the needle is smaller than the orifice in the valve
seat and passes through the orifice before the needle seats. This arrangement
permits a very gradual increase or decrease in the size of the opening in a
needle valve.
Needle valves are often used as component parts of other valves, more complicated
valves. For example,needle valves are used in some types of reducing valves.
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| Needle valve |
Needle Valve
Applications
Most
constant pressure pump governors have needle valves to minimize the effects of
fluctuations in pump discharge pressure. Needle valves are also used in some
components of automatic combustion control systems where very precise flow
regulation is necessary.
Types of Needle
Valve Body Designs
One
type of body design for a needle valve is the bar stock body. Bar stock bodies
are common, and, in globe types, a ball swiveling in the stem provides the
necessary rotation for seating without damage.
One advantage of needle valves is fine flow adjustments they offer. Needle
valves are frequently used as metering valves. Metering valves are used for
extremely fine flow control. The thin disk or orifice allows for linear flow
characteristics in metering valves (needle valves). Therefore, the number of
hand wheel turns can be directly correlated to the amount of flow.Needle valve specification should match the application where valve is going o be installed.
A typical
metering valve has a stem with 40 threads per inch. Needle valves generally use
one of two styles of stem packing: an O-ring with TFE backing rings or a TFE
packing cylinder. Needle valves are often equipped with replaceable seats for ease
of valve maintenance.
