Needle Valve Basic Function

Needle Valve have basic function as follows :

The Valve are one of the oldest and most basic mechanical compon ents in fluid handling systems. Although there are many variations in the types and designs of valves, most perform one of two basic functions of valve :
Isolation. The valve is function to open or closed; its function is work is to turn the flow on or off by connecting, it thus isolating it from the rest of the system.
Regulation. The valve is function to regulates the rate of flow through the system. It usual is neither fully open nor fully closed.

How Needle Valve Work

How Needle Valve Work

Isolation Valve which Screw actuation allows the valve to opened gradual and the thread stem is requires three or four turns of the handle to open and close the valve (see Fig. 2). For exceptionally high pressures general above 10.000 Psig (690 bar) with a special variation of needle valves has been design. Although similar to other needle valves for this type of valves contain unique design features with materials specially selected for high pressure operation.
Regulating and metering valves have function to design adjust the rate of flow. They usual have a long fine tapered stem tip and a fine pitch stem thread to open in five to ten turns. This type of Valve are not
suggested used for isolation service and are general designed they cannot used function as shut off (see Fig. 1)
Fig 2 : FITOK Needle Valve Design

Pressure Temperature Ratings


Needle Valve have pressure and temperature ratings specify the maximum and minimum temperatures and pressures which the valve can be operate safe. These ratings are based on the properties of materials and used in pressure containing parts and those of other materials that contact the system fluid. On design require and on performance tests. Design basis for our process and instru m ent valves, explains how pressure temperature ratings are determine and lists national codes and standards relating to valve ratings.



The material of the Needle Valve body must be select with suit the needs of the application. Three most common materials are stainless is steel, brass and carbon steel. Also used alloys of nickel, copper, chromium, and others. Valves can made of plastic are available for certain applications. This type is choice of material is determine by compatibility with the system fluid, which encompasses such factors as corrosion resistance, pressure, temperature and cleanliness. Materials are purchase in accordance with specifications published by the American Society for Testing and Materials (ASTM).



The size of a Needle Valve often is describe by the nominal size of the end connections. A more important measure of size is the rate of flow of the valve can provide. Flow through valves or other fluid system compo n ents depends primary on compo n ent design, inlet and outlet pressures and fluid den sity. Flow coeffi c ients (Cv) for each valve are publish in catalogs. Cv values, de ter mined by testing, and subse q u ent calculaions are con duct it’s include with accordance with methods and formulas specified by the International Society for Measurement and Control (ISA).



Stem seals will pre v ent leakage of system fluids from atmosphere is available in several designs for suit diffe r ent valves and applications. The system designers may select from these choices is to pre v ent leaks or minimize system fluid loss, and reduce maintenance or cost repair. Selecting the optimum seal Furthermore increase system efficiency include lower total costs of ownership.

PTFE packing cylinder fits close around the valve stem. When tightening the packing nut forces the soft plastic material outward against the body.
We pre v ent leakage and minimize need for freque packing adjust m ents by :
1. Fine surface finishes on the stem shank is reduce wear of the packing as the stem slides during.
2. Maintaining close tolerances it’s especial con c ent ricity of the packing, stem, and bonnet
3. Supporting the packing with metal or reinforced plastic glands and become pre v ent extrusion


Live Loaded Packing

Needle Valve Live loading maintains a constant pressure on the packing to ensure that it remains leak tight. This is especial valuable in applications with fre qu ent temperature or pressure changes with high operating temperature. It’s eliminates the need for fre qu ent packing adjust m ent and extends packing service life. The two most common methods of live loading are an elastomeric O ring seal or a Spring loaded plastic packing.
The simplest live loaded seal is an elastomeric O ring. Elastomers are made from synthetic or natural rubber like materials which return to their original shape after being deformation. The resilience of the elastomer it’s provides the live load which maintains until enough pressure on the seal to compensate for temperature or pressure changes and for wear.
Needle Valve Live Loaded


Spring loaded stem seals employ a plastic packing, because plastics are not as resil i ent as elastomers. The live loading is provide by a series of disc springs above a metal gland. The packing nut compresses the springs to maintain a constant load on the packing and compensating for packing wear and for changes in pressure or
temperature. For additional seal integrity is the packing is a two piece split chevron design that support by an anti extrusion ring and a metal gland. The two packing rings move uniform against the stem and bonnet, and form a larger seal area that also increases packing life (see Fig. ). Of course, the same smooth surface finishes, close tolerances, and con c ent ricity that characterize will con v ent ional packing systems are equal important in effective live loaded packing systems.

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