Valves needle globe

A type of miniature globe valve, needle valves are used in instrument systems for throttling of small volumes. They have metal to metal seats, but due to the small size, can be used for positive shut-off (Figure 15-8). Needle valves have small passageways that may plug easily and limit their use to very small flow rates. 

Some other tJiJes of valves arc the check valve, which permits flow in one direction only the butterfly valve, which operates in damperlike fashion by rotating a flat plate to either a parallel or a perpendicular position relative to the flow the plug valve, in which a rotating tapered plug provides on-off service the needle valve, which is a variation of the globe valve that gives... 

VALVE, NEEDLE - A form of globe valve that contains a sharp pointed, needle like plug that is driven into the and out of a cone shaped seat to accurately control a relatively small rate of flow of a fluid. 

Tremblay and Andrews studied the water and water-stream flow through a halfinch needle-type globe valve [45]. The valve pressure drop for water flow was correlated by calculating resistance coefficient, K. They observed that the resistance coefficient was constant and independent of Reynolds number. 

GLOBE VALVES TO —D d w 1 ]— X]— aH HXI— Globe Pneumatic Motor Hydraulic Needle Pneumatic Motor ... 

The two types of valves which have seen extensive service up to 1050 F in li(iiiid-nictal fuel systems are standard Y pattern globe valves and needle val es. Due to the stringent requirements of zero gas leakage (into or out of the metal systems), the only acceptable stem seal has been a steel bellows. Packings arc unacceptable. 

The needle valve at the pump discharge side is used to control the flow rate through the pump. This flow control is important and can be done by using either a needle valve or a globe valve. The check valve downstream of the needle valve is an absolute requirement. Without this check valve, tiie fluid will flow backward from the contactor to the pump and will cause tiie pump to rotate in the reverse direction. Without this check valve, it is almost impossible to start the pump operation. 

All three types of valves described above are on-off type devices (binary devices). A basic requirement in the design of these valves is that they offer minimum resistance to flow when open. For many types of calculations it is often justifiable to neglect pressure losses through such devices. But such a simplification cannot be applied to flow control valves. With these devices the control of flow is accomplished either by a constriction or by a diversion. In either case an additional resistance to the flow is introduced. Globe, angle, cross, and needle valves are typical devices of this type. Specific pressure drop correlations should be developed for such devices and used whenever possible. One such correlation used by Stoner (S5) takes the form... 

Most process gate valves are specified with an Outside Screw and Yoke because of the corrosive and high temperature service encountered in process streams. For noncorrosive service, the thread can be inside the valve body, screwing into the body like nonrising stem gate valves and small globe, angle, Y and needle valves. 

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