Instrument needle valve is an important part of the instrument measurement piping system, mainly globe valves and ball valves, its function is to open or cut off the pipeline path with. The ferrule type instrumentation valve has the advantages of easy installation and disassembly, tight connection, favorable to fire prevention, explosion-proof and high pressure resistance, good sealing performance, etc. It is a kind of valve with advanced connection method in the power station, oil refining, chemical device and instrumentation measurement pipeline.
I. The introduction of Needle valve .
Needle valve is a kind of throttling valve with relatively high adjustment precision. The valve is needle-shaped, along the water flow direction action, change the cross-flow area, to cut off or adjust the flow of the valve. Needle valve is a kind of fine-tuning valve, its valve plug is needle-shaped, mainly used for regulating gas flow. Fine-tuning valve requires the valve opening gradually become larger, from closed to open can be continuously fine-tuning.
Needle valve plug is generally hardened steel needle, and the valve seat is made of tin, copper and other soft materials. Valve needle and the valve seat ask the seal is to rely on its taper surface close fit to achieve. Needle taper 1:50 and 60 cone angle two kinds of cone surface to be fine grinding. Valve stem and seat sealing is realized by the bellows.
Needle globe valve sealing is good, long service life, even after the sealing surface is damaged, only need to replace the wear parts, can continue to use. Installation should be made so that the flow direction of the medium and the arrow direction on the valve body. Manual globe valves and ball valves can be installed in any position of the pipeline.
Low or medium pressure needle valves are generally equipped with two ferrule type live connection, live connection and pipeline generally with welding. High-pressure needle valves do not have a live connection, generally directly and pipe welding, as for the welding method depends on the specific circumstances, generally have electric welding, fire welding and argon arc welding.
Ⅱ. The operation of Needle valve .
The end of the mandrel is a tampered needle, which moves into the valve seat so that it can restrict or stop the flow of fluid through it. The in and out movement of the needle into and out of the seat is controlled by a spindle operated by a handwheel. Fluid passing through the valve will turn ninety degrees and then pass through an orifice, the size of which can be varied by placing a cone according to the seat. The needle plunger is at the end of the screw so that when the screw is rotated the plunger will retract and flow between the plunger and the seat is possible. Fluid flow will be impeded until the plunger retracts and flow adjustment is possible. Some properly threaded stems have a slow linear motion, so the full flow portion requires many turns, making needle valves suitable for regulating flow.
Needle valves can be thought of as a small globe valve, which is a form of globe valve, and they are used for small flows. The only difference between a ball valve and a needle valve is that the stem does not have a disk at the end, it has a long tapered point. The long taper of the valve allows for a smaller seat surface area than a globe valve, making needle valves more suitable as throttling valves.
III. The Uses of needle valves.
- Needle valves can be used in vent lines.
- Needle valvescan be used in sampling lines and other abrasive services.
- Needle valvescan be used in fluid power systems.
- Needle valvesare used in flow metering applications.
- Needle valves are used in automatic combustion control systems where precise flow regulation is required.
- Needle valvesare used in constant pressure pump governors to minimize the effects of fluctuations in pump discharge pressure.
Typically, needle valves are used to control flow and protect precision instruments from damage. Damage can be sudden pressure surges in liquids and gases, etc. They are widely used for pressure regulation, turbine bypass, discharge, air regulation, tank inlet and pump start-up. However, needle valves are ideally suited for use with lighter, less viscous fluid systems. These valves offer low-flow performance. Needle valves are also used in low-pressure hydraulic systems, chemical processing and other gas and liquid services to control flow.
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