Valves handwheel

Access to valve headwheels and instruments will influence piping arrangement around heat exchangers. Valve handwheels should be accessible from grade and from a convenient access way. These access ways should be used for arranging manifolds, control valves and instruments. 

Clearance is required to operate valve handwheels, sample points, and pushbutton stations. 

Valve parts such as valve handwheels and valve stems should not be broken or bent and must be intact. Valves with tapered threads at the cylinder connection should have a portion of threads exposed to ensure... 

Sometimes the valve handwheel has worked loose during shipment and simply tightening the handwheel slightly can stop the leak. The dustcap that is inserted into the cylinder valve outlet should also be tightened as a backup should the cylinder valve be accidently opened. Also the cylinder may leak at the threads where the cylinder valve is inserted into the neck of the cylinder. This type of neck leak is difficult to fix on site. If any of these leaks cannot be immediately corrected, then the cylinder should be moved to a hood where the leak can be safely vented, and the supplier of the gas should be notified. 

The cylinder valve is used to fill and empty the cylinder. The valve consists of a valve handwheel (or operating stem), a packing nut and gland, an overpressure safety device, and an outlet connection (Figure 17.2). 

Diaphragm Operated Control Valve with Handwheel... 

Figure 12-31. Capacity control suction valve unloaders are available in either of two designs with pneumatic operators (A) direct-acting (air to unload) (B) reverse-acting or fail safe (air to load), which automatically unloads the compressor in the event of control air failure (C) an innovation in manually operated unloaders. Here, the lever cam arrangement provides positive loading or unloading, eliminating the requirement to turn a handwheel completely in or out. (Used by permission Bui. 9-201B, 1991. Cooper-Cameron Corporation.)...

The outlet valves of refillable butane cylinders are different from those of refillable propane cylinders. The valve for propane is a handwheel type, with a female 5/8 in BSP LEFT-HAND thread for a POL metal-to-metal connector. A compatible half-coupling must always be used to ensure a leak-free joint. 

Small valves which are to he operated frequently have a packless gland, either a diaphragm or hellows, and a handwheel. 

Valves of all sizes which are only used occasionally will he sealed with O rings. As a safeguard against leakage, they have no handwheel fitted and the stem is provided with a covering cap which is only removed when the valve is to he operated. The stem will have flats for operation hy a spanner. Most such valves can he hack-seated to permit changing the O rings. 

Electric motor actuators vary widely in their design and applications. Some electric motor actuators are designed to operate in only two positions (fully open or fully closed). Other electric motors can be positioned between the two positions. A typical electric motor actuator is shown in Figure 39. Its major parts include an electric motor, clutch and gear box assembly, manual handwheel, and stem connected to a valve. 

The motor moves the stem through the gear assembly. The motor reverses its rotation to either open or close the valve. The clutch and clutch lever disconnects the electric motor from the gear assembly and allows the valve to be operated manually with the handwheel. 

A number of gases are supplied in liquefied form at relatively low pressures and these generally only require the use of a flow control valve. The valves on these cylinders are generally fitted with a handwheel. Again you should consult the supplier s technical data for information on the correct fittings and handling procedures. 

Flanged valves, when drawn to large scale, may have the over-all dimensions given, including the distance from the center to the top of the handwheel or valve stem when open and when closed, the diameter of wheel, etc. Separate flanges should be completely dimensioned, as... 

When the handwheel is turned, the torsional deflection will happen to the torsion rod of the control valve, and the spool of the control valve which is connected with the torsion rod is alto turned to the position, oil passage at one end is opened while the oil passage at other end is closed at the same time, which conveys the hydraulic oil to the side of the oil cylinder s piston and push the piston to move, thus driving the gear rack and realizing the rotation of front wheels. 

When a valve is in the closed position, it must be tight against its seat, but when in the open position it should NOT be tight against the spindle stop. Hence, if the handwheel is tight, the valve is shut, but if the handwheel is loose, the valve is open. 

If in doubt about which way to turn a valve, look on the hand-wheel for a directional arrow. Usually, clockwise rotation (when looking on the top of the handwheel) will close the valve. 

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