Needle valves metal

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. 

Greater speed of attainment of equilibrium as well as greater precision are possible with a block-type osmometer like the one shown schematically in Fig. 36. Osmometers of this type usually consist of a pair of matched, stainless-steel or brass blocks, in each of which is cut a shallow circular cell cavity. The membrane fits between the two blocks, preferably with a lead gasket on one side of the membrane. The blocks are firmly bolted together. Each cell may be emptied and refilled through a metal tube connected with the bottom of the cell and closed with a needle valve during operation. Various schemes have... 

For the more vigorous reactions, a twin-cell calorimeter was devised (188). It consisted of two nickel cylinders connected by a stainless steel needle valve and tubing and held rigidly to a metal top-plate. The cylinders and connections were immersed in a wide-necked Dewar vessel containing carbon tetrachloride which would react mildly with any BrF3 that escaped. Bromine trifluoride contained in one cylinder was transferred to the solid contained in the other cylinder by opening the valve and applying controlled suction. All measurements were made externally on probes in the carbon tetrachloride. 

Apparent near the bench on which the GC unit sits are pressure-regulated compressed gas cylinders of hydrogen and air (in addition to the carrier gas, helium or nitrogen). Metal tubing, typically ]/8-in. diameter, connect the cylinders to the detector. A needle valve is used for flow control. These valves are located in the instrument for easy access and control by the operator. 

Fig. 4. Schematic vacuum system for metal atom reactions. X represents the stopcock or Teflon-in-glass valve. Satisfactory components (for a general discussion of vacuum line design see References 1 and 4) forepump, 25 L/min free air capacity diffusion pump, 2 L/sec main trap is removable and measures about 300 mm deep main manifold has a diameter of about 25 mm, stopcock or valve in manifold should be at least 10 mm substrate container is removable container with 1-2 mm Teflon-in-glass needle valve connected to bottom of container. Connection between this needle valve and the reactor may be 1/8 in. od. Teflon tubing is used. Alternatively, the substrate may be added as shown in Fig. 3.

Apparatus in which fluorine is to be handled at room temperature may be made from a number of metals. Platinum, copper, nickel, magnesium, monel metal, brass, steel, and German silver are all known to be satisfactory. Most of these become coated with a film of fluoride which prevents further corrosion. If the metal is in contact not only with fluorine but also with a liquid such as water or hydrogen fluoride, corrosion frequently becomes troublesome. Under such circumstances, platinum usually behaves in the most satisfactory manner. With the gas alone, brass needle valves may be used with success, but the packing is eventually ruined. Fabrication of apparatus is best accomplished by welding, brazing, or silver soldering. Solder made from lead and tin does not resist attack. 

In a dry-box operation, a 3-ounce Fischer-Porter aerosol compatibility tube is loaded with approximately 10 g. of cesium fluoride and then equipped with a stainless-steel needle-valve adapter and a 323A Hoke valve, f After removal from the dry-box, Swagelokf connections are made from the valve to a metal standard-taper joint and the whole assembly attached to... 

Liquid bromomethane may be withdrawn from a metal cylinder fitted with a needle valve by inverting the cylinder. 

Figure 1. Experimental Set-up of high-temperature metal vapor sorption system I. Flow meter 2. Needle valve 3. Nj 4. O2 5. Steam generator 6. Gas mixer 7. Valve 8. Thermo gravimetric furnace 9. High temperature sorption bed 10. Thermocouple II. Filter 12. Impingers 13. Furnace controller 14. Silicagelbed IS. Vacuum pump 16. Dry gas-meter...

The vacuum line is isolated from the forepump, and a liquid-nitrogen bath is put around trap D. The fluorine metering system is partially evacuated with the water aspirator, as discussed above. Then the vacuum line is completely evacuated with the forepump. Fluorine is allowed to expand slowly into the metal system by means of the needle valve 3. As the pressure increases above atmospheric, some fluorine is allowed to bleed into the vacuum line and storage bulbs until a pressure of 650-700 mm. is reached. First needle valve 1 on the metal system and then the fluorine control valve 3 are quickly closed. (Some fluorine may escape from the blowout manometer during this operation.) Approximately a 10% excess of fluorine (0.023 mole in this case) is condensed into the metal pressure reactor containing the thionyl fluoride. The amount of fluorine used is measured by the pressure drop in a calibrated volume in the pressure range of approximately 700-400 mm., since fluorine has a vapor pressure of approximately 400 mm. at —196°. 

Constant level vessel, 2 — Needle valve, 3 = Observation bulb, 4 = Vacuum connection, o = Condensers, 6 = Metal block, 7 = Thermometer wells, 8 = Insulated jacket, 9 = Dephlegmator, 10 — Receivers, 11 = Vacuum connections. 12 — Burners... 

A spun stainless steel Hoke vessel (test pressure 13(X) psi) that is fitted with a stainless steel needle valve [Hoke] is passivated by condensing into it 2 mmol of chlorine monofiuoride and then heating the vessel in an oven at 150° for 24 hr. Any residual gas that remains in the vessel is removed by passing the gas slowly through a tube containing soda lime. Twenty millimoles (4.72 g) of (CF3)3C0H, which is weighed into a vessel that can be attached to the vacuum line, is transferred into the evacuated metal vessel, which is then cooled to —196°. Then 21 mmol (1 mmol excess) of chlorine monofiuoride is condensed into the vessel at —196°. The valve is closed, and the vessel is placed behind a shield, where it is allowed to warm to and remain at 0° for 12 hr. All of the... 

We can discuss here only a few of the numerous recommendations on how to introduce small quantities of gas into a vacuum, while retaining precise control over the flow. In many cases it is sufficient to file fine grooves in the plug of a glass stopcock, starting at the bore. In these cases, stopcocks with inclined bores (offset arms) should be used as much as possible. The Bodenstein valve is also usable for fine control, although the adjustment is not exactly reproducible. A metal needle valve is the best means of control. 

Fig. 37. Metal Fig. 38. a) Tombac tube valve needle valve. J) diaphragm valve. 

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