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Gas Valves Technical Notes


Gas1 Valve

Gas1 Valve

Gas1 Valve

All-Metal Leak Valves

MD Series leak valves control gas admission to UHV systems with zero contamination from construction materials. All valves are demountable for knife-edge and sealing pad replacement, and are bakeable to 450° C. Since bonding between knife-edge and pad is possible during high temperature bakeouts, the valves should remain open if baked above 250° C.

Model MD5: uses a Stellite faced knife-edge and nickel diaphragm to make the UHV seal. The valve withstands hot or corrosive gases and accepts inlet pressure of up to 10 bar. It has a minimal internal volume and operates at upstream pressures from atmosphere to 10-7 torr, with a minimum leak rate of 10-7TL/sec. With the valve open, conductance is 0.1TL/sec. and closed, 10-14TL/sec. closed. It is used in argon processing, sputtering and system purging.

Models MD6 & MD7: use the more conventional copper pad sealing against a knife-edge (MD6 - OFHC pad and sst knife-edge; MD7 - copper alloy pad and Stellite knife-edge). Both are more resistant to misuse and high bakeout temperatures than the MD5. A long lever between the handle and the pad provides high operating sensitivity and its fine control screw has minimum backlash.

MD6 is a fine control leak valve with an operating pressure range from 100 torr to below 10-10 torr and a minimum controllable leak rate of 10-10 TL/sec. Open and closed conductances are the same as model MD5. MD7 is physically interchangeable with the MD6 but has an operating pressure range from 10-4 to 10- 11 torr. Its spring lever with micrometer screw gives a minimum controllable leak rate of 10-11 TL/sec. MD7 is an ultra-fine valve used in UHV systems requiring especially sensitive and reproducible gas flow control.

Needle & Metering Valves

Please note that metering valves using "needles" are not shut-off valves. Attempting to use them as such, by brute-force tightening, usually damages the needle.

Nupro® Metering Valves: M- and S-series valves are forged 316 sst to control gas flow into high vacuum systems. Both operate up to 200°C and differ only in flow rate range: a wide open M-series valve conducts 100 atm.cm3.sec-1 with 1 psi pressure drop and 5000 atm.cm3.sec-1 with 800 psi; a wide open S-series pass roughly 10 atm.cm3.sec-1 for pressure drops of 0.4 psi and 1000 atm.cm3.sec-1 for 1000 psi.

The M- and S-series valves have four patterns, each with a specific application in vacuum processing. The straight-through or right-angle (Fig. 1) valves throttle gas flows from constant composition, high pressure sources. Choose the type that best fits the tubing geometry. The cross valve (Fig. 2) is used where the gas source varies in composition, for example when analyzing gases in a CVD or sputter chamber with an RGA.

Gas is extracted from the chamber by attaching a mechanical pump in the straight direction through the valve (Fig.3). This keeps a supply of fresh gas at the needle stem which is connected to the analytical instrument such as an RGA. Keeping volume of tubing between the chamber and the valve small, increases the volumetric flow rate, decreases the tube's 'flush' time and, hence, allows composition changes in the main chamber to be detected sooner. With 1/16" OD, capillary bore tubing between chamber and valve, this arrangement will sample atmospheric pressure.

The double-cross pattern (Fig. 4) is two needle valves in series. It provides the same service as the single straight-through valve but with much better control of low flow rates.

The fittings on M- and S- series valves include Swagelok®, VCR®, NPT and tube welds. Operating handles are chosen from vernier, a calibrated nylon handle for repeatable flow settings, fine-flow, with variable torque for precise control of low flow rates, and slotted, for screw-driver adjustment in installations with difficult access.

Edwards LV10K, an aluminum bodied needle valve with brass seat and martensitic sst needle, is a fine control device that, at 1 bar differential pressure, has a maximum flow rate of 0.1 atm.L/sec. It is used for gas admission to a vacuum chamber down to 10-5 torr. The terminations are QF10 (NW10) and can be mounted in line or on a panel.

Edwards FCV10K, a 303 sst bodied needle valve with ceramic filled PTFE and 316 sst needle, is an extra fine control device that, at 1 bar differential pressure, has a maximum flow rate of 0.015 atm.L/sec. With a 20-turn 'counting dial' control knob that allows the setting of repeatable flow rates, it is used for precise gas regulation within the pressure range 10-3 torr to 10-4 torr. The terminations are QF10 (NW10) and it can be mounted in line or on a panel. Note: The use of an inline filter on the inlet side of the valve is recommended to prevent damage to the valve by dust or grit.

Shut-Off Valves

For gas shut-off applications, we offer two series of Nupro® 316 stainless steel valves. H-series are compact, rugged valves with welded bellows-sealed bonnets and hardened stainless steel or Stellite stem tips. Valve terminations (connection between valve and tubing) include NPT, Swagelok® and weld adapters. The operating temperature range of -62°C to 315°C and maximum pressure of 1000 psi cover most gas/vapor applications in vacuum processing where a single-turn, manually operated twist handle valve with the highest gas integrity is needed.

B-series have demountable bellows-sealed bonnets allowing maintenance/cleaning of the valve seat. Both Kel-F or Stellite stem tips valves are offered, Kel-F for lower torque closure but limited high temperature applications. Terminations include Swagelok®, VCR® and weld adapters. Available actuators include multi-turn T-handles (for metal seats), twist handles (for Kel-F seats), snap-action toggles (for Kel-F seats) and pneumatic pistons for remote operation (for Kel-F or metal seats). With a maximum operating temperature of 315°C, replaceable bellows and many types of actuator, B-series valves are excellent choices for general purpose gas shut-off, coarse regulation or applications where particulates in the gas stream may warrant valve-seat maintenance.

Up-To-Air Valves

Edwards AV5A & AV10K aluminum bodied up-to-air valves (also called air admittance valves and occasionally 'UTA' valves) are simple tapered stem valves that act as shut-off valves with very low leakage rates across the seat but some degree of control when used to vent the chamber before flange removal. The valve inlet is open to the atmosphere or, better, to a tank of dry nitrogen (such as the gas outlet of an LN2 dewar). Filling the chamber with dry gas, allowing a good flow even when flanges are removed, covering the open port with aluminum foil, and leaving the chamber without flanges for the shortest possible time greatly assists rapid pump-down by reducing water outgassing when the vacuum system is restarted.

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