Our online catalog is being updated! Please contact us for current pricing. Valve Dictionary Actuator The external valve component which transfers motion to the valve stem in angle and inline valves or to the slide assembly in gate valves. Manual actuators are knobs, cranks, or levers. Pneumatic actuators use compressed air controlled by a separate solenoid valve, while motor actuators use an electric gear motor. Adsorption Adherence of atoms or molecules of a gas or liquid to the surface of another substance. Angle Valve Any valve with the inlet port at a right angle to the outlet port. Bellows A flexible metal connector, usually made of stainless steel, to accommodate: the expansion of stem seal vacuum valve bellows; to seal feedthrough shafts; isolate vacuum envelopes; isolate vibration; or to protect sensitive components from mechanical stress. Bellows are made by roll-forming, hydroforming, metal depositing, or welding of individual convolutions. The choice of bellows depends on applications: Welded bellows are made of two thin-contoured metal diaphragms welded on their inside diameter to form a section. The sections are then stacked and welded on their outside diameter to form a complete convolution. Welded bellows provide maximum flexibility and stroke with minimum size. Formed bellows are an alternative to welded bellows. They are good for applications requiring moderate flexibility and/or high-pressure resistance. They are made by corrugating walls of thin-walled tubing. Deposited bellows are miniature, precise and thin-walled. Bellows Assembly The valve mechanism which transfers motion from external drive components to vacuum side components through a metal bellows seal. Bi-Pass A solenoid-controlled option feature which equalizes pressure on both sides of the valve seat before the valve is opened. The bi-pass mechanism protects delicate samples from damage caused by sudden pressure changes. It also permits gas to be bled into the system. Bonnet The area where the actuator is joined with the case. This area provides access for valve maintenance. It consists of two flanges, a mechanism mounted on the top flange (such as a bellows assembly), and a gasket. Buna-N Elastomer, nitrile rubber. A synthetic rubber made by random polymerization. Used for gaskets and O-rings. Maximum service temperature is 121°C/250°F. Closure Seal Where prevention of gas passage between the outlet and inlet ports is achieved by means of a poppet or gate incorporating a gasket (the closure seal). Many types of gaskets are used, each with different capabilities. Fundamental to any closure is the application of force from the actuator through the bellows assembly to the seal assembly. At the end of the seal assembly is a gate or plug with a gasket which is deformed against the valve seat for sealing purposes. Conductance The figure of merit of a valve can be expressed as the maximum number of Torr l/sec of gas which can pass from the plane of the inlet port to the plane of the outlet port. To help you make comparisons, we have included some computed conductances with our valve specifications. Because the short tube approximation to the conductance equation was used which ignores the larger diameter in the valve body area, computed conductances are slightly less than actual conductances. Counterfeit Valves Vacuum valves that do not offer full conductance because of obstructions in the gas flow path such as gates or poppets that do no open fully. Unqualified valves are sometimes referred to as "counterfeit" valves. Desorption Release or outgassing of gases or vapors adsorbed by the interior walls of the vacuum envelope. Low desorption rates are made possible by selecting correct materials, cleaning processes, optimum surface finish and proper engineering techniques. Dielectric A substance with very low electrical conductivity, i.e., an insulator. Elastomers A general term for high polymers having the property of extensibility and elastic recovery, i.e., the ability to be stretched and to retract rapidly to approximately the original size. (See "polymer.") Electro-pneumatic A method of valve actuation utilizing a pneumatic cylinder and a solenoid valve to direct the air pressure to one end, or alternately to both ends of the pneumatic cylinder, thus opening or closing the gate or poppet. Gasket The replaceable, deformable metal or elastomeric component which, when compressed, prevents the passage of gas from one side of the seal to the other. Gaskets are used in the bonnet seal, the closure seal and the flange seals (when flanges are used). Metal gaskets provide the best seal by virtue of their low permeability, low outgassing rate and higher bakeout temperature. Elastomeric gaskets, chiefly Viton, are used when vacuum requirements are less stringent. They are economical and within limitations are reuseable. Metal closure seals are reusable, but must be replaced more often than elastomeric closure seals. Gate/Poppet The gasket carrier which moves the closure gasket into position with the valve seat and transfers the sealing force to the gasket. The gate/poppet in all TLI valves is fully retractable from the space between ports, ensuring full conductance. Gate Valve (See "gate/poppet" above.) This type of valve has three advantages: It offers a full line of sight transmission from port to port; it has the best conductance available; and it can be made in large sizes at a reasonable price. Indium A metal, element No. 49 in the Periodic Table. It is ductile and softer than lead with a very low vapor pressure. It is used for radiation resistant seals. Inlet Port A tubular opening, usually flanged, through a chamber wall, permitting access or installation of a device into the chamber. Inline Valve A valve with the outlet port parallel to, but not necessarily axial with, the inlet port. Kalrez A carbon-black filled compound with good mechanical properties and excellent chemical resistance, manufactured by DuPont. A maximum intermittent operating temperature of 366°C is recommended. It is used as a gasket material in high temperature applications. KEL-F A polymer with high thermal stability, resistance to chemical corrosion, high dielectric strength, and high impact and tensile strengths. It is used for gaskets and seals. Leak Detection The establishment by various detection methods that a leak is present and significant to system performance. Mass spectrometer helium leak detectors, offering sensitivity to about 5 x 10-10 Torr l/sec or better, are excellent for this purpose. NOTE: Teflon is permeable to helium, so care must be exercised to avoid saturating the Teflon tape used with thermocouple tubes. This permeation can sharply curtail the usefulness of a helium mass spectrometer. Macor A machineable glass-ceramic manufactured by Corning, which retains the usual hardness and strength of ordinary ceramics without needing to be fired after machining. Nitrile Rubber A synthetic rubber formed by random polymerization of acrylonitrile with butadiene used for gaskets and O-rings. Outlet Port A tubular opening through a chamber wall, usually flanged, permitting access for pumping or the extraction of components from the chamber. Over Center Locking A gate valve mechanical feature which ensures that the valve will remain closed in the event of loss of either air pressure or electrical power. Permeability In high vacuum devices, the degree of vacuum that can be maintained depends, in part, upon the quantity of gas passing through (permeating) the wall or gasket from outside the chamber. Materials used for gaskets and chamber walls should be of low permeability. Pneumatic A pneumatic valve is supplied with the pneumatic actuator alone, without a solenoid valve. (See "electro-pneumatic.") Polymer A chemical compound or mixture consisting essentially of repeating structural units. Polymers with special elastic properties are called elastomers. Polyimide A high molecular weight polymer with high temperature stability (up to 375°C) and low outgassing at high temperatures. It is used for gate, bonnet, poppet and other seals. It absorbs large amounts of water when exposed to air. Thus it should be avoided in systems which are frequently cycled using room air. Poppet A gasket or O-ring carrier which moves the closure gasket or O-ring into position with the valve seat and transfers sealing force to the gasket or O-ring to effect a leak-tight seal. Qualified Valve A valve that provides full conductance. All Thermionics valves are qualified valves. Seat The portion of the body which is polished and aligned to provide the docking/receiving surface against or into which the gate or poppet seals. Stem The axial shaft in angle and inline valves connecting actuator and bellows assembly. Many valve stems rise as the valve is opened, while other valves may have a non-rising feature. Straight Through Valve This valve offers a line of sight valve opening (generally somewhat smaller than port I.D.) from inlet port to outlet port. It is a design particularly suited for metal closure seals. Tee Valve A valve with an extra port on the system side. It is useful for roughing manifolds. Teflon A trademarked (DuPont) elastomer (tetrafluoroethylene) with good chemical resistance. It is used for seals, gaskets, O-rings, and recommended for temperatures up to 300°C. It is permeable to helium. It has no melting point, but turns into an amorphous jelly above 327°C. Above 400°C, it decomposes, releasing poisonous fluorine volatiles. Venting of Valve Plate/Poppet Provision for venting of any gas which might be trapped in the seal groove by means of a pumpout opening. Viton A trademarked fluoroelastomer used for bonnet, gate, poppet, and other seals. It can be used for 250°C continuous service, and is useful for ultra-high vacuum systems.