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Valves
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Q: What is a roughing port used for?
A: A roughing port on a gate valve provides an additional port to a vacuum chamber when all available ports are being used by other equipment. Since the path it provides is not straight, the typical application is to attach a flexible hose from a roughing pump to the port, hence the name. For more information, see Gate Valve Roughing
Port, Option-04, -05 and -06 on Gate
Valves Options section in the Technical Library.
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Q: Are "pneumatic" and "electropneumatic" the same thing or different?
A: In reference to MDC valves, both terms mean the same thing: pneumatic is simply a shortened version of electropneumatic. Pneumatic refers to the use of air pressure to operate a valve. The "electro" portion of electropneumatic means that electricity is used to direct the air pressure to make the valve either open or close. None of the MDC valves are operated entirely by electricity. All electropneumatic valves require both electrical and air service to operate.
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Q: What does "Air Open / Spring Close" mean?
A: Some of the smaller electropneumatic angle valves use air pressure to open the valve, but when the air pressure is removed a strong spring pushes the valve closed. Valves with ports larger than 2" would require a massive spring to close the valve and so use air to close the valve as well as open the valve. Those valves are "Air Open / Air Close".
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Q: Why can a gate valve be baked to a higher temperature with the gate open than with the gate closed?
A: As the temperature of the valve body goes up, the O-ring softens. If the O-ring softens while it is being compressed - that is, with the gate closed - and then allowed to cool under compression, the O-ring will form flats instead of returning to its original circular cross section shape. The flats will not seal as good as a circular shaped O-ring. To avoid developing flats on an O-ring, gate valves should be baked in an open position.
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Q: Can a leaky welded bellows be repaired?
A: No. It is extremely difficult to detect where a leak occurs in a faulty welded bellows and perhaps even more difficult to repair it - especially if the leak is on an inside weld. It would be more cost effective to replace a bellows with a new one.
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Q: What is the difference between a MESA valve and a MESC valve?
A: The only difference is in the name. MESA is the original name meaning Modular Equipment Standards Architecture, which has been replaced by MESC meaning Modular Equipment Standards Committee.
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Q: Why use a rectangular valve?
A: The main reason is to match the shape of the material being loaded through the valve into a vacuum chamber. Silicon wafers, CDs and DVDs are examples of the type of substrates for which rectangular valves have been developed.
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Q: What do the abbreviations "NO" and "NC" mean on valve drawings?
A: "NO" means normally open; "NC" means normally closed. The "normal" position for a valve is the position it is in at rest, with no electropneumatic actuation. An "Air Open / Spring Close" valve would be normally closed, since without any air pressure to open the valve, the spring would force the valve closed. Valves that are "Air Open / Air Close" can be set for either normally open or normally closed, depending on the user's requirements. "Air Open / Air Close" valves always have air pressure being applied to one side or the other of the air piston, unless the facility has a catastrophic failure where all electricity and air pressure is lost. Without activating the solenoid, if air is directed to the top of the air piston, the air pressure will hold the valve closed - this would be a normally closed configuration. If the air lines are reversed so that the air is directed to the bottom of the air piston when the solenoid is not activated, the air pressure will hold the valve open - this would be a normally open configuration. A user can switch the air lines when the valve is not in use.
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Q: What electrical requirements are necessary for actuating a solenoid?
A: The electrical requirements for a solenoid are up to the user and whatever requirements are specified. A label on the electrical coil portion (black section) of a solenoid state what the coil requires for actuation. This must match what electrical current the user's facility can provide. For the easiest match, the user should determine what current is available at his facility and provide those electrical requirements at the time of order.
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Q: Can a gate valve with metal seal port flanges have clearance holes rather than tapped holes?
A: Yes, but it would be a special order. The flanges would have to be mounted on a tubed neck in order to use the clearance holes.
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