Abstract: A sealed valve intended for use in ultrahigh purity applications uses a metal-to-metal seal in a crucial, but unacessible, portion of the valve. The metal-to-metal seal avoids the use of a weld which because of the location could not be adequately cleaned, and avoids the use of an O-ring seal. The O-ring seal typically would have a leak rate on the order of 10.sup.-7 standard cubic centimeters per second of helium, but the metal-to-metal seal provides a leakage rate of less than 10.sup.-13 sccm/s. In the preferred embodiment, the seal is formed by forcing a conical part into the opening of a bore. The force used is small emough to avoid permanent deformation of the sealing parts, and thus the seal can be opened and closed any number of times without degradation.

Abstract: In an ultrahigh purity sealed gas valve of the Y-type having a bellows located in a stem bore, a second seat is provided so that the seat seal engages the second seat to seal off the space within the bonnet tube and the bellows from communicating with the gas flow path, thereby preventing contaminating particles from the bellows from entering the gas system and also decreasing the dead space presented to the closed gas system by the valve. A purge port is located between the open and closed positions of the seat seal thereby permitting purging gas to bathe the sealing members and the bellows in both positions.