The 150/160 High Vacuum Bellows Sealed Valves come in an angle or inline body configuration. Since bellows are a critical factor in valve reliability, we incorporate formed bellows into our Series 150 valves. The first major advantage of using formed bellows is consistency. Since formed bellows do not have welds joining each membrane, there is no stress concentration and fatigue failure from non-uniform welds. The second advantage is that the bellows convolutions never touch completely in the compressed position. Many vacuum processes, like chemical vapor or thin film deposition contain particulate contamination. If small particles fall between formed bellows, they have no effect. If similar particles fall between welded, nested bellows, they deform the membranes, cause stress concentration, and lead to early bellows failure. An elastomer stem seal isolates the cylinder actuating pressure from the region within the bellows. The region within the bellows vents externally by grooves in the bonnet flange. If the stem seal fails, any air passing the seal would be vented harmlessly through these grooves. The vents also admit helium when leak checking the bellows. The nosepiece O-ring must be firmly retained, especially in a valve that opens to a pressure differential. Vents in the O-ring groove eliminate the possibility of virtual leaks caused by air trapped in the corners of the groove. A single acting cylinder opens the pneumatic valves up through the 3 inch size. When the cylinder is vented, a strong spring closes the valve. The spring within the bellows acts directly upon the nosepiece. Upon failure of the electric control voltage to the solenoid coil or upon failure of the pneumatic supply, the valve fails closed. Valves in the 4 inch size are available either without a closing spring, and have double acting cylinders. In all sizes the pneumatic cylinder is lubricated adequately for the service life of the valve.