Its outgassing rate makes rubber hose useful only in forelines. The tube must have sufficient wall thickness, or be internally reinforced with a spiral wire, to stop it from collapsing under vacuum. The presence of a plasticizer limits the ultimate pressure inside the PVC tube and confines its use to forelines. As with rubber, PVC needs internal reinforcement when evacuated. Never bakeout PVC tube.
Silicone is also very porous to helium.
The leakage tolerance for vacuum systems is lower than for pressure seals. Multiple O-rings are useful in a vacuum seal. Viton is a registered trademark of DuPont Dow Elastomers. Copyright 2000 Cahners Business Information , A Division of Reed Elsevier, Inc . Privacy Policy .