This post is a modified version of an article published in TechTalk by ANCORP, August 26th, 2020.
Vacuum bellows and flexible metal hoses are a common solution for applications involving prolonged vibrations and misaligned vacuum ports. Bellows are great for dampening vibrations, which can protect sensitive instrumentation, limit mechanical fatigue, and prevent loosening of bolt connections.
Hose Type
The most common hose types are hydroformed and PVC. Hydroformed hoses and bellows are inexpensive compared to edge welded hoses and provide sufficient flexibility for most applications. The hydroforming process involves using immense water pressure to form a single piece of metal or tube into a preset mold.
PVC hoses are a low-cost solution for rough vacuum and exhaust lines. These are ideal for corrosive applications and many chemical applications where metal is not suitable. PVC hoses feature a PVC covering around a metal coil that maintains structural integrity.
Wall Thickness
Most bellows feature a thin wall (starting at 0.006') that increases as tube O.D. increases. Bellows are recommended for roughing vacuum applications where maximum physical flexibility is desired.
Most flexible metal hoses feature a medium wall (starting at 0.008" or more) that increases as tube O.D. increases. The thicker the wall, the less flexible the hose will be.
Flange and Length
Flange type and overall length will vary depending on the specifications of your system. Common choices are tube end, CF, QF/KF/NW, LF (ISO), and ASA. Standard lengths range from 4-inches to 48-inches. The longer the length, the higher the flexibility, but also the lower the conductance.
PVC hoses can be connected to a flange using a hose adapter and a hose clamp. Stainless steel and aluminum hose-to-QF/KW/NW flange adapters
are commonly available.
Braided vs. Unbraided
A braided hose is an option that features metal braiding on the exterior of the hose. It provides protection for the medium wall metal hose from pressure, abrasion, impact and over-bending.
Conclusion: the choice with vacuum hose vs. bellows is mainly driven by the amount of space you have available, the mobility of the two things to be connected, and the amount of vibration and wear and tear the part will experience. Connecting a roughing pump to a blower stacked on top is best handled with a bellows. Connecting the exhaust of a pump to a scrubber, or a pump resting on the floor to a chamber, is typically handled with a vacuum hose.
Reference material:
ANCORP 2020 Vacuum Components Catalog (request a hard copy)
ANCORP 2020 Vacuum Components Catalog (download link)
ANCORP Roughing Components Brochure
IES Technical Sales ANCORP webpage
______________________________________________________________________________
IES Technical Sales is a manufacturer's representative and distribution firm located in Danvers, MA, and which represents ANCORP of Williston, FL in the northeast U.S.