Page 21 - dust collection systems

have permeability values greater than 50 ft/min (25 cm/s).
Permeability can be measured on clean or dirty bags. Dirty

bags are usually tested in the "as received" state. They are

then cleaned by vacuuming or washing and retested. These

measured values can be compared to the original clean

permeability of the fabric to determine if bags that have

been in service have become blinded. It is also possible that

the pores in the fabric will open wider after extended use,

which is shown by permeability values.

MIT Flex

The MIT Flex Test is used to measure the ability of fabrics to

withstand self-abrasion from flexing. This test method is

described in ASTM Standard D-2176-69.

The flex test has frequently been used to help determine the

rate of deterioration of fiberglass bags used in baghouses

installed on coal fired utility boilers.

Mullen Burst Strength

The Mullen burst strength test, described in ASTM Standard

D-231, is designed to show the relative total strength of

fabrics to withstand pulsing or pressure.

For new fiberglass fabrics, the Mullen burst test provides a

good indication of whether the fabric has been weakened by