These beds come with a flange on both ends.  They are NOT designed to be refilled.  However, it has been a common practice in the US for more than 20 years (with the older MC44 concentrators) to modify these beds for refilling.  This is not a complicated process but it does require some investment in terms of making a tool to help remove the end cap and also in fabricating a replacement end cap.  Below you can see the wooden jig we made to securely hold the sieve bed while we use an compressed air powered die grinder to cut into the flange.  First make a deep non-penetrating groove all around the flange, then penetrate in one location.  Use a strong pair of wire cutters to cut the flange in one location then use a pair of needle nosed pliers to peal the flange off.  As the wooden support are positioned to match the exact length of the sieve bed the cap stays in place despite the force from the spring.  Once the collar has been entirely removed you can carefully remove the sieve bed while holding in a vertical position so as not to loose any of the zeolite.  Keep the spring, disk and fabric to be used when refilling.

The DeVilbiss 525 concentrator uses as significantly smaller sieve bed with roughly half the volume of the 515.   The 525 sieve beds can be found in refillable and non-refillable versions.