A new acrylic can run you $250 or more by the time you add shipping, so I can see why someone would want to repair an acrylic if it is possible. I am not aware of anyway to seal a crack in an acrylic, but under many circumstances, you can stop a crack before it becomes a problem, as long as it is not in a place that poses a safety issue.

Most home tanning beds use the same acrylic in the bench and in the canopy of the tanning bed, and most of the cracks that happen to acrylics, do so to the bench since it takes all the stress. Often, you can just swap out the canopy and bench acrylics and just live with the crack in the acrylic. What you must avoid is lying on a tanning bed that has a crack in the bench: I have heard of a couple of cases of people actually getting pinched bad enough to need stitches due to a crack in the bench, so the risk isn’t worth it.

If you can put the cracked acrylic in the canopy and you want to prevent it from cracking any more, there is one trick I learned (of all sources) from guys who play drums in local bands. They sometimes get cracks in cymbals, which are very expensive, and they drill holes just passed both ends of the cracks to keep the crack from growing. This can be done, usually, with an acrylic in the canopy if you are very careful and take a few preventative steps.

Be forewarned: Drilling your acrylic to prevent a crack from growing can cause your acrylic to split and make the problem much worse! Even if you do everything right, there is no guarantee that you will not ruin the acrylic. If you do want to repair one, and you have the patience to do the job right, and the willingness to take a risk that you might make the crack worse, then it isn’t an overly difficult job. Before you run off and grab the drill, you want to read ALL this article, to prevent problems.

You should only try to use this method to fix short cracks, no longer than a foot and preferably shorter. You will need a drill, a new / sharp drill bit in 1/8th to 1/4th inch size, a block of scrap wood like a short 2 by 4. You will need to remove the acrylic that needs to be repaired and it MUST be secured down so it can NOT vibrate while you try to drill. If it can vibrate, it WILL crack more. This is the key.

Once you are done, you can GENTLY re-install the acrylic in the canopy and use the bed. You still have to be careful not to push the acrylic where the crack is, but it should save you the expense of a new acrylic for a few years.