In a previous blog I wrote about how to protect the bottom of your tank liner by using a rigid plastic shield system. Another method of protecting a drop in liner is to make a double bottom on the liner.
Using the same material that the PVC liner itself is made from a second, or false bottom, is attached to the liner. This second bottom is spot welded to the sides of the liner one to two inches from the bottom of the liner proper. Spot welding allows for solution to pass under the false bottom and provides a hydrolytic cushion to help stop falling parts from damaging the bottom of the liner.
The advantage to this system versus the rigid sheet concept is that the protective bottom is already built into the liner making it easier to install. The disadvantage is that the level of protection isn’t as great as the rigid sheets and when replacing the liner the double bottom has to be purchased again.