If you’re putting together a holography table on a budget, chances are good you’ll be using inner tubes as the primary isolation medium.
Chances are also good that you’ll need to adjust the pressure in the tubes once everything is piled on top of them.
Here’s one method for extending the valves so you can adjust the pressure anytime you need to.
Drop by the auto parts store and purchase as many replacement stems as you need. Any size will do. Then drop by the hardware store and purchase some clear tubing that just fits over the end of the stem.
Cut away the bottom of the valve stem so that you have about 1/2" that can fit into the tubing.
Using a pair of needle-nose pliers, unscrew the the core. To do this, slip the tips of the pliers into the stem so that as you turn the pliers, it moves the core.
To speed things up, take a paper clip and use it to spin the core out. This is much faster than unscrewing the core all the way with pliers.
Once the core is completely unscrewed, you should be able to pull the core out of the stem. Should you ever need to rapidly deflate a tire, this is also a method to do that very quickly. Just bear in mind that the core may fly across the room if you don’t put something over the end of the stem to catch it.
Mix up some epoxy and spread it around the end of the replacement stem.
Push the stem into the tubing and smear some epoxy around the stem and tubing to provide a good seal.
Here are a couple of stems sealed and curing.
At the inner-tube end of things, smear some epoxy around the valve stem and push the other end of the tubing over it to seal that end.
Once the epoxy has cured you’ll have convenient extension to your inner-tubes that will allow you to fill the tubes any distance you need. Just remember to measure and cut the clear tubing appropriately.