Son of Food posted the following to the "Comments" of the last post. The info is too good to be hidden away there, so I am posting it here on the front page. This information is for a whipper like this one, the iSi Gourmet Whip.
I did figure out my whipper problem from Thanksgiving, I wasn't taking the charger off before spraying. I had never actually seen one of these in action before. A bit of youTube reference revealed the secret. The following information gives us so much more to work with. Thanks, Son of Food!
Just checking in. So what you need to do, first, is be sure the canister isn't filled above the fill line, which should be 16 oz or 500ml for a 1 pt. whipper. I usually mix whatever I'm whipping in a measuring cup to be sure. The liquid shouldn't have lumps that might clog the dispenser, so strain if you're making something like avocado foam.
Attach the lid with a tip attached. Charge the canister by putting a cream cartridge (nitrous oxide) in the charging cylinder and screwing it in place, shake it up, and remove the cylinder. Don't shake too much. It may only need two or three shakes.
You can also make soda in the Gourmet Whip using soda chargers (CO2), but don't use soda chargers for things other than fizzy liquids, or they will create carbonic acid that will impart an undesirable flavor to things other than fizzy drinks.
To dispense the cream, hold the canister upside down, shake once to move the contents down toward the dispensing tip, and push the trigger slowly so you'll have some control over how much comes out. You can change tips once the whipper is charged. If you hold the canister with the tip up, the gas will be released, and the cream will be stuck in the canister, just like with a can of Redi-Whip.
Here's a website with some useful suggestions--
There are some good videos as well on starchefs--
This is an excellent collection of foam recipes in Spanish by Ferran Adrià, some of which appears in English translation on the isi site linked above--
This site has a compilation of recipes using hydrocolloids, including many foams that can be prepared in a whipper--