Pneumatics - Tanks

For example, let us say your air supply is giving air at around a rate of 100 litres/minute and you want to extend a cylinder at full speed. If the cylinder needs a flow rate of 150 l/min to extend at full speed (assuming a constant pressure) then obviously the rate at which your regulator is supplying air is too slow to achieve full speed extension. The way around this is to store some air outside of your supply which can be provided at a faster rate than the regulator could supply. Think of the buffer as a ballon. You need to take breaths to blow up a ballon (hence you have a slow flow rate) but the ballon can let the air out in one constant, much faster stream. So, you blow the ballon up, and then when you want to extend your cylinder, the air from the ballon is used rather than direct from your lungs. Your lungs can then re-fill the ballon at the pace they are happy with when there is more time.

The tank itself needs to be strong enough to hold air at your circuit pressure (typically 10bar) and probably needs to hold enough air for 2 extensions of your cylinder (if you want to keep the option of firing twice in quick succession). Typical tanks are either rodless cylinder cases (as seen in the picture above) or dry-powder fire extinguishers (which are cheap and lighter than CO2 ones). These can be bought from places such as auto shops and DIY stores where they are sold for home and car use. A connection will need to be made into the tank, but this can be done using pneumatic hose and epoxy resin. (Remove the original fitting and epoxy the hose into place. Then bake the unit to harden the epoxy). They can be lightweight because they don't need the huge strength of the main supply tank. You can also provide several tanks instead of just one. This allows flexibility when placing the tanks around the robot. Remeber though that thin powder tanks won't survive very long against an incoming axe - so don't place them somewhere too vunerable.