Are you talking about the hydraulic auto belt tensioner? usually they are put into a large vise and the vise will compresse the tensioner down real slowly. The vise will compress it but not quickly. There is usually a small pin hole where a thin steel pin is inserted and this holds the piston in check until it is placed on the engine then the belt is installed and then the pin is removed and the piston will then come out and make tension to the belt. This is how it works on most cars. Hope this helps.


