'Live' steam and time provide the sterilizing for an autoclave. Generaly, the cheaper autoclaves do a time/ temperature cycle with a known level of water to provide the necessary level of steam with temperature and pressure to give a sterilizer cycle. Too much water during the cycle will result in too much steam(pressure will pop the safety valve) and damage the items being sterilized. Too little water will give low pressure steam at too low pressure to sterilize. A good autoclave will have a pressure relief valve(automatic) and a valve to vent pressure at the end of a cycle so the autoclave can be opened after the cycle is complete. So, your autoclave should have a valve to let out excess temperature (which results in excess pressure)/pressure. Can be a resetable or a rupture disc which has to be replaced after each overage. An input valve for additiion of water to fill to optimum level. and a manuel valve to relieve pressure before opening.