Abstract: In an acid digestion reaction performed in a vessel, an elastic lid or septum can be mounted to the mouth of the vessel with a flanged band. In response to determining that a predetermined pressure has been reached in the vessel, a closing force being applied to the lid or septum can be reduced to initiate venting from the vessel. One or more parameters, including the closing force, can be monitored during the venting, and the closing force can be responsively adjusted to optimize the venting. The closing force can be provided by a clamping apparatus that may or may not include a hydraulic system. The clamping apparatus can be configured to increase the closing force in response to increased hydraulic pressure in the hydraulic system. The clamping apparatus can include an engager having an upwardly extending recess extending at least partially around a downwardly protruding portion of the engager.