An access probe for remote-sensing access through a viewing port, viewing volume, and access port into a vessel. The physical boundary around the viewing volume is partially formed by a porous sleeve lying between the viewing volume and a fluid conduit. In a first mode of operation, a fluid supplied to the fluid conduit encounters the porous sleeve and flows through the porous material to maintain the viewing volume free of ash or other matter. When additional fluid force is needed to clear the viewing volume, the pressure of the fluid flow is increased sufficiently to slidably translate the porous sleeve, greatly increasing flow into the viewing volume. The porous sleeve is returned to position by an actuating spring. The access probe thereby provides for alternate modes of operation based on the pressure of an actuating fluid.
The United States Government has rights in this invention pursuant to the employer-employee relationship of the Government to the inventors as U.S. Department of Energy employees and site-support contractors at the National Energy Technology Laboratory.