The batch digester opening at the top is either closed with a capping valve or a manual system using a blank may be employed in older mills. Replacing the manual blank with an automated capping Stargate-O-Port-Valve^®, which is interlocked with a pressure switch, prevents opening of the digester before the pressure is below a certain set-point, typically .5 psi at the end of the cooking cycle.

The diagram below shows a filling system for a batch digester. The system consists of a Stargate-O-Port-Valve^®. The side plates and the blade are shown to represent the Stargate-O-Port-Valve^®.

A new method of faster filling uses two elements: The first element of the assembly is the extended spool piece which in the extension consists of 3 parts; a part at the top, a portion in the length of the blade thickness and a lower part reaching down into the digester. This extended spool piece is called the filling tube. The lower portion of the filling tube has a double wall forming an inside chamber. Below the lower side plate of the capping valve a pipe penetrates the inner chamber, which allows the inner chamber to be filled with steam. The lower end of that inside chamber has angled outlet nozzles, which allow the steam to have a swirling action, wetting the wood chips, and settling the chips in a tighter packing in a more even distribution over the diameter of the digester. This allows filling more wood chips into the digester. The steamed chips are also wetted better and consequently penetrated better by the liquor. A 10 % higher tonnage can be achieved.

The second element of the assembly is the outside jacket of the filling tube. This outside chamber is connected to a suction fan, which creates a slight vacuum in the digester. The evacuated gases can be treated to prevent air pollution from the remaining gazes from the previous cook in the digester. The vacuum in the digester also allows the chips to fall into the digester faster because there is no draft of air flowing against the chips. Users of these evacuation systems claim a 15 % higher tonnage.

With the automation of the process uniform, high quality pulp can be manufactured preventing overcooking or undercooking of the chips.

Fast filling is one aspect of the Big Cap™ valves. The other even more important aspect is safety.

The Big Cap™ valves are equipped with a pneumatic locking device. This locking device locks the valve in the closed position. From the distance one can see whether the locking device is engaged. Additionally indicator lamps at the DCS, activated by limit switches on the locking device, show whether the locking device is engaged or disengaged.

The disengaging of the pneumatic locking device is to be interlocked with a pressure switch measuring pressure in the digester. Once the pressure is below a set point, usually 0.5 psi the solenoid for opening the locking device can be energized.

The opening respectively closing of the Big Cap™ valve should be a separate step in the cooking program, separate from the disengaging respectively engaging of the locking device. Only once the “Locking Device Open” position is reached and a second pressure switch in the digester indicates less than 0.5 psi in the digester the solenoid valve opening the Big Cap™ can be energized.

Both solenoid valves are single coil valves, which would “fail closed“ the Big Cap™ and the locking device in case of power failure. The normally closed contacts on the pressure switches are used to interlock the solenoids. These sets of contacts open when more pressure than the set point of .5 psi exists in the digester.

There is a redundancy in this system of controlling the opening of the digester, but it is safer to have the opening of the digester interlocked twice and independently from each other and based on two pressure switches. In case of failure of one of the pressure switches it is impossible to open the Big Cap™ valve accidentally because of the interlocking of the other switch and the mechanical lock through the mechanical blocking by the pneumatic locking device. In fact, in case of a failure of the valve actuator pressure switch an air pressure of 125 psi can be applied to the actuators without damage to locking device.

The blade of the valve protruding from the long end of the valve body with the locking device engaged allows seeing from the distance whether the valve is closed.