The capsule won't be over-ranged thanks to a technology called a three-valve manifold. It also enables the transmitter to be cut off from the process loop. Two block valves—a high pressure and low pressure block valve—along with an equalising valve make up this device. In order to maintain equal pressure on both sides, one equalise valve is positioned between the high and low transmitter process connections and two block valves isolate the instrument.
The two block valves are open and the equalising valve is closed when everything is operating normally. The valves must be operated when the transmitter is placed into operation or taken out of service so that excessively high pressure is never applied to just one side of the DP capsule.