The antipumping function is a very important feature of control circuits. Without the anti-pump function, if the user connected a maintained contact in the close circuit, and the circuit breaker were closed into a fault current, the protective relays would cause an immediate trip action, but the maintained contact in the close circuit would initiate closing (again) into the fault. This process is called “pumping”, and would lead to ultimate catastrophic failure of some element in the system, perhaps the conductors leading to the fault, perhaps the circuit breaker, or elsewhere in the system.
The anti pump relay is connected so that it seals in as long as the close signal is maintained. The anti-pump relay, when sealed in, opens a contact in the close circuit.
Thus, the circuitbreaker closes, but if the close signal is maintained, the close circuit has an open contact in the circuit, preventing further close operations as long as the close signal is maintained.
This relay can bee see as K0 in closing coil circuit in wiring diagram picture and you see the relay at the bottom.