SHAFT SEAL PROTECTING DEVICE

PURPOSE:To prevent generation of a back pressure through very simple structure by providing a bypass circuit running from the shaft seal liquid outlet side of a shaft seal device body to the shaft seal liquid inlet side through a pilot check valve, a pressure uniformizing pipe, and a high pressure priority type shuttle valve. CONSTITUTION:A shaft seal device (shaft seal chamber) 1 is used for the purpose of preventing leakage of the internal pressure of an agitating tank 2 to the outside and shaft seal liquid is usually pressurized and circulated by means of a pressure unit 3. A pressure in the tank is increased by means of a pressure in the shaft seal chamber 1. When a pressure produces a back pressure, a pressure in the tank is transmitted through a pressure uniformizing nozzle 4 and a check valve 5 to a pressure uniforming pipe 6, and progresses through shaft seal liquid 7 to circuits (g) and (f). Since the pressures of circuits (g) and (a) are (g) > (a), a high pressure priority type shuttle valve 8 closes the circuit (a) side, and the circuit (g) is connected to a circuit (b). A pressure that has progressed to the circuit (f) is progresses through a circuit (j) or (h), but return to a pressure unit 3 is cut off by means of high pressure priority type shuttle valves 9 and 10.