Metering device with screw pump

摘要

This disclosure relates to a metering dispenser which dispenses fluid in accurate proportion to the pump revolution speed, and to an improved shaft seal for the motor drive shaft of a metering dispenser. An elastic sleeve membrane is mounted inside an expanded area provided in a part of the peripheral wall of the pump casing so that a constant-pressure chamber is formed to the outside of this sleeve membrane, and the pressure inside the pump casing is maintained within a set pressure range by introducing a pressurized fluid into this constant- pressure chamber and releasing the pressurizing fluid from the constan- pressure chamber as needed. The improved shaft seal includes a circular channel formed at the center of the shaft seal, this circular channel and the aforementioned constant-pressure chamber being linked, and the internal pressure of the pump casing acting upon the pressure inside this circular channel via the elastic sleeve membrane of the constant-pressure chamber so that the pressure inside the circular channel and the internal pressure of the pump casing are always equal.