PURPOSE: To prevent the deterioration of volume efficiency in a force feed pump, vibration of a transport pipe system, and an overflow of slurry from a hopper.

CONSTITUTION: An S-shaped swinging pipe 1 capable of swinging with the axis O of a transport pipe as it center is arranged in a gate housing 2, and a hopper is arranged above it. A cocoon-shaped plate 1' is formed in a shape running along a swinging locus of a cylinder side opening end part of the S- shaped swinging pipe, and an opening part 1'-3 is arranged in the central part, and the cylinder side opening end part of the S-shaped swinging pipe is installed in a central part of the cocoon-shaped plate. Parts 1' 1 and 1'-2 are formed in both side parts of the cocoon-shaped plate 1' so as to open a delivery and suction side end part of a force feed cylinder in the gate housing when the S-shaped swinging pipe swings in one direction and is connected to the force feed cylinder as well as to open the delivery and suction side end part in a gate when it swings in the other direction and is connected to the force feed cylinder.