Reciprocating Compressor M Series
2-5
2.1.4 Unloader Mechanism
Fig. 2-9 Unloader mechanism
The capacity control (unloader) mechanism controls the operation of suction valve using unloader pistons. By
controlling the operation of the suction valve, it changes the number of cylinders which compresses gas to
change the suction capacity (performance).
The details of mechanism are as below.
z The suction valve (suction valve plate) are attached on the top of cylinder sleeve (flange). Gas enters
into the cylinder from the passage between the external and internal seats. A lift pin which moves
upward and downward is installed in the gas passage at the center of these seats. The top side of lift pin
contacts the suction valve. The bottom of the lift pin is on the inclined surface of a cam ring on the
cylinder which rotates.. This cylinder cam ring is rotated by the rod which is moved by the unloader
piston. This rotation moves the lift pin upward and downward.
z If the lift pin is moved downward to below the seating surface, the suction valve (suction valve plate)
operates depending on the pressure difference. However, when the lift pin pushes up above the seating
surface by the rotation of cam ring, the suction valve does not close even if pressure difference is
generated. In this state, even though the piston moves upward and downward in the cylinder, the gas
only passes in and out from the suction opening. Due to this, the pressure does not increase and the gas
is not discharged. At this time, this cylinder is in the unloaded state. As described above, this
mechanism controls the capacity by changing the number of cylinders which compresses gas.
z The cam ring is moved by oil pressure and the spring. If the unloader piston is not pressurized by oil, it
will unload by the force of the spring. Therefore, the capacity can be controlled by cutting off the oil
pressure during machine operation. This is performed by a three-way solenoid valve.
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