Self-positioning volume slide control for screw compressor

A compressor including a slide valve assembly, the compressor having at least three phases of operation, including start-up, normal operation, and shutdown, the compressor comprising:

• a slide valve carriage;
• a volume slide valve member secured to the slide valve carriage and slidably movable longitudinally with respect to the slide valve carriage, the volume slide valve member having a first end and a second end, wherein the slide valve assembly does not include a controller connected to the volume slide valve member to cause movement of the volume slide valve member during normal operation of the compressor, and the volume slide valve member is self-positioning longitudinally with respect to the slide valve carriage based on a plurality of pressure forces exerted on the slide valve member;
• a capacity slide valve member secured to the slide valve carriage and slidably movable longitudinally with respect to the slide valve carriage;
• and
• a volume slide valve balance piston that abuts the first end of the volume slide valve member, the volume slide valve balance piston being connected to discharge gasses of the compressor and by a suction gas valve to suction gasses of the compressor;
• wherein the suction gas valve is closed during normal operation.

A method of operating a compressor having a slide valve assembly, wherein the compressor has at least three phases of operation, including start-up, normal operation, and shutdown, and the slide valve assembly includes:

• a slide valve carriage;
• a volume slide valve member secured to the slide valve carriage and slidably movable longitudinally with respect to the slide valve carriage, the volume slide valve member being self-positioning along the axis of movement;
• a capacity slide valve member secured to the slide valve carriage and slidably movable longitudinally with respect to the slide valve carriage, the capacity slide valve member being slidably movable by a controller to control compressor capacity;
• and a volume slide valve balance piston that abuts the first end of the volume slide valve member, the volume slide valve balance piston being connected to discharge gasses of the compressor and by a suction gas valve to suction gasses of the compressor;
• the method comprising:
• operating the compressor in the start-up phase, wherein the suction gas valve is open;
• operating the compressor in the normal operation phase, wherein the suction gas valve is closed;
• adjusting the position of the slide valve member by self-positioning of the slide valve member in response to unbalanced forces during the normal operation phase;
• and
• operating the compressor in the normal operation phase under balanced conditions where there are balanced forces acting upon the volume slide member.