5.6　Compressor Cylinders and Connections

5.6.1　The compressor cylinders shall be in accordance with 6.8.1 and 6.8.2（excluding 6.8.2.2 and 6.8.2.6）of API Std 618-2007.

5.6.2　Unless otherwise specified in the data sheets or technical requirement requisition，cylinders shall be of horizontal and double acting design.Top suction and bottom discharge shall be provided，for compressing saturated gases or gases carrying injected flushing liquid.

5.6.3　Hands operating variable volume clearance pocket should not be used.

5.6.4　All cylinders shall have removable dry-type liners without contacting with cooling media.The liner shall be at least 9.5mm thick for piston diameters up to and including 250mm.For piston diameters larger than 250mm，the minimum liner thickness shall be 12mm.The liners shall have an interference fit，and shall be held in place by other positive mechanical means.

5.6.5　When non-metallic wear bands and piston rings are used，the inside surface of liners should be coated with PTFE or other measures.

5.6.6　Cast aluminum，fabricated steel pistons should not be used when the power is above 375kW per cylinder.

5.6.7　Cylinder heads，stuffing boxes for pressure packing，clearance pockets and valve covers shall be fastened with studs.The design shall make it unnecessary to remove any studs when removing these component parts.

5.6.8　Torque values for all studs shall be included in the vendor's installation and maintenance instruction manual.

5.6.9　Where captured O-ring type valve covers are used，two extra-long studs 180 degrees apart shall be provided for each cover.Extra-long studs shall be capable of having a full-threaded nut when the O-ring is clear of cylinder valve-port sealing bore.

5.6.10　Valve cage designs shall be of the cylindrical type held in place by a circular contact cover.Center-bolt or other through-bolt designs shall not be furnished.

5.6.11　All the piping connections or openings on compressor cylinders shall be flanged.Thread connections for piping sizes not exceeding DN20 may be used with purchaser's approval.

5.6.12　Flanges shall conform to ASME B16.1，B16.5，B16.42 or B16.47，as applicable，and may also conform to GB/T 9115，SH 3406 or HG 20615.When other standards are applied，the approval of the purchaser is needed.Specific flange standards，pressure ratings and types of flange facing shall meet the requirements on the data sheets.

5.6.13　All piping connections size on cylinders shall be DN20（ NPS）or larger.Size DN32，DN65， DN90， DN125， DN175 and DN225（ NPS， NPS，NPS，5 NPS，7NPS，and 9 NPS）shall not be used.