API 688 is a standard published by the American Petroleum Institute (API) that provides guidelines for the design, fabrication, testing, and documentation of reciprocating compressor valves. The standard is titled "Reciprocating Compressors for Natural Gas and Gasoline Service".

Unfortunately, API standards are not freely available for download. The American Petroleum Institute (API) sells its standards, including API 688, through its website or through authorized distributors. However, you can purchase the standard or obtain a copy through a library or subscription service.

In conclusion, API 688 is a standard that provides guidelines for the design, fabrication, testing, and documentation of reciprocating compressor valves. While a free download of the standard is not available, you can purchase a copy or access it through subscription services or libraries. By following API 688 guidelines, compressor valve manufacturers can ensure that their products are reliable, efficient, and safe for use in various applications.

The primary purpose of API 688 is to provide a standardized framework for the design, testing, and documentation of reciprocating compressor valves used in natural gas and gasoline service. The standard aims to ensure that compressor valves are reliable, efficient, and safe for use in various applications.