I want to install an EJ that was designed for 6.3" compression in an application that requires 4" extension. If I precompress the EJ by 4" for installation so it can expand back to its free length in service, how do I specify the spring rate? At free length the spring rate is 235 lb/in and with 4" of precompression the force it applies to the pipe is 940 lb but it goes to zero after 4" of extension in service back to its free length. The pressure force would still be present. I tried to enter a negative number for the spring rate but CAESAR II won't accept that. Thanks for any help.