Production and isolation valves are often included in a TCP string for the following applications:

• Run a completion or testing string containing a lighter column of fluid to create an underbalance when perforating
• Avoid difficulty in establishing the required underbalance before perforating where they are existing perforations or leaks below the packer
• Keep the tubing string sealed and enable the use of pressure-set packers, tubing hangers, and other pressure-operated tools such as TCP firing heads
• Keep high pressure away from the casing until perforating is completed for operations with extreme overbalance