These modular assemblies are ANSI/ISA 76.00.02 compatible and control each stream by a double-block and bleed module to eliminate cross contamination and maintain sample integrity. Valve functions reside within a single, compact module and modules can be added or removed as needed. The systems feature an integrated flow loop to streamline sampling and purging and provide consistent outlet flow. Other features include vented air gap to help prevent mixing of pneumatic actuator supply and system fluid under pressure, visual and tactile actuation indicators, color-coded caps for easy identification of the process stream, inlet and outlet connections that are 1/8-in. female NPT or Swagelok MPC compatible (ANSI/ISA 76.00.02), and built-in pneumatic actuator for repetitive shutoff.