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Description
INO/ICAL pilot experimental set up is running at TIFR,MUMBAI . Large area glass RPC detectors are under test on a continuous basis. The detector stack has capacity of 12 glass RPCs of maximum 2m x 2m size , connected in parallel . RPCs are continuously purged individually, with gas mixture of R134a , Isobutane and Sulphur Hexafluoride at a steady rate of 6 SCCM to maintain one volume change a day. To economize gas mixture consumption and to reduce the effluents from being released into atmosphere, a close loop system has been designed, fabricated and installed at the INO Lab in TIFR. This is unit is running continuously for more than 4 years. The close loop gas re-circulation system uses a simple pumping system consisting of pneumatically operated positive displacement cylinders in tandem. The pressure control is achieved through fine bore capillaries by dynamic pressure loss. Pressure reducing valves are used as safety device . The pressure and flow rate in the loop is controlled by mass flow controllers and pressure transmitters. Pneumatically operated high purity valves control flow loops and isolate the detector stack in case of unsafe pressure transients. The control is achieved through Siemens 1214C series Programmable Logic Controller through its I/Os. Gas Leak rate of 5.7 X 10E-4 SCCM ,equivalent to leakage of less than 3 Litres of gas mixture every 60 days backfill interval, has been achieved . In the same interval nearly 520 Litres gas mixture has been recirculated. The efficiency is calculated at 99.4% . The pressure balance is maintained at differential of 2 millibar +/- 0.1millibar over 960 to 1010 millibar Absolute Atmospheric pressure. The performance and integrity of RPCs in the pilot experimental set up is being monitored to assess effect of factors such as periodic fluctuation and transients in Atmospheric pressure and temperature , room pressure variation , flow pulsations , uniformity of gas distribution and Power failures . Capability of Close loop gas recirculation system to respond to these changes is also studied. The conclusions from the above experiment are presented . Validation of first design considerations and subsequent modifications have provided improved guidelines for design of Engineering Module Gas system and Main Module gas systems.
