Compressed Air Best Practices - October 2008 - (Page 58) | 10/08 Compressed Air Industry AUTOMOTIVE TRANSIT | REAL WORLD BEST PRACTICES APPLYING AIR HOSE AND QUICK DISCONNECTS FOR OPTIMUM PERFORMANCE The key to this success was measuring the end use workstation inlet pressure when equipment was idle and when working while simultaneously measuring the header pressure. If the header pressure stays steady, and the process inlet pressure falls, then the restriction is in the feed line from the header to the process. This example shows that the small compressed air hose was only part of the problem (12 psid), the other part (23 psid) was poor selection of quick disconnects. There are many types of fittings to connect hose to air supply and workstations and often, but not always, the “quick disconnect” is the best answer for overall productivity. Regardless of the fitting, the same rules apply — size the quick disconnect for the maximum expected flow and the allowable pressure loss if any. This performance data is available from all quick disconnect manufactures. “Air hoses. and quick disconnects both have the same best practice guidelines — do not select or apply them without all the data.” Some Quick Disconnect Guidelines p Never select by the connection size — select by acceptable performance at specified flow and entry pressure. If the plant wants to utilize the same quick disconnect on all processes for flexibility — do it!! But, be sure to size for the single largest flow demand in the plant at the lowest expected pressure. Remember, there may be two quick disconnects per feed and sometimes more. All larger quick disconnects should be of the style to shutoff the flow when disconnected to eliminate potential “hose whip.” This is a safety issue. There are exhaust type quick disconnects (meeting ISO 4414) available that not only shutoff air flow to control hose whip but also bleed off the trapped air inside the coupler/connection in a controlled pressure release. This eliminates blasting compressed air onto the operator at disconnect. Another safety issue. Of course it is also much easier to uncouple a depressurized quick disconnect. Quick disconnects should have proper safety latches, wires, keepers or be of the design that will not open when dragged over the ground, floor and/or machinery. p p p p p Do not assume because the couplers look to be similar in diameter, length and connection size that they are similar in performance. On a recent audit to help select the proper disconnect for a major tool operation, we ran pressure loss comparisons between two specific types of quick disconnect. A lock ring coupler with a ball check nipple and the exhaust type coupler with a standard nipple ñ these units all had the same size coupler body at 11⁄4" diameter and connections of 1⁄2" and 3⁄4". The lock ring type coupler utilized a ball check to shutoff the air in that direction. The exhaust type couplers have the full shutoff and exhaust to allow disconnect at zero pressure. 58 www.airbestpractices.com http://www.airbestpractices.com
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