Compressed Air Best Practices - October 2008 - (Page 56) | 10/08 | AUTOMOTIVE TRANSIT REAL WORLD BEST PRACTICES APPLYING AIR HOSE AND QUICK DISCONNECTS FOR OPTIMUM PERFORMANCE p A 50' length of 3⁄8" and 1⁄2" hose weighs about 13 lbs. depending on grade and a 50' length of 3⁄4" hose weighs 22 lbs. The operator may or may not be trained as to what size hose is required to run the tool. p p There is no reason to run a “longer hose” than necessary to reach the worksite and offer appropriate maneuverability for the operator if required. We often see “extra hoses” rolled up — this just steals pressure. Cut the hose to the proper length and install fittings as needed. Often piping can be used to minimize the required hole length. OSHA safety requirements: Going from 1⁄2" to larger hose will require personnel to run with a mandatory automatic air shutoff valve or “safety velocity fuse.” They are an excellent safety device when correctly applied. Reference the following document: U.S. Department of Labor, Occupational Safety and Health Administration — Power Operated Tools 1926.302, page 2, paragraph 1926.306(6)(7) — the “safety velocity fuse” is required on all hoses exceeding 1⁄2" inside diameter. This will of course not be required on hard piping or metal tubing. Recommendation Pneumatic tools used in most plants are what we refer to as “industrial tools.” The attached flow charts and data sheets reflect premium black industrial air hose which points out several things: p 3 ⁄8" is not considered as a viable supply hose for industrial tools. The smallest “industrial” power tool hose recommended is 1⁄2". p p p Using vertical grinders as an example, they use the following flow (cfm) by hp class to determine approximate pressure loss. Obviously p ⁄2" hose in 50 ft. lengths is really only applicable to 1 hp or smaller tools, air motors, etc. (Approximately 30 cfm/hp). 3 ⁄4" hose is acceptable at 60–90 scfm flow (2 hp–3 hp) depending on the length of run. 1 An Actual Case Study More often than not, certain processes require a minimum pressure. These “requirements” should always be traced to their origin. Are they actual OEM specifications or simply the perception of an operator or supervisor? p p For long runs (more than 50'), run larger hose or pipe supported on the walls or ground as required to eliminate pressure loss. To allow the operators more comfortable and easier operation, an 8 ft. to 10 ft. “whip hose” can be added to the larger 3⁄4" or 1" main line which may well have minimal effect on the performance but still gives the operator the “feel” of the lighter hose. p Example At a recent plant audit the client ran the plant headers at 100 to 110 psig because a very critical hand tool grinding process “required 98 psig to run correctly.” According to the production supervisor, “My grinders need 98 psig to run properly. Therefore, the system should PRESSURE LOSS PSIG / 50 FEET CFM / 90 PSIG 1 WT 3 FT 3 ⁄2" ⁄4" 1 ⁄2" ⁄4" 1 HP 2 HP 3 HP 30 cfm 60 cfm 90 cfm 2.4 psid 14.89 psid 41 psid (Does not include fittings) .4 psid 2.2 psid 4.6 psid .27 WT 50 FT .44 13.5 lbs. 22 lbs. 56 www.airbestpractices.com http://www.airbestpractices.com
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