Pneumatic And Hydraulic Equipment Page 1041

MH SERIES-CUSHIONS AND PRESSURE Sheffer pioneered tapered cushions, designed to provide gradual deceleration and eliminate shock upon entrance of the cushion pistons, have now been considerably improved. The tapered cushion has been married with a fine thread, wide range, adjusting screw. This new combination offers a positive, low-shock deceleration and a method to adjust the cushioning effect for speeds and loads. The adjusting screw is identified by a tag affixed to the head (or cap) and can be further distinguished by a cross-slot in the head of the screw. It does not project beyond the surface of the head (or cap) through its full range of ad- justment so no clearance need be considered on close fit installations. The adjusting screw and the cushion check can be interchanged in the same cylinder end. This flexibility can be important if, after installation, it is discovered that the adjusting screw is inaccessible. The cushion check, which does not require adjustment, has a single slot in its head. It does not project beyond the surface of the head (or cap). The cushion check plus the tapered cushion piston provides rapid acceleration out of cushioning. There is no spring in the cushion check to fatigue, hence, no worry of mechanical failure. Cushioning is designed to properly cushion the cylinder and is not intended to cushion large inertia loads. Cushions do not substitute for speed controls or deceleration valves on most installations. As indicated in Fig. 1, the standard positions for ports are 1 and 5. Where possible, the standard positions for cushion adjusting screws will be 2 and 6 and the standard positions for cushion checks will be 4 and 8. With some mounting styles, it is not possible to so locate the adjusting screws and checks. For example, a Trunnion Front Mount has the trunnion pins located in positions 2 and 4 on the head. With the port in position 1, the only side available for both adjusting screw and check is position 3. Since both will then be located on the same side, they will be located off-center. This example would hold true with the TR, CL, FHF and RHF mounts. See Chart A for standard positions that will be supplied unless otherwise specified. When requested, other positions can be supplied so long as there is no interference with mounting. Where access to an adjusting screw or check could be made difficult because of proximity to a mount, the locations of the screws will be slightly off-center. An example of this would be a small bore cylinder with a side lug mount. Because of space limitations, neither cushion adjusting screws nor cushion ball checks can be put into 1-1/2" and 2", 2-1/2" bore sizes for cushioned front when they are specified with 2:1 rod diameters. POSITION DIAGRAM FOR PORTS, AIR BLEEDS, CUSHION ADJUSTING SCREWS AND CUSHION CHECKS 1 2 3 4 5 6 7 8 9 The chart below shows the recommended working pressures for MH Series cylinders by bore and rod diameters. Note that the column "Operating Pressure" is based on a 3:1 safety factor. It is felt that this is an adequate safety factor for any well designed hydraulic system where shock conditions have been considered and reduced to an acceptable level. The "Max. Shock Service" column is based on a 2:1 safety factor and SHOULD NOT be used to determine operating pressures. All values on the adjacent chart are based on the cylinder as a pressure vessel. Use of the proper mounting style to withstand the thrust generated must be considered. The following factors in shock loading should be considered: Relief valves in the circuit do not protect the components from shock because of the time lag. Gauges do not necessarily register shock conditions, either because of their location in the circuit, or the short duration of the shock. The two general types of shock loading to be considered are pressure rise caused by quick stop of the flow in the circuit and quick pressure drop. Decompression shock is particularly important in large bore cylinders and can be as destructive as compression shock. CUSHIONS CHART A. CUSHION ADJUSTING CUSHION MOUNT SCREW CHECK TF AND FHF 3 and 6 3 and 8 CL 3 and 7 TR AND RHF 2 and 7 4 and 7 ALL OTHER MOUNTS 2 and 6 4 and 8 Standard positions for cushion adjusting screws and cushion checks in relation to port positions by style of mounting. PRESSURE AND SHOCK MAXIMUM PRESSURE RATINGS OPERATING MAX SHOCK PRESSURE SERVICE PISTON 3:1 SAFETY FACTOR 2:1 SAFETY FACTOR BORE ROD BASED ON YIELD SIZE DIAMETER IN PSI 1-1/8 5/8 3,600 5,400 1-1/2 ALL 2,250 3,375 5/8 1,400 2,100 1, 1-3/8 2,450 3,675 5/8, 1 900 1,350 1-3/8, 1-3/4 1,550 2,325 3-1/4 ALL 1,400 2,100 4 ALL 925 1,390 1, 1-3/8, 1-3/4 675 1,000 BALANCE 1,075 1,600 6 ALL 800 1,200 1-3/8, 1-3/4 625 940 BALANCE 875 1,300 1-3/8, 1-3/4 475 700 BALANCE 675 1,000 8 7 5 2-1/2 2 SPECIFICATIONS CYLINDER WEIGHT CHART BORE 1-1/8 1-1/2 2 2-1/2 3-1/4 4 5 6 7 8 ZERO STROKE 3 6 8 11 22 30 45 70 85 100 ADD PER INCH OF STROKE .25 .35 .6 .9 .9 1.2 1.7 2.5 3 4 NOTE: The above weights are based on an average value for cushioning, rod side, and the various types of mountings for uncrated cylinders to establish approximate shipping weights. Add 10% of cylinder weight to determine estimated weight of crated cylinder. Fig. 1 S H E F E R Sheffer cylinders JHF Catalog [ Volume 7 ] (314) 427-0600 800-444-0522 (FAX) 314-427-3502 www. j hf.com 1041 Prices Subject to Change Without Notice John Henry Foster pneumatic and hydraulic equipment

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