Pneumatic And Hydraulic Equipment Page 404

There are a number of factors that must be considered when selecting a hydraulic shock absorber. First, determine how much energy must be dissipated during each deceleration stroke (cycle). Second, find the total amount of energy that must be dissipated during one hour of operation. Third, be sure to consider the Effective Weight of your application. The formulas used to determine the amount of kinetic energy per cycle are derived from the equation KE = 1/2MV 2 . When used in the form KE = 0.2WV 2 , the equation yields an answer in inch-lbs that can be correlated directly to the shock absorber Energy Rating Chart. A moving object's energy will always consist of either pure inertia, or a combination of that inertia and a propelling force. BASIC FORMULAS E 1 = 0.2 WV 2 (or W x H for free-falling objects) in.-lbs. E 2 = F x S (or W x S for free-falling objects) in.-lbs. E 3 = E 1 + E 2 in.-lbs. E 4 = E 3 x C (cycles/hour) in.-lbs./hr. V = 5.36 x H determines velocity of free-falling object-ft./sec. g = .2 x V 2 S to determine G force, or stroke (S) V = Dis in Feet t to determine impact velocity when weight is moving at a constant speed over a distance-ft./sec. V = 2 x Dis in Feet t to determine impact velocity when weight is accelerating over a distance from a stopped position-ft./sec. F = D 2 x 8 x PSI to determine cylinder force in pounds F = 1375 x HP V to determine Propelling Force in pounds when using an Electric Motor t = S 6 V stopping time through stroke ENERGY CALCULATION SYMBOLS t = Time in seconds S = Shock absorber stroke in inches R S = Radius to shock absorber in inches R C = Radius to cylinder in inches K = Radius to center of gravity (c.g.) V = Impact velocity in feet/second g = Deceleration in G's D = Diameter in inches Dis = Distance in feet W = Weight in pounds (lbs.) W E = Effective Weight (lbs.) H = Height in inches (in.) F = Propelling Force (lbs.) C = Cycles per hour E 1 = Inertial energy (in.-lbs/cycle) E 2 = Propelling Force energy (in.-lbs./cycle) E 3 = Total energy per cycle E 4 = Total energy to be dissipated per hour PSI = Pressure (pounds per square inch) HP = Horsepower T = Torque (in.-lbs.) L = Distance (in.) EFFECTIVE WEIGHT The determination of Effective Weight has become an important factor in correctly sizing a shock absorber. Effective Weight will indicate if the shock absorber can be adjusted to perform properly. It prevents improper selection (over or under sizing) where propelling forces are involved, or velocities are very low or very high. A rough "rule of thumb" frequently used is to select the next larger bore size when impact velocities are below 1 ft/ sec and/or propelling force energy (F x S) exceeds 1/2 of the E 3 value, as calculated. Or, you may want to use an Enertrols SILVERLINE TM shock absorber if your requirements permit short-stroke models. If in doubt, contact John Henry Foster Co. for additional sizing information. However, high Effective Weight generates high set-down force at the end of the shock absorber stroke. Low Effective Weights can cause very high impact forces at the beginning of the stroke. These conditions must be considered for they may lead to severe damage over a period of time. All Enertrols shock absorbers carry Effective Weight ratings. Effective Weight is calculated using the equation: As an example of how to calculate and use Effective Weight in sizing an Enertrols shock absorber, consider the following examples: From the Rating Chart, select an Enertrols Model SALD 2 x 8 shock absorber. This unit will handle the energy per cycle and energy per hour requirements of the application. It also meets Effective Weight requirements. Following are a variety of examples selected to represent the most widely used installations of Enertrols shock absorbers. Although the calculations may look formidable at first glance, they are actually quite simple to use. When you have a new application, just substitute your numbers in the example that comes closest to your own. If you think you need additional help, contact John Henry Foster Co. There is no obligation. (W) WEIGHT FALLING HEIGHT STROKE (V) VELOCITY Calculations: E 1 = W x H = 1800 x 40 = 72,000 in.-lbs. E 2 = W x S = 1800 x 8 = 14,400 in.-lbs. E 3 = E 1 + E 2 = 72,000 + 14,400 = 86,400 in.-lbs E 4 = E 3 x C = 86,400 x 200 = 17,280,000 in.-lbs/hour W E = = = 2,160 lbs. E 3 H 86,400 40 V = 14.6 feet/second = 5.36 x H = 5.36 x 40 EXAMPLE 1 Vertical Free-Falling Weight W = 1800 lbs. H = 40 inches C = 200/hour S = 8 inches* *Selected stroke SELECTING THE CORRECT SIZE SHOCK ABSORBER W E = or E 3 0.2 V 2 E 3 H { for free-falling objects Enertrols (314) 427-0600 800-444-0522 (FAX) 314-427-3502 www. j hf.com JHF Catalog [ Volume 7 ] 404 Prices Subject to Change Without Notice John Henry Foster pneumatic and hydraulic equipment

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