Pneumatic And Hydraulic Equipment Page 403

SELECTING THE CORRECT MODEL SHOCK ABSORBER The Model type of an Enertrols shock absorber is determined by: n Type of accumulator-self-contained or external air/oil tank (AOT) n Method of piston rod return-spring, air, or mechanical Model and mounting selection are usually determined by the application. Self-contained models are generally preferred over the external accumulator-equipped models. They are pre-filled at the factory and ready to use when received. No external piping or other system components are required. Because Enertrols shocks stop a moving object in less time than non-linear decelerating devices, you should select a unit with the longest possible stroke that can be accommodated (without exceeding side-loading limits). This will minimize impact forces on the mounting structure and the moving object being stopped. ACCUMULATORS With internal accumulator models, the fluid displaced by the piston rod under impact is forced against a nitrogen-filled, closed-cell sponge in the body of the shock absorber. As the piston rod is returned, the sponge expands to help force fluid back into the high-pressure tube. Where conditions permit, internal accumulator models are preferred. Where more energy per hour (E 4 ), or heat dissipation is needed, as found in high duty-cycle applications, or high-temperature environments, external accumulator models should be used. The external accumulator is a tank or reservoir, either open or closed to atmosphere, BASIC MODEL DESIGNATIONS *Clevis fitting Type of Method of Model Accumulator Piston Rod Return Internal Spring SALD External Air (or Mechanical) ALD Internal Mechanical ALDA* External Spring ALDS Internal Spring (non-adjustable) SNALD External Air or Mech. (non-adjustable) NALD* Internal Spring (SILVERLINE) SASL External Air (SILVERLINE) ASL External Spring (SILVERLINE) ASLS Internal Mechanical (SILVERLINE) ASLA* that is connected to the shock absorber with appropriate size piping. The oil flows back and forth between it and the shock absorber, helping to cool the oil as the unit is cycled. The air/oil tank (AOT) of external accumulator- equipped models must be above the shock absorber and should be located as close to the shock absorber as possible. A 10-micron filter, installed between the exit of the air/oil tank and the shock absorber, is recommended. If the AOT must be located at a substantial distance from the shock use a positive oil recirculation circuit (Fig. 2A). Otherwise, oil may simply move back and forth in the lines and never reach the tank to be cooled. PISTON ROD RETURN The return of the piston rod is accomplished in one of three ways (spring, air/oil, or mechanically). Mechanical returns usually make use of clevis-mounting designs and may be operated by a lever arm actuated by some other moving part of the equipment. On self-contained models, or air/oil models with a spring, an externally mounted spring returns the rod when the load is removed. In external accumulator models, an air/oil system, or some other mechanical means, must be used to return the piston rod. ALD models permit a variable rate of rod return, time delay and/or lower rod return forces. This is accomplished by adding a pressure regulator (Fig. 2B) to the air/oil system, or by adding a 3-way valve and pressure regulator (Fig. 2C) to the system. ALDS models are shipped with a rod return spring installed. Thus, even when an external accumulator is used to improve heat dissipation, it need not be pressurized. The spring will provide the necessary rod return force. For best results, the accumulator should be vented to atmosphere with a filter/breather unit. Recommended air pressure for air oil tanks is 70-100 psi depending on the application. All mounting options for the Enertrols Gold Line and SILVERLINE Primary-Mount Series are shown here. From left to right they are: Front Flange, Clevis, Basic Primary unit, Lug (Foot Mount) and Rear Flange. FIGURE 2 2A 2B 2C E N E R T R O L Enertrols JHF Catalog [ Volume 7 ] (314) 427-0600 800-444-0522 (FAX) 314-427-3502 www. j hf.com 403 Prices Subject to Change Without Notice John Henry Foster pneumatic and hydraulic equipment

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