Enertrols has a complete product line with over 60 standard shock absorber models with capacities from 25 to over 1 1/2 million inch-pounds per cycle. Most models can be equipped with internal accumulators as self-contained units, or equipped with external accumulators and air/oil tanks for maximum heat capacity. They are available in both adjustable and nonadjustable types in all of the basic standard mounting styles.
In addition, we offer industry a choice of primary or welded fixed-flange moutning models in most bore and stroke sizes. Special application models, such as our PROX SHOCK™ line equipped with position-sensing electronic proximity switches, the QCM™ (Quick-Change Mount) Models, Standard Long-Stroke Models and designed-to-order specials are also available.
Every component produced for Enertrols products receives inspection coverage to assure conformance with all the requirements, specifications and drawings of our products. Both management and manufacturing, as well as all other personnel, are in complete agreement that the reliability requirements of our shock bsorbers preclude any compromise in the quality of any component part.
Before beginning the mathematical calculations to determine the correct size shock absorber you need, Enertrols suggests first considering the Type, or Style, and options that will be best suited to your application.
These shock absorbers offer real mounting versatility. Stud mounting, in or through a threaded hole; universal mounting brackets, threaded on and locked anywhere on the body; and clevis-type fittings let you install these miniature units almost anywhere. Available in both adjustable (SALD) and non-adjustable (SNALD) models.
This larger series also features versatility of mounting through use of optional accessories that are threaded on either end of the shock absorber body and securely locked against a machined shoulder. Primary series units are heavily used in environments that require a number of different style mountings of the same basic bore size and stroke length shock absorbers.
Conventional fixed flange Enertrols shock absorbers have permanently attached flanges. They are ideally suited for use by cost-conscious OEM's using the same basic shock ab- sorber in large volume. Positive set-down positioning when changing units is a major feature of this type.
Enertrols shock absorbers are available in a number of mounting configurations to meet most any need. For fixed flange series you must specify front or rear mount flanges, which are available in square, rectangular, lug or clevis-type choices. Primary series do not require choice of front or rear mounting since you may thread flanges on either end.
Internal accumulators are the most widely used and permit immediate installation and use with no piping or fitting required. High cycle rates and/or extremely high energy requirements may require an external accumulator for cooling the oil by recirculating it outside the shock absorber body.
Spring return piston rods, used with internal accumulators, are the most common type. Air (or mechanical) returns, used with external accumulators, permit delayed rod return type installations where required.
Certain types of options should also be selected at this time. Positive Stop Collars, Mounting Stop Collars and Positive Stop Bars have been among Enertrols fastest growing options items. They provide a unique, tamperproof positive top that establishes an accurate work-positioning point These attachments also prevent impact damage that might be caused by bottoming the shock absorber piston. As standard, stock items, they also eliminate the cost to design and fabricate external pos ive stops into your system. Soft pads, molded polyurethane pads that snap over the hardened steel impact button of our shock absorbers, prevent marring of the object being stopped and help to reduce noise. On-board proximity sensors are available for most of the shock absorbers in the Enertrols line. They electronically signal the end-of-stroke, or home position, of the piston rod to control interlocking motions, devices, etc.
The Model type is determined by:
| INTERNAL Accumulator | |
| Spring | SALD |
| Mechanical | ALDA, Clevis fitting |
| Spring (non-adjustable) | SNALD |
| Spring (Silverline) | ASLS |
| Mechanical (Silverline) | ASLA, Clevis fitting |
| EXTERNAL Accumulator | |
| Air (or Mechanical) | ALD |
| Spring | ALDS |
| Air or Mech. (non-adjustable) | NALD, Clevis fitting |
| Air (Silverline) | ASL |
| Spring (Silverline) | ASLS |
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 shcok 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 (E4), 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, 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 l 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. Otherwise, oil may simply move back and forth in the lines and never reach the tank to be cooled.
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 or a 3-way valve and pressure regulator 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.
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. Consult your sales rep for the formulas required to size your shock absorber.
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 propellin 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 velocites are below 1 ft/sec and/or propelling force energy (F x S) exceeds 1/2 of the E value, as calculated. Or, you may want to use an Enertrols Silverline™ shock absorber if your requirements permit short-stroke models. If in doubt, contact your local rep, or the factory 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 absorbesr carry Effective Weight ratings. Ask your sales rep for details on the effective weight formulas.