Properly applied hydraulic cylinders provide outstanding linear-actuation performance in a wide variety of applications. But if applied improperly, a cylinder in short order may not only ruin itself but also the equipment on which it is installed.
There are fundamentally three categories of mounting styles. Both fixed and pivot styles can absorb forces on the cylinder’s centerline and typically include medium- and heavy-duty mounts for accommodating thrust or tension. The third category of fixed styles allows the entire cylinder to be supported by the mounting surface below cylinder centerline, rather than absorbing forces only along the centerline.
There are several available standardized mounts within these categories. Engineers can use this variety of mount offerings for an ever-widening number of application requirements. NFPA Tie rod cylinders, which are used in the majority of industrial systems, typically can be mounted using a variety of standard mating configurations from trunnion-style heads and caps to extended tie rod cap and/or head end styles, flange-style heads, side-lug, and side-tapped styles, a range of spherical bearing configurations, and cap fixed clevis designs. Most of these mounting options are available for both single-acting and double rod cylinders.
The goal of every mounting design is to allow the mount to absorb force, stabilizing the system and optimizing performance. For rods loaded primarily in compression (push), cap end mounts are recommended; for those in tension (pull), a head-end mount is preferred.
It is the amount of tension or compression that determines piston rod diameter; it is the amount of pull or push that determines the bore diameter. Other relevant factors to consider when selecting a mounting style include:
Cylinder motion (straight/ fixed or pivot)
Every mounting type comes with its own benefits and limitations. For example, trunnions for pivot-mounted cylinders are incompatible with self-aligning bearings where the small bearing area is positioned at a distance from the trunnions and cylinder heads. Improper use of such a configuration introduces bending forces that can overstress the trunnion pins.
Many performance expectations that at first appear to require atypical mounts can be accommodated by existing styles, sometimes with only slight modifications, facilitating replacement and reducing costs.
One key is to focus on factors that impact cylinder performance. These include the cylinder’s size and force relative to load, the working environment, mounting hardware, and options that prevent wear and improve efficiency. Manufacturers, such as Parker, generally categorize cylinders by the type of action and physical construction. They usually group linear action into these three categories, which directly impacts the mounting options:
Single-acting cylinders provide power only on the extension or "push" stroke. A separate force, usually an internal spring, returns the piston to its original position in preparation for the next stroke.
Reverse single-acting cylinders are similar to single-acting, but with the port on the opposite end to provide power only on the retraction or “pull” stroke.
Double-acting cylinders have dual pressure chambers and provide pneumatic power on both extension and retraction, eliminating the need for a spring.
Select the mounting style based on the cylinder’s size, force, and function. All these factors are necessary because the wrong mounting or improper installation can sideload the rod, which creates excessive wear on the piston, piston rod, rod bearing, and seals. With wear comes leakage, and that is how cylinders fail.
Regardless of how well a hydraulic cylinder is designed and manufactured, it can fail if not mounted correctly. Proper mounting avoids problems like side loads that cause excessive seal and bearing wear, or even bend the rod or bind the load.
Contact Parker’s Cylinder Division or visit www.parker.com/cylinder if you have questions regarding which mounting style is right for your application.
Article contributed by Jim Hauser, senior engineer, Parker Hannifin Corporation's Cylinder Division
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