Double-Acting Telescopic Cylinders
In a standard Automotive Lift Repair Tampa Florida double-acting telescopic cylinder, extension occurs similarly to single-acting designs. However, retraction is made possible by sealing the piston area of each moving stage’s outer diameter with the inner diameter of the next larger stage and incorporating oil-transfer holes into each moving stage. These holes, located just above the pistons, facilitate oil flow into the smallest stage through a retraction port located at the top. This allows pressure to build in the volume between the two stages, generating the force needed to retract the smaller stage into the larger one.
Locating the retraction port on the top of the smallest stage simplifies the design of a double-acting telescopic cylinder. However, it typically necessitates an arrangement of hoses, hose protection, and reels to deliver oil to the moving stage. To prevent fluid power ports from being spaced too far apart when the cylinder is fully extended, many designs place both fluid ports in the smallest stage or plunger. This allows the cylinder to be mounted with the smallest stage stationary while the larger stages move during extension.
Cylinder size and the number of moving stages determine whether this design is feasible. Piston seals in double-acting telescopic cylinders are usually made from hard materials such as cast iron, ductile iron, or glass-reinforced nylon to minimize abrasion between the oil transfer holes and the ports.
Unique Combinations
Some unusual designs of Automotive Lift Repair Tampa Florida telescoping cylinders are intended for specific applications. For instance, a manufacturer of oil well equipment may use a type that combines single- and double-acting stages to position a work-over rig. This rig is transported horizontally to a site on a trailer, where telescopic cylinders extend to swing it into a vertical position. Once the work is completed, the cylinders pull the rig back to a horizontal position. However, once the rig starts to tilt, no additional pull force is required due to its weight, allowing gravity to facilitate retraction. This means hydraulic power is needed for the initial part of the retraction stroke, after which it operates as a single-acting unit.
In this design, the smallest moving stage is double-acting, while the others are single-acting, allowing the small stage to provide both push and pull forces. This type of cylinder may also be designed as a skip-a-sleeve design, where a stage is omitted to increase the effective area and retract force of the smallest sleeve or plunger. For example, a plunger diameter of 2.75 inches could fit into a 4.25-inch bore of a 4.75-inch sleeve, enhancing effective area and retraction force.
Constant Thrust and Constant Speed
A specialized Automotive Lift Repair Tampa Florida telescopic cylinder known as a constant-thrust/constant-speed cylinder is designed so that all moving stages extend simultaneously, ensuring constant speed and push force throughout the stroke, whether extending or retracting. This type of cylinder has been utilized to drive drill heads in underground mining, where such performance characteristics are essential, and space is limited. This more complex design achieves the desired action by trapping oil internally, matching extend and retract areas, and minimizing the number of moving stages.
Telescopic hydraulic cylinders, often referred to as multi-stage cylinders, are a type of linear actuator made up of a series of tubular rods known as sleeves. Typically consisting of four or five sleeves, these components gradually decrease in diameter and fit inside one another.
When hydraulic pressure is applied, the largest sleeve, known as the main or barrel, is extended first. Once the barrel reaches its maximum stroke, the next sleeve, commonly called a stage, begins to extend. This sequential extension continues until the final stage, known as the plunger, is reached.
There are two main types of telescopic hydraulic cylinders: single-acting and double-acting. Single-acting cylinders, which are the most prevalent, rely on gravity or another external force to retract the stages. When pressure is released, the load’s force pushes the hydraulic oil out of the system, allowing the cylinder to retract.
While Automotive Lift Repair Tampa Florida pneumatic telescopic cylinders do exist, hydraulic power is more commonly used, particularly for moving heavy loads. With a collapsed length that is typically 20-40% of the fully extended length, telescopic hydraulic cylinders are ideal for applications requiring extension in confined spaces. This extension capability allows for a longer working stroke compared to a single-stage rod-style actuator. Their ability to manage very heavy loads makes them popular in applications such as dump trucks, lifts, and garbage trucks.
Telescopic cylinders are a specialized design of hydraulic or pneumatic cylinders, as well as pulley systems, that provide an exceptionally long output travel from a compact retracted length. The collapsed length of a telescopic cylinder typically ranges from 20% to 40% of its fully extended length, depending on the number of stages. Some pneumatic telescoping units can have retracted lengths of less than 15% of their overall extended length. This compactness is highly appealing to machine design engineers when a conventional single-stage rod-style actuator cannot fit in an application that requires a specific output stroke.
Telescopic Cylinder Design and Usage
Heavy-duty Automotive Lift Repair Tampa Florida telescopic cylinders are generally powered by hydraulic oil, while lighter-duty versions may be powered by compressed air. These cylinders are also known as telescoping cylinders or multi-stage telescopic cylinders.
A common application for Automotive Lift Repair Tampa Florida telescopic cylinders is in the dump body of a dump truck on a construction site. To fully empty a load of gravel, the dump body must be raised to an angle of about 60 degrees. Achieving this long travel with a conventional hydraulic cylinder is challenging, as the collapsed length of a single-stage rod cylinder is approximately 110% of its output stroke. This makes it difficult for design engineers to integrate a single-stage cylinder into the chassis of a dump truck when the dump body is in a horizontal position. In contrast, a telescopic multi-stage cylinder can easily accomplish this task.
Design and Technical Specifications
Automotive Lift Repair Tampa Florida Telescopic cylinders consist of a series of steel or aluminum tubes with progressively smaller diameters, nested within each other. The largest sleeve is known as the main or barrel, while the smaller inner sleeves are referred to as stages. The smallest stage is often called the plunger or piston rod. These cylinders are typically mounted in machinery using pivot mounts that are welded to the end or outer body of the barrel and the end of the plunger.