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MAGM 262

Hydraulic Cylinders . Cylinders are basically linear actuators. Their outputs are straight line motion or force.The most common type of cylinders are single acting and double acting.The tubular housing is the cylinder body. Inside the cylinder body are the piston, piston seal and the rod.The bore

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MAGM 262

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    2. Hydraulic Cylinders Cylinders are basically linear actuators. Their outputs are straight line motion or force. The most common type of cylinders are single acting and double acting. The tubular housing is the cylinder body. Inside the cylinder body are the piston, piston seal and the rod. The bore refers to the inside diameter of the cylinder body The head end refers to the piston end of the cylinder. The rod end refers to the end from which the rod extends and retracts.

    3. Single Acting Cylinder The single acting cylinder is often used on vertical lift gravity return operations. The control valve directs oil to the head end of the cylinder. The oil pressure acts upon the piston to extend the rod and lift the load. Gravity acting on the load is used to retract the rod and lower the load.

    4. Double Acting Cylinder The most common of cylinders The National Fluid Power Association guidelines are used to standardize bore size, mounting styles, and overall dimensions. This allows cylinders to be interchangeable.

    5. Effective Area of a Cylinder The bore size refers to the inside diameter of the cylinder. A cylinder with a large bore size has a larger effective area. This in turn increases the cylinders available force for a given pressure but decreases its speed for a given flow rate. The rod side of the piston has less effective surface area. This decreases the available force for the same given pressure but increases the piston travel speed.

    6. Seals Different seals are used throughout the cylinder. The piston seal – designed so that pressure expands the seal increasing pressure against the cylinder wall improving sealing force. The head seal (o-ring) prevents oil escaping between the rod gland and the cylinder wall. The rod seal is a “U” shaped seal that prevents oil escaping between the rod and the rod gland and wipes excess oil from the rod as it extends out from the cylinder. The wiper seal is fitted to the cylinder and prevents dirt and grit from being drawn into the cylinder as it retracts. Seals are made of polyurethane, nitrile, or nylon. The material should be verified to be compatible with the fluid used and the operating conditions.

    7. Dampers When a moving cylinder runs into a dead end at the end of its stroke the concussion is called shock loading. Dampers (or Snubbers) are used to minimize or prevent shock loading. When the piston approaches full stroke, the damper moves into the return oil passage and restricts the return oil from the cylinder. This restriction causes an increase in the return oil pressure between the return oil passage and the piston. This oil pressure increase provides a cushion effect which slows the piston down and minimizes the shock that occurs.

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