Cylinders: The Basics and More

When hydraulic or pneumatic systems must produce linear motion, cylinders become their most important component by converting fluid pressure and flow to force and velocity.

The linear motion and high force produced by cylinders are big reasons why designers specify hydraulic and pneumatic systems in the first place. One of the most basic of fluid power components, cylinders have evolved into an almost endless array of configurations, sizes, and special designs. This versatility not only makes more-innovative designs possible, but makes many applications a reality that would not be practical or possible without cylinders.

The Basics

The most common cylinder configuration is double acting (Fig. 1). Routing pressurized fluid into the rod end of a double-acting cylinder causes the piston rod to retract. Conversely, routing pressurized fluid into the cap end causes the rod to extend. Simultaneously, fluid on the opposite side of the piston flows back into the hydraulic reservoir. (If air is the fluid medium, it usually is vented to the atmosphere.)

1. Cutaway view shows key features of a typical cylinder—in this case, a double-acting welded design for hydraulic service.

Because the area of the rod-end piston face is smaller than the cap-end area, extension force is greater than retraction force (assuming equal fluid pressures). Because total cylinder volume is less with the piston rod fully retracted (because of rod volume) than when it is fully extended, a cylinder retracts faster than it extends (assuming equal flow rates).

Single-acting cylinders accept pressurized fluid on only one side of the piston; volume on the other side of the piston is vented to atmosphere or returns to tank. Depending on whether it is routed to the cap end or rod end, the pressurized fluid may extend or retract the cylinder, respectively. In either case, force generated by gravity or a spring returns the piston rod to its original state. A hydraulic jack for vehicles represents a common application of a single-acting, gravity-return cylinder.

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Six Unique Challenges Of Subsea Cylinders

During recent decades the world has seen a decrease in coal mining, and many nations have raised concerns about the environmental impact of other types of land-based fuel sources. This has resulted in a move toward farming the sea for its rich energy sources— tidal energy, ocean energy and the piping of deepsea liquefied gas and oil. All of these resources need to be gathered with the greatest of care for the sake of the precarious oceanic environment and respect for the dangers that the oceans can pose for personnel working in these remote locations.

Fabrications placed on the seabed need to be durable and reliable to ensure the safety of personnel while avoiding any environmental disasters that could result from faulty machinery.

Highlighted below are six of the most challenging issues companies might face when producing hydraulics to be used within the subsea industry.

Remote locations

Many oil and gas wells are located off the coast of remote parts of Australia or South America, thousands of miles away from the cities where the hydraulic cylinders are manufactured. The main base is often an oil rig or floating LNG station many miles out in the sea. Beneath this base the fabrication being placed on the seabed can be hundreds of meters under water. The hydraulics used in these fabrications are among the most remote hydraulic systems in the world, and this means all hydraulic cylinders need to be precisely designed, manufactured and stringently tested to ensure they work the first time with no room for error. There is no scope for simply returning faulty machinery to the factory for repairs.

Read more: Six Unique Challenges Of Subsea Cylinders