Hydraulic Cylinders

• Figure 1, Parts of a Hydraulic Cylinder
  
  Everyone is familiar with dump trucks, front loaders, excavators and other hydraulically operated equipment. A key component that makes all of these machines possible is the hydraulic cylinder. Hydraulic cylinders are the simplest, most compact and efficient means of producing high-powered linear motion. That is why they are used in such a variety of applications.
  
  

Parts of a hydraulic cylinder

• The basic components of a hydraulic cylinder are shown in Figure 1. The cylinder barrel is the part that houses the whole mechanism and connects all the parts together. The inside of the cylinder barrel is machined to a micro-smooth surface. The cylinder cap closes off and seals the nonmoving end of the cylinder. The cylinder head closes off the other end, but has an opening with seals that allows the piston rod to move in and out of the cylinder. The piston separates one end of the cylinder from the other and is the key component in converting hydraulic pressure into linear motion. The piston rod transfers that linear motion to whatever it is that the cylinder is designed to move. The end away from the cylinder is attached to the load. The two oil ports provide connections for the high-pressure hydraulic fluid and for returning unpressurized fluid to the hydraulic fluid storage tank.
  
  

Operation

• Figure 3, Dump Truck Operation Using a Hydraulic Cylinder
  
  The control valve determines which direction the piston will move by directing hydraulic fluid above or below the piston and allowing the fluid from the other side of the piston to return to the tank. The hydraulic piston and piston rod move up because the hydraulic fluid is being directed to the cylinder-side oil port in order to push up on the piston. The oil from the rod-side oil port is being directed back to the hydraulic fluid tank.
  
  

Applications

• Figure 3 shows a dump truck in its normal position and one dumping its load. This is one of the many applications for a hydraulic cylinder. Hydraulic cylinders are used in fork lifts, bulldozers, front loaders and construction equipment as well as airplanes, spacecraft, ships and advanced robotic arms in an assembly plant. They can be as small as 1-inch long, or big enough to propel an elevator. They lift, tilt, turn, press and steer equipment. They give low-riders their bounce and monster trucks their stability. There is no end to the many uses for this basic tool.