When compressed hydraulic fluid engages a piston face and attached rod, it generates linear force and motion greatly surpassing the initial input force. Pumps and cylinders of this nature create tens of tons of work force from even small hydraulic cylinders. For this reason, these hydraulic devices and the pistons essential to their operation are vital to productivity in a number of industries. Hydraulic pistons are common in agriculture, construction, military, machining, automotive, oil and gas, aerospace and robotics industries among others.
In these applications the hydraulic pistons are designed to lift, turn, tilt, press, steer, pull and push heavy machine components and any attached loads. While the pistons and attached rods offer only linear motion, fittings attached to the exposed end of the rod allow for angular motion as well. With this heightened applicability, these mechanisms are found in such varied equipment as elevators, excavators, robotic arms, power steering, brakes, jacks and more.
Hydraulic pistons are composed of three main parts. The body, or face of the piston, is the cylindrical disc that fits precisely in the cross section of the cylinder barrel. Attached to the piston is the piston rod. This is the element that is housed partially within the barrel, but extends beyond the cylinder where the opposite end is attached to the machine components and work loads to be set into motion. The third and final component is the seal. There are actually several seals around both the piston face and rod.
The outer circumference of the piston is often machined with grooves where elastomeric or metal seals are placed. Seals, made of graphite, nitrile rubber, viton and other high temperature polymers, are also found around the cylinder head where the rod moves in and out of the barrel. These seals ensure that pressurized hydraulic fluids will not leak into, out of or from one compartment to another as this would cause a loss of pressure resulting in decreased functionality and productivity.
To further protect against leaks, all components of the hydraulic piston must be compatible with the specific fluid in use. Mineral, oil, ether or water composites are the most common solutions. Durable metals are often used to create the piston face and rod which must also withstand the wear of continued use and the friction inherent in movement.
Bronze, brass, steel, stainless steel, iron and nickel alloys are common materials. The cold-rolled rods are often chrome-plated for further protection before being attached to the piston body via threading or welding. Durable ceramics such as silicon carbide and alumina are sometimes used as well.