primary compounds used for wear bands are filled PTFE, woven fabric reinforced polyester resin, and bronze Other parts There are many component parts that make up the internal portion of a hydraulic cylinder. All of these pieces combine to create a fully functioning component. Cylinder base connection Cushions Internal Threaded Ductile Heads Head Glands Polypak Pistons Cylinder Head Caps Butt Plates Eye Brackets/Clevis Brackets MP Detachable Mounts Rod Eyes/Rod Clevis Pivot Pins Spherical Ball Bushings Spherical Rod Eye Alignment Coupler Ports and Fittings Single acting vs. double acting Single-acting cylinders are economical and the simplest design. Hydraulic fluid enters through a port at one end of the cylinder, which extends the rod by means of area difference. An external force, internal retraction spring or gravity returns the piston rod. Double acting cylinders have a port at each end or side of the piston, supplied with hydraulic fluid for both the retraction and extension. Designs There are primarily two main styles of hydraulic cylinder construction used in the industry: tie rod-style cylinders and welded body-style cylinders. Tie rod cylinder Tie rod style hydraulic cylinders use high strength threaded steel rods to hold the two end caps to the cylinder barrel. They are most often seen in industrial factory applications. Small-bore cylinders usually have 4 tie rods, and large bore cylinders may require as many as 16 or 20 tie rods in order to retain the end caps under the tremendous forces produced. Tie rod style cylinders can be completely disassembled for service and repair, and they are not always customizable. The National Fluid Power Association (NFPA) has standardized the dimensions of hydraulic tie-rod cylinders. This enables cylinders from different manufacturers to interchange within the same mountings. Welded body cylinder Welded body cylinders have no tie rods. The barrel is welded directly to the end caps. The ports are welded to the barrel. The front rod gland is usually threaded into or bolted to the cylinder barrel. That allows the piston rod assembly and the rod seals to be removed for service. Welded body cylinders have a number of advantages over tie rod-style cylinders. Welded cylinders have a narrower body and often a shorter overall length enabling them to fit better into the tight confines of machinery. Welded cylinders do not suffer from failure due to tie rod stretch at high pressures and long strokes. The welded design also lends itself to