The three most common lines used in fluid power systems are pipe, tubing, and flexible hose. They are sometimes referred to as rigid (pipe), semirigid (tubing), and flexible piping. In commercial usage, there is no clear distinction between piping and tubing, since the correct designation for each product is established by the manufacturer. If the manufacturer calls its product pipe, it is pipe; if the manufacturer calls it tubing, it is tubing.

In the Navy, however, a distinction is made between pipe and tubing. The distinction is based on the method used to determine the size of the product. There are three important dimensions of any tubular product-outside diameter (OD), inside diameter (ID), and wall thickness. The product is called tubing if its size is identified by actual measured outside diameter and by actual wall thickness. The product is called pipe if its size is identified by a nominal dimension and wall thickness.

PIPING MATERIALS

The pipe and tubing used in fluid systems today are commonly made from steel, copper, brass, aluminum, and stainless steel. The hose assemblies are constructed of rubber or Teflon. Each of these materials has its own distinct advantages or disadvantages, depending upon its application.

Figure 9-50.-Types of flexible hose installations and fittings.

Steel piping and tubing are relatively inexpensive, have a high tensile strength, are suitable for bending and flanging, and are very adaptable to high pressures and temperatures. Its chief disadvantage is a comparatively low resistance to corrosion.

Copper and brass piping and tubing have a high resistance to corrosion and are easily drawn or bent. Pipe or tubing made from these materials is unsuitable for systems with high temperatures, stress, or vibration because they have a tendency to harden and break.

Aluminum has many characteristics and qualities required for fluid systems. It has a high resistance to corrosion, is lightweight, is easily drawn or bent, and (when combined with certain alloys) will withstand high pressures and temperatures.

Stainless steel piping or tubing is relatively lightweight and is used in a system that will be exposed to abrasion, high pressure, and intense heat. Its main disadvantage is high cost.