TABLE OF CONTENTS The components of a pneumatic circuit are connected through lines. Today they are typically made of plastic tubes from nylon or polyurethane. The material is chosen to meet the required permissible pressure, bending radius, temperature etc. (see also M nzer and Mtiller-Lohmeier 2004). Copper tubes are used for heavy duty applications like actuation of process valves in chemical plants. For plastic tubes push-in fittings can be used which have a low resistance and the additional advantage that no tools are required to install or remove them.
When designing or analysing a circuit, different aspects may have to be studied: the steady-state resistance, the dynamic effects in a time domain simulation or the frequency response. The following subchapters give models for all three cases.
Major design criteria for long lines is the resistance. The ISO standard 4414 gives a table that bases the flow rates upon a 10 % pressure drop in 30 m of ISO 65 grade medium wrought iron pipe at 20 C (anon. 1998). Typical air velocity is between 10 and 40 m/s (Will and Str hl 1990:335; Stoll 1999:54), typical Reynolds numbers are between (Hennig 1982) 4 -10 3 ? Re ? 4 _10 6 , and the maximum pressure drop should be below 0.1 bar (Falkman 1975b:473 477).
Unless the lines are "long" they are typically not considered during the design or analysis of a pneumatic circuit. If necessary, their resistance,...
