The axle box guide moves in the lower spring seat filled with dashpot oil. The usefulness is also impaired if the internal dashpot is worn out. Approximately 1.5 liters of dashpot oil is required per guide arrangement. This dashpot provides the timing function. The design included some revolutionary features, foremost of which was the dashpot. Introduction of Hytrel washers was considered a breakthrough in the ICF dashpot design. The shock absorber usually consists of two parts&colon; a spring and a damper or dashpot. In some early aircraft the indicator was merely a pendulum with a dashpot for damping. This motion was smoothed by an oil-filled dashpot, one for each of the three servos. The process and instrumentation diagram (P&ID) symbol for a dashpot is . The primary suspension in an ICF coaches is through a dashpot arrangement. Some form of dashpot is usually used with a spring to provide viscous damping. In the dashpot arrangement, the top portion is called the axle box guide. Rate-dependence can be represented by nonlinear dashpot elements in a manner similar to viscoelasticity. The hydraulic cylinder in an automobile shock absorber is a dashpot.