الفهرس 
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Abstract
The present work is dealing with studying experimentally and theoretically a phenomena called jerky motion. This intermittent phenomena is associated with the descending of high inertia loads carried by hydraulic equipment. Pilot operated check valves are used to hold the load position to avoid load creep due to leakage in the hydraulic circuit. In practice, pilot control counter balance valve is used instead of pilot operated check valve to overcome the jerky motion. Therefore, the present study is concerned with the experimental as well as theoretical study of the performance of the hydraulic system using both types of valves one at a time.
A mathematical model is deduced for the studied system, considering the load lowering mode. A computer simulation program is developed on the basis of the mathematical model and used to calculate the transient behavior of the system. The system performance is also studied experimentally. The theoretical results showed good agreement with the experimental results. Both results showed that high inertia loads result in intermittent piston motion and considerable pressure oscillations in the cylinder. The validated mathematical model is used to estimate the parameters causing this phenomena and ways overcoming it.
The theoretical and experimental study is repeated using an pilot control counter balance valve instead of pilot operated check valve. And it was noticed from the experimental study that the resulting piston motion is regular with no pressure oscillation even with high inertia loads. A computer simulation program is developed too. The theoretical and experimental results showed good agreement. A steady state piston speed is reached, corresponding to the pump delivery flow rate.