1. The design of a single-stage relief valve with directional damping;Watton;The Journal of Fluid Control Including Fluidics Quarterly,1988
2. Simulation by Bondgraph;Thoma,1990
3. The Control of Fluid Power;Martin,1973
4. Fluid Power Control;Blackburn,1960
5. Symbols 2000, High Tech Consultants, STEP, IIT, Kharagpur, www.symbols2000.com