Page 13 - Fluid Power Engineering

xii Co n t e n t s

5.3.4 Control of the Directional
Control Valves . . . . . . . . . . . . . . . . . . 161
5.3.5 Flow Characteristics
of Spool Valves . . . . . . . . . . . . . . . . . . 167
5.3.6 Pressure and Power Losses in the
Spool Valves . . . . . . . . . . . . . . . . . . . . 169
5.3.7 Flow Forces Acting on the Spool . . . 170
5.3.8 Direct-Operated Directional
Control Valves . . . . . . . . . . . . . . . . . . 172
5.3.9 Pilot-Operated Directional
Control Valves . . . . . . . . . . . . . . . . . . 173
5.4 Check Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
5.4.1 Spring-Loaded Direct-Operated
Check Valves . . . . . . . . . . . . . . . . . . . 175
5.4.2 Direct-Operated Check Valves
Without Springs . . . . . . . . . . . . . . . . . 176
5.4.3 Pilot-Operated Check Valves
Without External Drain Ports . . . . . 176
5.4.4 Pilot-Operated Check Valves with
External Drain Ports . . . . . . . . . . . . . 178
5.4.5 Double Pilot-Operated
Check Valves . . . . . . . . . . . . . . . . . . . 178
5.4.6 Mechanically Piloted Pilot-Operated
Check Valves . . . . . . . . . . . . . . . . . . . 179
5.5 Flow Control Valves . . . . . . . . . . . . . . . . . . . . . 179
5.5.1 Throttle Valves . . . . . . . . . . . . . . . . . . 180
5.5.2 Sharp-Edged Throttle Valves . . . . . . 180
5.5.3 Series Pressure-Compensated Flow
Control Valves . . . . . . . . . . . . . . . . . . 181
5.5.4 Parallel Pressure-Compensated Flow
Control Valves—Three-Way FCVs . . . 184
5.5.5 Flow Dividers . . . . . . . . . . . . . . . . . . . 185
5.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
5.7 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Appendix 5A Control Valve Pressures and
Throttle Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Conical Poppet Valves . . . . . . . . . . . 191
Cylindrical Poppets with
Conical Seats . . . . . . . . . . . . . . . . . . . 192
Spherical Poppet Valves . . . . . . . . . . 193
Circular Throttling Area . . . . . . . . . . 196
Triangular Throttling Area . . . . . . . . 197
Appendix 5B Modeling and Simulation of a
Direct-Operated Relief Valve . . . . . . . . . . . . . . 198