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Directional Control Valves: Types, Functions, and Actuators

Learn about the different types and functions of directional control valves, including ball, poppet, and right angle valves. Explore the various actuator options and understand how to determine the valve's operating characteristics through schematic diagrams.

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Directional Control Valves: Types, Functions, and Actuators

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  1. Chapter 5 Directional Control Check Valves • Directional Control Valves • Directional Control Valve Actuators • Logic Valves

  2. The three different types of direct acting check valves are ball, poppet, and right angle.

  3. A restriction check valve has an orifice placed in the center of the poppet to permit restricted fluid flow through the valve in the NC position.

  4. Check valves are mainly used for pressure control and to bypass certain system components.

  5. A pilot-to-open check valve allows fluid flow in one direction and stops fluid flow in the opposite direction until it receives a pressure signal through a pilot line applied to the piston port.

  6. A pilot-to-open check valve is often used to hold a double-acting cylinder in place when the cylinder has a load suspended on it.

  7. A pilot-to-close check valve allows fluid flow in one direction until the pilot signal is sent to close the valve.

  8. The primary function of a directional control valve is to direct or prevent fluid flow to specific piping or system actuators.

  9. A schematic diagram can be used to determine the operating characteristics of a directional control valve.

  10. A way is the number of valve ports, and position is the number of different positions that a spool of a directional control valve is capable of moving into in a directional control valve.

  11. In a schematic diagram, internal arrows inside the position boxes depict the direction of fluid flow for each spool position.

  12. Naming standards include the number of positions, the number of ways, the types of directional control valve actuators, and the normal spool center position.

  13. Two-position, two-way directional control valves can turn on and off separate hydraulic systems that are powered by the same hydraulic power unit.

  14. A two-position, three-way directional control valve has two positions, one to allow fluid flow from the cylinder port to the tank port and the other to allow fluid flow from the pump to the cylinder port.

  15. Two-position, four-way directional control valves are typically used to control cylinders that lift heavy loads.

  16. An advantage of three-position, four-way directional control valves is that they have four different center positions that can perform four different operations.

  17. Open-center positions are typically used in applications where there is only one cylinder in the hydraulic system.

  18. When using a closed-center position, fluid flow created by a variable-displacement, pressure-compensated pump either goes through a relief valve or is automatically reduced to no flow.

  19. Tandem-center positions are used to hold a cylinder in the desired position while allowing fluid flow to be directed back to the tank without the need to activate a relief valve.

  20. Float-center positions allow a the piston in a cylinder to move while it is in the center position and can still direct fluid flow back to the tank.

  21. Subplate mounting allows for a directional control valve to be mounted to a plate that attaches directly to system piping.

  22. Spring actuators are used to shift the spool of a directional control valve to normal position.

  23. A pilot pressure actuator uses fluid pressure to actuate a directional control valve spool.

  24. Directional control valves can be single- or double-solenoid actuated.

  25. When shifting is required, fluid flow from a piggyback valve is directed as pilot pressure to either side of the main directional control valve spool.

  26. A pilot choke is mounted between a main valve and a pilot valve that is used to slow or briefly delay reversals in spool movement.

  27. A pilot piston allows a directional control valve spool to shift quickly by placing the pilot piston in a pilot-pressure chamber near the spool in the main valve.

  28. A detent operates by locking the spool in a desired position and not allowing it to move back into its normal position until it is manually repositioned.

  29. In an AND hydraulic circuit, pressure must be present from the hydraulic system (input 1) and through the pilot line (input 2) before the cylinder (output) can operate.

  30. A shuttle (OR logic) valve permits a hydraulic system to operate from either of two different hydraulic signals.

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