Understanding Hydraulic Valves
A Directional Control Valve is used for directing or preventing the flow of oil in a circuit. Choosing the correct control valve is critical in a proper working circuit. The following information should be helpful in understanding how to choose the correct valve.
FIRST: It is important to understand that there are (2) Basic Fundamentals to consider when choosing a valve type.
A) "Open Center Valves": (Tandem) Type: This type valve has Inlet Port Connected to the Outlet Port in the Neutral Position. Normally Used with a Fixxed Displacement type Pump.
B) "Closed Center Valves": This type valve has the Inlet Port blocked from the Outlet Port in the Neutral Position. Normally used with a Pressure Compensating type pump.
Types of Manually - Operated Control Valves
A) 3-Way, 3-Position: Valve has 3 ports and 3 positions and is usually Spring Loaded to the neutral position, includes an Adjustable Relief Valve and is used for controlling a Single-Acting Cylinder.
B) 4-Way, 3-Position: Valve has (4) Ports and is usually Spring Loaded to the center Position. Includes an Adjustable Relief Valve and is used for controlling a Double-Acting Cylinder.
C) 4-Way, 3-Position Valve with Detent Features: Valve has (4) Ports and can be outfitted with either (1) or (2) Detent feature. The Detent feature hold the spool in the choice of working ports required. Includes an Adjustable Relief Valve.
D) 4-Way, 3-Position Valve with Motor Spool Feature: Valve has (4) Ports and will operate a motor in (2) directions. In the Neutral Position all ports are connected to the tank allowing the motor to free wheel instead of an abrupt stop. Includes an Adjustable Relief Valve.
E) 4-Way, 4-Position Valve with Float Feature: Similar to Standard 4 way, 3- position valve with the exception that the 4th position allows the flow to be open to tank depending on load conditions. The working port is not completely blocked off as it would be with a Tandem Spool Type. Includes an Adjustable Relief Valve.
F) 3-Way, 2-Position Valve: Basic valve that is usually used as an ON/OFF Circuit type Valve.When valve is in the ON Position it is used to send Flow and Pressure in One Direction. Used for power beyond applications or cause a motor to rotate in one direction.
Multiple Functioning Valves
A) Mono-block Valves: Single-Casting type body containing up to 3-Spools that can be the same or different functioning characteristics. Available with Adjustable Relief Valves.
B) Sectional Valves: Valves that comprise of assembled body sections that can allow for up to (10) Spools that can be the same or different functioning characteristics. Available with adjustable relief valves.
NOTE: Control Valves can be supplied as Manually or Solenoid Operated.
NOTE: Control Valves are sized based on Flow and Pressure Requirements.
Circuit Considerations for Control Valves with more then One Spool
A) Open Center System with a Series Connection: Oil from the pump is directed to the multiple spools connected in Series. In the Neutral Position the oil passes through the valve in series and returns to the reservoir. When the control is operated, the oil is directed to the device that the valve serves. Return oil from the device is directed through the return line of the next valve.
NOTE: This circuit is satisfactory as long as only one valve needs to function at a time.
B) OpenCenter Systems with a Series/Parallel Connection: Oil from the pump is directed through the control valves in series, as well as in parallel. In Neutral, the oil passes through the valves in series. However when any valve is operating, the return is closed and the oil is available to all the valves through the parallel connection.
NOTE: When (2) or more valves are operated at once, the device that requires the least pressure will operate first, then the next device and so on.
NOTE: The advantage of this circuit is the ability to operate (2) or more valves simultaneously over the series connection.