Directional Control Valves Flashcards
What is the major downside of rotary spool valves
High internal leakage, this limits there use to low pressure and flow applications
Spool housing are usually made of what
Aluminum
Fine grain cast iron
What must be replaced if a spool is damaged
The spool and housing must be replaced as a matched set
What is the function of the groves in the valve spool lands
Trap oil for better lube
Allow pressurized oil to act around the full circumference of the valve land centring it in the bore, reducing binding against wall
What are the 2 styles of feathering notch
C notch
V notch
Diverter valve
2 position, 3 way valve
Has P, A, B ports but no T ports
Tandem center
Open center, closed port
Motor spool / float center
Open center, open port
motor or float spool
Closed center, open port
Detents
Devices used to hold a directional control valve in position
Mechanical detent
Springs hold a balls into grooves in the spool
Represented on a schematic by v notches in spool on end
Electromagnetic detent
Holds a spool in a set position until a pre-determined height is reached (proximity switch on a loader)
What other control valves are commonly found inside of the directional control valve
Relief valves - system and circuit
Load check valves
Anti-cavitation check valves
Flow compensators
Load Check
Spring loaded check placed between the pump port and the DCV spool. Stops oil from flowing backward when the DCV spool is moved and the pressure in the work port is greater then the current pump pressure
Anti-cavitation Check
Prevent void from forming in a actuator when the load drives the actuator faster then the pump can supply it.
Allows oil to flow from tank line to work port when pressure in work port falls below pressure in tank line
