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Hydraulic Circuits - Coggle Diagram
Hydraulic Circuits
1. Unload circuit
using fixed displacement pump
fluid return into tank through relief valve when cylinder stop
main valve: 4/3 solenoid controlled valve (P-R port bypass)
reduce power loss in system
types
1) Circuit using center bypass valve
for one single hydraulic drive
2) Vent unload circuit
have small size solenoid-controlled valve
reduce pressure, heat and power loss
8. Circuit for controlling high load
high load operation
switching made surge pressure
method to reduce surge pressure
1) Circuit using solenoid-controlled pilot-operated directional control valve
taper notch effect reducing shock switching
metering valve controlled switching time
2) 2-speed control circuit
small/large-capacity circuit
add solenoid-controlled valve in parallel
starting and stopping w/ small-capacity feeding
large-capacity feeding when need to increasing speed / stop feeding when need to decreasing speed before stopping
3) Decompression circuit
use pressure switch
reaches upper limit: Hi
main valve switching to neutral position
release pressure
reaches lower limit: Lo
main valve shift the position for lifting operation
use pressure-releasing valve
made noise & maybe explosion
2. Circuit to control pressure
required for hydraulic drive
types
1) Circuit for switching P-line pressure
not suitable for reducing pressure one or more driving units
3-relief valves that different set pressure for switching P-line pressure
not suitable for multiple driving units
2) Circuit for controlling pressure by series
used when more than one series system
relief valve controlled system pressure
sub relief valve controlled sequence operation
3. Control method
of flow control valve
2-methods
using variable displacement pump for changes the discharge rate
using a combination of metering pump and flow control valve
3-method to control flow control valve
1) Meter-out method
positive load
the head-end side has system pressure/ higher according to the rod size and force required to move the load
action smooth and steady
negative load
using pressing process
the head-end side has system pressure/ higher according to the rod size and load
directional control valve has 2 flow control valves w/ check valves for controlling flow rate
check valve controlled forward stroke
2) Meter-in method
directional control valve has 2 flow control valves w/ check valves for controlling flow rate
check valve controlled backward stroke
positive load
moment smooth and steady in resistive load
head cap side has system pressure less than end cap
negative load
being vacuum void because fluid can't enter fast enough
using a counterbalance valve to prevent load for falling
free fall depending on load size
cylinder produce force after vacuum voidfilled
3) Bleed-off method
(By-pass method)
using in load changes but below set pressure of relief valve
suitable for one hydraulic drive/ multiple actuator if operate at one time
fixed displacement valve
not suitable for precise speed control
precise or discharge rate varies load pressure/ fluid temperature changes
positive load
using pressure-compensated needle valve
reduce power loss that the actuator does not used to produce work
power loss less than meter-in/out method
negative load
not suitable, must use counterbalance valve to prevent free falling
4. Accelerating circuit
to produce speed faster than available
using pump discharge rate
method to accelerated
1) Differential circuit
(Regenerative circuit)
suitable for cylinder output not high
suitable for fast-travel cylinder piston in forward stroke
have a check valve - line at B port bypass to P port for accelerated speed in forward stroke
have check valve in main line to prevent fluid flow back to pump when operating forward stroke
flow rate of auxiliary line depending on area of cylinder head-side and piston speed
flow rate of A-port line is the sum between pump discharge rate and auxiliary flow rate (outflow)
2) Using auxiliary cylinder
used to large-diameter cylinder
hydraulic press
using the small cylinder w/ small pump
rapid-run
have prefill valve for fill the main cylinder follow the sequence
5. Circuit for sequential operation of cylinder
method to implement the sequence
1) Cylinder pressure detection
using sequence valve
different set pressure make the sequence operation
operate w/ one main valve
2) Cylinder position detection
using limit switch
used in conjunction w/
solenoid-controlled direction control valve
controlled by PLC
6. Circuit to maintain back pressure
(negative load)
using counterbalance valve
maintain back pressure by negative load
prevent free falling by controlled flow rate
(set pressure)
solenoid-controlled direction control valve
A-B ports not conntected
7. Position-keeping circuit
using pilot-operated check valve
to hold cylinder position
solenoid-controlled direction control valve
A-B ports connected
have auxiliary A-B line
9. Brake circuit
relief valve absorb inertial force
4 - check valve
2- parallel by
2- series
lower check valve w/ tank
for prevent negative pressure in line
10. Closed circuit
pump produce pressure and flow rate only in line w/ load
pump discharge switches
direction motor rotation
pump discharge rate control
number of revolution of motor
using charge pump
prevent negative pressure
using flushing valve
11. Filter circuit for hydraulic fluid
to maintain hydraulic fluid cleanliness
prevent contamination in fluid
higher pressure by smaller clearance
in pump and valve
extend the hydraulic equipment's life
method to used filter
1) Circuit in return side
suitable for small-size equipment
2) Circuit in discharge side
suitable for circuit that using valve
(servo valve)
need higher fluid cleanliness
3) Circuit dedicated to filtering purpose
suitable for large-size equipment
using small-size pump and filter