Chapter 8 And 10 Flashcards
4 ways to control a DCV
Manually, mechanically, electrically, and pilot pressure
4 center conditions
Open, blocked, tandem, and float
Open center
Pressure close to 0. Sends flow back to tank. Can only operate a single actuator and cylinder can’t be held in place.
Blocked center
P,t,a,b all blocked. Can stop cylinder motion. Can’t send flow back to tank, and spool tends to leak overtime.
Tandem center
P and t connected, and A and b blocked. Stops actuator movement and allows flow to go back to tank.
Float center
P blocked, and a, b, and t connected. Allows independent operation and free movement of each actuator on the same power source. Needs a pilot operated check to trap fluid and stop cylinder motion.
Solenoid controlled pilot operated dcv
When force to shift dcv is too high for a solenoid by itself. Flow is directed by a smaller dcv (master) to either side of main (slave) spool using pilot pressure to shift it.
Choke control (sandwich)
Used to reduce shock in the system. Meters flow by restricting how much enters the main spool. This slows down or speeds up the time it takes for each cavity to fill up. Needs a y drain back to tank to eliminate hydrolock
Pilot operated check valve
Allows free flow in one direction. Needs to see pilot pressure to allow flow in other direction.
Hydraulic accumulator types
Weight loaded, spring loaded, and hydro pneumatic.
Weight loaded
Maintains a force on the liquid by means of heavy weights acting on the piston. Can create shock generation
Spring loaded
Spring acts on a piston. The compression rate of the spring determines the stored fluid pressure
Hydro pneumatic
Most common. Applies compressed gas (nitrogen) contained in a separate area to exert a force on a liquid.
Three types of hydro pneumatic accumulators
Piston, diaphragm, and bladder
Accumulators functions
Stores pressure, absorbs shock, and supplements flow
How much nitrogen pressure in accumulator to maintain pressure
90% of pressure needed to move heaviest load and no less than 1/4 of the systems pressure
How much nitrogen pressure in accumulator to absorb shock
50% of system pressure
3 things that can be ran off main piping
Accumulator, pressure switch, and pressure gauge
