Hydraulics Flashcards
Where are pilot to open check valves used?
To lock cylinder in place without internal leakage until the main DVC shifts.
What is an advantage of a right angle check valve compared to a straight check valve?
Can handle flow 3 times as high
No turbulence
What are the five DVC centres?
Closed
Open
Tandem
Float
Regenerative
What are 3 types of servo valves?
Flapper nozzle
Jet pipe
Staging spool
What are the five types of centres?
Closed
Open
Tandem
Float
Regenerative
What is a disadvantage of an inline check valve?
Causes a drop in pressure.
Explain a counterbalance valve.
Used to control vertical loads
Similar to sequence valve the difference being the internal drain had replace the sequence valves external drain.
Normally closed
Reverse flow bypass
What would determine if a pressure control valve required an external pilot drain?
Outlet pressure (back pressure)
Which proportional DVC control provides the most accurate flow?
Closed outer loop
A pressure reducing valve can either be ______ acting of _____ operated.
Direct acting or pilot operated
What are some functions of an unloading valve.
Used in accumulator circuits
Shock protection
Allows pump to dump fluid back to tank with low pressure/effort.
What are 2 uses for a brake valve?
Prevent excessive pressure buildup when decelerating or stopping a load. ( pressure intensification)
Prevents run away loads.
Explain detent actuation.
Little groves in spool
Holds until forced out of groove ( normally leaver actuated)
Explain a closed inner loop and a closed outer loop system.
Closed inner controls the spool only
Closed outer had the greatest accuracy.
What is cavitation?
How is it recognizable?
What are some effect?
Is a violent collapse of vapour gas bubbles.
Rattling noise, low pressure at pump inlet.
Rapid erudition of metal suffices, severe pump damage, flow reduction.
Explain a regenerative circuit in a hydraulic system.
Is designed to provide equal speed and force when the cylinder extends and retracts.
What are 4 causes of cavitation?
Clogged inlet filter
Clogged breather
Inlet pipes to small
Fluid is to think
Oil level is to low
What are some advantages of hydraulics?
Infinitely variable speed control
Infinitely variable torque/force control
Highly accurate control of movement
Compact
Very little loss from friction
What are some disadvantages of hydraulics?
Expensive
Heavy
High pressure fluid hazard
Messy
What does pascals law say about fluid at rest in a container?
Pressure is undiminished
Equal in all directions to right angles in the container.
What are 3 measurement of pressure?
Gauge
Absolute
Atmospheric
How is pressure produced?
By a pump
Resistance to flow
What is the flow triangle used for?
Sizing cylinders
Sizing pumps
Calculating speed
Q = S x A S = Q / A A = Q / S
What is the maximum pump inlet velocity?
What is the maximum pressure line velocity?
Inlet. 2-4 feet per second
Line. 7-20 feet per second
What are the 2 types of cartridge valves?
What GPM would you use each one for?
Screw in, 30-35 GPM
Slip in, over 40 GPM
Note: screw in must be throw out after taken out because it has threads.
Explain dead band compensation.
Briefly boosts prowler to make spool jump across the overlap distance.
Explain what ramp means.
Controls speed of voltage
Controls acceleration/ deceleration of actuators.
No feedback means what?
No signal is returned to control RPM is change is needed. (Open loop)
