Hydraulics Test: Valves , Pumps And Actuators, Symbols Flashcards
Hydraulic systems
Transmit power
Use motor and actuators to transmit force
Use pressurized oil
Valves are used in a hydraulic system to ________ of an actuator?
Regulate pressure
Control speed
Change direction
Pascals law states:
A fluid at rest in a confined space has pressure acting equally in all directions and at right angles when a force is applied.
At 1000 psi, hydraulic only will compress _______%
1/2
1 bar is equal to _______ psi?
14.5
If you have a pressure reading of 30 psi absolute this would be _______ gauge pressure at sea level?
30 - 14.7 = 15.3 Psig
If you had a pressure of 1000psi acting on a cylinder piston of 3” in diameter what is the force in lbs it will push?
Force (lbs) = P(psi) x A (area)
Area = Pi x Rsquared
Area = 3.142 x 1.5 x 1.5
A = 7.07
1000 x 7.07 = 7068.6 lbs
If you have a 2 to 1 cylinder, this means:
The rod end annular area is equal to half the cap area.
The rod area is equal to the rod end annular area
Pressure in a hydraulic system is created by?
A resistance to flow
Flow in a hydraulic system can be expressed by:
GPM
Ft/min
Ft/sec
If you have flow rate of 2 GPM and cylinder with a capacity of 1 gallon, how long would it take the cylinder to extend fully.
30 seconds
Force =
Pressure x area
In the flow triangle, speed is equal to?
Inches per min
You need a certain size cylinder to operate at 2ft / sec with a 20gpm pump. What diameter cylinder would you need?
V = cubic inches/minute
S= inches/min
A= square inches
GPM x 231 = cubic inches/minute
Speed = distance x 60 (60 seconds in a minute)
A = V / S
20 x 231 = 4620 inches per min
24 x 60 = 1440
4620/1440 = 3.21
Square roots of 3.21/.7854
= 2”
The change in diameter of pipe has a direct affect on hydraulic oil velocity. If you change out a 1” pipe ID to a 2 inch ID pipe the cross sectional area of the inside diameter of pipe increases by how many times?
4 times
The recommended velocities for a hydraulic pressure line (working line) is _______ft/sec
7-20
Good Laminar flow in a hydraulic system helps:
Reduce heat
Reduces the possibility of cavitation
Cavitation damage occurs in the pump inlet or outlet?
Outlet
Aeration occurs when air becomes mixed in the fluid and the bubbles are imploded causing damage to the pump. Air gets into the system by_______?
Leaky inlet fittings
Low fluid levels in the tank
Shaft seal on the pump leaking
Bernoulli’s principle
Has fluid in motion
States if there is a pressure increase, there will be a velocity decrease in the fluid.
Work is force applied over a distance
True
Power is equal to?
Work / time
Force x distance/time
1 horse power actual is = GPM x psi x .0007
True
If you had a pump at 50 Gpm but only producing 30 Gpms the volumetric efficiency would be?
30/50 x 100 = 60 %
In an closed loop hydraulic circuit the return line goes back to the reservoir that is ________ times the volume of the rated capacity of the pump?
3/4
A closed loop system the return line connected to the main pump inlet. It used a _________ pump to make up the fluid loss from the case drains?
Charge pump
Hydraulic systems can operate at pressures exceeding 3000 psi if you come in contact with oils at that pressure it can kill you.
True
A maximum pressure relief valve is put in the hydraulic system to?
Set the maximum force a cylinder will exert
Protect components in the system from overloads
Diverts access flow to the tank when the cylinder get to the end of its stroke. (Non variable pump)
Directional control valves (DCV) can be operated electronically, hydraulically, pneumatically and manually
True
When a hydraulic symbol has a diagonal arrow running through it, it means ?
Variable or adjustable in its output
A double acting cylinder that has two rod ends that are doing equal work in either direction.
True
A pressure reducing valve is normally _______?
Open
A check valve is closed when the ball is pressed against a v shaped seat in a hydraulic symbol.
True
A sequence valve is used when?
You need to control the timing of two cylinders in a hydraulic circuit.
Meter in flow controls are not used when?
Extending a cylinder with a tractive load.
(Load pulling down)
Bleed off flow controls are used in hydraulic systems instead of meter in and out flow controls because?
They are more energy efficient.
Cross-port relief or cushions valves help with shock loading in a hydraulic system circuit. They are used with hydraulic ______?
Motors
Counter balance have the pressure setting ?
Just above the load but below the load plus the system pressure
Deceleration circuits allow the cylinder to extend part way at full speed but then slow down near the end of the stroke by using a roller cam that shifts a valve so the hydraulic oil ___________?
To Flow through the flow control
An unloading valve is used to
Depressurize part or all of the system
There are two designs of relief valves which one is more energy efficient?
Pilot operated/compound relief valve
Pressure override is equal to ______
Full flow pressure minus cracking pressure
In a vented relief valve the ________ is drained externally at a pressure. ___________ then the relief valve setting
Pilot stage
Lower
Unloading valves are used in an accumulator circuit to relieve all the pressure. This is done by hooking up an on/off valve solenoid to the electric motor starter for the pump. When the pump is shut off the valve opens and dumps all the pressure back to the tank.
True
Pilot operated pressure reducing valves are used instead of direct acting pressure reducing valves because?
They have a wider range of adjustment and are more accurate
If you had no pressure when adjusting a pilot operated pressure reducing valve the problems could be?
The valve is installed backward
External drain is plugged
There may be dirt on the check valve seat
On a sequence valve if the 2nd cylinder does not move the problem is most likely
Spring tension to high
If a counterbalance valve has a load Falling uncontrollably, you would _______ to fix it?
Increase the spring pressure
Brake valves are used on the discharge of hydraulic motors to?
Prevent oversweep when a overrunning load is applied
Prevents excess pressure build up decelerating or stoping a load.
All pressure control valves are externally drained if there is pressure down stream of the valves.
True
Direction control valves can be:
Rotary
Sliding
Or
Poppet
Detentes help the valve hold the spool in different positions
True
A single acting cylinder can be controlled by a
3 way 2 position valve
A double acting cylinder can be controlled by a ________
4way 2 position valve
A solenoid controlled, pilot operated directional control valve has the main stage spool shifted by ?
Hydraulic pressure
If a solenoid controlled, pilot operated directional control valve will not shift. You can check to see if it shifts manually by activating the manual override button. (Located at the end of the solenoid) with a small screw driver. Pump needs to be running but power to valve must be off.
True
A float centre in a directional control valve allows?
The A and B ports to flow back to tank
A regenerative centre in a directional control valve is used with a 2 to 1 cylinder to?
Have equal pressures on both sides of the cylinder
Have equal speed in both directions
A right angle check valve allows ?
3 times the flow of a check valve
Pilot to open check valves have pilot pressure to push the ball off it’s seat and open it to flow.
True
When using a meter out flow control on the cap end of a cylinder it is controlling the retraction of the cylinder.
True
If a flow control has a bypass check valve you would be controlling flow in how many directions?
1
Flow controls can have pressure compensators such as bypass restrictors types to_______?
Control the speed of the oil going through the valve
The temperature compensator in a flow control valve helps keep a constant flow through the valve when _______ changes
Viscosity
Stack valves use a sub plate that has a stack valves mounted on it. The first valve mounted on the plate is the ?
Maximum pressure relief valve
The sub plate ends for stack valves have _______ port connections
Pressure and tank
Screw in cartridge valves are _______ if they wear out?
Thrown away
Slip in cartridges can be rebuilt
Slip in cartridges are used for larger flow rates the. Screw in cartridge valves
True
Area ratios in the seating are of slip in cartridge valves can be?
1:1
1:1.1
1:2
Proportional valves are?
More rugged than servo valves
The spool in proportional valves have metering notches that help control the flow rate from the valve.
True
The movement in a proportional valve is?
Proportional to the electric input
Dither is rapid movement of the spool back and forth a few thousands of an inch to help ensure the valve will move freely
True
The closed inner loop system uses LVDT’s to sense the spool position
True
The plate and nozzle type pressure controls in a proportional valve are activated by?
The proportional solenoid
________ motors are unique to servo valves
Torque motors
Pick ups or sensors that measure position, pressure or velocity are called transducers
True
Servo valves that control the movement of the Armature and the _________ that controls the position of the spool
Flapper nozzle
Jet pipe
Hydraulic pumps create ________ and are __________ pumps
Flow
Positive displacement
Hydraulic pumps have some internal leakage between sealing components which can be around _______%
5-15
All hydraulic pumps have _______ and ________ chambers that create the pumping actions
Increasing inlet and decreasing outlet
To change the output flow of a fixed displacement pump you would ?
Change the rpm of the electric motor
Change out the cartridge (vane pump)
Recirculate some of the oil back to the inlet with flow controls and a relief valve
To change the output of an axial pump you would?
Change the angle of the swash plate
Load sensing compensator with a pressure limiting sensor compensator is a highly efficient hydraulic pump
True
The preload spring on a axial piston pump is a safety concern because?
It can fly out and hit you when you remove the retaining clip
A bent axial piston pump can tolerate a high vacuum at the inlet, this allows it to be mounted above the fluid
True
A variable displacement rotary pump uses a _________ that moves from side to side to change the volume of the pump
Reaction ring
Radial piston pumps are driven in and out of the cylinder by a cam in the centre
True
An unbalanced vane pump rotor is driven by a _________ that is supported by ball bearings at the drive end and_______\ bearings at the other side
Splined shaft
Needle
A balanced vane pump has _______ 180 degrees apart and have _______
2 pumping chambers
A circular cam ring
The vane pump uses centrifugal force to help seal the vane against the cam ring
True
A small vane called an intra vane is used in combination with holes drilled from the outside of the rotor to the root of the vane to control the _________\
Vane tip loading and wear
Always have the trailing edge of the vane in the cane pump facing the feed notch
True
Combination in vane pumps would be _______ and cavitation would be _______
Circular scoring on the vane faces
And
Pitting on the outlet side
Gear pumps have two basic designs internal gear and _______
External gear
Gear pumps use needle bearings and bushings to help offset ________
Side loading from being unbalanced
Flow through and external gear pump is
Around the gears and against the housing
The crescent seal in an internal gear pump rotates with the?
It does not rotate
The Gerotor internal gear pump is quit running because the treaty are shaped like lobes and are unique because the outer gear has at least one more tooth than the internal gear
True
Gear pump is _____% efficient and a piston pump is ______% when new?
85
95
Hydraulic cylinders convert ________ to ______ energy
Hydraulic
Mechanical
With telescoping cylinders the first cylinder to move is the largest
True
A single acting cylinder uses _______ to return the cylinder from extension?
Gravity and weight
Spring pressure
A differential cylinder is a _______ cylinder
Double acting
The component that keeps the rod clean and rod seal protected is the
Rod wiper
Cusions allow for the cylinder to slow down at the end of the stroke and can be controlled by a
Needle valve
Stop tube is used in a cylinder that is
Long and has side loading
Clevis mounted cylinders move in a slight arc motion?
True
O-ring boss ports are considered the best because they are?
Leak free
Bleed ports in cylinders should be orientated with them at the top when the cylinder is mounted vertically so the air can bleed off
True
When installing a new cylinder you should fill the cylinder with oil and once it is running _______
Cycle back and forth until all air is pushed out of the cylinder ( no squealing or jerky motion)
Hydraulic motors are driven by
Hydraulic pumps flow
Limited rotation motors have _______ number of shaft rotations
Less than one
Displacement inside a hydraulic motor is measured in
Cubic inches per revolution
Torque produced in a hydraulic motor depends on :
System pressure setting
Surface area of the motor components (vanes, gears, pistons)
Radius of rotating elements
Volumetric efficiency is the input flow divided by the output flow
True
The speed of a hydraulic motor depends on
The flow rate of the pump
The volume of the fluid pumping chambers in the motor
External gear motors operate by meshing the gear teeth and driving the fluid between the outer edge of the gear and the housing
True
When you assemble a gear motor and you find you cannot rotate the rotor by hand the problem is________
There is no problem it is assembled properly.
Tight clearance makes it hard to turn by hand
When assembling orbiting gear motors and roller vane gerotors you must time the gears with the rotary valve (assembled in phase) if they are out 180 degrees the motor will
Rotate backward
When using hydraulic vane motors they will have ________ to help seal the vanes against the cam ring before oil helps it turn over
Springs
An in line axial piston motor has a swash plate set just about straight up and down will cause the pump _______ speed and ______\ torque
High
Low
When removing the spool on a radial piston motor, make sure to mark its position with respect to the housing and also mark the crankshaft position in respect to the housing so you will not have the unit running backwards when you put it in operation
True
All hydraulic motors and pump will have external drains mounted on their housings to
Drain fluids that are leaking by the internal seals
This symbol represents
Pressure relief valve
Double acting cylinder with cusion on both ends
Pressure reducing valve
Always open
3 way 2 position
