190301fA Flashcards
From the list below, select two (2) classifications that apply to pressure control
valves.
b) normally open
d) normally closed
A normally closed pressure control will block the flow of oil through the valve when
system pressure overcomes valve spring force.T/F
false;
For a pressure control valve, the difference between cracking and full flow pressure
is known as _________
pressure override.
The main advantage of using a pilot operated pressure control valve is that it:
provides minimum pressure override.
A relief valve that limits the pressure in one branch of a hydraulic system is called a:
circuit relief valve.
State three (3) safety precautions that must be observed when installing a pressure gauge into a hydraulic system.
a) Depressurize the system before installing the gauge.
b) Select a pressure gauge approximately twice maximum system pressure.
c) Be sure all lines and fittings will withstand at least twice maximum system
pressure.
A hand pump is sometimes used to test system relief valve pressure setting.T/F
false;
Hydraulic accumulators perform the following four functions. They are:
a) energy storage
b) shock absorption
c) gradual pressure buildup
d) constant pressure maintenance
List two (2) safety precautions that must be observed when working on hydraulic systems that contain accumulators.
a) never use oxygen or compressed air in gas-charged accumulators
b) always discharge systems equipped with accumulators prior to performing
service
State the function of an unloader valve.
An unloader valve allows full pump flow to return to the reservoir while maintaining
minimum pressure at the pump outlet.
Which of the following components is not used in a closed centre hydraulic system
that is supplied with a fixed displacement pump?
a relief valve
The unloader valve in a demand type hydraulic system that is supplied by tandem
fixed displacement pumps is open when:
the load on the system is high.
A pressure reducing valve will block oil flow through the valve when pressure
upstream of the valve overcomes the valve spring.T/F
false;
Two (2) functions of a sequence valve are:
a) to cause actions in a hydraulic system to occur in a certain order and
b) to maintain a predetermined minimum pressure in a primary function while a
secondary function is in operation.
All backpressure valves are located in the:
the actuator return line.
Care must be taken not to excessively restrict the flow from the rod end of a doubleacting
cylinder because
Pressure intensification may result in damage to system components.
One of the primary purposes of a lock valve is to prevent the load from drifting due to leakage. T/F
true
A pressure compensated flow control valve maintains constant flow through the
valve by:
maintaining a constant pressure drop across its orifice.
State the most appropriate flow control valve circuit for an application where the
actuator load changes direction and strength.
a meter out flow control circuit
The flow control valve that splits a single flow among two or more circuits is called
a:
proportional flow control valve.
What is the function of the priority flow control valve used in heavy equipment
steering systems?
The priority flow divider provides a relatively constant flow rate to the steering
system regardless of fluctuations in steering pressure or engine speed
The 3 back pressure valves in the module are?
Counterbalance
Brake valve
Lock valves
Counterbalance valve is a safety device used to control?
The lowering of a vertical load so it does not fall freely
Counter balance valves do not work well with varying loads because?
Power is wasted opening valve when load is lighter than maximum
Static oil pressure in actuator may hold the valve open if max load is exceeded
What is the purpose of the spring-loaded poppet valve in a bladder style gas accumulator?
Prevents the rubber bladder from being pushed through the port if the gas pressure becomes too high in relation to oil pressure in the oil chamber.
What are 4 reasons accumulators are installed in heavy equipment hydraulic systems?
- energy storage,
- shock absorption,
- gradual pressure buildup and
- constant pressure maintenance.
Unloader valves differ from relief valves in 2 ways:
- are always used in conjunction with a check valve and
* pilot pressure to open the unloader is sensed from the high pressure side of the check valve.
What determines the actuator speed?
The internal capacity of the actuator and the input flow rate supplied to the actuator
Define flow rate.
The function of the displacement and driveshaft speed of the hydraulic pump. Can be determined with a mathematical formula. Flow rate=Volume/Time.
With an orifice in a circuit, where is pressure the lowest?
Pressure is always the lowest in the orifice.
What is meant by the greater the drop, the greater the flow?
This is the pressure drop across the orifice.
There are 3 things in total that determine the amount of oil that will flow through an orifice, name them.
The orifice size and shape.
The pressure drop across the orifice.
The viscosity of the oil.
An orifice can be adjusted. T/F
True.
What is required when you ned an accurate control of the actuator speed?
A pressure compensated flow control.
Define compensator.
Normally closed pressure sensitive valve installed in parallel to carry away any flow that exceeds the regulated flow through the orifice.
