Module L Flashcards
Pressure is defined as:
force per unit area
Pressure is calculated by:
Dividing the force by the area over which the force is distributed or P=F/A
The amount of work is equal to:
The distance moved (in m or ft) times a force exerted (in N or lbf)
What does ISO stand for?
International Organization for Standarization
A ______________ is a linear actuator.
Cylinder
Cylinders are available with either _____________ or ______________ motion
single or double-acting motion
Describe the housing of a cylinder
It is sealed with a cap on one end and the head on the other end
What is the difference between single and double acting cylinders?
Single: applies force in one direction only
Double: Have hydraulic fluid delivered under pressure to both sides of the piston.
Force exerted by the piston is different from one side to the other.
In a cylinder, the cross-sectional area of a piston rod is __________the piston face area
less than half
If the cross sectional area is more than half the piston face area, it is considered a ___________
ram
How can a rod be returned in a single acting cylinder?
Spring return
If there is the same fluid supple exists on each side of a cylinder, why is the speed of the piston different when extending vs retracting?
Because the piston rod takes away some of the surface area from the piston and also creates a smaller cavity for the fluid to fill.
In a single piston rod, the force exerted by the piston is ________ on the side with the piston rod
less
In a ____________________, where the rods are the same diameter, the forces on the piston can be the same
double-rod cylinder
Double-acting cylinders are often designed with a _______________to slow down the piston as it approaches the end of its travel.
cushioning device
________________ have two pistons attached to one rod.
Tandem cylinders
What is the purpose of a tandem cylinder?
This design allows for higher forces at the rod end without an increase in fluid pressure or cylinder diameter
What orientation should a cylinder be mounted in?
Any position, provided they are mounted on a strong and rigid base and aligned with the part they are to move
What should a millwright do when designing or troubleshooting hydraulic circuits?
calculate cylinder forces and speeds
What unit is cylinder speed measured in?
inches/minute (if the area is in imperial)
How do you calculate cylinder speed?
cylinder speed= flow rate x 231/area
What is the main difference between hydraulic pumps and hydraulic motors?
Pumps drive the hydraulic fluid
Motors are driven by hydraulic fluid
In a hydraulic motor, a __________ oil supply to the motor allows the motor to be run over a wide range of speeds
Variable
Oscillating motors are designed to give a shaft rotation of _______________
less than 360 degrees
Oscillating motors are also called
rotary actuators
When designing and troubleshooting circuits, millwrights must be aware of these 5 factors
- displacement
- Pressure
- torque
- mechanical efficiency
- Rotary speed
_______________ is the amount of liquid handled in one rotation of the motor
displacement
displacement is usually expressed in __________________
cubic centimeters per revolution (cm3/rev) or cubic inches per revolution (in3/rev)
Torque output is a function of the system pressure and the _____________
motor displacement
Torque is expressed in _____________
newton-meters (N.m) or inch-pounds (in.lb)
How do you calculate mechanical efficiency?
mechanical efficiency = actual torque delivered/theoretical torque x 100%
How is rotary speed determined when using imperial units?
speed= flow rate x 231/area
If using the metric system, the flow rate is measured in liters per minute. To calculate the rotary speed when using metric units, the equation is ____________
Rotary speed= flow rate x 1000/area
What is used to control the direction of hydraulic fluid flow?
Direction control valves (DVC)
What are the two types of DVCs?
- Single position- Maintains uni-directional flow pattern
- Multiple position- Start, stop or change direction of flow to or from hydraulic actuators
What type of DVC is a check valve?
single position
What symbol represents a transitory condition that a valve passes through, but does not stop in the position.
An envelope with dashed ends
What are the four types of check valves?
- Free check
- Spring Loaded
- Restricted flow
- Pilot-controlled types
What is the benefit of a spring loaded check valve?
Because it uses a light spring to hold the valve seated regardless of its mounting position. A free check valve uses gravity and must be mounted correctly.
Check valves with ____________________ typically used to control the rate of decompression before shifting (activating) the main DVC.
Restricted flow
What is commonly used to lock cylinders in place until the main DVC shifts?
A pilot-controlled (pilot-to open) check valve
Pressure control valves control the ___________ in all or part of the circuit.
hydraulic pressure
_______________ controls the hydraulic pressure in the circuuit
Pressure control valve
Tre or False: Pressure control valves are normally open valves.
False - Pressure control valves can be normally open or normally closed
A direct- acting relief valve is a normally _________ valve
closed
How does a direct-acting relief valve work?
It uses a ball or poppet held on a seat by a spring similar to a check valve.
If a large amount of fluid is to be relieved under a small pressure differential, then a ________________ valve is used.
pilot operated pressure relief valve
What is the function of an unloading valve?
It returns pump output to the reservoir after the required system pressure has been reached.
What is the purpose of a sequence valve?
In hydraulic circuits with more than one cylinder, it is often necessary to work the cylinders in a specific order. This can be done with sequence valves (or by hand or electrical control)
Which type of valve is a normally closed, pressure control valve that uses pressure to keep a weight on a press?
Counterbalance valve
What is a platen?
A weight used in a counterbalance valve
In a counterbalance valve, a pilot line senses the ___________ of the inlet port and an internal drain.
Pressure
The speed of a motor or the rate of travel of cylinder is regulated in a fixed capacity pump by _____________________
flow control or flow metering valves
How does a hydraulic pump convert mechanical energy into hydraulic energy?
- The mechanical action of the pump creates a partial vacuum
- This vacuum allows atmospheric pressure to force fluid through the inlet line
- The pumps mechanical action then forces the hydraulic fluid to the pumps outlet and into the system
_________________ pumps run at a given speed, delivering a constant flow rate. They may be gear, vane or piston pumps.
Fixed capacity pumps
_______________ pumps run at a given speed, delivering a variety of flow rates from maximum to zero in one or both directions. They may be vane or piston pumps.
Variable capacity pumps
What type of pump (fixed or variable) must a gear pump be?
Fixed capacity
How do you change the direction of a vane pump?
Flip reachion ring and rotor
What is the difference between a strainer and filter?
A strainer is considered a course filter. It removes larger solids from fluids travelling in a straight path.
What are the three types of filters?
- Mechanical (metal)
- Absorbent
- Adsorbent
______________ filters contain materials such as paper, wood pulp, fabric waste, or wool.
Absorbent
_______________ filters remove impurities by both mechanical and chemical means.
Adsorbent
Bone-black, charcoal, fuller’s earth are examples of filtering materials using in _____________ filters.
Adsorbent
What does an adsorbent filter remove from the fulid?
All solid particles and insoluble sludge, plus nearly all water and soluble, oxidized material.
Why must you be cautious when using an adsorbent filter?
They can remove most additives used in inhibited hydraulic fluids
How can you calculate the volume of fluid in the reservoir?
It is normally equal to two to three times the rated pump delivery for one minute.
What is the reservoir tank made of?
Steel plate with all welded joints
What is a baffle plate?
It is a plate in a reservoir that prevents a direct flow of fluid from the return line to the suction line.
What is the function of a baffle plate?
Slowing the oil down allows trapped air to escape and foreign material to settle on the bottom.
How do hydraulic circuits isolate the accumulator from the system?
With an automatic bleed down
__________________________ use compression springs instead of gravity to supply resistance.
spring-loaded accumulators
In a spring-loaded accumulator, the springs exert __________ (minimum or maximum) pressure when it is at low volume.
minimum
Spring loaded accumulators exert maximum pressure at __________________
high volume
Gas-charged accumulators depend on the ___________________ of a gas (such as nitrogen or air)to produce the necessary pressure at high volume.
compressibility
What is Boyle’s Law?
At constant pressure, the volume of a gas varies inversely to the absolute pressure.
or P1V1 = P2V2
________________ is commonly used in medium-to high-pressure systems because it is inert (will not react) to oil.
Dry Nitrogen
Explain Bernoulli’s principal
If the flow rate is constant, the sum of the kinetic energy and the potential energy at various points in the system is constant
Describe a pressure-compensating flow-control valve
It maintains a constant rate of flow through the valve regardless of down-side pressure
List 5 types of hydraulic fluids available today
- Petroleum oil
- Fluids with high water content
- Invert emulsion fluids
- Glycol Fluids
- Synthesized hydrocarbon hydraulic fluids
- Vegetable or grain oil
For black pipe, the _______________ diameter remains the same and the __________ diameter decreases as the wall thickness increases.
the outside diameter remains the same and the inside diameter decreases as the wall thickness increases.
When installing tubing, what are some important points to remember?
- start from a fixed point
- use the proper fittings
- use as few fittings as possible
- use least number of bends as possible
- make sure joints are easily reached
- ensure the line will not be a hazard to workers
- ensure the line will not interfere with other equipment
When installing tubing you should use the least number of _________________ as possible
fittings/bends
True/False: When installing tubing you should bend the tube instead of using a fitting when possible
True
What should you consider when determining the size and type of pump for a hydraulic system?
It must be able to supply the required flow and handle the necessary pressure
In hydraulic systems, instruments are used to measure which three conditions?
- Pressure (Bourdon and Schrader gauges)
- Flow
- Temperature
What is a schrader gauge?
A pressure gauge with a calibrated dial face with a pointer attached through linkage to a plunger and bias spring
__________________ is a petroleum-based liquid with 40% water content which acts as an oil
invert emulsion fluid
How do you determine which hydraulic fluid to choose?
Based in its quality and ability to perform its required tasks
What are the qualities of hydraulic fluid that should be considered?
- Viscosity- rate of pour at a given temperature
- Viscosity index- its change in viscosity over a given temp range
- Pour point- the lowest temp at which oil will flow
The pour point should be ________ degrees lower than the expected temperature
20 degrees F
High water content (HFA) fluids are soluble oils or synthetic ____________________
chemical emulsions (oils-in-water)
High water content (HFA) fluids generally contain ____________% oil
5-10%
What must you be cautious about regarding using HFA fluids?
They are not necessarily compatible with seals, metals and protective coating
HFB fluids are also known as _________________
Water in oil fluids
HFB fluids are invert emulsions which contain more __________________ than ___________________
more oil than water
Water glycol fluids are also known as _______________
HFC fluids
Water glycol (HFC) fluids consist of 30% to 40% ______________ dissolved into _____________
30% to 40% water dissolved into glycol
Because water glycol (HFC) fluids are heavier than oil, what must you remember?
- Use a very short suction lift
- Use a special inlet design
- They can be used in situations where the fluid level is above the pump inlet
Synthetic fluids are also known as:
HFD fluids
__________________ fluids are special chemical compounds which do not support combustion
HFD (synthetic) fluids
Since HFD fluids have no water content they can therefore be used at ______________________ with no evaporation problems
high temperatures
What must you remember when changing to a synthetic fluid?
- Even the spare valves and components must have seals changed.
- Filters and strainers must also be compatible
