Hydraulics Flashcards
Which cartridge valve is best for LOW flow (less than 35 gpm
Screw in Cartridge valves
What cartridge valve is best suited for high flow?
Slip in
What Valve should be mounted first on the subplate in a stack valve assembly
Pressure relief valve
What are ways?
Ways refer to number of connections
What are cartridge valves mounted to?
Manifold block
What are the advantages of stack valves
Mounted together, with no external plumbing, very compact, eliminate potential leak point in external plumbing
What are the advantages of Proportional Valves?
Controlled electronically
Greater accuracy and control
Simpler circuit design
Ideal for applications that can use electronic control without accuracy of servo valve
More rugged and dirt tolerant than servos valves
What is spool overlap?
Where the spool land is larger than the port is wide.
What are advantages of metering notches on a valve spool?
Accurate control of speed
Wider speed ranges than solid spool
Can minimize Valve overlap
Soft Shifting ; slower buildup of pressure, preventing shock
What is dead band?
No flow through the valve
How is dead band reduced?
Spoke to boost power in the solenoid to minimize lag
What is gain?
Ratio between input signal and the larger output current flow
Eg output/input
What is a ramp function?
Ramp function controls how fast the current and voltage to solenoid is increased and decreased ( acceleration, deceleration)
What is the dither signal?
A small high frequency alternating current applied to solenoid to move it rapidly back and forth to reduce any hysteresis (hang up)
What is an open loop system?
A system where the controller cannot sense how accurately the actuator is responding to the control setting
What is the most expensive feedback system?
Closed outer loop system
Where is a nozzle pressure control normally found?
As a pilot stage on PCV’s or for controlling compensator settings on a pressure compensated Variable Displacement Pump
Where is a plate pressure control Valve commonly used?
In injection moulding machines to provide smoother control
Why is a plate pressure control valve desirable?
They are highly responsive and accurate as they do not need springs to control pressure
What are the advantage of a nozzle pressure control
Small nozzle, small flow
Used as pilot stage for other valves
Very accurate
Can be controlled from plc
What are the advantages of a servo valve?
More accuate than other pressure control valves, built in feedback loop
More precise
What are the disadvantages of a servo valve?
Less rugged and dirt tolerant, must have a pressure line filter installed before servo
More expensive
What are the 3 ways to change output on a hydraulic pump
Flow controls, changing the speed of the driver, and using a variable displacement pump
What is the formula for volumetric efficiency?
Where is the overall efficiency of a pump relatively low?
Lower pressures and max pressures
What are the four types of piston pumps?
In line axial piston pump
Bent axis piston pump
Rotary piston pump
Radial piston pump
What is the most common piston pump?
In line axial piston pump Rotary
In line axial pumps can be….
Fixed displacement
Variable displacement
Pressure compensated or
Load sensing
What are the 3 MAIN types of hydraulic pumps
Piston pumps
Vane pumps (which can be balanced of unbalanced)
Gear pumps (internal or external)
What are the main parts of an in line axial pump
The cylinder block,
The swash plate
A shoe plate
A valve plate
The drive shaft
And a case
In what position does the swash plate create no flow?
Perpendicular or 0 degree angle
What is the purpose of a pressure limiting compensator?
To save energy and pump wear when flow is not required
What component is combined with a pressure limiting compensator
Load sensing compensator
To increase efficiency and save energy when moving loads
What hydraulic pump would you use for year round operation?
A bent axis pump
(More reliable, built for continuous operation)
Why is a bent axis piston pump more reliable than an axial piston pump?
No swash plate, or piston shoes
Pistons have ball joints at the ends eliminating potential wear
They can also withstand high vacuum inlet pressures
How can you change displacement on a rotary piston pump?
You can change displacement by moving the reaction ring
Where are rotary piston pumps used?
Small Hydrostatic transmissions and applications requiring large volumes (eg 200 cubic inches of displacement)
What is a key difference between rotary and radial piston pumps?
Radial pumps use a stationary block whereas rotary pumps use a dynamic block and stationary pintle
What application would you find a radial piston pump?
Low flow, high pressure equipment, such as plastic injection molding machines. These pumps are capable of operating at pressures up to 10,000 psi
What is the main disadvantage of an unbalanced vane pump?
The casing and bearings must be fairly large to support the large radial thrust loads
What is the difference between balanced and unbalanced vane pumps?
Balanced vane pumps are fixed displacement, with 2 inlets and 2 outlets offset from the other by 180 degrees, they also have an elliptical shape
How do you differentiate from a vane pump and a vane motor
Motors have SPRINGS inside
How can you increase efficiency in a vane pump?
Intra-vane design combined with equalizer holes increase efficiency and reduce wear
What are the common causes of failure on vane pumps?
Contamination (look for tip wear, frosted appearance, circumferential marks falling on inside of cam ring, circular scoring of flex/support plates
And cavitation or aeration damage
(Ripple marks inside cam ring, erosion at fish tail grooves at inlet/outlets)
In unbalanced vane pumps, what does the maximum volume stop do?
Restricts movement of the ring
What are the main disadvantages of gear pumps?
Unbalanced design, and no support for variable displacement
What are the 2 types of gear pumps
External gear and internal gear
What are the 3 gear cuts used in gear pumps?
Spur gear, helical gear, and herringbone gears
What are the advantages of spur gears in a gear pump
Cheap, dirt and contaminant tolerant but are also the noisiest
What are the 2 types of internal gear pumps?
Crescent pumps and gerotor
What is the difference between crescent pumps and gerotor pumps
Gerotors have a star shaped rotor with one less tooth than the gear, crescent pumps have a crescent seal that provides a positive seal between suction and discharge
What are the characteristics of a gerotor pump
Quietest running, least dirt tolerant, can be used as a charge pump
The efficiency of a gear pump is dependent on…
Close fit of teeth to casing and close fit of teeth to end plates, wear of these plates will allow recirculation
Is a gear pump more volumetrically efficient than a piston pump?
No, gear pumps peak at 85% volumetric efficiency, whereas piston pumps are 90-95% efficient
Valves control what?
Direction, flow (speed), pressure (force)
What is the recommended maximum pump inlet velocity?
2-4 ft/second
What is the recommended maximum pressure line velocity?
7-20 ft/second
What is the function of the maximum pressure relief valve?
Provides overload protection, automatically diverts excess flow to tank, sets maximum pressure at which system operates
What valves can be used to protect a motor from shock loading?
Cross port relief valves or brake valves
How does pressure affect the output of a cylinder?
Pressure determines the force it exerts
How does flow affect the output of a cylinder?
Determines the speed of a cylinder
Why must you attach an external drain to a sequence valve or to a pressure reducing valve?
To drain the spring chamber of pressure and prevent the valve from locking up
Name 3 types of flow control
Meter in, meter out, bleed off
What is the purpose of a flow control valve?
To control the speed of actuators
What causes a decrease in volumetric efficiency?
Internal leakage, usually caused from worn parts
What are 6 possible negative side effects of high fluid velocity in a hydraulic system?
1) increased friction
2) increased heat
3) loss of power
4) increase in wear
5) possibility of turbulent flow
6) shocking components
What is pressure override?
Pressure override= full flow pressure - cracking pressure
Define cracking pressure
Pressure required to open the valve and let the first drop past the seat. Minimum pressure at which the fluid will divert to tank.
Define full flow pressure
Pressure required to hold the valve open during full flow
What are 4 DCV spool centre positions?
Closed, open, float, tandem
True or false. A right angle check valve can handle three times the fluid of an in-line check valve?
True
Which check valve is also called a “lock valve”?
Pilot-to-open check valve.
In the event of a leak or rupture it can hold a suspended load. “Locking” the load. Typically two valves, with pilots connecting to opposing ports
Pg 43 of 160302b-cA
Where would you commonly use a pilot-to-close valve?
With an accumulator
What is the potential danger when using meter-out flow control?
Pressure intensification. Pressures can exceed the main relief valves setting. Install a circuit relief valve between the flow control and rod end port of cylinder
Pg 49, 160302b-cA
Pros and cons of bleed-off flow control
Most energy efficient but not accurate and provides no control for runaway loads
What happens if you install a brake valve on a hydraulic motor without connecting the external pilot line?
The motor will not turn
What is the general term for the output component in a hydraulic system?
Actuator
What component in hydraulics delivers linear force?
Cylinder
How can cylinders be classified?
- Single acting cylinders
- Double acting cylinders
What is a single acting cylinder?
A cylinder that exerts force in one direction only
What forces are required for the piston to move in the opposite direction in a single acting cylinder?
- Gravity
- Spring force
What are some types of single acting cylinders?
- Ram type
- Telescopic cylinders
- Spring-return single acting cylinders
What does a ram type cylinder consist of?
A piston tube that slides within the cylinder barrel
What is the function of the guide ring in a ram type cylinder?
Supports the inner end of the piston tube but does not seal the piston
How is the outer end of the piston tube sealed in a ram type cylinder?
By cylinder packing fitted into the cylinder barrel
How is the cylinder extended in a ram type cylinder?
By directing pump oil flow into the inlet/outlet port
How is retraction accomplished in a ram type cylinder?
By connecting the inlet/outlet port to the reservoir
What is a telescopic cylinder?
A telescopic cylinder is a type of cylinder that obtains additional stroke length from a compact retracted package, constructed with two or more stages.
How does a telescoping single acting cylinder operate?
It operates with stages where the first stage slides back and forth in the barrel, and each successive stage fits into the previous one.
What changes occur in force and speed as stages of a telescoping cylinder are moved?
Force generation decreases and speed increases with each successive stage.
Which stage of a telescoping cylinder develops the greatest force?
The first stage develops the greatest force.
In a telescoping cylinder, which stage generates the slowest speed?
The first stage generates the slowest speed.
What is a common application of telescoping cylinders?
They are commonly used as the lift cylinder under the box on a dump truck.
What is the function of the drain port in a spring-return single acting cylinder?
The drain port relieves any accumulation of leakage fluid from the spring chamber.
What components are included in a spring-return single acting cylinder?
It includes piston rings and rod seals.
What ports are typically found on a spring-return single acting cylinder?
A drain port on the spring end and a pressure port on the cap end.
Fill in the blank: A telescopic cylinder is constructed with _______.
[two or more cylinder rods called stages]
True or False: The spring-return single acting cylinder has only a pressure port.
False
What is the most used cylinder in hydraulics?
Double acting cylinder
The double acting cylinder is the most common type used in hydraulic systems.
Name the three types of double acting cylinders.
- Differential double acting cylinder
- Double rod cylinder
- Tandem cylinder
These types differ in design and application.
What are the features of a differential double acting cylinder?
- Two pressure ports
- Unequal areas on each side of the piston
- Piston and rod seals
- Can exert force while extending and retracting
This type of cylinder is characterized by its differential action.
True or False: The extension speed of a differential double acting cylinder is faster than its retraction speed.
False
The extension speed is slower than the retraction speed.
In a differential double acting cylinder, which has greater force: extension or retraction?
Extension
Assuming constant pressure and flow, the force during extension is greater.
What characterizes a double rod cylinder?
- Equal piston areas
- Equal volumes on both sides
- Same force and speed capabilities in either direction
This type of cylinder is known as a non-differential cylinder.
What is a typical application for a double rod cylinder?
To push and pull simultaneously
This functionality is useful in various mechanical applications.
What are tandem cylinders?
Tandem cylinders are two pistons attached to a single rod used to obtain extra force.
When are tandem cylinders typically used?
They are used in short stroke, high force requirements when there would be insufficient space for a larger diameter cylinder.
What standard sizes are cylinders in North America made to?
Cylinders are made to inch sizes standardized by the National Fluid Power Association (NFPA) or the Joint Industry Conference (JIC).
What metric sizes are used in European equipment?
European equipment uses cylinders sized in millimetres.
What features do the NFPA and JIC standardize?
They standardize common features such as:
* Bore and rod diameters
* Mounting dimensions and styles
* Port location and sizes
* Piston seal types
What are the two types of cylinder construction designs?
The two types of cylinder construction designs are:
* Tie-rod cylinders
* Mill-type cylinders
What are the 3 main types of actuators?
Linear, as In a cylinder
Rotary (bi and uni directional motors)
Limited rotation motor
What is the function of the barrel in a cylinder?
Contains the load pressure and has a honed finish to minimize friction and wear
A honed finish allows piston rings to seal effectively.
What components enclose the ends of the barrel in a cylinder?
Cap and rod end head
These can be attached to the barrel with tie rods and seals.
What do the ends of a cylinder contain?
Ports, cushion valves, and cushion passages
The rod end head also contains the rod bushing assembly.
What is included in the rod bushing assembly?
Rod bushing and rod seal assembly
The rod bushing provides a bearing surface and holds the rod seal assembly.
What is the purpose of the rod seal assembly?
Consists of a pressure seal and a rod wiper
The pressure seal retains pressurized fluid while the wiper prevents contamination.
What happens if the wiper seal fails?
Dirt and air enter the cylinder each time the rod retracts
This contamination can be discharged into the rest of the system.
What does the piston do in a cylinder?
Transmits the fluid force to the rod
What are the two types of piston seals?
Synthetic rings and cast iron rings
Synthetic rings provide a positive seal, while cast iron rings are more durable.
Which type of piston seal is used when no cylinder creep can be tolerated?
Synthetic rings
What are the characteristics of cast iron rings?
More durable, less frictional drag, withstand higher temperatures and pressures
They are non-positive seals.
What is the function of the piston rod?
Transmits fluid forces to the load
It is chrome-plated and threaded for attachment to the load.
What additional components may the piston rod have to mitigate mechanical shock?
Cushion collar and plunger
What are seals used for?
To prevent internal and external oil leakage
Seals are crucial components in various mechanical applications to maintain fluid integrity.
What are the key considerations for seal material and selection?
- Operating pressures and temperatures
- Fluid compatibility
- Cylinder speed
- Clearance to be sealed
- Internal friction
- Finish of the sealing surface
- Chemical reaction with the product
- Durability
These considerations ensure optimal performance and longevity of the seal.
What are the two main types of seals?
Positive seals and non-positive seals
These seals are utilized in either dynamic or static applications.
What is a positive seal?
A seal that does not allow leakage
Positive seals are essential in applications where leakage is unacceptable.
List examples of positive seals used in hydraulics.
- Flat gaskets
- O-rings between stationary surfaces
- Metal-to-metal joints on housings
- Sealant between metal surfaces
- Connector fittings on pipes, tubes, and hoses
- Plugs
- Poppet and seat
Each of these examples serves to enhance the integrity of hydraulic systems.
What is a non-positive seal?
A seal that allows controlled leakage for lubrication
Non-positive seals are typically used in dynamic applications where movement occurs.
Provide examples of non-positive seals.
- The rotating element of a pump or motor against the valve plate
- Vane tips against the cam ring
- Pistons against the cylinder walls
- Gear teeth against the casing and against each other at the mesh point
- Between the high-pressure lip seal and the drive shaft on pumps and motors
- Between valve spools and the bore
These seals facilitate necessary lubrication while minimizing wear.
What are static seals?
Seals that provide a seal between two surfaces that do not move with respect to each other
Static seals are critical in preventing leakage in stationary applications.
What are dynamic seals?
Seals that must seal against a moving surface
Dynamic seals often allow for controlled leakage to reduce heat and wear.
True or False: Non-positive seals are used exclusively in static applications.
False
Non-positive seals are primarily used in dynamic applications.
What are piston seals?
Internal seals that prevent or minimize fluid bypassing from one side of the piston to the other.
What are the two general classes of piston seals?
- Non-metallic
- Metallic
List some common types of non-metallic piston seals.
- Dynamic O-rings
- U-cup packing
- V-cup packing
- Cup seals
- T-ring seals
What is a dynamic O-ring?
An O-ring used as a piston seal that has a smoother finish than static O-rings.
Why do dynamic O-rings require a backup ring?
To prevent extrusion and damage of the O-ring.
What are the three purposes of a backup ring for dynamic O-rings?
- Allows more clearance to reduce compression and friction
- Supports the O-ring against extrusion
- Acts as a wiper to exclude abrasives
Fill in the blank: Piston seals prevent or minimize fluid bypassing from one side of the _______ to the other.
[piston]
What are U-cup and V-cup packings primarily used for?
Piston seals
They are effective at preventing internal leakage.
How are U-cup and V-cup packings installed?
In sets held in place by a gland
The open face of the seals faces the pressure side.
What role does pressure play in the function of U-cup and V-cup packings?
It forces the lip of the seal to seal against the cylinder wall.
In a double acting cylinder, what is required for sealing?
A second set of packing to seal each side of the piston.
What supports cup seals?
Steel back plates
Cup seals are held in place with a nut threaded onto the end of the piston rod.
What type of seals are supported by backup rings?
T-ring seals.
What is the function of cup seals?
They are pressure actuated.
What clamps cups tightly in place for cup seals?
Backing plate and retainers.
Fill in the blank: U-cup and V-cup packings are effective at preventing _______.
internal leakage.
True or False: T-ring seals do not require backup rings.
False.
What is the cross-section shape of metallic piston seals?
Rectangular or square
What materials are metallic piston seals usually made of?
Cast-iron, steel, or chrome plated
List the characteristics of metallic piston seals
- Hard wearing
- Compatible with high temperatures
- Withstand high pressures
- Allow some leakage
True or False: Metallic piston seals do not allow any leakage.
False
What happens to metallic seals under load due to leakage?
They creep under load
If creep cannot be tolerated, what should be done regarding metallic seals?
They should not be used
What components are included in a rod seal assembly?
- Rod seal
- Rod bushing
- Rod wiper
What is the purpose of the rod seal in a rod seal assembly?
To seal the rod end of the cylinder to prevent external leakage
What supports the rod as it extends in a rod seal assembly?
Rod bushing
What is the function of the rod wiper in a rod seal assembly?
To prevent contamination from coming into the cylinder as the rod retracts
What are cylinder cushions used for?
To slow the cylinder piston at the end of the stroke to prevent mechanical shock
Where can cylinder cushions be applied?
On one end of a cylinder or both ends depending on the application
How does a cylinder cushion assembly work?
The piston travels at a constant speed until the plunger blocks the discharge flow at the main port
What controls the discharge rate in a cylinder cushion?
A needle valve within a small cushion passage
What happens when the discharge flow is restricted in a cylinder cushion?
The piston is forced to slow down to a controlled speed at the end of the stroke
What is the function of the cushion collar on the rod side of the piston?
To slow the piston down when the cylinder extends
Fill in the blank: Cylinder cushions can be used on _______ of a cylinder.
[one end or both ends]
True or False: Cylinder cushions help prevent hammering of the piston against the end cap.
True
What is the main benefit of having cylinder cushions in a hydraulic system?
To reduce mechanical shock and improve the lifespan of components
What kind of control is a cylinder cushion?
Meter out flow control
Keep in mind this type of flow control put pressure on the rod seals
What is a stop tube?
It is a metal collar that fits over the piston rod next to the piston, it is used on cylinders with long rods to better support side loads and reduce load on the rod bushing
What does torque depend on?
Torque depends on:
* Inlet pressure
* Surface area of motor elements
* Radius of rotation
How does inlet pressure affect torque?
Increasing inlet pressure increases input torque
What is the relationship between surface area and torque?
Larger surface area of pistons, gear teeth, or vanes delivers more torque
What is the formula for force in relation to pressure and area?
Force = Pressure x Area
How does the radius of rotation influence torque?
A larger radius of rotation increases torque
What is starting torque?
Starting torque is the amount of torque required to start the motor turning
What factors influence starting torque?
Starting torque depends on:
* Amount of static friction
* Mass of moving parts
True or False: Static friction is always lower than dynamic friction.
False
What is the significance of starting torque in hydraulic motors?
Starting torque indicates the maximum torque available to begin motion when at rest
What is efficiency in the context of machines or engines?
Efficiency is the ratio of work done or energy developed compared to energy supplied
How is mechanical efficiency defined?
Mechanical efficiency is the actual torque delivered compared to theoretical torque with no friction
What reduces mechanical efficiency in motors?
Internal friction in the motor
What are the features of Low Speed High Torque hydraulic motors?
Smooth operation under heavy loads
High starting and stall torque
Start smoothly under full load
Little torque variation over the speed range
What are some applications of low speed high torque motors?
Crane hoists, dynamic earth rollers,
Slow turning vacuum screens and drums in process plants, power steering motors on heavy equipment
What are the common types of low speed high torque motors?
Radial piston, cam type radial piston
And Roller vane generators
What are some features of high speed low torque motors
Operate continuously at high speeds
Maintain high speed at constant or variable loads
What are some applications of HSLT motors?
Fans, generators, compressors
What are the common types of high speed low torque motors?
In line axial piston, bent axis piston, vane and gear pumps
What is a limited rotation motor?
A motor that has been modified to only allow the motor to turn part of a revolution
What is one advantage of hydraulic systems regarding torque or force control?
Hydraulic systems have infinitely variable torque or force control.
How do hydraulic systems control the direction of movement?
Hydraulic systems have instant control of the direction of movement (such as forward, reverse, and stop).
What aspect of movement control do hydraulic systems excel in?
Hydraulic systems control movement very accurately.
What happens when a hydraulic system is overloaded?
Hydraulic systems automatically stop transmitting power when the system is overloaded and restarts automatically when the overload is relieved.
What is a key flexibility advantage of hydraulic systems?
Hydraulic systems are highly flexible in terms of transmitting power over distances and into difficult-to-access locations.
How compact are hydraulic components?
Hydraulic components are very compact with respect to the amount of power they can transmit.
What is the efficiency of power transmission in hydraulic systems?
Power is transmitted very efficiently through fluids, with very little loss from friction.
Fill in the blank: One disadvantage of hydraulic systems is that they can be _______.
expensive.
Fill in the blank: Hydraulic systems can be _______ due to their components.
heavy.
True or False: Hydraulic systems operate at low pressure.
False.
What is a potential hazard associated with hydraulic systems?
High pressure can be a hazard if there is a failure.
What issues can fluid leaks from hydraulic systems cause?
Fluid leaks are messy, difficult to control, and could pose an environmental risk.
What fire hazard is associated with hydraulic systems?
Hydraulic fluids may present a fire hazard.
What is pressure in a hydraulic system?
Pressure is created by resistance to flow, which can be due to a restriction in the flow’s path or a load acting on a contained fluid.
How is pressure transmitted in hydraulic fluid?
Pressure transmits almost instantly through the fluid because hydraulic fluid is almost incompressible.
What is the unit of pressure in the imperial system?
Pounds per square inch (psi).
What is the unit of pressure in the metric system?
Bar.
What does Pascal’s Law state?
Pressure acting on any fluid at rest in a confined container is transmitted undiminished, equally in all directions, and at right angles to every point on the inside surface of a container.
When does Pascal’s Law apply?
Pascal’s Law applies when a fluid is not flowing.
What are the three elements that Pascal’s Law relates?
- Force, measured in pounds (Ib) or Newtons (N)
- Pressure, measured in psi, kPa or bar
- Area, measured in in² or metric (mm², cm², or m²)
Fill in the blank: Pressure is created by _______.
[resistance to flow]
True or False: Pressure in a hydraulic system creates a force when it acts on an area.
True.
Section 2B
What are the benefits of petroleum based hydraulic fluids?
Low cost, readily available, good viscosity index, additives for corrosion inhibitors and anti foam, good lube qualities, relatively low toxicity
2B what are the main disadvantages of petroleum based fluids?
At temps above 60’c the oxidation rate doubles every 10’ over reducing fluid half life,
Compared to other fluid’s petroleum based are more flammable/combustable due to low flash point (+300’f)
2B what are the functions of hydraulic fluid?
Lubricates moving parts,
Helps seal clearances,
Carries heat away from components,
Flushes contaminants from components
2B what is the result of reducing friction?
Power savings, reduced heat, and more accurate movement in valves and actuators
160302b-ce
2B what are other properties that need to be considered when selecting a hydraulic fluid?
Compatibility with seals and hoses;
Ability to resist foaming;
Ability to seperate from air/water;
High viscosity index; ( maintain viscosity throughout temp range)
Low pour point;
Fire resistance in some applications
2B what are the types of hydraulic fluids?
Fire resistant
Petroleum
Biodegradable fluids
2B what are the main kind of fire resistant fluids?
Water based; HWBF, Invert emulsions, water glycols
Synthetics; Polyol-ester, phosphate ester
What are the types of biodegradable fluids?
Sections 2B
Vegetable based and synthetic
160302b-cE
At what temperature does the iso measure viscosity?
40’c (104’f) measuring kinematic viscosity which is measured in centistokes
Section 2B
What are the characteristics of water based fluids?
More expensive than petroleum based
Heavier than petroleum based so pump inlet should be below reservoir
Oxidize faster, must change more frequently
Section 2B exam
What is different about HWBF?
Type of fire resistant fluid, typically 60% water 40% oil but can go as high as 95% water content
Section 2B
What is the difference between HWBF and invert emulsions?
HWBF has a higher water content whereas invert emulsions use a higher oil content
Section 2B
What problems arise when using emulsions for hydraulic fluid?
Decreased lubrication (shortening component life)
Under certain conditions they can support bacteria growth which can block off passages/filters
Sometimes difficult to maintain the emulsion, causing water/oil seperation
Not designed for low temps, will freeze
Tend to foam
Section 2B what are the main advantages/disadvantages of a water/glycol fluid compared to other water bases?
Glycol mixes with water and will not seperate
More fire resistant fluid
Operate at lower temps, lower freezing point the disadvantage however is they do not lubricate as well as
Section 2B exam
What are the 2 main types of synthetic fluid?
Phosphate Ester
Polyol Ester (biodegradable)
Section 2B what are the characteristics of synthetic fluid?
Better resistance to oxidation
Reduced friction
High viscosity index
Increased life with longer change out intervals
Operate at high pressure
Available in fire resistance types
May require special seal and hose material
Section 2B
What are the drawbacks of phosphate ester?
Toxic, not compatible with paints adhesives, some polymers and seal materials, can damage system components when exposed to water,
May react with metals like zinc, brass and bronze
Section 2B when are biodegradable oils used?
When environmental consideration are important, the oil must meet the following conditions; must be possible for 70-80% of the base fluid to be broken down within a given time
And the fluid must be non toxic
Section 2B what are the characteristics of vegetable oils?
Poor thermal stability,oxidize rapidly, break down much faster than non vegetable oils, create sludge, typically made from soy or canola, suitable lube properties, cheap, non toxic, fire resistant
Section 2B what are the characteristics of polyol ester?
Fire resistant, good lube properties, environmentally friendly, can use nitrile seals, however use is limited by extremely high cost
Section 2B
What is the function of a reservoir?
Warm/cool fluid as needed
Deaerate fluid
Allow contaminants to settle out
Reduces turbulence from return lines
Can serve as platform for pump, motor or other system components
Section 2B how are tanks sized?
2-3 times the pump output
Section 2B
What is the purpose of the baffle in a hydraulic tank?
To prevent turbulence;
Promote cooling
Promote settling of contaminants
Allows air to escape to reduce foaming
Provide a barrier between return lines and inlet to keep return oil from circulating immediately to pump inlet
Section 2B what is the purpose of the angle cut on the return line outlet?
Reduce fluid velocity, directs fluid to tank wall, promoting heat exchange
Section 2B
Why is the breather necessary on a reservoir?
Allows air in/out
Prevents air pressure from being too low which would cause cavitation or conversely being too high which would cause aeration
Responsible for contamination control (3 micron filter is good size)
Section 2B what are some accessories of reservoirs ?
Heaters, coolers (air/water), filler fittings (quick connects), level indicators/alarms
Magnets for contamination
Section 2B what are the 3 types of reservoirs?
Open, pressurized and closed circuit
Section 2B what are the 3 kinda of fluid conductors?
Pipe, hose, tubing
Section 2B how do you size fluid conductors?
Pipe; nominal/ wall thickness (sked number
Hose; inside diameter (dash number/16)
Tubing; outside diameter, max 2” then its pipe
Section 2B when flaring tube for a hydraulic system, what angle must the flaring be, and how would you check?
37 degrees, check with a business card
Section 2B how are hoses sized?
By inside diameter in 16ths of an inch, give as a dash number eg -6 is a 3/8” hose
Section 2B when are flexible conductors such as hoses used in hydraulics?
When components move relative to each other ( moving cylinder )
When lines are subject to movement or flexing
Excessive vibration
Frequent pressure pulsations
What is one advantage of hydraulic systems related to speed control?
Hydraulic systems have infinitely variable speed control.
This allows for precise adjustments in speed for various applications.
How do hydraulic systems manage torque or force?
Hydraulic systems have infinitely variable torque or force control.
This feature enables operators to fine-tune the amount of force exerted.
What allows hydraulic systems to control movement direction instantly?
Hydraulic systems have instant control of the direction of movement.
This includes options to move forward, reverse, or stop immediately.
How accurately do hydraulic systems control movement?
Hydraulic systems control movement very accurately.
This precision is essential for applications requiring exact positioning.
What happens when a hydraulic system is overloaded?
Hydraulic systems automatically stop transmitting power when overloaded and restart automatically when the overload is relieved.
This safety feature helps prevent damage to the system.
What is a key advantage of hydraulic systems regarding power transmission?
Hydraulic systems are highly flexible in transmitting power over distances and into difficult-to-access locations.
This flexibility makes hydraulic systems suitable for various industrial applications.
How compact are hydraulic components compared to the power they transmit?
Hydraulic components are very compact with respect to the amount of power they can transmit.
This compactness allows for space-efficient designs in machinery.
What is the efficiency of power transmission in hydraulic systems?
Power is transmitted very efficiently through fluids, with very little loss from friction.
This efficiency is one of the reasons hydraulic systems are widely used.
What is one disadvantage of hydraulic systems related to cost?
Hydraulic systems can be expensive.
The initial investment and maintenance costs can be significant.
What is a potential concern regarding the weight of hydraulic systems?
Hydraulic systems can be heavy.
This can limit their application in weight-sensitive environments.
What is a safety concern associated with hydraulic systems operating at high pressure?
High-pressure operation can be a hazard if there is a failure.
Failures can lead to dangerous situations, including bursts and leaks.
What issues are associated with fluid leaks in hydraulic systems?
Fluid leaks are messy, difficult to control, and could pose an environmental risk.
Managing leaks is critical to maintaining safety and environmental standards.
What fire hazard is associated with hydraulic fluids?
Hydraulic fluids may present a fire hazard.
Proper handling and storage of hydraulic fluids are essential to minimize fire risks.
What is pascals law?
States that pressure acting on any fluid at rest in a confined space is transmitted
Equally in all directions, undiminished, and at right angles to every point inside the surface of the container
