lecture 32 - wordpress.com · list the most common causes of hydraulic system breakdown. explain...
TRANSCRIPT
1
Lecture 32
MAINTENANCE OF FLUID POWER SYSTEMS Learning Objectives
Upon completion of this chapter, the student should be able to:
List the most common causes of hydraulic system breakdown. Explain the importance of cleanliness of hydraulic systems. Explain the problems caused by air in hydraulic systems. List the causes and remedy for excessive noise, incorrect flow, pressure and faulty operations. Describe the various general safety rules for electricity and electronics. List possible faults in solenoid valves. Explain the method for maintaining and disposing of fluids.
1.1 Introduction
The working medium in hydraulic systems is a fluid. Till the early 20th century, water was used as a
fluid. Water as a working fluid had many drawbacks, such as low freezing point, corrosive (rust
formation) nature and poor lubrication characteristics. Gradually, various oil-based fluids that had the
desirable properties were developed for use in hydraulic systems.
In a hydraulic system, a hydraulic fluid has to perform various functions, such as follows:
To transmit power, which is the primary function?
To lubricate various moving parts, so as to avoid metal-to-metal contact, and reduce wear and
noise.
To carry the heat generated in the system due to friction between moving parts and moving fluid, and to dissipate to the environment either through a suitable heat exchanger or through the reservoir.
To perform these functions and make the system work efficiently, a hydraulic fluid must be clean and
should possess certain properties.A hydraulic system is fairly easy to maintain: the fluid provides a
lubricant and protects against overload. But like any other mechanism, it must be operated properly. You
can damage a hydraulic system by too much speed, too much heat, too much pressure or too much
contamination.
The following is a list of most common causes of hydraulic system breakdown:
Clogged or dirty oil filters.
Inadequate supply of oil in the reservoir.
Leaking seals.
Loose inlet lines that cause the pump to take in air.
Incorrect type of oil.
Excessive oil temperature.
Excessive oil pressure.
Most of these and similar kinds of problems can be eliminated if a plant-preventive maintenance
program is undertaken. This starts with the fluid power designer in the selection of high-quality,
properly sized components. It is important for the total system to provide easy access to components
requiring periodic inspection such as filters, strainers, sight gauges, drain and fill plugs, flow meters, and
pressure and temperature gauges.
2
Over half of all hydraulic system problems have been traced directly to the oil. The test kit may be used
on the spot to determine whether fluid quality permits continued use. Test that can be performed include
the determination of viscosity, water content and particulate contamination level. Viscosity is measured
using a visage viscosity comparator. Water content is determined by the hot-plate method. Contamination
is eliminated by filtering a measured amount of hydraulic fluid, examining the particles caught on
the filters under microscope and comparing what is seen with the series of photos indicating
contamination levels.
For preventive maintenance techniques to be truly effective, it is necessary to have a good report and
record system. This report should include the following:
The types of symptoms encountered, how they were detected and the date.
The description of the maintenance performed. This should include the
replacement of parts, the amount of downtime and the date.
Records of dates when oil was tested added or changed. Dates of filter changes
should also be recorded.
Proper maintenance reduces hydraulic troubles. By caring for the system using a regular maintenance program, we can eliminate common problems and anticipate special ones. 1.2 The Importance of Cleanliness
Cleanliness is the first requirement when it comes to servicing hydraulic systems. Keep dirt and other contaminants out of the system. Small particles can score valves, seize pumps, clog orifices and cause expensive repair jobs. How to keep the hydraulic system clean? Let us put it this way:
Keep the oil clean.
Keep the system clean.
Keep your work area clean.
Be careful when you change or add oil.
1.3 Importance of Oil and Filter Changes
We cannot get peak performance out of a hydraulic system that is not clean. Despite all the precautions taken when working with the hydraulic system, some contaminants get into the system anyway. Good hydraulic oils hold these contaminants in suspension and filters collect them as the oil passes through. Good hydraulic oil contains many additives that work to keep contaminants from damaging or plugging the system. However, these additives lose their effectiveness after a period of time. Therefore, oil should be changed at the recommended intervals to make sure that the additives do their job. The system filters can absorb only a limited amount of dirt particles and other contaminants from the oil. After that the filters stop working. At this point, the filters should be cleaned or replaced with new ones so that the cleaning process can be maintained.
3
1.3.1 Draining the System
Periodic draining of the entire hydraulic system is very important. This is the only positive way to
completely remove contaminants, oxidized fluid and other substances from the system. The machine
operator’s manual tells the method to be used, and the frequency, depending on conditions.
1.3.2 Cleaning and Flushing the System
In some hydraulic systems, there might be deposits left in the system. It is advisable to clean and flush the system after draining the oil out. After draining the system, clean any sediment from the reservoir and clean or replace the filter elements. Flush out the old oil remaining in the system after
draining, particularly if the oil is badly contaminated. Drain out the flushing oil and refill the system
with clean hydraulic oil of the recommended type. Be sure to clean or replace the system filters
before refilling the system.
1.3.3 Filling the System
Before filling the system, be sure the area around the filler cap is clean. Fill the reservoir to the
specified level with the recommended hydraulic oil. Use only clean oil and funnels or containers, and
then be sure to replace the filler cap before operating the equipment.
1.3.4 Preventing Leaks
There are internal and external leakages. Internal leakage does not result in actual loss of oil but it
does reduce the efficiency of the system. External leakage does result in direct loss of oil and can
have other undesirable effects as well. A hydraulic system should always be monitored for leaks and
remedial actions should be taken immediately.
1.3.5 Preventing Overheating
Heat causes hydraulic oil to breakdown faster and lose its effectiveness. This is why cooling of the oil
is needed. In many systems, enough heat is dissipated through the lines, the components and the
reservoir to keep the oil fairly cool. But on high-pressure, high-speed circuits, oil coolers are needed to
dissipate the extra heat.
To help prevent overheating, keep the oil at the proper level; clean dirt and mud from lines, reservoirs
and coolers; check for dented and kinks lines; and keep relief valves adjusted properly. Also be
careful to not over speed or overload the system and never hold the control valve in power position
longer than necessary.
1.4 Problems Caused By Gases in Hydraulic Fluids
Gases can be present in a hydraulic fluid (or any other fluid) in three ways: free air, entrained gas and
dissolved air.
1.4.1 Free Air
Air can exist in a free pocket located at some high point of a hydraulic system (such as the highest elevation of a given pipeline). This free air either existed in the system when it was initially filled or
was formed due to air bubbles in the hydraulic fluid rising into the free pocket. Free air can cause the
hydraulic fluid to possess a much lower stiffness (bulk modulus), resulting in a spongy and unstable
operation of hydraulic actuators.
4
1.4.2 Entrained Gas
Entrained gas (gas bubbles within the hydraulic fluid) is created in two ways. Air bubbles can be created when the flowing hydraulic fluid sweeps air out of a free pocket and carries it along the fluid
stream. Entrained gas can also be created when the pressure drops below the vapor pressure of the
hydraulic fluid. When this happens, the bubbles of hydraulic fluid are created within the fluid stream.
Entrained gas can cause cavitation problems in pumps and valves. These gases can greatly reduce the
effective bulk modulus of hydraulic fluids, resulting in spongy and unstable operation of hydraulic
actuators.
Vapor pressure is defined as the pressure at which a liquid starts to boil and thus begins changing into a
vapor. The vapor pressure of a hydraulic fluid (or any other liquid) increases with an increase in
temperature. Petroleum-based and fire-resistant phosphate ester fluids have very low vapor pressures.
Cavitation occurs because the vapor bubbles collapse as they are exposed to the high pressure at the
outlet port of the pump, creating extremely high local fluid velocities. This high -velocity fluid
impacts internal metal surfaces of the pump. The resulting high impact forces cause flaking or pit ting the
surfaces of internal components such as gears, vanes, etc. Cavitation also interferes with the
lubrication of mating moving surfaces and thus produces increased wear.
One indication of cavitation is a loud noise emanating from the pump. The rapid collapsing of gas bubbles
produces vibrations of pump components, which are transmitted into pump noise. Cavitation also causes a
decrease in the pump flow rate because the pumping chambers do not completely fill with the hydraulic
fluid. As a result, the system pressure becomes erratic.
1.4.3 Dissolved Air
Dissolved air is in the solution and thus cannot be seen and does not add to the volume of the
hydraulic fluid. Hydraulic fluids can hold an amazingly large amount of air in the solution. A
hydraulic fluid, as received at atmospheric pressure, typically contains about 6% of dissolved air by
volume that increases to 10% when pumped.
Dissolved air creates no problem in hydraulic systems as long as the air remains dissolved. However,
if the dissolved air comes out of the solution, it forms bubbles in the hydraulic fluid and thus becomes
entrained air.
The following will help control or eliminate pump cavitation by keeping the suction pressure above the
vapor pressure of the fluid:
Keep suction velocities below 1.5 m/s.
Keep pump inlet lines as short as possible.
Minimize the number of fittings in the pump inlet line.
Mount the pump as close as possible to the reservoir.
Use low-pressure drop-pump inlet filters or strainers.
Use a properly designed reservoir that can remove entrained air from the fluid
before it enters the pump inlet line.
Use proper oil as recommended by the manufacturer.
Keep the oil from exceeding the recommended maximum temperature level.
5
1.5 Troubleshooting Guides
The following troubleshooting guides are arranged in five main categories. The heading of each is a
symptom that indicates some malfunction in the system. The causes and remedies are given in Tables
1.1–1.5.
1.5.1 Fluid Maintenance Fluid maintenance can be done in the following ways:
Before opening a drum, clean the top and the bung
Use only clean containers and hoses to transfer the hydraulic fluid.
Provide a 200-mesh screen in the reservoir filter pipe.
Store drums indoor or under a roof.
1.5.2 In-Operation Care of Hydraulic Fluid This can be done in the following ways:
Keep the system tight and repair all leaks immediately.
Use proper air and fluid filtration.
Establish fluid change intervals.
Keep the reservoir filled properly to take the advantage of its heat-dissipating characteristics
and prevent moisture from condensing on inside walls.
Table 1.1 Excessive noise
Symptom Cause Remedy Pump noisy Cavitation Any or all of the following:
Replace dirty filters. Wash strainers. Clean the clogged inlet line. Clean the reservoir breather vent. Change the system fluid. Change to proper pump drive motor speed. Overhaul or replace the pump. Check fluid temperature.
Air in fluid Any or all of the following: Tighten leaky inlet connections. Fill the reservoir to proper level. Bleed air from the system. Replace the pump shaft seal.
Coupling misaligned
All of the following:
Align unit.
Check the condition of seals, bearings and couplings. Pump worn or damaged
Overhaul or replace defective parts
Motor noisy Coupling misaligned
All of the following:
Align unit.
Check the condition of seals, bearings and couplings.
6
Motor or coupling worn or damaged
Overhaul or replace defective parts
Relief valve noisy
Setting too low or too close to another valve
setting
Install and adjust pressure gauge
Table 1.2 Excessive heat
Symptom Cause Remedy Pump heated Fluid heated See symptom “fluid heated”
Cavitation Any or all of the following:
Replace dirty filters. Wash strainers. Clean the clogged inlet line. Clean the reservoir breather vent. Change the system fluid. Change to proper pump drive motor speed. Overhaul or replace the pump. Check fluid temperature.
Air in fluid Any or all of the following: Tighten leaky inlet connections. Fill the reservoir to proper level. Bleed air from the system. Replace the pump shaft seal.
Excessive load All of the following:
Align unit.
Check the condition of seals, bearings and
couplings. Locate and correct mechanical binding. Check for workload in excess of circuit
design.
Pump worn or damaged
Overhaul or replace defective parts
Relief or unloading valve set too high
Install and adjust pressure gauge
Motor heated Fluid heated See symptom “fluid heated” Relief or unloading valve set
too high
Install and adjust pressure gauge
Excessive loading All of the following:
Align unit.
Locate and correct mechanical binding. seals, bearings and couplings.
Check for workload in excess of circuit design.
Motor or coupling worn or damaged
Overhaul or replace defective parts
Relief valve heated
Fluid heated See symptom “fluid heated” Valve setting incorrect
Install and adjust pressure gauge
7
Worn or damaged valve
Overhaul or replace defective parts
Fluid heated System pressure too high
Install and adjust pressure gauge Unloading valve set too high
Install and adjust pressure gauge Fluid dirty or low supply
Change filters.
Check system fluid viscosity, change if necessary.
Fill the reservoir to proper level.
Incorrect fluid viscosity
Change filters.
Check system fluid viscosity, change if necessary.
Fill the reservoir to proper level.
Faulty fluid cooling system
Clean the cooler and/or strainer.
Replace the cooler control valve. Repair or replace the cooler.
Worn pump, valve, motor, cylinder or other
component
Overhaul or replace defective parts
Table 1.3 Incorrect flow
Symptom Cause Remedy No flow Pump not receiving fluid Any or all of the following:
Replace dirty filters.
Clean the clogged inlet line. Clean the reservoir breather vent. Change the system fluid. Overhaul or replace the pump.
Pump drive motor not operating Overhaul
8
Pump to drive coupling sheared Check for the damaged pump Replace and align coupling.
Pump drive motor turning in the wrong direction
Reverse rotation
Directional control set in the wrong direction
Any or all of the following: Check the position of manually
operated controls. Check the electrical circuit on
solenoid- operated controls. Repair or replace pilot pressure
pump.
Entire flow passing over the relief valve
Adjust part Damaged pump Check for the damaged pump
Replace and align coupling.
Incorrectly assembled pump Overhaul or replace part Excessive flow Flow control set too high Adjust part
Yoke actuating device inoperative (variable displacement pumps)
Overhaul or replace part
Rotation per minute (RPM) of pump drive incorrect
Replace with correct unit
Improper size pump used for replacement
Replace with correct unit
Low flow Flow control set too low Adjust part Relief or unloading valve set too low Adjust part Flow bypassing through the partially open valve
Overhaul or replace part or any or all of the following:
Check the position of manually operated controls
Check the electrical circuit on solenoid- operated controls.
Repair or replace the pilot pressure pump.
External leak in the system Bleed air from the system.
Yoke actuating device inoperative (variable displacement pump)
Overhaul or replace part
RPM of pump drive motor incorrect Replace with correct unit
Worn pump, valve motor, cylinder or other
Overhaul or replace part
9
Table 1.4 Incorrect pressure
Symptom Cause Remedy No pressure No flop See “incorrect flow”, symptom
“no flow” Low pressure Pressure relief path exists See “incorrect flow,” symptom
“no flow” and “low flow” Pressure-reducing valve set too low Adjust part Pressure-reducing valve damaged Overhaul or replace part Damaged pump, motor or cylinder Overhaul or replace part
Erratic pressure Air in fluid Tighten leaky connections.
Fill the reservoir to proper level.
Bleed air from the system.
Worn relief valve Overhaul or replace part Contamination in fluid Replace dirty filters and system
fluid Accumulator defective or had lost charge Check the gas valve for
leakage. Change to correct
pressure.
Overhaul if defective.
Worn pump, motor or cylinder Overhaul or replace part Excessive pressure
Pressure-reducing, relief or unloading valve misadjusted
Adjust part
Yoke actuating device inoperative (variable displacement pumps)
Overhaul or replace part
Pressure-reducing, relief or unloading valve worn or damaged
Overhaul or replace part
10
or replace part
Table 1.5 Faulty operation
Symptom Cause Remedy No movement No flow or pressure See “incorrect flow”
Limit or sequence device
inoperative or misadjusted Overhaul or replace part
Mechanical bind Locate bind and repair No command signal to the servo amplifier
Repair command console or interconnecting wires
Inoperative or misadjusted servo amplifier
Adjust, repair or replace part
Inoperative servo valve Overhaul or replace part Worn or damaged cylinder or
motor Overhaul or replace part
Slow movement Low flow See “incorrect flow” Fluid viscosity to high Check fluid
temperature. Check system fluid
viscosity, change if
necessary.
Insufficient control pressure for
valves See “incorrect pressure”
No lubrication of machine ways
or linkage Lubricate
Misadjusted or malfunctioning
servo amplifier Adjust, repair or replace part
Sticking servo valve Clean and adjust or replace part.
Check the condition of system fluid and filters.
Worn or damaged cylinder or
motor Overhaul or replace part
Erratic movement Erratic pressure See “incorrect pressure” Air in fluid See “excessive noise” No lubrication of machine ways
or linkage Lubricate
Erratic command signal Repair command console or
interconnecting wires Misadjustment of
malfunctioning servo amplifier Adjust, repair or replace part
Malfunctioning feedback
transducer Overhaul or replace part
Sticking servo valve Clean and adjust or replace part.
Check the condition of system fluid and filters.
Worn or damaged cylinder or
motor Overhaul or replace part
Excessive speed or movement Excessive flow See “incorrect flow” Feedback transducer Overhaul
15
1.6 General Safety Rules for Electricity and Electronics
Following are the general safety rules for electricity and electronics:
Use approved tools, equipment and protective devices.
Avoid wearing rings, bracelets and similar meal items when working around
exposed electric circuits.
Never assume that a circuit is OFF. Double check it with an instrument that is
supposed to be surely operational.
Some situations require a “buddy system” to guarantee that power would not be turned ON
Never tamper with or try to override safety devices such as interlock (a type of
switch that automatically removes power when a door is opened or a panel
removes).
Keep tools and test equipment clean and in good working condition. Replace
insulated probes and leads at the first sign of deterioration.
Some devices, such as capacitors, can store a lethal charge. They may store this
charge for long periods of time. It must be certain that these devices are
discharged before working around them.
Do not remove grounds and do not use adapters that defeat the equipment ground.
Use protective clothing and safety glasses when handling high vacuum
devices such as picture tubes and cathode ray tubes.
Do not work on equipment before knowing proper procedures and having
awareness of any potential safety hazards.
1.6.1 Solenoid Valves Pneumatics will continue to dominate the power section and retain its positions in the control section. On
the other hand, it is impossible to deny the advances made by electronic controls, systems and
components due to the following advantages:
Low power consumption.
Short switching times.
Higher contact ratings.
Long service life.
Maintenance-free operation.
1.6.1.1 Possible Faults in Solenoid Valves Following are the possible faults:
Directed short (at power supply, electrical bus and load): A direct short is when too much
current is sent back to the power supply overloading it, generally blowing a fuse.
Cross short: A cross short is created by one or more wires (cables) bypassing the load causing a
direct short to occur.
High resistance connections (too many connections at the terminal eye).
Low voltage or over voltage at the solenoid.
Corrosion.
Partially or fully blocked hoses.
16
Wire connections are open internally
Lack of source pressure (at the compressor or on the service unit).
Sticking spool.
Diaphragm not working.
Exhaust ports blocked.
Gaskets mounted incorrectly.
Faults caused by wear or external influences.
Caution: Short circuiting of the power supply is not recommended without the installation of a
“circuit breaker” to protect the equipment and the user.
Causes and remedy for troubleshooting for direct shorts and faults in relay coil is given in Tables 1.6
and 1.7.
Table 1.6 Troubleshooting for direct shorts
Fault Cause Remedy When the push button is pressed, solenoid Y1 is not
activated and the circuit breaker must be reset.
Relay coil K1 has been shorted
directly to the ground bypassing the load (relay coil K1)
Pull the ground cable connected to solenoid Y1, retry the circuit.
If the power supply continues to short, the location of the direct short is at relay coil K1. If not,
the direct short is at solenoid
Y1.
Solenoid Y1 has been shorted directly to ground bypassing the
load (solenoid coil). This causes the relay coil to buzz (noise like
a bee) and the circuit breaker
must be reset. When proximity limit switch a1
and pressure switch a2 are
activated, solenoid Y3 is not
activated and the circuit breaker must be reset.
Relay coil K2 has been shorted
directly to ground, bypassing the load (relay load).
Pull the ground cable connected to solenoid Y3. Retry the
circuit. If power supply continues to short, the location
of the direct short is at relay coil K2. If not, the direct short is at
solenoid Y3.
Solenoid Y3 has been shorted
directly to ground, bypassing
the load (solenoid). The circuit
breaker must be reset.
15
Table 1.7 Faults in relay coils
Fault Cause Remedy When powered, the relay coil does not function.
One or more of the wires (leads) have an infinite resistance.
Use the voltmeter to check the
potential difference across each
cable and the push button when switch is open, then closed. If
the problem is with any of these
components
Open (infinite resistance) in the coil. Low voltage: Below specification.
Relay coil is not energized by
electrical limit switch (or
proximity limit switch).
The electrical limit switch is not being activated.
Visually examine the electrical limit switch to make sure that
the roller is fully activated. If
not, reposition the sensor so that
physical contact is achieved (or
see LED).
Use the voltmeter to test the
difference in potential across
the limit switch (24 V when open, 0 V when closed); replace
if not functioning or remove the
limit switch from the circuit and
use the ohmmeter to measure
the resistance of the limit switch
(infinite pressure when open,
approximately 0 when closed). One of the cables (wires) is
either not connected or there is
infinite resistance in the cable
(wire).
Use the multimeter to check the difference in potential across
each cable (wire) in the
corresponding ring. Then
remove the suspect cable(s) and
use the ohmmeter to confirm
your findings, replace the cables
if required. The relay coil itself is
malfunctioning, that is, low
voltage, an open (infinite
resistance) circuit, loose
connection, high-resistance
connection.
If the voltmeter identifies low
voltage, then check the power
supply and original source.
Replace or modify the source as
required. If an “open” infinite resistance,
loose or high connection is
suspected, use the ohmmeter to
determine the exact location of
the problem and repair/replace
as required.
16
1.7 Maintaining and Disposing of Fluids
Controlling pollution and conserving natural resources are important goals to achieve for the benefit of
society. Thus, it is important to minimize the generation of waste hydraulic fluids and to dispose them
in an environmentally friendly manner. The following are some recommendations that should be
adhered to strictly for properly maintaining and disposing hydraulic fluids:
Select the optimum fluid for the application involved. This includes the consideration of the
system operating pressures and temperatures as well as the desired fluid properties.
Utilize a well-designed filtration system to reduce contamination and increase the useful life
of the fluid. Filtration should be continued and filters should be changed at regular intervals.
3. Follow a proper storage procedure for the unused fluid supply. For example, outdoor
storage is not recommended, especially if the fluid is stored in drums as it is affected by increment weather and resulting weakening of drum seams may occur and cause leakage and contamination.
Fluids from the storage containers to the hydraulic systems should be transported carefully as
the chances of contamination depend to a large extent on handling. The transfer containers
should be covered when not in use.
Operating fluids should be checked regularly for viscosity, acidity, bulk modulus, specific
gravity, water content, additive levels and particle contamination.
The entire hydraulic system, including pumps, piping, filters, actuators and reservoir, should
be maintained according to the manufacturer’s specifications.
Corrective action should be taken to reduce or eliminate leakage from operating hydraulic
systems. Typically leakage occurs due to worn seals or loose fittings. A preventive maintenance program should be implemented to ensure ideal operating conditions and reduce
contamination, leakage, etc.
Fluids must be disposed properly because a hydraulic fluid is considered to be a waste material when it has deteriorated to the point where it is no longer suitable for use in
hydraulic systems. The various environmental government agencies also suggest against mixing hazardous wastes with waste hydraulic fluids being disposed. It is also not allowed to
burn these waste fluids in non-industrial boilers.
Pollution control and conservation of natural resources are critical environmental issues for
society. Properly maintaining and disposing of fluids not only protects the environment but
also conserves our natural resources.
15
Objective-Type Questions
Fill in the Blanks
1. The primary function of a hydraulic fluid is to transmit .
2. Over half of all hydraulic system problems have been traced directly to the .
3. Entrained gas can also occur when the pressure drops below the of the hydraulic fluid.
4. Cavitation occurs because the vapor bubbles collapse as they are exposed to the
pressure at the outlet port of the pump, creating extremely high local fluid velocities. 5. Oxidation is caused by the chemical reaction of oxygen from the air with particles of .
State True or False
1. Dissolved air creates no problem in hydraulic systems as long as the air remains dissolved.
2. Most of fire-resistant fluids are compatible with most natural or synthetic rubber seals. 3. The neutralization number is a measure of the relative acidity.
4. A 10 µm filter is one capable of removing contaminants as small as 10 µm in size. 5. Free air can cause the hydraulic fluid to possess a much lower stiffness.
Review Questions
1. Name five reasons for the overheating of the fluid in a hydraulic system.
2. Name four causes of low or erratic pressure. 3. What three devices are commonly used in the troubleshooting of hydraulic circuits?
4. Name five of the most common causes of hydraulic system breakdown.
5.List eight recommendations that should be followed for properly maintaining
and disposing hydraulic fluid.
6.Name two items that should be included in reports dealing with a maintenance procedure.
7. Name the three ways in which a hydraulic fluid becomes contaminated.
8. Name five things that can cause a noisy pump.
9.Name four causes of low or erratic pressure. 10.Name four causes of no pressure.
11.If an actuator fails to move, name five possible causes.
12.If an actuator has slow or erratic motion, name five possible causes. 13. Why is loss of pressure in a hydraulic system not a symptom of pump malfunction?
16
Answers
Fill in the Blanks
1. Power
2. Oil 3. Vapor pressure
4. High 5. Oil
State True or False
1. True
2. False
3. True 4. True
5. True