Heavy equipment technician

State three different safety precautions that must be observed when installing a pressure gauge into hydraulic system

1 Depressurize the system before installing the gage 2 Select pressure gauge approximately twice maximum System pressure 3 Be sure all lines and fittings will withstand at least twice maximum system pressure

Hydraulic accumulators perform the following 4 functions

1 Energy storage 2 shock absorption 3 gradual pressure build up 4 Constant pressure maintenance

List five advantages of hydrostatic transmissions.

1. Infinite motor speed control from maximum to zero in both directions of rotation. 2. Accurate motor speed can be maintained regardless of the load on the motor output shaft. 3. Quicker response to speed and direction changes then any other type of transmission. 4. Provides a hydrostatic lock of the motor when the output shaft speed is at zero. 5. The load cannot overrun the motor when the load is being decelerated, (A form of dynamic braking)

How much output power (in kW) must of the cylinder produce to accomplish a task described in question 13?round off your answer to the nearest two decimal places

10.39 kW

If the cylinder describing question 12 has a Rod diameter of 5.5 cm and a stroke length of 4.25 m what flowrate in liters per minute would be required to move the load from the fully extended position to the fully retracted position in seven seconds? round off your answer to the nearest 2 decimal places

199.56 L/min

Hydraulic cylinder but has a bore of 10 cm and a stroke of 4.25 m. How much pressure (in MPa) is required to overcome a load of 250 KG when the cylinder is extending? Round off your answer to the nearest 2 decimal places.

3.12 MPa

Flow meter test showed that the no load flow of a palm is 185L/min and the full load flow is 133L/min. The pump efficiency is?

72% No the pump efficiency is below 80% efficient and requires replacement or repair.

A diverter valve is a___ way ___ position directional control valve

A diverter valve is a 3 way 2 position direction control valve

What is a fault code?

A fault code is generated by the CPU to indicate the location and nature of a fault.

Define the term hydrostatic transmission, or HST?

A hydrostatic transmission is a Rotary Drive system that consists of a hydraulic pump, which is the input component, and a hydraulic motor which is the output component.

State with most appropriate flow control valve circuit for an application where the actuator load changes direction and strength

A meter out flow control circuit

If you wanted to measure the maximum pressure in a hydraulic system that is designed to operate at maximum pressure of 18MPa or 2610psi, you should use pressure gauge with the range of?

A pressure gauge with a pressure rating of 0-36MPa or 0-5000psi should be used.

How does a reference voltage sensor work.

A reference voltage sensor works by a predetermined voltage from the control device to the sensor, depending on the conditions acting upon it the sensor will return a voltage signal back to the control device. The control device will then make a decision based upon its comparison of the voltage signal to reference voltage.

What is a "snubber"

A snubber is an orifice that is placed in the inlet of a pressure gauge to dampen pressure spikes but could damage but internal mechanism of the gauge.

Which of the following components is not used in a closed center hydraulic system that is supplied with a fixed displacement pump A. relief valve B. Unloader valve C. Accumulator D. A closed directional control valve

A. Relief valve

List 4 advantages of hydraulic control of heavy equipment machinery functions

A: Hydraulic components are relatively compact, powerful light in weight B: components can be easily placed in the best position on the equipment C: easy cooling and lubrication of systems D: several functions can be operated at the same time increasing productivity E: precise and smooth implement positioning F: Easley protected from overload conditions without breakage or stalling

List 4 disadvantages of hydraulic control of heavy equipment machinery functions

A: fluids under pressure can result in personal injury or death if not handled safely B: there is always some noise produced by the system C: Oil leaks are a source of contamination and fire D: temperature variations affect component reliability and machine performance. E: Air trapped in the flow of oil can produce erratic and spongy machine operation and can result in component damage F: hydraulic systems must be manufactured and maintained correctly or they will operate inefficiently

Defined the term actuator cycle time.

Actuator cycle time refers to the amount of time required for the actuator to complete one cycle. For example, The time taken for an excavator bucket to move from fully dumped to fully Curl is known as bucket curl cycle time.

All backpressure valves are located in the

Actuator return line

A hydraulic system is defined as

All of the interconnected hydraulic components mounted on a vehicle or piece of equipment

State the function of an unloader valve

An unloader valve allows for full pump flow to return to the reservoir while maintaining minimum pressure at the pump outlet

Select two classifications that apply to pressure control valves A. Open center B. Normally open C. Closed center D. Normally closed E. Pressure compensated

B. Normally open D. Normally closed

The main disadvantage of electrically controlled hydraulic system is that they are? A: very expensive. B: not able to provide variable speed control. C: not very energy-efficient. D: operate on less than full system voltage.

B: not able to provide variable speed control.

On HST systems that are equipped with variable displacement motors, motor torque generation will?

Be reduced as motor displacement is reduced, or increase as motor displacement is increased.

The function of input devices in an electronic controlled hydraulic system is to? A: be the brain of the control system. B: actuate hydraulic components. C: send information in the form of electrical signals to the ECU. D: divide system self diagnosis.

C: send information in the form of electrical signals to the ECU.

What is a CPU?

Central processing unit. The CPU receives the input signals from the ECU, and compares the input signals with specifications in its internal programming. When necessary triggers a voltage output that is used to actuate the output components of the system. But the ECU may also be linked to other on board electronically controlled systems through a datalink connection, such as hydraulic system, engine and transmission.

The most commonly used HST in mobile heavy equipment is a?

Closed circuit system with a variable displacement, reversible pump.

Open center hydraulic systems are sometimes called?

Constant flow systems.

Proximity switches are commonly used in loader bucket kick out and lift height control systems. When the detector plate is in close proximity to the switch, the switch is? A: energized. B: grounded. C: Open. D: closed.

D: closed.

Why is it important to determine the root cause of a hydraulic system fault?

Determining the root cause of a hydraulic system fault and repairing it will prevent the system from failing again shortly after the initial repair.

What is the difference between discrete input sensor and variable input signal sensor.

Discrete input sensoris a switch the signal is either on or off. Variable input signal sensor such as a potentiometer or a variable resistor provide a variable voltage signal.

What are the advantages of an electronically controlled system?

Electro hydraulic systems provide a higher degree of operating speed and accuracy then other types of control systems. Electrically and electronically controlled hydraulic systemsdo not require as much maintenance as mechanical controlled systems. The performance of electrohydraulic control systemsare much more effective over long distances. Such as remote control radio control or laser for operator safety. When I microprocessor is incorporated into an electric hydraulic control system, it is possible to monitor hydraulic system operations. System monitoring can inform the operator of actuator position, speed, oil temperatures and pressures. Microprocessors can also offer laborsaving feature of self-diagnosis. System faults can be recognized coded for identification, time of occurrence and stored in memory for future retrieval by a technician.

What is a ECU?

Electronic control unit. The ECU is the brain of the control system, taking input signals from the sensors, comparing those signals with the parameters established in an internal program and actuating output devices as required.

The law of conservation of energy states that

Energy cannot be created or destroyed

When pressure testing a hydraulic system, you found working pressure to be abnormally high. One cause for the high reading could be?

Excessive friction or binding in the actuator or connecting linkages.

Actuator cycle times that are longer than manufacturers specifications normally indicate?

Excessive internal leakage.

A pressure reducing valve will block oil flow through the valve when pressure upstream of the valve overcomes the valve spring True False

False

Closed center directional control valves that are supplied by fixed displacement pumps use a relief valve to limit maximum system pressure. True or false

False They use a unloader valve to limit system pressure

One characteristic of open centre systems is high system pressure when the directional control valve is in the neutral position. True or false.

False. One characteristic of open center System is "low" system pressure when the directional control valve is in the neutral position.

In order to perform circuit leakage test with a flowmeter, the inlet of the flowmeter is connected in series in the pump outlet line. True or false?

False. The flowmeter is connected in parallel with the pump outlet line and the flowmeter outlet is connected to the reservoir.

Closed center directional control valves that are supplied by fixed displacement pumps use a relief valve to limit maximum system pressure. True or false

False: "Closed centre directional control valves that are supplied by fix displacement pumps use an unloader valve to limit maximum system pressure.

In an engine chemical energy in the fuel is converted to mechanical energy in the engine combustion chamber? True or false

False: Chemical energy in the fuel is converted to heat energy in the combustion chamber

Three disadvantages of testing a hydraulic system with a flowmeter are?

Flowmeter testing of a hydraulic system is often more time consuming than performing operational test. Connecting a flowmeter into a system requires that the system be opened up, running the risk of contamination entering the system. If the flowmeter was last used to test a system that had experienced a serious failure, contamination may be passed on to other systems being tested.

Potential energy in a hydraulic system is responsible for creating?

Force

Work is defined as a

Force acting through a distance

A group of interconnected components within a hydraulic system that are intended to perform a specific function is called a

Hydraulic circuit

At hydraulic actuator converts

Hydraulic energy into mechanical energy

List four conditions that should be looked at when performing a visual inspection of a hydraulic system.

Hydraulic oil level and tight. Hydraulic oil condition. Hydraulic oil leaks Signs of overheating. Obvious damage. Evidence of the quality of maintenance. Machine modifications.

Open centre hydraulic systems are most often used in applications where?

Hydraulic operations are not a high percentage of the machines duty cycle.

Why are loadsensing hydraulic systems more efficient than other types of systems?

Load sensing hydraulic systems are very efficient because they provide, as closely as possible, The precise amount of flow and pressure to perform the work demanded by the systems actuators.

Low charge pressure in a closed circuit hydrostatic transmission could cause________ damage to the hydrostatic pump.

Low charge pressure in a closed circuit hydrostatic transmission could cause cavitation damage to the hydrostatic pump.

List for safety precautions that must be observed before installing hydraulic test equipment.

Lower or mechanically secure all suspended loads. Relieve the pressure from the hydraulic tank system is equipped with a pressurized reservoir. Relieve any static pressure that it's trapped in the system. Depressurized any accumulators in the system.

Is it useful to operate the machine as part of the troubleshooting process. List three things that you should be looking for while operating.

Machine response. (slow, jerky). Smoothness of controls (no binding). Unusual noises. At what point in the machines cycle does the problem occur. Engine performance. Overheating components.

A pressure compensating flow control valve maintains constant flow through the valve by?

Maintaining a constant pressure drop across its orifice

List three sources of information that can be used as resources for technicians troubleshooting hydraulic systems.

Manufacture service manuals. Manufacture service bulletins. Operators manuals.

How can a fault code be accessed?

Many manufacturers use a display in the cab of the machine or on the ECU it's self. A series of flashing LEDs or a digital readout. Other systems use data line scanners or laptop computers interfaced with the ECU to access the diagnostic information.

List 4 common forms of energy?

Mechanical energy Hydraulic energy Heat energy Electrical energy Chemical energy Light energy Sound energy

Loader bucket kickout position and lift height can be adjusted by?

Moving the position of the proximity switch in relation to the detector plate.

List two safety precautions that must be observed when working on hydraulic systems that contain accumulators

Never use oxygen or compressed air in gas charged accumulators Always discharge systems equipped with accumulators prior to performing service

What are the two types of electronic control systems commonly used in mobile heavy equipment?

Open loop electronic control systems. Closed loop electronic control systems.

Auxiliary closed center directional control valve can be connected into existing closed center systems by connecting the auxiliary valve in_____

Parallel

What type of switches are generally used in electronically controlled hydraulic system?

Power switches, switch power on and off to the electronic control system. Operator control switches, why was the operator to control the electronic control system. Pressure switches, her actuated at a predetermined pressure. Proximity switches, indicate the location of system components.

Care must be taking not to excessively restrict the flow from the rod end of a double acting cylinder because

Pressure intensification may result in damage to system components

For pressure control valve the difference between cracking in full flow pressure is known as

Pressure override

The main advantage of using a pilot operated pressure control valve is that it

Provides maximum pressure override

Constant horsepower open center hydraulic systems maintain a constant power draw from the engine by varying?

Pump displacement proportionally to the load on the system.

What are the two categories of input devices or sensors?

Reference voltage sensors. Voltage generating sensors.

Voltage generating sensors produce their own voltage signal. What are the two types of voltage generating sensors?

Reluctance voltage generator. Rotating permanent magnet generator.

In a hydraulic system controlled by a microprocessor, Input devices are often referred to as?

Sensors.

The passage that carries pump oil flow through an open center directional control valve when it is in neutral is called the ____ passage

Series passage

Joysticks are lever operated potentiometers, and are commonly used as operator controls for electronic control systems. Are the two configurations of joystick controls?

Single axis "back and forth". Dual axis "Side to side and back-and-forth".

Energy is defined as?

The ability to do work

When two functions of open center, series parallel directional control valve are actuated at the same time, how will the actuators react?

The actuator with the lightest load will move first

The identifying characteristics of a closed center hydraulic system is?

The directional control valve always blocks pump flow when it is in neutral.

Connecticut energy in a hydraulic system is created by?

The flow of oil through the system

Although output components like warning lights or electric motors are sometimes used what is the most commonly used output component?

The most commonly used output component used in heavy equipment electrohydraulic systems is the solenoid.

What is the best source of information about how a machine had been performing prior to failure?

The operator.

The problem with a cylinder that heats up more rapidly than normal is?

The piston seals are leaking.

When testing pump efficiency with the flowmeter, the no load flow is found to be significantly lower than specification. The most common likely cause is that.

The pump inlet is restricted.

Excessively low pressures measured at the pump inlet indicates that?

The pump inlet is restricted. The pump drive shaft speed is too high. The wrong oil is being used.

In a HST motor state the function of a shuttle valve?

The shuttle valve or flushing valve in an HST pump directs some oil from the charge pump into the motor case for motor lubrication and cooling when the motor is rotating.

Excessively high neutral pressure in an open center hydraulic system indicates that?

There is excessive resistance in the lines, fittings, directional control valve, filter, or other return line components.

Why are closed center systems equipped with pressure compensated pumps often called demand type hydraulic systems?

These systems are called demand type hydraulic systems because flow is only provided when there is work to preform.

Two functions of a sequence valve are

To cause actions in a hydraulic system to the occur in a certain order and to maintain a predetermined minimum pressure in a primary function while a secondary function is an operation

A pressure compensator spools purpose is?

To limit maximum system pressure.

A circuit relief valve purpose is?

To protect each circuit against excessive pressure when the directional control valve is in the neutral position.

A regeneration valves purpose is?

To provide a fast bucket dump cycle time by restricting return oil and allowing it to supplement pump oil flow.

Flow compensator spools purpose is?

To regulate pump flow proportional to load pressure.

Force is the push or pull that is capable of producing or change in the motion of a body? true or false

True

One of the primary purposes of a lock valve is to prevent the load from drifting due to leakage True False

True

A pilot control circuit is low pressure hydraulic circuit used to remotely operated a directional control valve. True or false?

True.

Close center systems may be supplied with either a fixed or variable displacement pump? True or false?

True.

Internal leakage in a hydraulic motor can be quickly checked by measuring the amount of oil flowing from the drain line when the motor is at full load. True or false?

True.

The difference between an open and closed circuit HST is that the path of oil flow between the pump and motor is interrupted by the reservoir in the open circuit. True or false?

True.

The function of the bucket kick out on a wheel loader is to hold the bucket control lever in the rollback position until the bucket reaches the correct digging position? True or false.

True.

State three methods of connecting a directional control valve into an open center hydraulic system

Use a diverter valve Use a power beyond sleeve Use a flow divider

What is the purpose of a voltage generating sensor?

Voltage generating sensors are often used to sense the rotational speed of a hydraulic motor or it's driven component.

Hydraulic oil temperature is not an important factor to consider when performing tests. True or false.

false. Internal leakage increases significantly as hydraulic oil temperature rises.

You found that engine speed drop excessively when performing a hydraulic stall test on an open centre hydraulic system. The cause could be:

lack of engine power or the relief valve has been adjusted higher than manufactures specification.

What are output components of an electronic control system?

output components of an electronic control system are actuators that receive electrical power from the ECU so that a output action can be performed.