Hydraulics Pneumatics Revision What is meant by Viscosity

Hydraulics & Pneumatics Revision

What is meant by Viscosity

What is meant by Viscosity A hydraulic fluid's resistance to flow. As temperature increases, viscosity decreases.

What is meant by Viscosity Index

What is meant by Viscosity Index A number describing how the viscosity of a fluid changes with temperature. Fluids affected by temperature extremes have a low viscosity index, while fluids that maintain viscosity have a high viscosity index.

Items that have a direct influence on Oil

Items that have a direct influence on Oil • • Cooler Heater Baffle Plates Filters

State items, other than dates and signatures that should be included on a report form after a hydraulic maintenance or installation task has been completed.

State items, other than dates and signatures that should be included on a report form after a hydraulic maintenance or installation task has been completed. • Location of work. • Description of system or identification number of machine. • Time taken. • Brief description of work undertaken. • Spares or other materials used. • Staff involved. • Test or commissioning data.

Explain the main reason why a report form should be completed.

Explain the main reason why a report form should be completed. • Determining condition of machine (eg repair or replace in future). • Planning future maintenance.

Name types of hydraulic accumulator.

Name types of hydraulic accumulator. • • • Deadweight. Spring. Piston. Bladder. Flexible membrane. Free contact.

With reference to fitting flexible hydraulic hoses, explain what is meant by Damage and Distortion

With reference to fitting flexible hydraulic hoses, explain what is meant by Damage and Distortion • i) Damage • Use of (two) spanners of incorrect size on pipe and fittings which round off the nut. • ii) Distortion • Severe changes in direction, sharp corners, heat.

Explain reasons why accumulators are used in some hydraulic systems.

Explain reasons why accumulators are used in some hydraulic systems. • Maintain pressure in case of pump/power failure. • Smooth out pulsations (eg from piston type pumps). • Safely absorb pressure surges. • Provide additional pressure for peak periods. • Compensate for changes in volume due to variations in system pressure and temperature.

What is meant by Pour point.

What is meant by Pour point The pour point is the temperature at which a fluid begins to flow.

What is meant by Flash Point

What is meant by Flash point The temperature at which the hydraulic fluid surface emits enough vapour to ignite in the presence of a flame.

State factors that must be taken into account when planning a hydraulic system to keep pressure losses to a minimum.

State factors that must be taken into account when planning a hydraulic system to keep pressure losses to a minimum. Avoid long pipework runs Diameter of pipes. Internal condition of pipes. Sharp bends. Excessive use of adaptors. Number of components. .

Describe a characteristic other than viscosity that must be considered when selecting hydraulic oils.

Describe a characteristic other than viscosity that must be considered when selecting hydraulic oils. • • Viscosity index. Reaction with seals/components. Pour point. Flash point. Cost.

Explain different ways in which hydraulic oil can become contaminated.

Explain different ways in which hydraulic oil can become contaminated. • • • Lack of care during maintenance or assembly. Internal erosion. Seal failure. Moisture. Oxidation from overheating.

State benefits of using flexible hydraulic pipes compared to using rigid pipework.

State benefits of using flexible hydraulic pipes compared to using rigid pipework. • • • Special provision for bending not needed. Easier to fit in awkward situations. Absorb vibration. Absorb some pulsation. Easier to remove and replace for maintenance access.

With reference to the forces indicated, state the effect on force F when pressure is applied simultaneously to port ‘a’ and port ‘b’

With reference to the forces indicated, state the effect on force F when pressure is applied simultaneously to port ‘a’ and port ‘b’ It Reduces the force

Explain the function of the component

Explain the function of the component For raising a load. The cylinder needs to have a force exerted on the rod to cause it to in stroke after pressure is removed.

The figure below shows a part section of a pneumatic component. Explain the sequence of events and directions of air flows as the piston completes its stroke in the direction indicated on the diagram.

The figure below shows a part section of a pneumatic component. Explain the sequence of events and directions of air flows as the piston completes its stroke in the direction indicated on the diagram. Air is exhausted directly through the outlet port until the piston enters the reduced section. The remaining air can then only exhaust via the restrictor which cushions the piston movement.

Describe the purpose of Item A.

Describe the purpose of Item A. To admit air directly to the piston at the start of the reverse stroke.

Explain what is meant by a ‘Held’ or ‘Maintained’ signal.

Explain what is meant by a ‘Held’ or ‘Maintained’ signal. When a signal sent to a DCV to operate an actuator is still present and when the signal to reverse the actuator movement is received on the same DCV or signals act on both ends of a DCV at the same time.

State methods of overcoming Held problem.

State methods of overcoming Held problem. • Time delay (restrictor and reservoir system). • Impulse generator. • Cascade system.

With reference to electropneumatic circuits name types of sensors used.

With reference to electro-pneumatic circuits name types of sensors used. • • Magnetic. Induction. Reed switches. Photo-sensitive (or LED operated).

Explain the purpose of an electrical relay.

Explain the purpose of an electrical relay. • A device for converting a low power input from a signal source into a higher powered electrical output or a single signal that can cause a number of simultaneous electrical outputs.

Explain how a Programmable Logic controller (PLC) is set up to operate a pneumatic circuit.

Explain how a Programmable Logic controller (PLC) is set up to operate a pneumatic circuit. • The operational signals for the required sequence of the DCVs is loaded into the controller. The output leads from the controller are connected to the DCVs. Feed back signals from the limit switches are fed back to the controller.

Name the type of operating method used for limit switches and directional control valves in a PLC system.

Name the type of operating method used for limit switches and directional control valves in a PLC system. • Solenoid operated.

Explain advantages and limitations of using plastic/nylon pipes for pneumatic installations instead of copper pipes.

• • • Advantages No problems with bending or forming. No need to clean or de-burr. Flexible and not subject to vibrational stress. Different colours for easy identification. Limitations. Difficult to fasten neatly. Easily damaged by mechanical impact. Limited use in high temperature areas. Kink with sharp bends.

Describe precautions that must be taken when connecting components using nylon pipe.

Describe precautions that must be taken when connecting components using nylon pipe. • Carefully measure and cut to avoid sharp bends or excessive loose sections of pipe. • Clip securely to avoid moving parts (actuators or mechanical machinery). • Arrange methodically to facilitate tracing for fault diagnosis.

State items, other than dates and signatures, that should be included on a report form after a pneumatic maintenance or installation task has been completed.

State items, other than dates and signatures, that should be included on a report form after a pneumatic maintenance or installation task has been completed. • Location of work. • Description of system or identification number of machine (for example). • Time taken. • Brief description of work undertaken. • Spares or other materials used • Staff involved. • Test or commissioning data.

Explain the main reason why such a report should be completed.

Explain the main reason why such a report should be completed. • Determining condition of machine (eg repair or replace in future). • Planning future maintenance.

Explain factors that must be considered when selecting pipework for pneumatic systems.

Explain factors that must be considered when selecting pipework for pneumatic systems. • • • Volume of air that needs to be passed. Pressure of air. External temperatures. Methods of connecting. Risk of external damage.

Explain factors that can cause pressure drops throughout a pneumatic system.

Explain factors that can cause pressure drops throughout a pneumatic system. • • • Number of fittings. Reducing connector. Length of pipe. Internal condition of pipe. Velocity of air. Number and/or sharpness of bends.