Lecture 9 Flashcards
What is hydraulics?
The branch of science and technology concerned with the conveyance of liquids through pipes and channels, especially as a source of mechanical force or control
What are the properties of hydraulics?
Consume less energy than pneumatics
Produe highly define actions
Are self lubricating and aid anti-corrision
What is hydraulic fluid?
Held within a closed system
Are considered to be incompressible therefor they can exert extreme pressures
Is a contaminant and therefore is not suitable for use in certain applications
What is pnuematics?
The branck of physics and technology concerned with the mechanical properties of gases
It is about relative pressure, hence a vacuum is also a property of pneumatics
What gases are used in pneumatics?
The gase used is inert and is often air or nitrogen
However, in the space industry, helium is used for Reaction Control Systems (RCS) for attitude control
When are pneumatics used?
The are considered clean and are therefore oten used in specialist industrial environments such as the food and robotics industries
Compare pneumatics to hydraulics
Due to rapid movement of air from a compressed source and also the venting process, pnuematic control systems are much faster than those of hydraulics, however miniaturisation reduces this difference
How do pneumatics work?
Pneumatics systems, in general, vent the gas used for actuation and therefor need a compressed source which is continually replenished
Compressed air can contain water that can cause problems
What is the centrifugal pump?
They have impellers i.e. a rotation component which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the centre of rotation
What are the advantages of a centrifulgal pump?
Suction and delivery occur at the same time
Simple operation and construction and therefore relatively cheap
What are the disadvantages of a centrifugal pump?
Requires priming
As the output resistance increases the discharge reduces because it is not a sealed system
There is a limit to the maximum pressure than can be delivered
What are some examples of a centrifugal pump?
Aquarium pump
Central heating pump
Industrial fluid pump
Screw centrifugal pump
What is the positive displacement pump?
Makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe
What are the advantages of a positive displacement pump?
Unlimited output pressure
Flow rate is constant for changes in output pressure
Can be used on high viscosity fluids
They create a vacuum at their input and can therefore perform suction lift
What is the disadvantage of a positive displacement pump?
Must have safety protection to limit output pressure
What are examples of a positive displacement pumps?
Linear pumps
Rotary pumps
How does a pump work?
A pump produces liquid movement or flow: it does not generate pressure
It produces the flow necessart for the development of presssure which is a function of resistance to fluid flow in the system
E.g. the pressure of the fluid at the pump outlet is virutally zero for a pump not connected to a closed system.
Further, for a pump delivering into a system, the pressure will rise only to the level necessary to overcome the resistance of the load
What does a circle represent in pump schematic symbols?
Circle represents motorised
What does a solid triangle represent in pump schematic symbols?
Solid triangle represents hydrualics rather than pneumatic
What do the number of triangles represent in pump schematic symbols?
One triangle - unidirectional
Two triangles - bidirectional
What does an arrow represent in pump schematic symbols?
Arrow indicates that the pump has variable displacement
What are the different activation methods?
Lever
Foot
Push button
Solenoid
What is a hydraulic fluid reservoir?
Although many hydraulic systems can be closed, many use a reservoir to replenish lost fluid for safety or to supply dynamic changes within the system design
What are hydraulic valves?
In order to create a hydraulic system, valves must be used to control the flow of fluid
