Linear actuators can be powered by electricity, pressurized fluid, or air. In this post, we will break down the key advantages and disadvantages (pros and cons) of hydraulic, pneumatic, and electric linear actuators. Additionally, you will be able to see the key differences of an electric over hydraulic linear actuator or a pneumatic over electric linear actuator, for example.
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Hydraulic linear actuators utilize a piston-cylinder configuration. An incompressible liquid from a pump fills the cylinder and forces the piston to move. With increased pressure, the piston moves linearly inside the cylinder, and the speed can be adjusted by changing the flow rate of the fluid. A high-speed hydraulic actuator is not only fast, but can supply a significant force. The piston returns to its retracted position by either a spring-back force or fluid being supplied to the opposite side.
Hydraulic actuators can hold a constant force without the pump supplying more fluid due to the use of an incompressible fluid.
They can produce very high forces and speeds.
It can produce high speeds.
Hydraulic fluid can leak, which leads to a loss in efficiency. This can also lead to cleanliness issues.
Require many accompanying components including a fluid reservoir, pumps, motors, release valves, heat exchangers, and noise reduction equipment.
High maintenance systems with numerous components to monitor constantly.
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Pneumatic actuators function in a similar way to hydraulic actuators with the difference being the driving fluid is air rather than hydraulic fluid. The gas is compressed in a piston-cylinder setup which creates a linear force.
A pneumatic linear actuator is very simple. Most aluminium cylinders have optimal maximum pressure ratings which allows for a range of forces.
A pneumatic linear actuator is often used in areas of extreme temperatures due to the safety of using air rather than hazardous chemicals or electricity.
It is a low-cost option.
Pressure losses and the compressibility of air make pneumatic devices less capable than other linear motion methods. A compressor must run continuously to maintain the operating pressure even if there is no movement needed.
Pneumatic actuators must be sized for a specific job in order to be efficient. This requires proportional sized valves, regulators, and compressors which raises the cost and complexity.
The air can be contaminated by oil or lubrication, leading to downtime and maintenance.
Electric linear actuators convert rotational motion into linear motion. Rotational motion is first generated by the electric motor. This high-speed rotational motion is then reduced by a gearbox to increase the torque that will be used to turn the lead screw. The turning of the lead screw results in linear motion of the acme drive nut. Think of it like driving a screw into a piece of wood, but rather than the screw moving towards the wood, the wood will be moving towards or away from the screw depending on the direction of rotation.
Electric linear actuators are adaptable, convenient, and provide the highest precision control!
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Electric actuators offer the highest precision.
Scalable for any purpose or force requirement.
They can be easily networked and programmed quickly. Immediate feedback for diagnostics and maintenance is available.
They provide complete control of motion, offering custom speeds, stroke lengths, and applied forces.
They are quieter than pneumatic and hydraulic actuators.
The initial cost is greater than that of pneumatic and hydraulic actuators.
They are not suitable for all conditions, whereas a pneumatic actuator is safe in hazardous and flammable areas.
The electric motors can be large.
Final Word
All three technologies have their place in the industry, but the flexibility of electric linear actuators, coupled with the fact that the price of electric components has been steadily decreasing over the years, makes them a more popular choice than they once were. Knowing what actuator is best for your application depends on your working environment.
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The electro-pneumatic action is a control system by the mean of air pressure for pipe organs, whereby air pressure, controlled by an electric current and operated by the keys of an organ console, opens and closes valves within wind chests, allowing the pipes to speak. This system also allows the console to be physically detached from the organ itself. The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.
Invention
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Although early experiments with Barker lever, tubular-pneumatic and electro-pneumatic actions date as far back as the s, credit for a feasible design is generally given to the English organist and inventor, Robert Hope-Jones.[1] He overcame the difficulties inherent in earlier designs by including a rotating centrifugal air blower and replacing banks of batteries with a DC generator, which provided electrical power to the organ. This allowed the construction of new pipe organs without any physical linkages whatsoever. Previous organs used tracker action, which requires a mechanical linkage between the console and the organ windchests, or tubular-pneumatic action, which linked the console and windchests with a large bundle of lead tubing.[1]
Operation
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When an organ key is depressed, an electric circuit is completed by means of a switch connected to that key. This causes a low-voltage current to flow through a cable to the windchest, upon which a rank, or multiple ranks of pipes are set. Within the chest, a small electro-magnet associated with the key that is pressed becomes energized. This causes a very small valve to open. This, in turn, allows wind pressure to activate a bellows or "pneumatic" which operates a larger valve. This valve causes a change of air pressure within a channel that leads to all pipes of that note. A separate "stop action" system is used to control the admittance of air or "wind" into the pipes of the rank or ranks selected by the organist's selection of stops, while other ranks are "stopped" from playing. The stop action can also be an electro-pneumatic action, or may be another type of action
This pneumatically assisted valve action is in contrast to a direct electric action in which each pipe's valve is opened directly by an electric solenoid which is attached to the valve.
Advantages and disadvantages
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The console of an organ which uses either type of electric action is connected to the other mechanisms by an electrical cable. This makes it possible for the console to be placed in any desirable location. It also permits the console to be movable, or to be installed on a "lift", as was the practice with theater organs.
While many consider tracker action organs to be more sensitive to the player's control, others find some tracker organs heavy to play and tubular-pneumatic organs to be sluggish, and so prefer electro-pneumatic or direct electric actions.
An electro-pneumatic action requires less current to operate than a direct electric action. This causes less demand on switch contacts. An organ using electro-pneumatic action was more reliable in operation than early direct electric organs until improvements were made in direct electric components.[2]
A disadvantage of an electro-pneumatic organ is its use of large quantities of thin perishable leather, usually lambskin. This requires an extensive "re-leathering" of the windchests every twenty-five to forty years depending upon the quality of the material used, the atmospheric conditions and the use of the organ.[2]
Like tracker and tubular action, electro-pneumatic action&#;when employing the commonly used pitman-style windchests&#;is less flexible in operation than direct electric action [citation needed]. When electro-pneumatic action uses unit windchests (as does the electro-pneumatic action constructed by organ builder Schoenstein & Co.[3]), then it works similarly to direct electric action, in which each rank operates independently, allowing "unification", where each individual rank on a windchest can be played at various octave ranges.
A drawback to older electric action organs was the large amount of wiring required for operation. With each stop tab and key being wired, the transmission cable could easily contain several hundred wires. The great number of wires required between the keyboards, the banks of relays and the organ itself, with each solenoid requiring its own signal wire, made the situation worse, especially if a wire was broken (this was particularly true with consoles located on lifts and/or turntables), which made tracing the break very difficult.
These problems increased with the size of the instrument, and it would not be unusual for a particular organ to contain over a hundred miles of wiring. The largest pipe organ in the world, the Boardwalk Hall Auditorium Organ, is said to contain more than 137,500 miles (221,300 km) of wire.[4] Modern electronic switching has largely overcome these physical problems.
Modern methods
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In the years after the advent of the transistor, and later, integrated circuits and microprocessors, miles of wiring and electro-pneumatic relays have given way to electronic and computerized control and relay systems, which have made the control of pipe organs much more efficient. But for its time, the electro-pneumatic action was considered a great success, and even today modernized versions of this action are used in many new pipe organs, especially in the United States and the United Kingdom.
References
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Further reading
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full citation needed
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