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Hydraulic actuators use liquid pressure rather than instrument air pressure to apply force on the diaphragm to move the valve actuator and then to position valve stem.
Nearly all hydraulic actuator designs use a piston rather than a diaphragm to convert fluid pressure into mechanical force.
The high pressure rating of piston actuators lends itself well to typical hydraulic system pressures, and the lubricating nature of hydraulic oil helps to overcome the characteristic friction of piston-type actuators.
Given the high pressure ratings of most hydraulic pistons, it is possible to generate tremendous actuating forces with a hydraulic actuator, even if the piston area is modest.
In addition to the ability of hydraulic actuators to easily generate extremely large forces, they also exhibit very stable positioning owing to the non-compressibility of hydraulic oil.
Unlike pneumatic actuators, where the actuating fluid (air) is “elastic,” the oil inside a hydraulic actuator cylinder does not yield appreciably under stress. If the passage of oil to and from a hydraulic cylinder is blocked by small valves, the actuator will become firmly “locked” into place.
This is an important feature for certain valve-positioning applications where the actuator must firmly hold the valve position in one position.
Some hydraulic actuators contain their own electrically-controlled pumps to provide the fluid power, so the valve is actually controlled by an electric signal.
Hydraulic actuators are a good choice when:
The movement you need to control is simple, without speed changes or multiple stops and starts.
You cannot afford “wiggle room.” There is no give in hydraulic pressure because it is virtually impossible to compress fluid, so hydraulic actuators can maintain force and torque steadily. For applications that require smoother travel, a cable-style, low-pressure hydraulic actuator may be the best choice.
For instance, if you need to raise and lower the platform on a parts elevator, smooth travel is essential. When the platform stops, a hydraulic actuator will hold it stationary. If you were to use a pneumatic actuator, any slight change in air pressure could cause the platform to move a little. Another good example is when you need to spray a smooth, uniform coating on a part.
The operating environment includes harsh conditions. Hydraulic actuators are both durable and reliable under duress, including shock loads. This is why you often see them used for outdoor applications. That said, in some working environments, temperature extremes can affect hydraulic performance either by causing premature seal failure or changing the viscosity of the hydraulic fluid.
Hydraulic actuators use liquid pressure rather than instrument air pressure to apply force on the diaphragm to move the valve actuator and then to position valve stem.
Nearly all hydraulic actuator designs use a piston rather than a diaphragm to convert fluid pressure into mechanical force.
The high pressure rating of piston actuators lends itself well to typical hydraulic system pressures, and the lubricating nature of hydraulic oil helps to overcome the characteristic friction of piston-type actuators.
Given the high pressure ratings of most hydraulic pistons, it is possible to generate tremendous actuating forces with a hydraulic actuator, even if the piston area is modest.
In addition to the ability of hydraulic actuators to easily generate extremely large forces, they also exhibit very stable positioning owing to the non-compressibility of hydraulic oil.
Unlike pneumatic actuators, where the actuating fluid (air) is “elastic,” the oil inside a hydraulic actuator cylinder does not yield appreciably under stress. If the passage of oil to and from a hydraulic cylinder is blocked by small valves, the actuator will become firmly “locked” into place.
This is an important feature for certain valve-positioning applications where the actuator must firmly hold the valve position in one position.
Some hydraulic actuators contain their own electrically-controlled pumps to provide the fluid power, so the valve is actually controlled by an electric signal.
Hydraulic actuators are a good choice when:
The movement you need to control is simple, without speed changes or multiple stops and starts.
You cannot afford “wiggle room.” There is no give in hydraulic pressure because it is virtually impossible to compress fluid, so hydraulic actuators can maintain force and torque steadily. For applications that require smoother travel, a cable-style, low-pressure hydraulic actuator may be the best choice.
For instance, if you need to raise and lower the platform on a parts elevator, smooth travel is essential. When the platform stops, a hydraulic actuator will hold it stationary. If you were to use a pneumatic actuator, any slight change in air pressure could cause the platform to move a little. Another good example is when you need to spray a smooth, uniform coating on a part.
The operating environment includes harsh conditions. Hydraulic actuators are both durable and reliable under duress, including shock loads. This is why you often see them used for outdoor applications. That said, in some working environments, temperature extremes can affect hydraulic performance either by causing premature seal failure or changing the viscosity of the hydraulic fluid.
