What is a hydraulic positioner?

Exploring Hydraulic Positioners

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What Constitutes a Hydraulic Positioner?

A hydraulic positioner is an apparatus that receives an electronic signal and translates it into specific valve movement or cylinder rod displacement.

Val Controls' Intelligent Hydraulic Positioner (IHP24) manages solenoid activated on/off valves, enabling an actuator to reach the designated set point. This includes modulation for open and closed functions, intermediate operations, or step control for choke valves. The IHP24 is specifically engineered for maneuvering hydraulic entities. Upon installation and setup, the IHP24 automatically calibrates, identifying both the fully open and fully closed positions of the device.

Pneumatic actuators are typically employed in processes that demand quick and precise responses, given their relatively low power requirements.

However, in scenarios where significant force is necessary to actuate a valve (for instance, in main steam system valves), hydraulic actuators are preferably utilized.

While hydraulic actuators present various designs, the piston-type actuator remains the most prevalent.

A standard piston-type hydraulic actuator is depicted in the accompanying figure, showcasing its composition, including a cylinder, piston, spring, hydraulic supply and return line, and stem.

The piston ascends and descends inside the cylinder, partitioning it into two distinct chambers: the upper chamber houses the spring, and the lower chamber contains hydraulic fluid.

The hydraulic supply and return line is linked to the lower chamber, enabling fluid circulation in and out of the actuator. The stem conveys the piston's motion to a valve.

Initially, with no hydraulic fluid pressure present, the spring's force keeps the valve closed. As fluid enters the lower chamber, the pressure within this chamber begins to rise.

This increase in pressure generates a force on the underside of the piston, counteracting the force exerted by the spring. When hydraulic pressure surpasses the spring force, the piston ascends, compressing the spring and allowing the valve to open.

As hydraulic pressure continues to heighten, the valve further opens. Conversely, when hydraulic oil is removed from the cylinder, hydraulic pressure diminishes, leading to the piston descending and the valve closing. By adjusting the volume of hydraulic oil supplied or drained, the valve can be positioned anywhere between fully open and fully closed.

The operational principles of hydraulic actuators are akin to those of pneumatic actuators, as both rely on a motive force to overcome spring resistance to shift the valve. Additionally, hydraulic actuators can be engineered for fail-safe functionalities, either to fail-open or fail-closed.

1. Hydraulic actuators are robust and ideal for applications requiring high force, producing forces up to 25 times greater than similar-sized pneumatic cylinders, capable of functioning under pressures as high as 4,000 psi.
2. A hydraulic actuator can maintain consistent force and torque without necessitating additional fluid or pressure due to the incompressible nature of liquids.
3. These actuators permit pumps and motors to be situated at significant distances with minimal power loss.

Hydraulic systems are prone to fluid leakage. Similar to pneumatic actuators, loss of fluid can lead to efficiency reductions and cleanliness challenges, potentially inflicting damage on adjacent components and areas.

Furthermore, hydraulic actuators necessitate various ancillary components including a fluid reservoir, motor, pump, release valves, and heat exchangers, in addition to noise reduction systems.