Valve Positioners - IMI Critical

IMI is an industry-leading manufacturer of valve positioners. A valve positioner is a device used on an actuator (hydraulic or pneumatic) that provides feedback to the controller, ensuring that the actual movement of the valve stem aligns with the required movement. This functionality guarantees that the valve effectively responds to system demands. IMI STI actuator positioners, such as FasTrak, are digital-pneumatic valve controllers known for their high capacity, precision, excellent dynamic performance, and substantial flow characteristics. These pneumatic positioners are compatible with both single and double-acting actuators, whether or not they include a spring, piston, or diaphragm.

With competitive pricing and timely delivery, OLIVET sincerely hopes to become your trusted supplier and partner.

An actuator is an electric component within a machine, designed to move and control a system. It operates by utilizing a source of energy along with a control signal, which may be current, voltage, human power, hydraulic force, or pneumatic force. The primary function of an actuator is to convert energy from these sources into mechanical motion once a control signal is received. Various types of electric actuators exist, including soft, electrical, pneumatic, thermal, mechanical, and hydraulic actuators. This article focuses specifically on hydraulic actuators, detailing their functionality and applications.

What is a Hydraulic Actuator?

A hydraulic actuator is defined as a device that converts the pressure energy of a fluid into mechanical energy. It typically consists of a cylinder or fluid motor functioning through hydraulic power for mechanical operation. The mechanical output is available in the form of rotary, linear, or oscillatory motion. Hydraulic actuators utilize large forces since liquids are nearly incompressible.

The working principle of hydraulic actuators involves the use of liquid pressure instead of air pressure to exert force on a diaphragm and move the valve actuator connected to the valve stem. Most hydraulic actuators incorporate a piston rather than a diaphragm to convert liquid pressure into mechanical power.

Types of Hydraulic Actuators

Hydraulic actuators can be classified into three categories based on the mode of actuation:

• Linear Actuator: This actuator is used for linear movement and generates force or motion along a straight line. These hydraulic actuators are commonly referred to as hydraulic cylinders.
• Rotary Actuator: This type is used for rotary movement, generating torque and rotational motion. They are called hydraulic motors and can achieve constant angular movement.
• Semi-Rotary Actuator: These actuators are capable of partial angular movements, which may involve multiple complete revolutions; however, movements typically range up to 360 degrees.

Specifications of Hydraulic Actuators

Key specifications of hydraulic actuators include:

• Supply voltage is typically a full bridge of 24 V ± 10%
• Battery voltage varies from 20 V to 36 V
• Maximum input power is 40 VA
• Controlled current outputs range from 0 to 1.6 A
• Pulse width modulated signal operates at 160 Hz
• Primary current ranges from +0.2 to 1.1 A
• Maximum current is 1.6 A
• Differential inlet is 0 to ± 10 V or 0 to ± 20 mA
• Ramp time adjusts from 1 to 10 seconds at 100% of nominal value
• Ambient temperature typically falls between -10 °C and 70 °C
• Connections include Plug connectors, 64-pole & DIN

Hydraulic Actuator Systems and Operation

The schematic of a hydraulic actuator system operates based on Pascal's Law, which states that pressure applied to a confined fluid transmits evenly throughout the liquid and its container without loss.

If pressure (P) is applied to an area (A), the resulting output force can be calculated as:

F = P * A

When a specific force, F, is applied to a smaller area incorporating pressure P in a confined fluid, the generated force on a larger area can exceed that of the initial force generated by the pressure.

This method allows the pressure applied to a specific point to produce substantial forces, which forms the basis of numerous hydraulic systems. Key components of a hydraulic actuator include a spool or pilot valve and a main or power cylinder.

Operation begins when a pressure differential occurs across two areas of the main cylinder, prompting the piston to move. The cylinder comprises two regions and two chambers, separated by the main piston.

The fluid flow rate within the cylinder is regulated by the spool valve, which has four ports linked to different system parts. The first two ports connect to the drain and fluid supply respectively, while the other two connect to separate chambers in the main cylinder.

Initially, the spool valve is positioned at neutral, preventing fluid flow. Once input displacement is applied, the spool valve moves right, allowing fluid to transfer from the high-pressure source into the left chamber, thus increasing force on that side compared to the right, resulting in movement of the load.

The load follows the fluid flow direction, demonstrating power amplification as the force used to operate the valve is considerably less than the force generated to move the load. Hence, that's how hydraulic actuators function.

Advantages and Disadvantages of Hydraulic Actuators

Hydraulic actuators present several advantages:

• Simple design
• Cost-effective
• Robust construction
• High force capabilities
• Engine overload protection
• Quick mode change via rotating parts
• Simple transformation from rotary to reciprocating movement
• Can generate forces 25 times greater than comparable pneumatic cylinders
• Operational pressures can reach up to 4,000 psi
• Superior pressure and torque stability
• Pumps and motors can be placed at a significant distance with minimal power loss.

However, hydraulic actuators also have disadvantages:

• Lack of flexibility
• High maintenance requirements
• Temperature sensitivity
• Limited partial motion control
• Inadequate data collection abilities
• Overall low operating efficiency
• Efficiency is generally lower than other systems
• Operating conditions can significantly affect performance
• Require several supplemental components such as reservoirs, pumps, motors, heat exchangers, and noise reduction systems
• Fluid loss can result in reduced efficiency and potential hygiene issues, risking damage to surrounding components.

Applications of Hydraulic Actuators

Hydraulic actuators are widely used in various applications:

• High force-based applications
• Used in cranes, winches, self-driven cranes, excavators, wheel motors for military vehicles, feeders, agitator drives, mixers, roll mills, trammels, kilns, drum drives for digesters, automotive shredders, tires, drilling rigs, lawn trimmers, and trench cutters.
• Hydraulic jacks
• High-precision positioning for heavy loads
• Hydraulic brakes
• Closed-loop velocity control
• Hydraulic rams
• Also used as sensors

This article provides an overview of hydraulic actuators, their functionality, and applications. They are primarily employed to transform fluid pressure into mechanical energy, where the fluid's pressure acts on the piston, generating motion. Consequently, the piston rod can perform significant work. For further inquiries about hydraulic actuators, please visit our website at Remote Control Welding Positioner Manufacturing.