REXA

Xpac Series

The REXA Xpac is a superior positioning device that is particularly well suited for applications requiring critical control and high reliability. The product is designed to thrive in the most hostile ambient environments and will harness control of the most severe process conditions. Our actuators and drives provide to final control elements capabilities to match the most sophisticated instrumentation and Distributed Control Systems.

Standard Configurations

REXA offers as standard: linear actuators (L series) with thrusts ranging from 2 000 to 120 000 lb and strokes to six inches; rotary units (R series) with rotations up to 90 degrees and torques ranging from 600 to 400 000 lb·in; and drive configurations (D series) with torques up to 200 000 lb·in and rotations up to 120 degrees.
 
Custom crafted units can provide considerably greater thrust or torque and longer strokes or rotation. Drives with multi-million pound inch capabilities are available.
 
The Electraulic power module is available in B, C, 1⁄2D and D sizes. The different power modules provide vari- ous stroking speeds for a given cylinder size as well as enhanced frequency response. This approach to prod- uct configuration offers a high degree of commonality to reduce spare parts inventory.

 

Advantages

CONTROLLABILITY—low deadband, immediate response, high stiffness, 100% modulating duty cycle The unit can respond to control signal changes as low as 0.05%.


HYDRAULIC STABILITY
 the process forces acting on the final control element will not move the Xpac.


TOTAL ELECTRIC OPERATION—self-contained, discrete movement, consistency of operation
A single electrical power source supplied directly to the control enclosure operates all aspects of the Xpac. Remote pumps or hydraulic sources are not required. Low power consumption is inher- ent, with the motor only turning when repositioning is required.


LOW MAINTENANCE 
Few moving parts (most of which are immersed in high quality motor oil) and sealed construction eliminate the need for routine mainte- nance. Parts inventory and repairs are simplified through consistent and modular design.


ELECTRONIC CALIBRATION
 Set-up is quick and simple with keypad calibration. There are no torque switches to adjust, potentiometers to turn, or dip switches to set.


CUSTOM MOUNTING
 REXA’s linear, rotary and drive configurations can be applied to virtu- ally any installation.


FAILURE POSITION
 A known position upon loss of electrical power can be provided by either a mechanical spring or hydraulic accumulator.


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Operation

By using the stroke and signal ranges set during calibration, the Central Processing Unit (CPU) converts the control signal into a target position. The actual position is determined through the active feedback assembly mounted on the actuator. The difference between the target and actual position is the error. If the error exceeds the deadband (user set), then the CPU will initiate corrective action by starting the motor.
 
A reversible hydraulic pump, driven by the motor, can pressurize either side of a double acting cylinder through one of two Flow Matching Valves. Each FMV is comprised of a ported spool with an integral pilot operated check valve. The construction of both FMVs is identical.
 
To move the cylinder shaft to the left, the pump turns in the direction to pressurize FMV-2 through port A. The spool in FMV-2 becomes unbalanced by the pressure differential and moves to the left, opening port A to port E. Check valve is lifted by the spool pilot to allow cylinder backflow.
 
High-pressure fluid flows through the check valve of FMV-1 in the normal direction and into the right side chamber of the cylinder. Since the hydraulic circuit is closed, the same amount of oil that flows into the right side of the piston must be extracted from the left side. This oil flows through the open check valve of FMV-2 and into pump suction via port B.
 
By reversing the direction of pump rotation, the FMVs
operate in reverse to move the cylinder shaft to the right. 
When the pump stops, both check valves close. The 
hydraulic oil is locked within the cylinder. Motor operation is not required to maintain position.

 

 

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Applications

Any industry involved with process control will improve the bottom line by using ElectraulicTM technology. Electric power generation, oil and gas pipelines, municipal water and wastewater head the list, but many others (paper, mining, refining/chemical, etc.) benefit also. Different applications present many challenges to valves and dampers. When control is the issue, you can rely on REXA.

 

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