REXA, Terminal Inlet Pressure Control Application Spotlight (2/5/14)
Title:
Electraulic® Actuators Protect Terminals from Excessive Pipeline Pressure Variations
Background: In the transfer of crude oil and petroleum products from the main line to the terminal, control of the delivery pressure can be critical. Reductions in variations in delivery pressure will result in uniform delivery flow rates and will provide protection from over-pressure conditions in the terminal systems.
Such reductions in variation can be accomplished with a terminal inlet pressure control valve (also known as “holding pressure” or “delivery pressure” control) installed in the delivery line.
The Key to Success of this application is in engineering a valve/actuator assembly that is capable of with precise modulating control and rapid response to the normal pressure disturbances that occur in the main line. Pressure differentials across the valve ranging from 50 psid to 250 psid are considered normal during continuous duty. Any unwanted pressure excursions due to poor valve performance can cause unscheduled line shutdowns and result in unit downtime.
Problem: High pressure differentials are of particular concern, due to the potential for cavitation in the flow through the terminal inlet pressure control valve. Cavitation can be serious, in that pressures below the vapor pressure of the fluid can lead to vapor pockets or bubbles that can suddenly implode with possible damage to the flow line or equipment.
Pipeline companies seeking a solution to the problem of delivery pressure variation have found that REXA actuators provide stable control with high reliability.
Solution: Clearly, fast response to commands and precise modulation of the of the terminal inlet pressure control valve are essential to controlling flow and achieving pressures that are stable and within the acceptable range for safe operation. To meet these requirements, REXA’s X2 actuators based on the company’s proprietary Electraulic® technology have been selected. The self-contained X2 actuators combine the simplicity of electric operation, the power of hydraulics, the reliability of solid state electronics, and the flexibility of user-configured control.
Electraulic® technology is comprised of two primary subassemblies: a mechanical subassembly
and an electrical subassembly. The principle behind its technology is a unique hydraulic circuitry
called the flow match valve system. The actuator incorporates a bi-directional gear pump coupled
to either a stepper or an servo motor that provides a highly efficient method of pumping hydraulic fluid
from one side of a double-acting cylinder to the other. The discrete operation of the motor and pump creates action only when a position change is required. Once the required position is reached, the motor shuts off and the flow match valve system hydraulically locks the actuator in place. Minimal power is required to maintain actuator position. The motor and pump sit idle until a new command signal is received.