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SwRI engineers develop new compressor plate valve
San Antonio -- December 29, 2005 -- Engineers at Southwest Research Institute® (SwRI®) have developed a long-life, semi-active plate valve for reciprocating compressors.
The new valve is one of several technologies developed during the Advanced Reciprocating Compression Technology program, conducted at SwRI and jointly funded by the Gas Machinery Research Council and the U.S. Department of Energy Office of Fossil Energy-National Energy Testing Laboratory Delivery Reliability Program.
Typically, reciprocating compressors use passive compressor valves. These valves experience high plate impact velocities that often result in fatigue failures and a short operating life, leading to frequent valve replacement.
"The SwRI-developed valve aims to increase the plate's life by drastically reducing plate impact velocities," said Dr. Klaus Brun, a program manager in SwRI's Mechanical and Materials Engineering Division and the principal developer of the valve. "Rather than springs, the design uses electromagnets to actively control impact velocities. The valve plate starting motion (both opening and closing) is sensed using an electric inductive motion sensor controlled by the electromagnets. Thus, no pressure transducers or shaft encoders are required to control plate motion," he said.
Stub shafts are rigidly connected to the valve plate to move with the plate. Electromagnetic coils are directly mounted on the stub shaft, and the stub shaft coils are surrounded by stationary, opposing force electrical coils. Movement of the plate results in induced current in the coils, which can be directly measured to determine the plate's velocity and location. If the plate's velocity exceeds the desired impact velocity, the magnetic coils can be used to control the position of the plate by inducing an opposing current.
During valve operation, once the valve plate's motion initiates because of a pressure differential across the valve, an electric current is induced into the coils. This current is sensed by an external controller, and the controller applies a larger counter-current to actively control the motion and impact velocities. Either a single current coil or two separate coils can be used for sensing and control.
This simple concept allows control of valve plates without the need for internal pressure transducers. Plate lift and impact velocity can be finely controlled to improve valve efficiency, capacity and life. If the plate control or electronics should fail, the shaft can be removed and the valve will continue to function in the same manner as a passive valve.
"A prototype version of this valve was successfully tested at SwRI's reciprocating compressor test bed facility. Results showed that the semi-active valve's plate impact velocities were reduced by up to 90 percent, increasing plate life by a factor of 15," Brun added. Further prototype development is ongoing, with field trials expected to start in 2006.
For more information about the semi-active plate valve and compression research at SwRI, contact Brun at (210) 522-5449 or via e-mail firstname.lastname@example.org.
For more information, contact Deborah S. Deffenbaugh, Communications Department, (210) 522-2046, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.