We were asked to develop a pressure chamber (aquarium) for evaluating how fish react to fast pressure changes associated with hydroelectric turbine passage. Some of the requirements of the project were:
1. Simulate the pressure excursion felt by fish as they approach and pass through a hydroelectric turbine. This included a depressurization spike with rates up to 300 psi/sec.
2. 45 psig maximum pressure.
3. A clear window around the chamber providing 360 degrees of visibility of the fish inside.
4. Maintain pressure for extended time periods while circulating river water.
5. Monitor and record pressure and temperature for extended periods.
6. Automate pressure controls for accurate and repeatable tests.
7. Provide a portable testing laboratory with 4 chambers that could be moved to different locations.
We chose to use Labview automation software for monitoring and controlling the chambers. Labview provides an environment for developing a custom computer graphical user interface (GUI) with a wide variety of controls and data logging options. Since the pressure change rate was so fast we decided to use a piston arrangement to change the pressure in the chamber. The piston was in contact with the water in the chamber so that when the piston moved, the pressure would change in the chamber. The piston was driven by a lead screw driven by a servo motor. The servo motor provides precise control of the pressure by a feedback loop. The inputs to the feedback loop are chamber pressure and chamber pressure set point. The output from the feedback loop was motor current and in turn motor torque - lead screw torque - piston force - chamber pressure.
The entire system is unique in the fact that it combines technology from aquaculture, hyperbaric chambers, environmental chambers, servo motor control, and laboratory automation. Some of the unique features of this system are:
1. A cylindrical acrylic pressure vessel window around the chamber. The window had to be cylindrical in order to be strong enough to resist the pressure. In order to eliminate visual distortion an additional rectangular window was fitted around the cylinder. The interface between the acrylic windows was filled with water. The flat sided window filled with water corrected the visual distortion of the cylindrical pressure vessel window.
2. A single computer was used to control the pressure of all 4 chambers. The typical testing protocol was to place the fish inside of the water filled chamber. Install the top cover then pressurize the chambers to an acclimation pressure for about 24 hours. After the acclimation period each chamber is run through it's pressure spike simulating the turbine passage. After that the fish were removed and examined.
3. The chambers designed and built using the PVHO (pressure vessel for human occupancy) standard based on the ASME pressure vessel code. Each chamber was stamped and registered.
4. The chambers have a lid that can be removed without tools. The lid also has a specially designed interlock that minimizes the chance of removing it when the chamber is pressurized. The lid is also supported by a spring loaded cable that gently lifts the lid out of the way when it is removed.
This project shows some of Tice Engineering's many various capabilities when it comes to solving problems for our customers. Please let us know if you have an unusual or demanding engineering project that we might be able to help with.