Project challenge: Simulate rigorous pressure gradients using a hyperbaric chamber

Natural Scientific Services was asked to conduct an environmental impact study prior to the building of a dual-direction Hydro Electric dam. Part of the study was to determine whether a specific species of fish could survive passage upstream or downstream, and cross-breed with other fish at the destination – an undesirable upset to a delicate ecosystem.
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It was required that we build a device that could accurately simulate the rigorous pressure gradients that would be experienced through the system, the worst of which was 0 bar to 80 bar in 0.2 seconds.

DETERMINE WHETHER FISH SPECIES CAN SURVIVE THE PRESSURE GRADIENTS

JAD solution

The requirement was to fill the chamber with water and then rapidly increase or decrease the pressure in the chamber, given a pressure profile from a spreadsheet file. 

A typical pump situation profile was required to precisely profile the pressure on the fish from 0 bar to 71Bar ( 942 PSI ) in 170mS within 1% deviation, then release the pressure over a further 30 second. 

In a typical discharge situation  the profile of the pressure on the fish gradually increased from 0 bar to 71 bar over 30 seconds and then released to atmosphere over 170mS via a specific profile.

JAD Systems developed a comprehensive solution as follows: 

• We supplied a 0.7m x 0.35m cylindrical tank with one end sealed, and on the other end a Moog hydraulic actuator was mounted. The entire tank could be filled with water and the fish being studied, and the pressure altered using the hydraulic actuator to reduce the volume of the tank.
• By measuring the pressure inside the tank, and controlling the actuator at a frequency of 1KHz, we were not only able to attain a controlled pressure gradient from 0 to 80 bar in 0.2 seconds, but were able to input a sequence of pressurisation and depressurisation gradient profiles to simulate passage through various sub-components of the dam.
• A 1000 sample / second log file of the desired vs actual pressure values was produced after each test run.

Component breakdown: 

• A 20 litre custom hyperbaric chamber is filled and bled off from the top to ensure no air in the system
• The hydraulic ram is controlled by a high-speed Moog valve, powered by a 5Kw pump with  a 200 Bar hydraulic storage vessel.
• The pressure in the chamber is measured using a high bandwidth 100 bar Gems pressure transducer.
• The control logic runs off a Beckhoff controller.
• The logging and display PC runs a custom LabView application.

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