Prototype Conundrums

Yesterday I finished re-assembling part of the dismantled RaSSCAL prototype. All government operations require acronyms and my charge is no different: RaSSCAL means Randolph Steady State Core Analysis Laboratory. Essentially, the RaSSCAL flows a gas (N2, CO2, CH4, He) from one reservoir, through a rock sample, to a second reservoir at steady state to determine the rock sample’s permeability.

The rock sample is located in the core holder. The initial tank (first reservoir) in the system and all of the tubing leading to the core holder is upstream and the tubing going from the core holder to the second reservoir is downstream. Through out the upstream and downstream systems there are a series of paired valves (the electrically controlled solenoid valve uses air to actuate the pneumatic valve) which serve to isolate different stages along the tubing string. After I finished tightening the fittings, I opened the valves to flow gas through the system and … nothing.

This should not happen. Fluid (gas or liquid) flows from high pressure to low pressure. This is true every where (on earth). Whether getting oil out of the ground into a well bore or soda from the glass into the straw and then your mouth, fluids flow from high to low pressure.

Problem Solving Steps

  1. Check, double check, triple check all valves are open. Yes.
  2. Is the soft ware communicating with the DAQ board? (DAQ = data acquisition) As far as I could tell, yes. Asked colleague to confirm and he agreed.
  3. Is DAQ board actually outputting data? Given that downstream pressure is the only off reading and everything else registers, yes.
  4. Is the pressure transmitter functioning? Here, I essentially hijacked the Calibrations Specialist. He came down to my shop with his volt meter and determined that yes, there is a reading coming from the pressure transmitter. But, he could not confirm that it was actually calibrated, only that it output a reading. So we disassembled that portion of the system and he took the pressure sensor back to his calibrations lab for testing.

    The problem that I could not get past was the fact that the upstream pressure gauge kept registering positive pressure in the system, at least up to the core holder. Logically, the only reason it would not flow downstream is if there was a block or the upstream was isolated. But the valves were open — all valves green-lighted on my electrical panel.

    Before cranking up “Welcome to the Jungle,” grabbing my wrenches, and tearing the entire machine apart, I asked one of the Techs to come take a look. Maybe he could see something I missed.

  5. Walk through thought process with Tech to get him up to speed. Tech found the problem in relatively short order. It turns out that the house air valve (outside the RaSSCAL system) was closed. This means that although my panel, full of green lights, said the valves were all open, the air to actuate the pneumatic valves had been cut off. So, no, the valves were not open.

Tech was very gracious, said it was an honest mistake and one he’d made a dozen times. I thanked him, sprinted to the Calibrations Specialist’s lab to get the pressure transmitter back and let him know the Tech found the source of the problem. Sprinting might be an overstatement since a) I was wearing work boots and b) it was nearly 90 degrees with staggering humidity. I arrived gasping for breath.

The best part? You know I had fun.

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