Pneumatic co2 Extraction Machine Problems

I have been having some issues lately that I haven’t been able to resolve over the phone with the machine builder or manufacturers of individual components. The machines are Critical Solutions units. They use a Haskel chemical pump and a Maximator booster pump for their operation. The unresolved problem is culminating in the Maximator pump air drive section. The internals on the air drive section start to freeze over on the side closest to the high pressure housing. That then migrates up the pump in to the spool valve eventually freezing over. Every component in the Maximator pumps have been replaced with fresh seals as well as replaceable hard parts. The manufacturer of the systems pointed us in the direction of the air supply possibly having a failed air dryer since we were seeing a significant amount of water at the machine. Replaced the air dryer, which gave us notably cleaner air, but it’s still freezing the pumps over. I am honestly at a loss and could really use some help from someone with some more practical experience with these machines or something similar such as eden labs. I will post our current parameters and hopefully someone may be able to point something out that we may be overlooking. Cheers!
Setup Parameters:
1800PSI in Material Vessels
120F extraction vessel Temp
35F Chiller Temp
45F Separator Temp
65F incoming Air Temp

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How cold is the icing issue? Sounds like you are getting a leak from the head into the drive section. Even a small CO2 leak will cause pretty significant icing.

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You don’t have the pump output bushed up by any chance?

I’ve is weird, usually the compressed liquid co2 is coming off quite hot off the pump. It seems like it’s expanding somehow…

As the machines are pumping up I have been monitoring the air section temperature. We have two machines that we can get to operate properly which is telling me that our operating parameters are close to optimal. I have been thinking we were getting a co2 leak as well but the high pressure side of the pumps are freshly rebuilt across the board. We had two machines run full pulls today, we went to fire two more and they froze almost immediately during pump up.

The air incoming to the air drive has been stable at 65F, as the machines were pumping up I noticed the section gradually getting cooler and cooler until we reached the freezing pt of water 32F. Then it cascades quickly to 0F.

I have been monitoring the High pressure side of the pump as well when this problem starts. The high pressure side chamber, which is the co2 pump side, is stable at 55F and does not freeze when the air drive section freezes.

Do you have any suggestions on how to test to see if I’m getting co2 leakage from the high pressure side in to the drive section?

Testing at static is easy with CO2, just put it under pressure and look for the ice. Unfortunately if you just rebuilt it, you probably won’t see it unless it’s moving. I’ve found that simple green is the absolute best leak tester short of a helium MS unit.

Does that pump have a distance piece between the air drive and head? Also, if the CO2 is carrying a lot of terps, it will chew through a new seal kit in a hurry

The haskel pumps have a distance piece. If Im understanding how the pumps work I believe the haskel is what is physically pumping co2 into the system. It pumps it in to the maximator pump which is the pump that then drives the co2 to operating pressure in the material vessel. The haskel pumps are operating fine and do not freeze when this issue occurs. It is only the air drive setion of the booster (read maximator) pump that the freezing occurs.

I assume the maximator is a gas booster, which is basically the same thing as the liquid pumps are (two check valves with a piston in between them). The reason I asked about the distance piece is that it would rule out the leak from the head (because it would just vent into the room).

Another thought though, what is your air drive pressure to the pump? Also could you estimate how fast it’s running (cycles per minute)? How cold is the drive getting/how quickly?

I see what you were asking now. There is no distance piece on the maximator. The co2 sude of the pump is directly mated to the air drive housing.
Air deive pressure is regulated at the compressor but not at the machines. Output from the compressor is 150psi. The maximators max rated pressure is 145psi though. At the machine I plumbed in a 160psi gauge and the pumps are burying the gauge when the compressor goes through a loading cycle. I’m assuming it may be from line size restricting down.

I would say they were running roughly 80-100 cycles per minute.

The first machine we got running went through a full pull now problems. One of the guys reloaded this morning and its running now but the maximator sounds labored. It’s running significantly slower 50-60 cycles per minute.

Scratch that last post. They turned down the flow going in to the pump to slow down the cyclic rate.

You do not need your inlet air pressure set any higher than 120 PSI to maintain adequate compression for the maximator and haskel on this system. My system is automated and these pumps are typically fed 60-100 PSI.These pumps should rarely be operating together at the same time unless you are circulating CO2 via the maximator pump and attempting to remove or add gas into the system with the haskel.

What is your separator and accumulator pressures when you run 1800 PSI in your extraction vessel? 45F is pretty damn cold for the separator on these systems. Even when I do sub-critical runs our vapor temperature rarely goes that low (but the temperature at the separation point can definitely get into the negatives).

I have 20,000+ hours on the maximators and honestly I have only seen the airdrive freeze a handful of times, and never to the point where it freezes shut. Typically something is out of parameter or obstructed.

Do you have additional filtration to remove water and particulate post compressor? I stack 3 FESTO filter housings in a 40um-40um-5um series just prior to the air manifold that feeds both pumps. The filtration is a little overkill but I have an automated control cabinet that is highly susceptible to oil and water contaminating my components if not controlled.

I’ll DM you my email in case you have more questions.

Post a video?

I don’t think 150psi drive pressure is a problem nor is it likely enough to cause substantial cooling (enough to ice) from the vent pressure. Sometimes when we run off our high pressure supply (200-215psi) we can get some decent cooling off of air leaks. 100 cpm shouldn’t be too much trouble after a fresh rebuild but it might be a little hard on the pump, 50-60 is pretty ideal. Obviously we all do mean things to these pumps in the name of throughput though.

The CO2 temperature should have almost no bearing on the air drive temperature, and the compression ratio (P-in : P-out) dictates the temperature a lot more because of how compressible CO2 is. I suspect that is a red herring. If it was process fluid, the head would freeze up way before the air drive

If I had to guess, I’d bet money something got scratched during the rebuild and you’re leaking CO2 into the air drive.

I going to pull one that just froze and go through it this weekend. I’ll let you guys know what I find. I also have a video to upload. I really appreciate the input.

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Anyone ever seen anything like this? It looks like the seals burned on start up.

I’m not familiar with the maximator seal design but it looks like that gland nut may have been overtightened? I assume that primary bearing is not supposed to be split?

Edit: typo

The support bearing is designed to be split. The seals are actually sandwiched between two bearings that are in stainless housings. When you tighten the gland it squeezes the seals between those two housings.
What I’m trying to figure out now is if this was an assembly problem or a pressure problem. I rebuild hydraulic equipment for a living and im fairly familiar which proper assembly procedures and torque specs. A preliminary look at the seal lip makes me think the high pressure side of the pump is seeing too much pressure and is extruding the seal lip.