HomeChoice disposable fluid transfer set. How does it work?

[PaulBC]

Copying this over from my reply to pdresearcher on the intros page. I'd be happy to hear from anyone else too:

I've been admiring the disposable fluid transfer system in the Baxter HomeChoice cycler we are using. It's a sealed system with just two places to apply pressure (or maybe suction?). I don't see any moving parts (valves) inside. Somehow the machine moves fluid in all different ways just by applying these two controls. Is that correct?

I'm just curious if there is any documentation readable by the layperson to describe how this thing works. Every day I throw out one of these amazing devices taking care of my daughter, and I thought I might clean one out and recycle it for a science project.

Note: I just did a little searching and no wonder it's so cool. Dean Kamen was involved in its design. I've been using it for over a month and did not know that.

[jcanavera]

If you look at the back of the cassette you will see soft spots that are the valves.  The cycler behind the membrane can exert pressure on these soft spots thus effectively shutting down the flow from different tubes.  It has a multi stage pumping system that draws fluid, moves it to another chamber where is accumulated and then squeezed out into the drain tube.  My neighbor was involved in designing and building the sterile enclosures that robotically build the cassettes.

Jack

[Simon Dog]

I've been admiring the disposable fluid transfer system in the Baxter HomeChoice cycler we are using. It's a sealed system with just two places to apply pressure (or maybe suction?). I don't see any moving parts (valves) inside. Somehow the machine moves fluid in all different ways just by applying these two controls. Is that correct?

If it;s like the Freseius Liberty, yes.  The key is that in addition to those two places for pressure/suction, there are clamps that selective close off certain lines at specific points in the pressure/suction cycle - so the only path for the fluid to move to/from is the desired flow direction.

[PaulBC]

If you look at the back of the cassette you will see soft spots that are the valves.  The cycler behind the membrane can exert pressure on these soft spots thus effectively shutting down the flow from different tubes.  It has a multi stage pumping system that draws fluid, moves it to another chamber where is accumulated and then squeezed out into the drain tube.  My neighbor was involved in designing and building the sterile enclosures that robotically build the cassettes.

Thanks for this and informative replies to my other postings. I thought it might be something like this, but the only spots that obviously looked flexible were the large ones. Is there a way to get specs that show which spot controls which flow? I guess it wouldn't be too hard to reverse engineer, but I haven't taken a close look.

[Simon Dog]

I think you're stuck with reverse engineering.   I know NxStage did not respond favorably when I asked for the spec for their IP interface.   Look for something in the machine that will push on the lines to clamp them shut at particular points.

If you want to sound like you know what you are talking about, use the term diaphragm pump.

[PaulBC]

If you want to sound like you know what you are talking about, use the term diaphragm pump.

Thanks for the tip! It helps with web searches too.

[PaulBC]

Looking up "diaphragm pump" definitely helped. I found some relevant patents, such as US8070709, which is available online and contains detailed diagrams. I haven't read it carefully, so I can't say how easy it is to understand.

[Simon Dog]

Looking up "diaphragm pump" definitely helped. I found some relevant patents, such as US8070709, which is available online and contains detailed diagrams. I haven't read it carefully, so I can't say how easy it is to understand.

As long we are on the topic of pump terminology, the pumps like those used in hemo machines are peristalic pumps.