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Peristaltic Pump as a Motor? 1
- Thread starter bluduc
- Start date
MikeHalloran
Mechanical
I'm pretty sure you can backdrive them, in general, but not in every specific case. ... and don't expect to transfer much power or get long tube life.
Mike Halloran
Pembroke Pines, FL, USA
Mike Halloran
Pembroke Pines, FL, USA
Compositepro
Chemical
They are commonly used as motors in directional-drilling of oil wells. But I'm sure that they are built for one application or the other. A pump is not optimized to operate as a motor.
Compositepro
Chemical
Sorry, I was confused and thought you were referring to a progressive cavity pump. My comments still apply to peristaltic pumps except for the use as drilling motors.
My gut feel is maybe, a lot would depend on the peristaltic pump configuration - but why would you want to do it?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
- Thread starter
- #7
I have my reasons for wanting to use it- they are proprietary to the project I am working on, and can't be discussed.
That said... does anyone have any hard input as to whether or not it will work. I appreciate the 'gut' responses, but I can make a guess; I was hoping for potentially more enlightened or empirical input.
Thanks all.
That said... does anyone have any hard input as to whether or not it will work. I appreciate the 'gut' responses, but I can make a guess; I was hoping for potentially more enlightened or empirical input.
Thanks all.
-
1
- #8
MikeHalloran
Mechanical
I have direct experience with two radically different peristaltic pumps.
The first was someone's attempt at making a tubing-friendly pump. It used a dozen or so parallel flat bars that were raised and dropped in a 'wave' action against a platen, with several peri tubes stretched between the bars and the platen.
The bars were in turn driven by ball bearings on hex-bore eccentrics pressed on hex shafts, riding in slots in the bars.
It had so many moving parts, and so many tolerance stackups, that it was difficult to drive forward; I don't think it would backdrive at all. Of course the eccentrics were arranged so that the bearings' ODs formed a discretized 'screw'. Maybe if there were an actual screw involved it would work, but the effective pressure angle was ... well, I don't know, and the design had other problems, as in ball bearing outer races don't work with point loads like cam followers.
The second was a more classical peri pump, four cylinders in a rotating drum, with silicone tubes stretched over three at a time, no platen. The lumen of those tubes was quite a bit smaller than the roller diameter. Backdriving with that little effective area would probably not overcome the friction between the tubes and the rollers, despite the ball bearings on the rollers and on the drum shaft. I don't know whether to call it friction or something else, but the interaction between the rollers and the peri tube clearly costs some energy. The tubes get warm, and make noise.
I can't help but think that a larger diameter tube might do a better job of backdriving, thanks to the higher lumen area.
One of the performance problems with peri pumps as pumps is that after the rollers have passed over the tube, you are relying on the elastance of the tube to open itself to round again, against the suction pressure. For that reason, peri pump tubes usually have an OD of twice the lumen diameter, and that thick-wall tube is hard to crush closed, so the rollers have a hard time, etc.. But I'm thinking that as a pump, you aren't faced with the same problem of the tube having to provide all the suction lift, so you wouldn't need so much wall, except of course to deal with the drive pressure.
So, I'd like to amend my original response, as follows:
I think it could be made to work.
I think you'll need a platen; tube tension alone will not close the tube, with the drive pressure working to open it.
I think you can use a relatively large- bore tube, with a relatively thin wall.
I think that the tube requirements are considerably different from those necessary for a peri pump, so you will need a development program to find, or have manufactured, the tube that you will need.
Development programs of that sort don't fit nicely into conjectured schedules, i.e. they tend to be open- ended, and they typically consume a _lot_ of money, even if you stumble upon the solution in a short time.
I.e., if you can't find a peri pump maker who is willing to state in writing that his pumps will work as motors, and has enough experience with it to provide performance curves, well, there's a fair chance that you can do it, but you will need persistence, time, and deep pockets. Yeah, I know; nobody has any of that today.
Mike Halloran
Pembroke Pines, FL, USA
The first was someone's attempt at making a tubing-friendly pump. It used a dozen or so parallel flat bars that were raised and dropped in a 'wave' action against a platen, with several peri tubes stretched between the bars and the platen.
The bars were in turn driven by ball bearings on hex-bore eccentrics pressed on hex shafts, riding in slots in the bars.
It had so many moving parts, and so many tolerance stackups, that it was difficult to drive forward; I don't think it would backdrive at all. Of course the eccentrics were arranged so that the bearings' ODs formed a discretized 'screw'. Maybe if there were an actual screw involved it would work, but the effective pressure angle was ... well, I don't know, and the design had other problems, as in ball bearing outer races don't work with point loads like cam followers.
The second was a more classical peri pump, four cylinders in a rotating drum, with silicone tubes stretched over three at a time, no platen. The lumen of those tubes was quite a bit smaller than the roller diameter. Backdriving with that little effective area would probably not overcome the friction between the tubes and the rollers, despite the ball bearings on the rollers and on the drum shaft. I don't know whether to call it friction or something else, but the interaction between the rollers and the peri tube clearly costs some energy. The tubes get warm, and make noise.
I can't help but think that a larger diameter tube might do a better job of backdriving, thanks to the higher lumen area.
One of the performance problems with peri pumps as pumps is that after the rollers have passed over the tube, you are relying on the elastance of the tube to open itself to round again, against the suction pressure. For that reason, peri pump tubes usually have an OD of twice the lumen diameter, and that thick-wall tube is hard to crush closed, so the rollers have a hard time, etc.. But I'm thinking that as a pump, you aren't faced with the same problem of the tube having to provide all the suction lift, so you wouldn't need so much wall, except of course to deal with the drive pressure.
So, I'd like to amend my original response, as follows:
I think it could be made to work.
I think you'll need a platen; tube tension alone will not close the tube, with the drive pressure working to open it.
I think you can use a relatively large- bore tube, with a relatively thin wall.
I think that the tube requirements are considerably different from those necessary for a peri pump, so you will need a development program to find, or have manufactured, the tube that you will need.
Development programs of that sort don't fit nicely into conjectured schedules, i.e. they tend to be open- ended, and they typically consume a _lot_ of money, even if you stumble upon the solution in a short time.
I.e., if you can't find a peri pump maker who is willing to state in writing that his pumps will work as motors, and has enough experience with it to provide performance curves, well, there's a fair chance that you can do it, but you will need persistence, time, and deep pockets. Yeah, I know; nobody has any of that today.
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #9
Thanks Mike. Your insight has spurred my thinking about the interplay of frictions and pressures relating to this proposed system. For instance... the large diameter and thin wall tube may indeed increase the net torque applied to the rotor, however that tube would not be able to hold as much pressure as the initial smaller tube. It seems scaling the system up would be tough.
You've got me thinking. Thanks again.
You've got me thinking. Thanks again.
bluduc:
" That said... does anyone have any hard input as to whether or not it will work. I appreciate the 'gut' responses, but I can make a guess; I was hoping for potentially more enlightened or empirical input."
Well don't guess, get a peri pump and try out your theory, can't get much better than that for an answer.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
" That said... does anyone have any hard input as to whether or not it will work. I appreciate the 'gut' responses, but I can make a guess; I was hoping for potentially more enlightened or empirical input."
Well don't guess, get a peri pump and try out your theory, can't get much better than that for an answer.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
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