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Peristaltic Pump RPM

R/C Submarine modelers

Peristaltic Pump RPM

Postby Captain Nemo12 » Sat Jan 21, 2012 12:11 am

Hey guys!

I'm currently scratchbuilding a peristaltic pump for use as the main pump for a central ballast tank. In the process of selecting an appropriate motor and gearbox, I've come across motor/gearbox combinations rated at 60, 70 and 100 RPMs. For those who use these pumps in subs, which RPM rating would be best suited to pump water at a moderately fast speed? I know that a lower RPM rating will yield a higher torque, which is desirable in a pump of this type since the rollers are pressed against the rubber tubing of the pump and must rotate. Will the 60 RPM gearbox be too slow to pump water? Should I go with the 100 RPM one to be safe even though the torque might be lower?

Thanks in advance!

Nate
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Re: Peristaltic Pump RPM

Postby JWLaRue » Sat Jan 21, 2012 12:47 am

Nate,

I don't know that your question can be answered strictly on the basis of motor RPM. It seems to me that what needs to be understood is the flow rate of the pump compared against the total ballast volume that you need to move over the desired time.

In other words, how large is the ballast tank and how fast do you want to be able to fill/empty it? That should lead you towards the answer of the RPM that you need.

-hope this helps,

Jeff
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Re: Peristaltic Pump RPM

Postby Bigdave » Sat Jan 21, 2012 8:33 am

Hi Nate,
I am no expert on peristaltic pumps but I do have two different types in subs.
The ones I have move much faster in the RPM range.
The pumps put out such small flow rates that at lets say 60RPM which is only one RPM per second :roll: .
Lets just say it would take you all day to transfer fluid. :shock:
I have not measured the RPM but I would say more it the 2400RPM range or higher.
Even at this it takes a while to pump.
I will try and find out the RPM's of mine. BD.
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Re: Peristaltic Pump RPM

Postby Ramius-II » Sat Jan 21, 2012 9:39 am

Hi Nate,
Maybe this will help?

http://www.masterflex.com/techinfo/tech ... htm&ID=576

Best, Ed
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Re: Peristaltic Pump RPM

Postby Sub culture » Sat Jan 21, 2012 5:03 pm

Servocity.com do a wide range of geared motors that will work well for peristaltics.

The bigger you can make your pump, the better. Also don't forget you can make the rollers deeper and run two or more sets of tubing, to parallel up the flow rate.

Most designs use no more than three rollers for efficiency. You can get a rough idea of the amount of water your pump will flow for a certain RPM, by dividing the circumference of the tubing diameter by two, then multiply it with the cross-sectional area of the inside tubing, and multiply that by the RPM. This doesn't account for the tubing pinched up by the rollers, but it does give you a clue that you're moving in the right direction.

e.g.

A pump which is 5cm diameter with 4mm tubing operating at 250RPM will pump about 250ml a minute.

5x3.14/2= 7.85

0.2x0.2x3.14= 0.13

0.5x7.85= .98

250x.98= 246.5

The flow rate of these pumps is typically very poor when compared with geared or centrifugal pumps. They're primary advantage is that they self seal, and are easily rebuilt.

Doubling up the tubing will double the flow rate, assuming your motor can maintain the same RPM. You can also increase RPM, however be careful running too fast as this will reduce the life of the tubing. The service life of a pump like this in a model is likely to be considerably extended over industrial applications, but a burst pipe could have unpleasant consequences for the longevity of your sub! You could fit the pump head in the free-flooding space. This serves two purposes- it removes any heat put into the tubing by the action of the rollers, and should the worst happen and the tubing split, the ballast tank will flood, but the dry spaces should remain intact.

Be sure to fit a pressure switch in or some sort of mechanical relief valve. Whilst other types of pump will tend to stall, perstaltics are capable of reaching dangerously high pressures unless chcekced in some way, so it's important to have some means of purging the pump should it get stuck on for some reason. Norbert Bruggen sells pressure switches, and the Thundertiger Neptune also has one fitted as standard equipment, so it should be available as a spare part.
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Re: Peristaltic Pump RPM

Postby Captain Nemo12 » Sat Jan 21, 2012 11:56 pm

Thanks for the response guys!

I've done some calculations based on what Sub culture posted and it seems that even at 300 RPM, it would still take about 2 mins to completely fill a a 450ml tank... In that case, I might invest in a gear pump instead. Heck, I might even build one since it seems so simple! To my knowledge, gears pumps are genereally bi-directional, are they not? My U-boat will be trimmed such that when the ballast tank is full, the tip of the conning tower will still be above the water. So the plan is to use a vented ballast tank, with the UZO column disguised as a venting tube.

Regards,

Nate
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Re: Peristaltic Pump RPM

Postby Sub culture » Sun Jan 22, 2012 1:34 pm

If the tank is vented i.e. not pressurized then you can use a high flow low volume pump. Mike's subworks supplies a bi directional pump-

http://www.mikessubworks.com/pumps.html

Another option would be to use a centrifugal pump (e.g. windscreen washer). You can flood the tank by opening a valve on the bottom (you need to make this, and it should be large in area), and use the pump to empty the tank. That type of system is detailed in Norbert's book.
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