Home made peristaltic pumps - Page 5

silverbrewer · 06-18-2009, 03:36 PM

It's been worrying me that during sparging, with two of these pumps working in unison, the mash could get sucked onto the false bottom, as these pumps won't "cry uncle" like the March pumps would.

It has just dawned on me that if a flow loop is provided so the flow can get back to where it came from if there is a restriction then the flow can be controlled with a couple of taps, or even a couple of clamps to just squeeze the silicone pipe!

**conpewter** · 06-18-2009, 04:25 PM

If there is too much suction going on the silicone tubing will just collapse.

silverbrewer · 06-18-2009, 10:03 PM

Doh! why didn't I think of that!

)

Yorg · 06-19-2009, 03:16 AM

So what's the thinking on hose compression:
If I used jdcillin's design, I would still have to design the roller assembly ( it would be great to have a CAD of that to discuss) and I would have to decide the measurement that would result in the hose being compressed by the wheels. So would I compress the hose so that it just closes off and use that measurement as the width/thickness of the compressed hose, or would I give it a good press and use this smaller measurement as the thickness?

silverbrewer · 06-19-2009, 10:05 AM

Compress the hose just enough to give it an air tight seal. (check by blowing down it) Any more than that will only cause unnecessary strain on the entire assembly. I think I got my gap right, but my wheels were about a 1/16" too thin so there is a slight air leak and I cannot do anything about that until MK 2 The air leak past the wheels causes a reluctance to prime in air unless the revs are increased. Once it is pumping water, everything is fine. If a single wheel system is employed then you only have one wheel to position correctly, so you could even include a bit of adjust ability in the system. Note that with a single wheel, the tube must overlap itself before it leaves the circular wall and the wheel width must be twice as wide to accommodate two squeezed tube widths.

**beerthirty** · 06-19-2009, 11:22 PM

Peristaltic pumps are notorious power consumers. If the wiper motor is getting that hot a cooling jacket will have little effect. It is the windings that are producing the heat and they are insulated with lacquer as they are wound. This thin layer will burn off under high heat causing the motor to short. Cooling the case will do little to reduce the winding temp.
SB, try wrapping the rollers with a couple layers of duct tape to increase the diameter and create a positive seal. I know its ghetto but they don't call it 100MPH tape for nothing, its tough stuff.
Many peristaltics use spring loaded rollers to account for minor machining and assembly descrepencies and reduce the chance of blowing tubes from over collapse or pressure spikes while still keeping a positive seal.

Yorg · 06-20-2009, 01:31 PM

Those seem to be sound observations and suggestion Beerthirty.
Any suggestions/ scanned hand sketches on a design for spring mounted rollers - one for a CAD talented brewer to draw up for the rest of us to critique?
(Open source peristalitic pump design

)

**beerthirty** · 06-20-2009, 02:38 PM

To prevent the roller from cocking to one side from uneven pressure, the roller would need to be mounted to a carriage that would slide on the rotor arm. The spring could be placed inside the carriage against the end of the rotor arm.

silverbrewer · 06-20-2009, 11:02 PM

When designing the Mk 1 pump I did indeed consider making the radius that the wheel was set at adjustable. The initial thought was to make the adjuster so wheels clamped tight in various positions, like the adjustable chain tension on an MX bike..... but then having it spring loaded crossed my mind. I was thinking along the lines of a trailing arm pivoted where my wheel is now and about two inches long. The wheel is then at the end of this arm and an adjustable link, or a spring loaded link goes across to the main arm from the wheel end of the trailing link. I ruled out these options as un-necessarily complicated, and un-needed provided the pump was made accurately. The air problem with my pump is because the wheels are not wide enough. It is not diameter, concentricity or gap related.

My Mk 2 pump is going to be made out of 1/4" (or thicker) walled alloy tube. Two alloy, or clear acrylic end plates are going to be turned up to fit perfectly into each end of a 4 inch (or longer) length of this tube and give support for two sturdy sealed ball races with a ID to suit my 15 mm drive shaft. This way concentricity should be held within a few thousandths of an inch, and the tube will be in a sealed cavity, so it can be lubricated with something, perhaps food grade white grease? I will have only 1 wheel to reduce wear on the tube.

I fully agree that using a windscreen wiper motor to run this pump is pushing your luck. As soon as a properly engineered Mk 2 pump is in existance, I will run the thing with a watercooled wiper motor 24/7 just to see what reliability we can expect from such a cheaply avaliable motor. Mine ran fine on a small 4amp battery charger

With all these things sorted, it could still go pear shaped once we try to pump hot liquids for any length of time, but I am crossing my fingers and hoping that empirical testing proves all our worries are un-founded

jcdillin · 06-21-2009, 01:30 PM

I've been trying to draw up a design for different spring loaded versions and from what i've been doing I think it makes it all a bit complicated.

Wouldn't it better just to have different sized rollers that you could put onto the shafts that way you could make adjustments just by changing the size of the roller.