Can’t make good pump seal

[mpatterson]

I have been applying tape to the pumps because most of them have been making a poor seal (I can see air moving through the tubing). I am using the same tubing as is recommended in the ChiBio documentation. I have tried autoclave and/or labelling tape. For some pumps I have needed several layers of tape in order to create an appropriate seal, but I am concerned that this is too much because the pump visibly turns slower than the others by eye with this much tape, and that this will damage the pump in the long term.

• This topic was modified 2 years, 9 months ago by mpatterson.
• This topic was modified 2 years, 9 months ago by mpatterson.

[harrison]

Hello,
If it is visibly turning slower / seeming to struggle it seems to imply that there is plenty of resistance in there (you want the resistance since this is arising from compression of the pipe – which leads to sealing).
So – how do you know they are not making a good seal? It is unclear to me what you mean by “air moving through the tubing”. If air is going in the direction you want liquid to travel, this doesn’t necessarily mean anything. The problem would be if air is going the opposite way (perhaps this is what you meant).

If air is going the opposite way other fixes might be to make sure neither end of the tubing is MUCH lower than the other. Or, make sure when you put the pipe into the pump head you push it down into the head – e.g. so that it touches the bottom of the cream coloured plastic below the rotor, and is not bulging up and out of the rotor (e.g. touching the clear lid) as it rotates. Let me know if this explanation doesn’t make sense…

[mpatterson]

Hi,

Regarding your question about the air- if the pump is not running, I can still see a bubble of air moving through the tubing, in the opposite direction that the liquid is pumped. Sorry for being vague.

Regarding potential fixes,
For the first, to check tubing ends: maybe I am not understanding what you mean, but doesn’t one end of the tubing always need to be higher than the other? If the reactor and pump are sitting above the level of a media reservoir, the inlet for Pump 1 must be near or at the bottom of the media reservoir, but the outlet will go into the reactor sitting above. Likewise, the inlet of Pump 2 will also be attached to the reactor waste line and then outlet into a waste container (which does not need to extend to the bottom of a waste container, this is true).
For the second fix, checking the level of the tubing in the pump head: I have tried both alining the tubing precisely with the groove and pushing it all the way down into the pump head, it does not help. The only way I have been able to fix this is by applying several layers of tape, which is when I notice the pump turning slower than other pump heads that require either much less tape or no tape at all. If this struggling doesn’t risk damaging the pump long-term, that is fine, but I was concerned about there being a risk of damage if the pump needs to struggle through so much resistance every time it runs.

[harrison]

Hello,

Yes, one tube does need to be higher than another, but the absolute difference doesn’t have to be ~meters. It is OK if only 20cm. How is it set up at the moment?

As to your second point – I think if the pump is still turning then it should be OK. From my experience yes, adding tape can slow it down, but unless it is REALLY struggling (i.e. going like 10% of the default speed without tape) then it should not be a major issue.

Likely the reason you may have these difficulties is that the particular pumps came from a batch manufacturered with slightly different tolerances etc. The Chi.Bio suppliers Labmaker source these pumps in bulk so there is pump-to-pump variation, I guess this is what we expect when going for a cheap pump model!

[mpatterson]

Ah, okay, the difference is certainly not meters. Right now I just have the pumps on the benchtop with both ends of the tubing going into a flask. I’d estimate there’s only about a 5 cm difference between each inlet and outlet when they are set up this way. But the stands the reactors sit on leave the tops ~ 25 cm above the bench, so it is helpful to know that more than 20 cm could be a problem.

And yes the pumps are definitely still turning, and not struggling as drastically as 10% of the default speed. So that is also good to know, thank you!

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