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# Why is there a ball-like portion on the pipette?

likeabreeze
You must have noticed there is a ball-like portion on some kinds of pipette.
the functionality of it?
_AVG_
Do you mean the bulb at the top? I suppose if you cover it with a tight rubber suction and squeeze then it increases the air pressure thereby inducing fluid to flow up. I would guess that the shape of the bulb facilitates this pressure change.
likeabreeze
 _AVG_ wrote: Do you mean the bulb at the top? I suppose if you cover it with a tight rubber suction and squeeze then it increases the air pressure thereby inducing fluid to flow up. I would guess that the shape of the bulb facilitates this pressure change.

I mean the bulb at the midpoint of the pipette.
kelseymh
likeabreeze wrote:
 _AVG_ wrote: Do you mean the bulb at the top? I suppose if you cover it with a tight rubber suction and squeeze then it increases the air pressure thereby inducing fluid to flow up. I would guess that the shape of the bulb facilitates this pressure change.

I mean the bulb at the midpoint of the pipette.

It provides a low-velocity region for the fluid flow, so that you can better control the fill. The liquid will rise very rapidly, then slow down in that bulb region. That gives the pipetter a "lag time" to reduce the suction without overflowing the pipette.
likeabreeze
 kelseymh wrote: It provides a low-velocity region for the fluid flow, so that you can better control the fill. The liquid will rise very rapidly, then slow down in that bulb region. That gives the pipetter a "lag time" to reduce the suction without overflowing the pipette.

You gave me a reasonable answer, thanks!
By the way, are you really from SLAC National Accelerator Laboratory?
I just can't believe that I got a opportunity to talk to a scientist.
kelseymh
likeabreeze wrote:
 kelseymh wrote: It provides a low-velocity region for the fluid flow, so that you can better control the fill. The liquid will rise very rapidly, then slow down in that bulb region. That gives the pipetter a "lag time" to reduce the suction without overflowing the pipette.

You gave me a reasonable answer, thanks!
By the way, are you really from SLAC National Accelerator Laboratory?
I just can't believe that I got a opportunity to talk to a scientist.

Yes, I am. I'm not the only scientist on these forums. Ankhanu, if I recall, is an astrophysicist (and I hope he'll correct me if I'm wrong). I don't remember Bikerman's speciality, but he's also a scientist. There are electronics engineers and other professionals who contribute here as well.
Bikerman
Well, not really a scientist - a science fan certainly, but a teacher/lecturer in IT IRL...
likeabreeze
 kelseymh wrote: Ankhanu, if I recall, is an astrophysicist (and I hope he'll correct me if I'm wrong).

His profile says he is a biologist.
kelseymh
 Bikerman wrote: Well, not really a scientist - a science fan certainly, but a teacher/lecturer in IT IRL...

Computer scientist then