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Subject:
From:
"Linda Pohl, IBCLC" <[log in to unmask]>
Reply To:
Lactation Information and Discussion <[log in to unmask]>
Date:
Sat, 29 Mar 2003 20:58:27 -0700
Content-Type:
text/plain
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Anne asks is the size of the bottle on a breast pump affects suction.

The answer is:  it depends.

If the pump is a valved type of pump, no the size of the bottle does not
affect the vacuum generated by the pump.  By "valved type" pump I am
referring to a pump that contains the vacuum in the flange by use of a valve
system like the Medela and Hollister/Ameda products.  The Medela Pump has a
little yellow piece that fits below the flange with a white flapper over it.
This pump will create vacuum by pulling the white flapper against the yellow
valve and the breast against the flange.  The Hollister pump has a single
white valve at the bottom of the flange.  It creates vacuum by pulling the
bottom of the valve closed and the breast against the flange.  This type of
pump will have the same suction whether you are pumping into a 2-oz bottle,
an 8-oz bottle, or a freezer bag.

There are some brands of pumps, (Nurture III by Bailey Medical Engineering,
the Gerber, and the White River pump come to mind) that do depend of the
size of the bottle to determine the suction.  The smaller the bottle the
higher the vacuum created.  This is a law of Physics (remember from High
School?)  PV=nRT, where P is pressure and V is volume.  As the volume (size
of the bottle) decreases the pressure (vacuum) increases if the rest of the
equation stays the same.  Conversely if the volume (size of the bottle)
increases the pressure (vacuum) decreases.  This pump needs to evacuate the
bottle to create vacuum.  This means the pressure is not only over the
flange area but the bottle as well.  As the bottle gets bigger the same pump
will create less suction because it has to evacuate a bigger volume.

As I read this over, I hope that I do not create more confusion.  Please
note that although I do mention brand names, I am not commenting on the
quality of the pump, only their designed function.

It may be that the pump felt more comfortable to the moms after the larger
bottles were put on because:
   a.  The pumped was not a valved system.
   b.  The mom perceived it to be more comfortable because someone told her
it would be (mind over matter)
   c.  Mom had pumped for a while with the 2-oz bottles, softened her breast
and when the 4-oz bottles were put on was softer and
        did not feel the vacuum as keenly due to the decreased fluid
pressure in the breast.

Cordially,

Linda L Pohl, IBCLC
Lactation Consultant, Engineer, Computer Nerd, Mom, Wife, Programmer, ......
Phoenix AZ

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