Inexpensive Recirculation Pump

kim at kim at
Thu Oct 8 14:11:45 EST 1992

Inexpensive gel recirculation pump.


This is an "impeller"-type pump which is open to air, so it does not create a
closed system as does the peristaltic type pump.  It has a flow rate, at "zero
pump head" which is comparable to peristaltic pumps that cost up to hundreds of
dollars, but can be constructed mainly of used materials (free) and very
inexpensive purchased parts ($2 - $3 at Radio shack.  Since the pump chamber is
made of disposable syringes, the parts that contact electrophoresis buffer are
very resistant to chemicals and can be rendered RNAase-free using "cold"
chemical methods.  It is not autoclavable.

The two pumps that I use regularly have been very reliable, but they have the
potential of disasterous failure in accordance with Murphy's Law.  Use it at
your own risk.

The construction procedure includes cutting plastics with sharp instruments and
melting and burning plastics in a Bunsen burner.  These are unpleasant and
potentially hazardous operations, kind of like everything else in this
profession, so BE CAREFUL.  Use a fume hood to avoid breathing toxic combustion
products.  Don't use syringes that had previously held contaminated blood.  Use
your head.

I have not submitted this procedure to the powers-that-be here at Los Alamos
National Laboratory, nor at the University of New Mexico.  They don't know that
I do this, and probably wouldn't approve, since it involves fire, sharp things,
etc.  I'm trying to say something equivalent to "opinions stated here are my
own and do not reflect . . . etc.", so take these ramblings in that spirit.


10 ml syringe barrel (used is OK)
1 ml syringe (same here)
small electric motor (for use with 1.5 v battery)
thin electrical wire
18 g needle (used is OK)
Bunsen burner
Razor blade
cork borer (about the same diameter as the 1 ml syringe)
Pipetman tip
lab tape

1.  Remove the plunger from the 1 ml syringe and cut the barrel with the razor
blade at about the 0.1 to 0.2 ml mark at a roughly 30 degree angle.

2.  Use the cork borer, placed at a tangent to the 10 ml syringe barrel, to
bore an oval hole in the side of the syringe barrel.  The hole should be at
about the 1 ml mark.

3.  Using the Bunsen burner, melt the cut end of the 1 ml syringe barrel
slightly.  Place this cut end on the hole in the 10 ml syringe barrel such that
the assembly, viewed end-on, forms a shape resembling the letter small sigma.
Do not worry about a watertight fit at this point.  Let cool and harden.

4.  Place the small end of a Pipetman tip in the flame until it starts to burn.
Let the melted plastic drip onto the joint between the two syringe barrels,
sealing the joint.  Extinguish any fires that may ensue.

5.  Heat the tip of an 18 g needle red-hot and use this to melt a hole into the
center of the flat end of the 1 ml syringe plunger.  The hole should be 3 or
more mm deep and just wide enough to snugly the hold the shaft of the electric
motor.  This will become the impeller of the pump.  Try it on for size a few
times.  The plunger does not have to be perfectly in line with the motor shaft,
but it should be close.

6.  Re-ignite the pipet tip and drip melted plastic onto the joint between the
plunger and motor shaft.  Don't get plastic into the motor.  Put out fires.

7.  Trim the end of the plunger such that, when the motor is placed on the open
end of the 10 ml syringe barrel, the cut end of the plunger is just above the
hole for the 1 ml syringe barrel.  There is a lot of slop here (as there is
everywhere in this procedure).  The end of the plunger should not be so long
that it can catch on the hole when the motor is running.

8.  Mount the pump vertically on a test-tube holder on a lab stand.  Wire up
the motor and connect it to a "D" cell battery.  Take note of the direction of
rotation and adjust the polarity so the rotation is the same direction as the 1
ml syringe is pointing.  This helps a little with the efficiency of pumping.
Let the motor run and adjust its position on the pump to minimize contact
between the impeller (the 1 ml syringe plunger) and the sides of the 10 ml
syringe.  You may have to trim the end of the impeller a bit to eliminate all
contact while the pump is running.  If the impeller is so off-center that it
scrapes the sides of the pump all the time, you may want to remove it and mount
a new one.  Once these adjustments have been made, tape the motor to the top of
the syringe barrel to hold it in place.  It may be necessary to kind of squeeze
it around a bit to re-adjust it.

9.  You're done.  A single "D" cell will probably be sufficient to run the pump
for 16 - 24 hours.  Two batteries will give you more power.  For added economy
and reliability, the motor can be connected to a 1.5 - 3 V power supply.  I am
using the recharging stand for a "Mopet" pipettor.

Running your pump:

1.  Fit the pump with Tygon tubing connected to your empty horizontal gel box.

2.  Adjust the height of the pump so the level of the buffer will be  about at
the 2 ml mark.  It may be necessary to raise the gel box a bit in order to do

3.  Pour buffer in the chamber of the gel box that is connected to the inlet
port (10 ml syringe Luer port) of the gel box to start the buffer flowing and
let the pump chamber fill up from the bottom.  The buffer should start to pass
through the outlet port (1 ml syringe) and reach the opposite chamber of the
gel box.

4.  When the pump tubing is filled with buffer, fill the remainder of the gel
box with buffer.

5.  Connect the pump to its power source and check that it is running properly.
The impeller rotation should whip the buffer in the 10 ml syringe into a vortex
that climbs up the walls of the pump.  Adjust the height of the pump so the
vortex reaches the 8 ml mark.  Remember that there is nothing between the
buffer and the motor, so do not let buffer get so high that it wets the motor.
For less buffer flow, raise the pump to get a shorter vortex.

6.  Turn off the pump and load the gel.  Pre-run so the sample enters the gel
matrix, then turn the pump on again.  You may be able to see bubbles from the
Platinum wires of the gel box being deflected by the flow from the pump.  Quite

7.  You may want to pre-run newly-constructed pumps a few times for long
periods to become confident of their reliability before using them on a
valuable overnight run.                 

More information about the Methods mailing list