16
World Precision Instruments
TROUBLESHOOTING THE HOLD PRESSURE
If the
Hold
regulator can’t reduce the pressure low enough to keep the liquid from
coming out of the pipette tip, DO NOT try to shut off the pressure by forcing the
regulator knob counterclockwise. The regulator is designed so that the flow can’t
be shut off completely. It should, however, be able to reduce the pressure to below
0.2 PSI, which is low enough for most applications. If the regulator can control the
pressure above 0.5 PSI, but not below 0.5 PSI, a simple reset will fix the problem.
The reason that the regulator can’t reduce the pressure below 0.5 PSI is because
the dampening O-ring inside the regulator is stuck. The O-ring is connected to
the regulator’s diaphragm. It prevents the diaphragm from oscillating in high flow
conditions. The diaphragm moves the valve shaft. The diaphragm uses the output
pressure to counter-balance the spring force that is controlled by the knob. When
the output pressure becomes very low, the force generated on the diaphragm
becomes low. Sometimes, it is not enough to overcome the friction of the O-ring to
push the valve to the completely closed position. A high pressure from the output
port will push the diaphragm and return the O-ring to the seat.
To introduce a high pressure:
1. Remove the 1/4” hard pressure tubing from the back of the pump.
2. Use pieces of tubing with 1/4” OD to make a small 1/16” ID drop down
extension.
3. Position the extension inside the end of the 1/4” hard pressure tubing.
4. Place the other end of the extension on the Eject port
5. Then, apply an injection at 20 PSI for 10 seconds.
6. Once the O-ring re-seats, it will remain there even when the output pressure
again increases, as long as there is no high flow output. When there is no
restriction at the output and the pressure is adjusted too high, the diaphragm
has to move a substantial distance to allow the valve to open more to
compensate the for pressure loss. This also causes the O-ring to move.
Therefore, if low-pressure regulation is very important for the application, you
should not set the
Hold
regulator at the high-pressure position when there is no
restriction at the output. There are two ways to achieve this:
•
Always reduce the regulator pressure to minimum before assembly and
disassembly of the injection pipette.
•
Turn off the
Hold
pressure valve before assembly and disassembly of the
injection pipette.
NOTE
: If you have a problem/issue with that falls outside the definitions of this
troubleshooting section, contact the WPI Technical Support team at 941.371.1003 or
[email protected].
