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Installing the Piston Wash Seals
The 2 mL pump heads supplied with the Varian 212-LC pumps are
capable of being configured for washing the back of the piston. This is
important when pumping with a mobile phase containing a high
concentration of buffer.
Over a long period of time, a small amount of mobile phase will leak
through the high pressure piston seal and accumulate on the back of the
piston were the solvent will evaporate leaving buffer crystals which can
shorten the life of the piston seal and piston. To prevent the
accumulation of buffer on the back of the piston, it is possible to flush this
area continuously with a solvent and thus prevent buffer accumulation.
As shipped, the 2 mL pump heads do not contain the necessary seals for
piston flushing. The seals and necessary tubing are included in the pump
accessory kit.
To install the wash seal:
1. Remove the pump head as described in Replacing the Piston Seal
Assembly on page 24.
2. Remove the pump head manifold as described in Replacing the
Wash Seal Assembly page 25.
3. Remove the white Teflon® piston wipers as shown in Figure 12.
Use the flat side of the piston wiper to help push the wash seal onto
the ceramic piston. One wash seal is installed on each piston. The
actual piston seal is embedded in a tan-colored PEEK® disk
assembly. Make sure the seal is visible and faces you when placed
on the piston.
4. Reassemble the pump head following the instructions referenced in
steps 1 and 2 above.
The Teflon tubing is now connected to the flush ports on the two pump
heads as shown in Figure 5. The 36" (90 cm) section of tubing is
connected to the side flush port on Pump A using the supplied nut and
ferrule. The 12" (30 cm) piece of Teflon tubing connects the lower flush
port of Pump A to the side flush port of Pump B. The 10' (300 cm)
partially coiled length of Teflon tubing is attached to the lower flush port
on Pump B.
The piston flush works using a gravity siphon. Start the siphon by
temporarily connecting the tubing coming out of the Pump B lower flush
port to a 10 mL syringe containing the flush solvent. A typical flush
solvent would be 5% 2-propanol in 95% HPLC grade water. Push on the
syringe plunger until all air bubbles stop coming out of the tubing that is
connected to the Pump A side flush port. Insert this tube into the flush
solvent bottle and place it on top of the pump. See Figure 5.
Disconnect the syringe and place this tubing at the bottom of a waste
bottle at bench level. With flush solvent supply and waste bottles located
as described, you will have a flow rate of 5-20 µL/min. To lower the flow
rate, raise the waste bottle closer to the height of the supply bottle or
raise the level of the tip of the tubing within the bottle. To increase the
flow rate, raise the supply bottle or lower the waste bottle. The flow rate
is determined by the height of the liquid level of supply and waste bottles.
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