Chromatography Forum

Dear all,

In our lab we use a constant volume Eldex Optos 2SI single-head reciprocating pump (PEEK flow path; ruby seats and sapphire balls) to create a very thin liquid jet for spectroscopic study of the resultant jet solution. Since this single-head HPLC solvent pump introduces pulsing (which is terrible if you want to overlap the jet with a laser, for example) two pulse dampeners downstream of the HPLC pump were introduced. (SSI Lo-Pulse LP-21; PEEK). Inlet tubing is 1/8'' OD PTFE and the outlet tubing is 1/16'' OD PEEK rated to 5000 psi.

These pulse dampeners dampened the pulsations considerably. Since these dampeners are rated to work optimally at 1000 psi, I introduced a 1000 psi backpressure regulator (Upchurch; PEEK) after both the pulse dampeners, however the pulsations again returned after installation of the regulator.

I figure that I must be doing something fundamentally wrong with the backpressure regulator such that I re-introduce pulsations. Is it a matter of tightening the backpressure assembly at a given flow-rate such that the pulsations disappear? I'm unsure as to whether the regulator needs recalibration at different flow rates.

All the best,
Ryan

You said that the pulse dampeners reduced the pulsation "considerably". Was the level acceptable? If it was, I would advise you "if it ain't broke, don't fix it!"

If it's still not scceptsble, then yes, you should fine-tune the regulator.

Dear Tom,

Thanks for your reply. The maximum flow rate for the pump is 10 ml per min. Installing two pulse dampeners made it possible to achieve a flow rate of about 5 ml per minute without any appreciable pulsing.

I was of the opinion that since the pulse dampeners work optimally with a backpressure of 1000 psi then installing a backpressure regulator would mean that I could achieve a lower flow rate (1 ml per minute or less) without pulsing; this appears to be wishful thinking.

A lower flow rate as possible is better for this application (since I don't have to re-fill my reservoir of solution, which is critical because the solution is air and moisture sensitive). Adjusting the tightness of the backpressure regulator does not seem to bring about a change in the pulsing.

All the best,
Ryan

If you want a lower flow but need to be at 10 mL/min for optimum pulse damping, would it be practical to split the flow with a return line to the reservoir?

Steve Reimer wrote:
If you want a lower flow but need to be at 10 mL/min for optimum pulse damping, would it be practical to split the flow with a return line to the reservoir?

This is what I was thinking also. It might be possible to configure it so that the pulses travel in the return line to give a more steady flow to the end point of the system. Possibly using the packpressure regulator after the split so that what is coming out at the end has a steady pressure.

Dear all,

Yes that might be a sensible option.

Thanks for all of your help everyone.

All the best,
Ryan