[coquim]

Hi people!!

I´m looking and cleaning some filters and check valves and could see that there is no filter before the primary inlet check valve. The filter suction in the bottle is actually the first one, but after these the solvents pass trough the solenoid valve and reach the primary inlet check valve, only passing trough the suction filter in the bottle ( someone know the efficiency of these filters??)
So, i think there must be some filter before the solenoid valve or before the check valves.
I really wanna know what you think about...

Best regards! 

[Arkcon]

The upper check valve is generally just a ruby ball in a seat of some sort of plastic.  The lower check valve often has a sintered metal cup, that's just to hold the ball on position while you're tightening the check valve into position.  If you've lost it, or someone else has and it's been missing, your pump won't work at all.  Although, I'd heard that real old style pumps didn't even have pre-pump head check valves.  I know that sounds  , but you've got to realize, what's going to happen, fluid backwashes all the way back to the eluent bottle on the pressure stroke?  Unlikely.  Still, crappy ancient design.

Is the little metal cup you've found in the check valve what you're talking about? Or are you talking about something else?

The filters on the end of the solvent inlet line are usually 10µ or 7, or 5, good for removing dust that's fallen in, but you should have pre-filtered your prepared eluent through 0.5 to 0.2µ, but sometimes people are in a rush and skip it, that can be bad.  That eluent bottle filter, I've often done without it, it's really more a weight to sink the line to the bottom of the eluent bottle.

There's lots of places people can put filters -- the in-line frit (sinker) to remove dust and insoluble material you should have gotten rid of first.  Post pump frits, to remove check valve particles, post-injector frits to remove rotor particles, ostensibly, but also sample particles, which you should have filtered anyway, pre-column filters for all the stuff you've missed to protect the column, yes, even post column filters, so column material doesn't plug you flow cell, in case the column frits fail.

But ... each frit adds dead volume, and potentially back pressure.  And filtering samples may remove some analyte, many times, I've seen people dispense with many inline filters, yeah, it's bad for the system, but sometimes you're in a hurry.

[JGK]

Mobile phase inlet filters are usually 2 µm pore size some may be 10 µm. they are normally located on the end of the solvent line placed in the mobile phase reservoir.

If you filter you mobile phases prior to placing them on your system (I vacuum filter through a Nylon 0.2 µm filter as a routine), there should be no need to have any further filters on the solvent lines.