Check valve or active check valve?

[zlb215]

Hello,folks;
In some hplc system(e.g.,agilent 1200),check valve is repalced by active check valve;however still one ball check valve be retained as a outlet check valve.Check valve really bring lc pumps with most trouble of all components.So if it "can" be reduced, why not replace all?What's the difference between check valve and acitive check valve?
Best regards!

[Consumer Products Guy]

An active inlet check valve uses electricity to operate the valve, traditional check valve just uses a spring. Agilent apparently feels active is better for their systems. We don't have much trouble with those, maybe they are correct.

[lmh]

The way it's always been explained to me is this:

The inlet valve is the trickier of the two, which is why Agilent use an active valve here, and a passive valve for the outlet.

The outlet is held closed by the huge pressure of the hplc system. It is opened positively by the equally huge pressure generated by the pump piston. It's unlikely ever to get stuck closed.

The inlet valve is opened by a very small pressure difference, since the pump can only pull a vacuum, and there is only 1 bar available in the solvent reservoirs. If it gets stuck closed, the solvent can easily cavitate (if that's the word), and nothing gets pumped.