Number of pumps used in binary and quatenary

[afzal]

hy everybody

i know that in binary gradient system there are two no. of pumps which can mix two eluents
but i dont know that in a Quaternary system why a single pump used and how it can mix four eluents.
can anyone tell me about that........
thnx

Muhammad Afzal

[rwjohnson]

Hi. The quaternary pump meters the solvents before it gets to the pump. Quaternary pumps use low-pressure mixing and binary pumps use high-pressure mixing. I can't say why you would prefer one mixing technique over another though.

Any comments from others?

Ron J

[HPLCaddict]

The advantages of quarternary systems (aka one pump) are quite clear: You need only one pump (less costs, less maintenance) and got four solvent channels.
Binary systems (two pumps) on the other hand usually have lower dwell volumes (aka gradient delay volumes) than quarternary systems. Therefore they're more suited for fast gradients than the one-pump systems. Drawbacks: higher costs, more maintenance work, only two eluent channels (might be upgraded to more by solvent-switching-valves, but you can only use two at the same time).

[uzman]

Low pressure gradient systems have a tendency to make air bubbles in the pump head during mixing of the solvents ; if the solvents are not degassed properly.
This creates stability problems.

[wulisheng2]

The pump works not only for mixing solvents, but also for driving the mixed mobile phase with sample through the system. The forward and back movements of a single pump has two dead voids at two pump ends and thus cause the flow fluctuation like a sine wave. Binary pumps work like two 45 degree difference sine waves. It can compansate the zero points, ie dead voids, of a single sine wave. So the binary system can make the flow rate much steady or less fluctuation. As the same reason, the quaternary system has four pumps, four sine waves with 22.5 degree difference each other resulting in much lower fluctuation or much steady flow rate.

[HPLCaddict]

Erm, quaternary system with four pumps?
Usually, the term "quaternary system" defines a HPLC with four SOLVENT CHANNELS and a SINGLE pump. Can't imagine someone really wants to go through the hassle of maintaining (and paying the price for) four single pumps in one system. At least if we're talking about a "plain vanilla" analytic system. Might be different for special purposes...
By the way, the nowadays standard two-pumpheads-design usually already reduces pulse fluctuations even of single pumps to a minimum. At least I don't see so many differences regarding base line pulsations between our binary and quaternary systems...any different experiences?

[lmh]

and one practical point: binary pumps with high-pressure mixing will very often supply the correct solvent mix even at near-zero back-pressure, whereas quaternary pumps with low-pressure mixing very often rely on a decent back-pressure to close the gradient proportioning valves, which means that if there isn't a good back pressure (>20bar), they pump random mixtures instead of the correct mixture. This is of relevance if you try to do a gradient test without a back-pressure restrictor, or if you use the LC part of an LC-MS system merely as a solvent-supply for the MS.

(explanation: the gradient proportioning valve is 4 valves, each letting one solvent into a mixing chamber. Each valve is opened in turn during the pump's cycle to let a little of its solvent in. To make a 30/60/10 mix of A:B:C, for example, the valves would open for 30%, 60%, 10% and 0% of the cycle. If they don't close promptly, you get the wrong mix. They're often opened electronically, and allowed to close under back-pressure).

[uzman]

Hi lmh ,

How can a pump apply backpressure to the valves , since there is a checkvalve between the pump head and the valve ?

I think during the compression period of the pump , checkvalve will close and no solvent must return back to the suction tube so to the valves.

[Andy Alpert]

Uzman:
The proportioning valves for low-pressure mixing are not check valves; they are solenoid valves. These are driven electrically, as LMH says, not by fluid pressure. At each cycle, the valve opens and takes in a fixed volume of liquid (say, 5 µl). The output from all of the valves is then combined in a stream to a regular pump head with a piston and (yes) a set of check valves. The ratio is determined by how frequently the solenoid valve for Mobile Phase A opens compared with the frequency for the solenoid valve for Mobile Phase B.

[uzman]

Hello Andy ,

Thank you for the explanation.
I know the difference between the proportioning valve and the checkvalve.
I mean , there is an inlet checkvalve on the pump head which prevents the solvent backflow into the proportioning valve.
Under this condition , how a pressure can be applied to proportioning valve ?
When the pump piston begins pushing the solvent into the system , the inlet checkvalve close immediately , so the solvent cannot backflow to the proportioning valve.

Otherwise no pump can function properly.

[rwjohnson]

I took a look at the LC's I use more closely after reading this post today. Interestingly, I have an Agilent 1100 quaternary that has an active (i.e. electric-controlled solenoid) inlet checkvalve between the pump and the proportioning valve, but the Agilent 1200 (a newer model) quaternary has a regular checkvalve (i.e. one that closes with backpressure).

What do you guys have? Why would Agilent go from an active inlet to a regular checkvalve?

Another question: Can anybody provide more detail on the proportioning valve? How fast do the individual valves cycle? Would it cycle numerous times per piston stroke?

Ron J

[HPLCaddict]

@uzman: Of yourse, you're right, when the inlet check-valve closes, no eluent will enter the pump head. That's why old single-headed pumps produced a nice pulsating flow. Modern pumps have two pumpheads, usually employed as accumulator-piston pumps. Here one pump-head feeds the other (and the system) at twice the flow rate (inlet check-valve closed, outlet open). Afterwards the second pump-head feeds the system while the first one recharges (inlet check-valve open, outlet closed). There are also pump designs with three check-valves.

[lmh]

uzman, I see your point, I can only assume that the pump's check-valves are also not at their best when working at zero-back-pressure??? I just know that a Thermo Surveyor quaternary pump pumping at less than 4 bar backpressure can easily be 20% away from its designated solvent mix, but the same pump with 50bar added will be correct to 1% (and this is what the manufacturers expect; correct me some Thermo person if I'm wrong?). So there must be some way in which back-pressure affects the gradient proportioning valves in at least this quaternary system? An Agilent 1100 binary pump will be correct to 1% even at no back-pressure.

[unmgvar]

lmh, as explained earlier, the proportion valves open and close for a fixed amount of time from the solenoids. small electromagnets coupled to a spring.
as they open a specific valve, 100% fluid from that valve goes in the pump, it start some sort of mixing there, but the real mixing is done in the mixer.
solvent mix very poorly every where else since the flow in an HPLC is laminar and not turbulent (that allows mixing, the mixer)
the mixer does feel the pressure and the flow and is influenced by it

[lmh]

umgvar, I'm aware of that, but what I'm trying to understand is why the system pressure strongly influences the accuracy of gradient pumping in a quaternary pump from Thermo.

Given a check valve between the pump heads and the mixing chamber with its 4 gradient proportioning valves, uzman correctly pointed out that the proportioning system should be completely isolated from system pressure. And yet it isn't (at least in Surveyor quaternary pumps). Is this some special characteristic of Thermo's Surveyor pump, or is it so in all quaternary pumps?