5890 no gas purging

[MSCHemist]

I think I have the valve partially working but it probably still needs replacing. I am getting gas flow through the valve and I can get a somewhat stable 1 ml/min flow (it fluctuates .995-1) but I can't get it when I open the mass flow controller more than ~50 ml/min and I cannot get zero flow when it set it to 0 or off which I assume means it is partially plugged and providing resistance. I think it fully opens for 0 column flow so there is no resistance so that the gas goes completely out the split vent since the column provides resistance and the split line doesn't.

[Peter Apps]

It sounds as if you have nothing to lose - try dumping it into an ultrasonic bath while pushing some inert solvent through it.

Peter

[MSCHemist]

Now it is clogged again obviouly the valve parts are all gummed up.

BTW does anyone make a specific chemical trap for the 5890 split line? The one that was on the carrier gas line I tried to hook it in between the split and valves but I had to hook it in the reverse direction as one end of it has the tube attached with a finger tight plastic o ring fitting which is not compatible with the inlet split fitting. Anyways it was providing a fair amount of flow resistance which won't work. It could be the trap is just old even though it just sat on the carrier line with already clean helium flowing through. This will just happen again if I don't protect those valves from split sample.

I don't think the sonicator will help as I don't think the sound waves can penetrate the thick metal body.

[Yama001]

I would just do without the old chemical trap. I think it is just a mol sieve, so if you really want it there you can be restore it by running inert gas at hi temp. I recall removing them from VOA instruments back when 5890s were state of the art - I do not recall why, but I know we did not miss them.

It is too late now, but HP did sell that inlet configuration with an optional split filter. The labs I worked at never bothered and killed several valves that way. The problem is easily handled if the split line and solenoid are cleaned periodically, but analysts often never learn about it.

[Yama001]

Oh, I think Restek still sells that gas line trap if you really want it. The part is 21610.

[MSCHemist]

Yep that was the one I had on the carrier gas line between the mass flow controller and inlet. The trouble is it was causing extra back pressure on the split lines which will interfere with its regulation as resistance on the split line is how the 5890 EPC regulates column flow. I'll call Restek and see if it can be used the way I intend otherwise I can jerry rig something with 1/8" line coming from the inlet on the split and then a 1/8 to 2mm reducer union (It looks like all the steel lines are 2mm as they are bigger than 1/16")

even periodically cleaning the split line I still don't trust that it won't eventually kill the valves. The split line (which is 2mm not the 1/8" on the 6890) didn't seem that bad but I did see deposits at the base of the solenoid where it attached. I had a 6890 where almost the entire 1/8" tube up to the trap was filled with tar.

[Peter Apps]

Now it is clogged again obviouly the valve parts are all gummed up.

I don't think the sonicator will help as I don't think the sound waves can penetrate the thick metal body.

On the contrary - ultrasound propagates very well through solids. Worth a shot anyway.

Peter

[MSCHemist]

I seem to have the valve working now at least partially. I sonicated it in cheap isopropanol. It can't deal with total flows <200ml/min but at 10 ml/min it seems to be able to maintain flows from 0.1-3 ml/min which is what I use it at. (I always keep it a 10:1 split on a standard 30m .25mm .25um column 1 ml/min) I'll still eventually replace the valve when the opportunity arises.

Edit I seems to stop being able to cope when the flow gets to at or above 200 ml/min which is higher than I need. Now all I need is a 2mm union (I had to cut it out of the instrument). and to figure out the deal with a trap.

[MSCHemist]

I left it running overnight and today it is able to maintain the flow up to the maximum flow allowed the the mass flow controller ~600 ml/min He. Now I just need to figure out the trap situation. Any trap that causes back pressure on the lines will interfere with regulation so that is a no go. I can either get a new one like Restek sells or splice something together on 1/8" lines with a 1/8" to 2 mm reducing union. The Steel lines are all 2mm.

[MSCHemist]

So I spoke with Agilent. Aparently any chemical trap I use will put backpressure on the line on mess with the EPC. They recommend getting some 1/8" tubing, attach it to the inlet, and just have several feet of it coiled up in the instrument and using a 1/8 to (I can't tell if the tubing is (2mm or 1/16") reducer to hook it up to the tube to the solenoid valve.

[JCASTIGLIONE]

Check if the gold seal was placed in inverse way, the groove must face up.

[MSCHemist]

Nope gold seal is fine It is working ok now but I cannot achieve 0 flow when set. When I do it has a flow of .04 ml/min and the PCV gets pretty hot so there is probably still a source of back-pressure on the line somewhere maybe at the inlet split aperture as the solenoid is new and I hit the PCV hard with solvent followed by high gas flow followed by warming it fairly hot with a hair dryer the volatilize off stuff. I took Agilent's suggestion and put a coil of 1/8" copper followed by a reducing union and 1/16" tube to the solenoid.