5973 Cal Gas Valve-Diff vs. Turbo Pump

[benhutcherson]

I have-over the past month-upgraded my 5973 from a diffusion to a turbo pump. Actually I should say that I bought an untested parts turbo pump 5973 chassis on Ebay, transplanted my known side plate/analyzer to it, then after confirming it working(using the GPIB eMod) transplanted my GLTS LAN-upgraded eMod to the turbo chassis. It's been a fun adventure, and I've so far been really pleased with the results on the whole. BTW, with help from Geoff at GLTS, I made my own G1099-60435 turbo pump power cable for about $30 in parts(and have two I need to send Geoff)-it beats the $375 Agilent charges for this cable. If anyone wants the Digikey PNs for the connector along with instructions, or wants me to build one for them, let me know...

That aside, in the past couple of days, things kind of went to heck on it. It was tuning beautifully with the EM at around ~1350V, and literally overnight went to a very ugly/noisy tune at ~2400V. I've gone through it, recleaned the source(which did not seem dirty) and basically am at a loss.

I know cal gas issues can cause tune issues. There is plenty of PFTBA in it(if I look just right I can BARELY see the bottom of the mensicus below the the nut where the tube goes into the valve body). The valve is definitely opening-with ~1.2mL/min flow of hydrogen(lowest I can go with the column I'm using), the hi-vac with valve closed is ~3.8x10^-5 torr(gauge reading) and will jump to 4.1x10^-5 when I toggle the valve open. Just to be sure, I have tapped the valve with a screwdriver handle.

In the back of my mind, though, I keep thinking about how when the turbo chassis was delivered in December, the box arrived upside down. I've never taken one of these valves apart, but I feel like I have heard of issues if PFTBA is allowed to saturate the frit. I'm also a bit afraid to try cleaning it as I've also read of a very fragile glass capillary.

The obvious thing to do would be to swap the known good valve off my other 5973 chassis, but I'm afraid to try this. The valves both look different(the turbo one has a black box solenoid on top, the turbo is a metal cylinder) and if I'm not mistaken the turbo and diff pump cal gas valves have different PNs. I can't think of WHY they would be different, but they seem to be.

Does anyone know if this is actually the case? If they're the same, I'll swap valves tomorrow and see if anything changes, but also don't want to mess things up by mixing and matching valves...

[James_Ball]

I would think the only possible difference would be the Diff version might has a tighter restrictor due to the lower pumping capacity of the high vacuum system.

As long as the solenoids have the same volt and amp rating, though different shapes to the magnet housing, they should be interchangeable. The main board and power board are the same so the draw of that solenoid should be the same also.

[LALman]

I went from a standard 70L/s turbopump to a used Edwards EXT255 Turbo Pump (also from Geoff at GLTS). The higher pumping capacity does make the instrument tune differently. To keep it consistent, I do a peak scan for 5-10 minutes every morning before doing a QuickTune. I think the ID of the capillary in the valve is larger for low vacuum systems and thinner for high capacity vacuum systems. But the cost of a new tuning valve (~$2500 last time I looked); makes me willing to do the work around rather than try getting a new valve.