Chromatography Forum

I tuned and air/water checked my 5973 GC/MS. they showed there is an air leak in the system. I tried to figure out the leak source by spraying a leak detection gas (dust removal) on injector, interface, vent valve and in the slot of side plate O-ring around source; As I sprayed in the slot the edit MSDS window monitored a noticeable respond to the gas as it was sucked into the MSD and ionized.
I rinse the O-ring by Methanol at first step; since I still had leak I order a new O-ring (which was expensive) and replace it. It did not help at all and also increased the leak. I replaced a broken Repeller's isolator a few days before seeing leak, but I do not know if this is related to this air leak issue at all!!!
Any idea after cleaning and replacing side plate O-ring?

Do you have an ion gauge? What does it read? Did you wipe down the side plate with methanol as well? The mating surface may have a particle preventing a good seal against the o-ring.

Your air-water check reports a 4:1 ratio of 28 to 32?

__yes, I wiped down the side plate with methanol as well; I saw some small back particles around it next to O-ring too.
__N2/O2 ratio is kind of 4/1 and it is getting bigger every day!!!
Friday was 36.5/10.59 and today is 57.36/16.55
Thanks for your help,

yes, ion gauge shows 1.9-4

Hi
The first step is to found the leak.....
Use Argon to verify if the leak is at the interface nut, scan mass 40....habitually, the leak is at this place.
Often, the gasket is dry and some leak can appear at this place, so, you can use a small quantity of APIEZON L grease (Agilent# 6040-0289) to lubricate the gasket.

Did you try replacing the o-ring behind the vent valve knob? When venting this can become slightly misaligned and result in a leak, dust detector sprayed around the MSD door could be sucked up through here.

I do not have extra valve O-ring right now. This morning I sprayed leak detector gas over injector port, interface nut, vent valve knob but, I did not see any respond in Edit parameter profile.
I sprayed in slot I saw some response (peak on prof) then I spayed it around the MSD door it showed higher peak especially on the lower left hand side.
Thanks everybody for your help

Sometimes that sideplate O-ring gets dented or creased; you may have to replace it. I have an Agilent part number, its about $120.

Prior to that you may want to remove the o-ring and clean it with methanol all around, then replace it (replacement can be a challenge). This might fix the problem.

For the newer Agilent 5975, if you have continuing problems with this seal, they recommend adding some Apezion hi-vacuum grease to the o-ring, maybe once a year. The idea is to rub a little of it all the way around, then do a methanol wipe, leaving the o-ring shiny but not greasy.

Do you have a diffusion model or a turbomolecular model? If turbo, can you check the turbo speed, to see if it is at 100%? If it's a diffusion pump model, maybe you need to replace the pump oil to get better suction. Do you know if the oil has been changed/checked recently?

How about the roughing pump? Is the level between the lines? Have you ballasted it recently? Is the oil clear/yellow or dark/brown? Are there bubbles in the oil? When was it changed last (I think 6 months is recommended interval).

How old is the system, in general? Maybe the pumps just aren't "doing it" any more. I personally have 3 turbo 5973s and one diffusion model I look after, and I don't recall running into something like this that wasn't solved by wiping down the gasket and the door face.

Do you use the shipping bolts to hold the door shut when pumping down? Do you hold it closed with your fingers?

I also have a new 5975, and that thing is a PITA to pump down...

I also have a new 5975, and that thing is a PITA to pump down...

I have seen the same thing. It's like the groove for the big O-ring is deeper than the 5973, so it sticks out less, and the door has less of the o-ring to stick to.

You would think this would improve with time, not the other way around!

That Apezion grease was recommended by my 5975 installer, btw.

There is an o-ring on one of the feed throughs ( I think it is for the white wire) that is another leak spot. Don't forget the o-rings for the ion gage triode at the back of the instrument. The o-ring for the vent valve is an injection liner o-ring.