Chromatography Forum

The manual recommendations are...

Yearly: Inspect & clean inlet filter, gas ballast control, site glass, motor fan cover and enclosure

15000 hrs: clean and overhaul the pump

30000 hrs: fit new blades


What do all of you do? Are the overhaul kits worth it?

Maybe I'm a bit lax on this sort of stuff, but generally I only tear into an Edwards pump when it starts leaking oil, which I've found they all tend to do sooner or later.

Generally speaking too, if the pump is otherwise still pulling good vacuum when that happens, I'll split the case and replace every easily accessible seal-that generally means the big gasket between the pump body and motor(I've made these in a pinch, but don't recommend it-I make gaskets for my hobby cars all the time so keep gasket material on hand and use thinner cork for the Edwards, but I'm probably 80% on getting them to not leak and gasket material seems to get more difficult to find every year) along with the O-ring on the drain plug and the other easy to access O-rings.

Usually from there, I button it up and with fresh oil the pump is back to its old performance.

I should also qualify that this is for GC-MS systems. The RV3 is one of my preferred pumps, especially for systems like the HP/Agilent 5973/75/77. There's quite a bit of discussion around here and you'll hear also from a lot of the independent service engineers that the tiny pumps shipped with these systems(Edwards E2M1.5 or a Pfeiffer equivalent) have a lot of downsides and upsizing the pump to something like an RV3 makes a lot of sense(quieter, cooler, and usually will improve ultimate vacuum in the system as well allow faster recovery from pressure spikes like the solvent peak).

On the whole, though, the rough pump on a GC-MS lives a pretty easy life. The biggest contaminant they deal with is usually the solvents in your samples, and if you're running a splitless method they might handle whatever volume you get from 1 microliter of solvent at the time. That's only once per run, too, and of course is not counting what gets ionized into something totally different in the MS. Even doing a "fast" method I doubt a high throughput lab is doing more than 5 samples an hour or so(for what I'm running now I'm lucky to get one an hour). The solvents are often volatiles like DCM or chloroform, and a GC-MS method with water would be pretty uncommon. Other analytes get injected into the GC literally in nanogram quantities-my most concentrated standard I'm using for my method I inject ~70ng of my analyte(1,4-Dioxane) and most "real" samples have much less. Throw in split injections, and you're getting even less of any of this.

All of that means that, practically speaking, I never have the real need to even open the gas ballast on my pump(I'm using a Varian DS102, which is essentially interchangeable spec-wise with the RV3. I make a point of opening the ballast for a few minutes once a week or so, especially since I do sometimes get water in my samples(I'm doing SPE from aqueous samples that gets eluted off the SPE cartridge with DCM).

And along with that, provided that you use good oil that gets changed regularly, the pump itself doesn't wear much. If I do a 6 month oil change, the oil that comes out tends to be amber(Inland 45 is colorless when fresh), presumably from heat causing some hydrocarbon break-down, but that's about it. In a past job, I had one research lab that took all my drained GC-MS oil and used it in their ancient Welch belt-driven pumps on their Schlenk lines-they said that my used high grade oil worked better than the standard grade oil they bought!

Of course if you're running LC-MS and ingesting a lot of water and/or other mobile phase, the equation can change a lot. The last LC-MS I spent any time running was a Finnigan LCQ-Duo. It wasn't THAT long ago that I was running it, but it was pretty old then so take that for what it's worth. It used a massive(from my perspective) E2M8 pump, and I think daily upkeep called for 15 minutes of gas ballast at the end of the day and monthly oil changes. That pump had definitely been used hard!

I know this is a lot of rambling, but I'd say in general to renew the veins/do a major rebuild if the pump isn't performing up to par rather than doing it on a schedule. If it's on a GC-MS and given regular oil changes, it may never get there. I think James Ball on here is still running E2M2s, which haven't been made in several years. On an LC-MS, use your judgement.

Of course if uptime is paramount and time is money, being able to schedule downtime on the pump for a rebuild may be better than having a sudden failure. The last I priced them, a new RV3 is around $3K, and if you REALLY need uptime it's probably not a terrible idea to keep a new or reconditioned one on hand. Then if you have issues, just swap the pump and rebuild when you have time.

Rebuild kit wise-the vanes certainly can wear, and I did mention seals. The other side of that I'd mention, though, is that in the past I use to source rebuild kits through Capitol Vacuum in Chantilly, VA. When I went looking a few months ago, it certainly looked like that end of their business(pump parts and supplies) was no more. The last time I priced things out, which was maybe 2019, Capitol Vacuum charged about as much if not a little less for a major rebuild kit(with vanes) as buying a minor rebuild kit(seals only) from Edwards. The major kit was about double Capitol's price. This was on an E2M1.5, and I suspect the bigger RV3 would be mroe expensive.

Ben, thanks for your reply (I wish I asked a long time ago).

Could you explain a little more about the gas ballast? "Pretend" I had no clue what it was until I saw your post. It's a setting that allows some air in to sweep out contaminants, like solvents, that the oil may have picked up? You can switch from 0 to I while the pump is operating without effecting the GC/MS?

Michael,

I don't pretend to be an expert in vacuum pumps, but basically as I'm sure you probably know, rotary vane pumps really aren't meant to pump a lot of air(or gas). The oil is an important part of what serves to transport any pumped gases through the pump. You can sort of in the real world that large volumes of air(such as during initial pump-down or if you have a leak) that you get large amounts of oil misting.

In a two-stage pump with a gas ballast, it's my understanding that the ballast introduces air into the second stage, and doing that helps to flush contaminants out of the oil. Opening the ballast, at least on every pump I've ever used, causes a LOT of oil mist.

My 5973 now has a turbo pump, which means I lost the low-vac gauge. When I was still on a diffusion, I remember that the gas ballast would increase the foreline pressure although it didn't seem to affect hi-vac at low column flow rates. I suspect it would at higher column flow rates(I generally only opened it when I was running a .5mL/min resting flow rate).

At the end of the day, though, like I said I don't see a ton of necessity for using the gas ballast on a typical GC-MS. Others may disagree, particularly with high throughputs of dirty samples. I suspect that most potential oil contamination in a GC-MS pump happens infrequently enough(relatively speaking) and in such small volumes that the pump oil flushes it out without the help of the ballast.

The RV3 lets you bleed a small amount of air into the the vacuum stream (second stage IIRC) to help get rid of moisture if for example you are using a Tekmar 3000 with a Vocarb trap. Even with moisture control they dump quite a lot of water into a 5973/6890 system. So I have that bleed going and at the cost of slightly higher backing pressure it gets rid of any water vapor that gets into the backing pump oil.