Sciencemadness Discussion Board - Edwards Speedivac pump

Edwards Speedivac pump

Antigua - 25-12-2021 at 09:31

Hi!
I have an Edwards ED75 double stage rotary vane pump that I've been using for vacuum distillations for the last year or so. So I thought it's high time to actually take good care of it, as this chunk of steel is 55 years old now.

I'm attaching some photos - the pump, a makeshift fitting I made for it from a rubber cork that may be causing my vacuum to be weak (~5 torr) and the original steel fitting with the flange.

My questions are - does anyone know how to look for a fitting for the inlet? I'd like to connect a hose, so some sort of gasket + barb fitting would be the best.

The pump has been making a worrying noise lately too, when the gas ballast is fully closed there's audible knocking coming from the vane department. When it's open just a little bit the noise is more quiet. Has anyone got any experience reparing these? The manual seems to indicate that this may be connected to the valve related to the gas ballast, but I'm not sure if they just mean the needle valve that the gas ballast is made of or some other inside. Attaching screenshots from the manual too. I was worried that maybe the vanes are hitting against something.

Additionally, what oil would be the best for it? Edwards doesn't produce the recommended Speedivac No. 16 and No. 18 oils for it anymore, so I've been using ISO VG 100 viscocity vac. pump oil. Edwards recommended to me that I use their Ultragrade 19, which is ISO VG 46 in the matter of viscocity and also insanely expensive where I live. Does the viscocity matter that much? Will a 46 oil pull a better vacuum than a 100 one?

A great-written manual is here: https://www.idealvac.com/files/manuals/Edwards_ED75_ED150_ED...

Thanks in advance!

[Edited on 25-12-2021 by Antigua]

Panache - 25-12-2021 at 17:13

When running that exact vac pump for several years a few years back I used a synthetic oil made by cps (American company that makes vacuum pumps and associated gear for the HVAC industry). It's a good product.
The pump itself is also a stalwart, I recall seeing a photograph of about a hundred of them installed in a room side by side, something to do with that small Apollo project NASA ran in the 1960's...

The knocking you describe chimes with me and I'm.trying to recollect it's source, when/if I do lII update, but in the interim I'm sure it was of no consequence, just super annoying when it occured then it would abate at deeper vacuums (if I recall correctly.).
Finally...to finding fittings...do what you can...Edwards stuff from that era utilised proprietary threads if I recall..so trying to find matching is utmostly infuriating...

Panache - 25-12-2021 at 17:17

How's the mechanical seal on the belt side? Does it leak any oil? That seal wasn't trivial to source if I recall, and although it didn't affect the vacuum losing Oil constantly was a pain,

Antigua - 26-12-2021 at 03:05

Do you mean the shaft seal? Like here: https://www.youtube.com/watch?v=jidG7yJDaVg?
I wasn't able to remove the pulley yet, was a bit too scared to screw things up. But I'm not losing any oil there, no significant leakage. Regarding fittings I think I'm just going to get a proper barb to fit the rubber cork and screw it up from underneath to make it air-tight. Silicone sealant on the outlet/cork gap and that should do the trick. I'm still a bit worried about the knocking though.

monolithic - 26-12-2021 at 15:54

The rattling might be from the gas ballast valve. These old style pumps (like on a Precision Scientific pump that I once owned) have a spring-loaded ball bearing within the gas ballast valve assembly. If the spring it weak you might get some rattling of the ball bearing. The PDF of the manual you linked (page 28/74) shows that it can be disassembled pretty easily. I'd start there. Maybe pull it off and plug the hole with your finger (or a piece of rubber) and start it up, see if the rattling sound goes away. If not, it might be a broken vane.

You might be able to get a better seal with some good vacuum tubing and a hose clamp, and then a reducer with a hose barb.

wg48temp9 - 26-12-2021 at 20:58

Finding an adapter

There probably were adapters made that fit the outlet flange of your pump and connect to a plastic pipe but that flange is not now common in vacuum work so it will be very difficult to source one. You could ask Edwards but any thing from them is likely going to cost £100 and up.

I suggest you remove the short 1" ID pipe from the exhaust and take it to a plumbing shop to find a short piece of flexible tubing that will fit over the tube and fit a a reducing connector/coupling both secured by jubilee clips. You could also show the pipe to one of the shop assistants and explain what you want to do and ask if they have any suggestions.

You should also check the o-ring on the sleeve of the flange fitting or preferably replace it.

Below is a picture of a reducing copper pipe coupling that could be used. Plastic stepped hose connectors are also available that can fit a range of pipe diameters.
1-1-8in-x-5-8in-reducing-coupling_min_14613_P_1.jpg - 6kB

1-1-8in-x-5-8in-reducing-coupling_min_14613_P_1.jpg - 6kB

PS: The one way flapper valves in exhaust path can be noticeably noisy.
A vacuum of 5 torr for a dual stage vacuum pump is terrible if you don't have leak. Perhaps your oil is contaminated you could replace the oil and perhaps replace it with a more viscous oil to compensate for the wear of the pump parts.

[Edited on 12/27/2021 by wg48temp9]

Antigua - 27-12-2021 at 02:24

Thanks for the suggestions!
I'm not sure if it could be related to the flapper valve, because IIRC the knocking is present when the vacuum inlet is closed too, so there shouldn't be any air to sway the flapper (if that's how it works). I'll check the gas ballast though. Regarding the fittings, the pipe isn't threaded internally or externally, so I'm not sure how I could connect a pipe coupling like that. Not really keen to do welding, but I could just solder it?

The o-rings are in a surprisingly good condition, the flange-pump connection shouldn't be the problem. A good vacuum gauge would help in diagnostics, but these are really expensive :/

Antigua - 27-12-2021 at 04:32

I feel pretty dumb now!
I was able to get the gas ballast assembly out, but I have no clue where the pressure valve is. I wasn't able to find 129 on any of the drawings and the dissasembly part doesn't make it obvious either.

Should I try turning the pump on with the gas ballast hole closed?

monolithic - 27-12-2021 at 05:30

Yes, plug the hole with something and turn the pump on. If the rattling goes away then you know it's a faulty spring or some sort of blockage in the ballast valve.

Antigua - 27-12-2021 at 05:40

I took the entire gas ballast apart and put it back together, when turned out the pump didn't seem to rattle much, but I will be sure in 3 days when I get the oil. I don't want to run the pump dry to check for sure.

Antigua - 28-12-2021 at 06:32

So I noticed another type of noise that could happen because the belt was too tense. I loosened it up a bit and it disappeared.
Here's a video: https://streamable.com/04b3cw

But the gas ballast rumble still happens (videos: https://streamable.com/0r2sma and https://streamable.com/cesbuh - on and off, sometimes it's present and sometimes not). My colleague thinks that all these could be related to the bearing that transfers the torque onto the shaft. But I wasn't able to find it anywhere on the drawing.

Once again, does anyone know where the pressure relief valve is? The one that could be responsible for the gas ballast noise.

monolithic - 29-12-2021 at 08:08

Quote: Originally posted by Antigua

So I noticed another type of noise that could happen because the belt was too tense. I loosened it up a bit and it disappeared.
Here's a video: https://streamable.com/04b3cw

But the gas ballast rumble still happens (videos: https://streamable.com/0r2sma and https://streamable.com/cesbuh - on and off, sometimes it's present and sometimes not). My colleague thinks that all these could be related to the bearing that transfers the torque onto the shaft. But I wasn't able to find it anywhere on the drawing.

Once again, does anyone know where the pressure relief valve is? The one that could be responsible for the gas ballast noise.

Pressure relief valve is only found on the ES35 (see page 16/74 of the PDF.) I was looking at the wrong picture -- weird design, looks like the ballast valve on Precision Scientific pumps. I watched the last two videos and I don't hear anything wrong? My pump always made sounds like that, I believe it's normal.

If you're still getting bad vacuum then start with changing the oil. I believe the recommendation for flushing is to let the pump get up to temperature before draining, drain, add new oil, drain (flush), and then add new oil again. Operating procedure is to let the pump run with ballast open for an hour or so, and then close the ballast and let it pump down some more. http://www.hyvac.com/ has some good pointers on general pump maintenance and troubleshooting.

If you're still getting bad vacuum after this, then start at the top by fabricating a better vacuum inlet adapter. It doesn't look like you have anything to clamp the white rubber cork to the inlet adapter so you're undoubtedly leaking vacuum there. The inlet tube looks like it has some rust, that's not helping. Clean it up with some sandpaper. The rubber looks thin walled, you're probably leaking vacuum THROUGH the rubber. I have a digital vacuum gauge and these seemingly insignificant leak sources can make a big difference when you're trying to go from a few torr down to the rated 0.01 torr or whatever. (It's even worse if you're measuring vacuum at your glassware, since you have to contend with leaks at the glassware vacuum adapter, imperfections in the ground glass joints, how well your joint grease is sealing, etc.)

I saw you inspected the o-ring on the inlet. How closely did you inspect it? There might be microcracks at rest or under compression i.e. when it's torqued down. Replace it, it's cheap. Then Frankenstein together some hose barb adapters, with vacuum clamps, to thick walled vacuum tubing. Or pay a welder to attach a hose barb or KF flange to the inlet.

If you're still seeing poor vacuum at this point, there's probably something internally wrong with the pump. A bad exhaust flapper, leaks in the rotor assembly, a stuck/cracked/out of spec vane, etc.

[Edited on 12-29-2021 by monolithic]

Antigua - 29-12-2021 at 08:22

Thanks, I updated the inlet somewhat. The jubilee clip on the rubber is really tense and I don't think there'd be much leakage there. The rubber is actually somewhat heavy-walled. I changed the oil to a ISO VG 46 one and degassed it with the ballast open for half an hour. We'll see if it holds a good vacuum in action.

[Edited on 29-12-2021 by Antigua]

[Edited on 29-12-2021 by Antigua]