Caring and feeding an Edwards speedivac?

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Amazing pumps those Edwards Speedivacs, though I would have thought it overkill for varnish impregnation! When I was a "callow youth" two or three years ago (ok back in the late 1960's) and worked for Mullards, we had rows of them evacuating sputtering chambers where we were making indra-red devices for the MOD. A very satisfying gupling sound they make

AWEM

I'm pleased it arrived. I'll make enquiries to see if a manual can be found, in the meantime this company, a Google search found, may be able to offer advice.

Partially answering myself: Couldn't resist and opened it. No gaskets hurt. Damned imperial spanners. :-) Thankfully a lot of allen heads (?) where I do have a set of. Simple to disassemble.

Several reasons:

• The plate where a reed valve sits on is rusty. Fixed with an oil-stone.

• Crud and water in the case. The new oil is white now. Thankfully, I bought

2 liters (well, almost: two quarts) of the oil and one bottle is more than enough. Almost cleaned.

• The vanes (it is a rotary pump) do have some wear and a little bit of rust. I guess they will wear in again into the "cylinder" that also got a bit rusty (not really rust). But, the length of the vanes is 0.06mm shorter than the cylinder is high. So I *guess* they can't seal well on their sides. I'll assemble it again tomorrow and if it doesn't get better, I'll ask a friend to grind off 0.04mm (or so, if I only would know) of the cylinder so the vanes fit again. I have something else to grind, so I can send him two workpieces and some beer tokens.

Nothing tragic, can all be fixed. Good old solid British engineering!

And to the question why I need a speedivac for VPI: Well, the young lady I got the oil from also asked me what a private person is doing with such a pump. :-)) At least it isn't undersized.

Nick

Yes. The ballast allows a small amount of air to leak into the pump to prevent vapours condensing-evaporating-condensing-evaporating in the pump.

Re-your later comments about the 0.04mm clearance. Don't forget that the vanes will get quite hot in use. don't make them too good a fit in case they seize. Have you run the pump with the new oil? Let it run for a while with a closed inlet and the ballast valve open. Let it get hot to evaporate any moisture and see what vacuum you get then?

May be simpler than cleaning varnish out of the pump :-)

You said before that the varnish was water based. Is it worth refrigerating it to lower its vapour pressure? The varnish that we used at work many years ago was designed for a low vapour pressure, but I don't know what was in it!

Worth what you paid for them :-)

regards Mark Rand RTFM

Making sense.

Yes. The old one simply wasn't enough. :-)

After having disassembled it, I think it simply needs more time to break in again. The water in the oil went off, when I have put the oil (in a can) into the oven (at 140°C) while baking a coil. Flashpoint?

Just phoned with the dealer. It is OK if the varnish boils in vacuum. If it gets to thick, it can be thinned back again with water. Now the trick with curing it: Sloooooowly! It takes 48hours in an controlled oven. 60°C, then 90°C and then the curing temperature for 3 hours. He said that they initially had problems too. Still he is selling it as "fast curing" :-))

Sounds like a good idea.

Nick

I may be teaching granny to suck eggs, but I used speedicvac and genevac pumps for many years in lab work, so here goes.

Normal atmospheric pressure is 760 mm Hg (15 psi). If you pull a vacuum of say 1mm then the external pressure on the walls is 759 mm. If you go to

0.001 mm the external presusure is 1mm greater! In other words if what you are trying to do id generate a force, for example for impregnation, vacuum forming, pressing veneers or making composites then any vacuum is good enough. The difference between lousy (1 mm) and good (0.001 mm) vacuum is only important for things like vacuum distillation, or when you need very pure, clean conditions. Putting it another way, the implosion hazard for a vacuum of 10 mm is just the same as for a vacuum of 0.001 mm.

Incidentally, there must be loads of these old pumps being scrapped in university chemistry and physics labs and even pretty much worn out ones are good enough for many things. I do vacuum bag veneering of wood with an old genevac which was being scrapped at work. We must have scrapped several hundred over the last ten years.

A speedivac in good condition, working hard against a closed system and with well degassed oil will pull about 0.001 mm. For what I think you are doing (vacuum impregnation?) even a clapped out one will do the job. The vacuum you can achieve will be limited by the vapour pressure of the liquid which will be quite high if it's solvent based.

The gas ballast valve leaks a small flow of air into the pump on the exhaust side. Its job is to help flush crap out of the oil, but it also slightly reduces the ultimate vacuum. In my spedivac days, we ran with it closed most of the time and opened it for a while every now ang agin to clean the oil.

Some more egg sucking points:

Don't run the pump for long periods with the inlet open - you'll aerate the oil and spray it out of the exhaust.

Don't turn the pump off without letting air into the inlet (some have auto air admission valves) - you'll suck oil out of the pump into the equipment.

Do have a pipe on theexhaust leading outside - all the crap which goes into the pump comes out the exhaust.

Don't expect full vacuum immediately from a newly filled pump - it can take an hour of two to degas the oil.

Hope granny is of some help!

Sounds as if you're getting deep into vacuum technology!

and

are useful references.

I think you'll find that the .04mm end clearance is close to normal and I would be very hesitant on reducing it. Rotary pumps rely more on the oil film for the running seal rather than spectacularly close clearances.

The big problem is water. The gas ballast option is really only intended to deal with traces of condensible gases from a nominally fairly dry system. Water containing varnish that is boiling merrily will both overwhelm the gas ballast and contaminate the oil.

So long as you're using a water suspension varnish you need both hot varnish to aid removal of the water and a good cold trap on the pump inlet to prevent most of it reaching the pump.

Jim

Don't disctract me!

I don't know. It were 0.06mm. I consider that as quite a gap for something running that slow. But it was just an observation. I'm breaking it in again and see what I get. But what I do have now is enough for what I need.

Yes, I'm getting aware of that. When I have used up that crap, I'll look for something different.

Things are getting more and more complex. A new domain, but interesting to understand.

Nick

[lots of useful information snipped]

Sure granny! That pump is getting interesting. I'm aware that I could be happy with what I get now and shouldn't invest any more time in it. OTOH, it's fun to learn more than needed and to have tools that perform better than required.

Nick

PS: Hopefully, the third attempt to make a seal for the vacuum chamber's top-cover out of perspecs (Plexiglas) works.

Hi Nick,

I restored one of these pumps a couple of years ago. They're great little machines. Here are some before and after pictures of mine:

If you haven't already done so, it's a good idea to drain all the oil and remove the water, even if you use the same oil again. There was perhaps 1/4 to 1/2 pint of water in my pump.

I believe the valve you mention is the "gas ballast valve". Opening it helps avoid the pump collecting water, but reduces the ultimate vacuum attainable.

Edwards don't keep spares for these pumps anymore, but there are a couple of companies in the UK which do. I got my parts from GE Scientific and Island Scientific (I can find URLs and phone numbers if you need them).

Edwards did however send me the maintenance manual for their early belt driven pumps. I've put it online for you here. It's a big file (around 18 MB in size):

What model is your pump? Mine is an ED 35.

Best wishes,

Chris

I replaced it two times. :-)

Yes, that's how it is called.

I found one in the UK who would have a gasket-set for my model. But I don't think that I need one. Currently, the manometer gives a reading of below 20mbar. The error of the gage is 1.6% (0 .. -1 bar, thus +/-16mbar). I am quite sure that the actual error is positive (+16mbar), so that would be 4mbar in the best case.

It's not my model. Mine looks to be elder. It is a 1SC30. Anyhow, the manual is helpful. I'll reread the alignment-procedure for the "cylinder" and the "piston" and see how well I guessed it.

Nick

In most cases you probably don't need new gaskets. Most of the gaskets I removed from my pump were fine. The shaft seal was the worst, if I remember correctly. I just decided to replace them all because I'd gone to the effort of stripping the whole pump.

If I remember correctly, it'll be an ISC 30 rather than 1SC 30. I think the number refers to a single stage 30 litres/minute pump. I believe the ISC and ES/ED ranges were manufactured concurrently, although I'm not certain of this. We had a small Edwards ISC pump when I was in high school (quite possibly an ISC 30). Recently I went back to my old school and they'd built an entire new laboratory, but they still had the same old Edwards pump!

Glad the manual was of some use. If you like, I can give Edwards a call for you and see if they have the correct service manual for your pump. But I doubt there are too many differences.

Best wishes,

Chris

That's the only seal I did not remove. I guess there is an outer seal (very simple, would not stop anything from air being drawn into) that I did remove and an inner seal that seals the oil from being drawn into the pumping chamber. I didn't remove this one because there was rust on the shaft and I feared to ruin the seal by pulling the shaft over it. If I would know that it is a standard seal, I'd do that.

That's clearly a "1". I just rechecked.

That's a very kind offer. Bob already offered that to me, so I think I'll get the manual through him.

Mine has less bells and whistles, and the whole construction looks to be simpler. So an earlier model.

Nick

The oil seal in the ES/ED range of pumps is just a rubber disc with a hole in the centre of it. The hole is slightly smaller than the shaft, so that when you pull it over the shaft it forms a cone shape. I doubt you would destroy the shaft seal by pulling it over some rust, but there's no point removing it unless it leaks oil. I was told by a man at GE Scientific (where I got my pump spares from) that a leaking shaft seal doesn't affect the maximum vacuum attainable; it's just a nuisance. Somewhere I have a spare shaft seal for the ED 35, which might be the same size as the seal used on your pump, but I've no idea where I've put it! If by any chance you find that your shaft seal leaks, let me know and I'll see if I can find it.

Guess I must have been mistaken!

Best wishes,

Chris