Selecting a Vacuum Pump

[mangozac]

[Hoobie]

Howdy folks,

I've been doing detailed undercut cold casting without pressure or vacuum for a while using pinkysil moulds and a variety of different flexible polyurethanes at 50-80 shore A. I'm over the fail rate from bubbles now and pondering the Supercheap 'blackridge' Auto paint pot setup teamed with something like this:


or this:


and my 3hp 80 litre air compressor will do fine for the pressure side of things.

if it all goes well I'll go and make up a lexan/perspex/polycarb lid and maybe set up a solid chamber, but right now I'm just kicking about ideas for parts.

opinions? smiting? experiences? all are welcome

[mangozac]

Hi Hoobie,

I'm running the first pump you linked to (8CFM) and find that it's more than adequate for use with a 10L pressure pot. I've always just used the pressure pot with its metal lid for degassing so I've never actually been able to watch it in person, not that I've ever found a specific requirement to.

If you do make up a perspex lid, make sure it's at least 12mm thickness. Any less is insufficient in the long run.

Note that if you don't service the pump periodically it does seem to impact the absolute vacuum it can reach. I've never had mine serviced and although I do keep the oil topped up I've noticed performance isn't as good as when it was new. It hasn't degraded enough to be a problem though

[Hoobie]

Cheers mango,
I like the idea of watching it do its thing so I'll probably end up making a funky lid anyway.
When you say 'service it periodically' what exactly does this involve? oil changes, replacing seals or tearing it to bits and throwing stuff away and buying replacement parts?
I'm also thinking of setting it up to do some CF bagging as it's a bugger to make it lay out nicely with a cheap brush.

Thanks for the info

[Hoobie]

aaaaand one more thing... specwise the 9cfm is supposed to be better and and costs $249.90. It also weighs 4 kilos less. This makes the spidey sense tingle. Stick with the 8CFM tested one like yours or go for broke(n)? whatcha think?

the 8cfm one seems to be missing its model number...

but how suss is the 9cfm spec?


it is possible that I have trust issues.

[mangozac]

The difference between 8CFM and 9CFM is fairly minimal. The lack of model number on the 8CFM is inconsequential.

Looking at the specs and pictures, the 9CFM pumps seems to be more deluxe - I particularly like the basic filter on the exhaust port, as well as the intake port fittings. I'd probably go for it

[Hoobie]

cheers mango,

still wondering why the 9cfm is 17.5 kg and the 8cfm is 21.8kg. generally less weight means thinner or less parts, which is a little worrying for something with a supposed better rating. I will mull it over. The testicles say GO 9CFM and the brain is saying GET THE MOST RELIABLE ONE.

sadly testicles and brain are usually mutually exclusive.

[mangozac]

Hahaha yeah I know what you mean. The "little brain" gets us into lots of trouble!

The weight difference may be due to the use of more aluminium in the larger pump. Also, there may be more efficiencies in a 1hp motor compared to a 3/4hp (but don't quote me on that).

[Magnetic Duckling]

Hello,

Revival Duckling here.

I was wondering, how often should I replace the oil on my vacuum pump? Because the oil's colour slightly changed and according to the user's manual I'm supposed to replace it if that happens. What do you think? I am afraid of damaging it if I keep using it.
Also can I use any oil labelled "vacuum pump oil" or is there specific oil for specific brands?
Thanks ;_;

[mangozac]

Hey MD great to hear from you again!

Good question! I've never changed the oil on mine so I don't know (I do make sure I keep the oil topped up though). I'm nearly out of the oil that came with the pump, so I guess I'll have to find a replacement soon too!

For our purposes anything labelled vacuum pump oil should do the trick. Since the pumps we use are originally intended for refrigeration and airconditioning it's probably best to use those search terms too. Just something along the same lines as this:

Apparently old oil will affect the performance of the pump, so it might be worth me doing a full oil change anyway...

[Fleafa]

Depends how big the change is. These units are intended to run almost constantly, or at least very frequently, as part of a refrigeration set-up. I'd be surprised if you have used it enough, but maybe you have.
Any vacuum pump oil should be fine.

[mangozac]

[Fleafa]

Ah, of course! That makes sense...

[TomG]

If I count correctly. 72 l/min (my current pump used primary for creating molds) is something about 2,6 CFM and a bit better pump with power 198 l/min is ekvivalent to 7 CFM. Question is, it is enought for aprox 12L chamber and combined with presure?

[mangozac]

Hi Tom,

The 7CFM pump should be adequate for the 12L pot doing combination vacuum and pressure casting. A little higher (8-10 CFM) would be ideal but I'm not sure exactly how much difference it would make.