Calling all vacuum press users - is this big enough?

[Steve Maskery]

Evening all.

I no longer have my Airpress and I miss it somewhat. I've been looking at building my own system, as off-the-shelf ones are good but pricey.

I've bought a vacuum pump off ebay. It was described as used, but it is brand new, complete with the little plastic sheath to the plug and a sealed bottle of oil. So far so good.

However, it was described a dual-stage pump with an 8CFM displacement. The one I have received is a single-stage pump with only 4CFM displacement.

The seller is selling it "for a friend" and has a 100% satisfaction rating.

I emailed him at lunchtime and gave him the opportunity to rectify things, and, despite being at work all day, he has responded this evening.

The pump cost me £50 (39.99 + £10 carriage). He is offering a £30 refund and I keep the pump. TBH it seems like a decent offer. I'm sure it would do compliant veneer, but is it big enough to press, say, a chair back onto a mould? Would it hold down a panel for routing?

I don't know enough about pumps to know really. If it would, then I think I have a bargain, but I don't want to "waste" my £20 if it won't do the job.

What would you do?

 

[worn thumbs]

If you don't have massive leaks,the CFM rating is a bit of a red herring.What you need is the ability to hold a good vacuum for the duration of the process.The disadvantage of a lower CFM rating is that it will take a tiny bit longer to reach ultimate vacuum level.How many vacuum bags have you used that held more than 35 cu.ft. of air to begin with?In the past I have used bags up to twenty feet long and fifteen feet wide and even then you can get a lot of air out with the workshop hoover before applying a pump.

 

[Steve Maskery]

OK, thanks, that makes sense.
Looking at the manual, the one I thought I was going to get is top-of-the-range (4D), this one is entry-level (2S).

It gives Ultimate Vacuum (Pa)/(micron) as
2s - 6/45
4d - 2/15

Those numbers mean nothing to me. Can you shed any light?

 

[Myfordman]

According to google conversion, 1 pascal =0.000145038 lbs per sq inch = 7.5 microns of mercury

Using the PSI figure, 6 pa = 0.000870226 which is going to be more than enough.

Assuming atmospheric pressure to be 15 PSI, your vacuum bag will exert 14.9999129774 (approx!!) on the job.

 

[Myfordman]

Or thinking about it another way

Atmospheric pressure is about 760mm of mercury, the pump goes down to 45 microns of mercury so the bag pressure will be 759.955mm of mercury.

 

[SVB]

And with all the above in mind, you'll at least double your money if it is no good for your application as it would be perfect for someone I'm sure.

S

 

[custard]

I use an 8cfm Airpress, I thought the advantage was that the 8cfm models can handle two bags at the same time (because they have twin connectors) and also evacuate the air twice as fast, the 4cfm models were limited to one bag and are slower with evacuation. But I've never heard any suggestion that 4cfm aren't man enough for the job. Given that even the cheapest Airpress pump and bag kit now costs nearly 500 quid I'd definitely take the gamble.

Incidentally, I've recently upgraded to 600 micron seamless polyurethane bags. Can't say I notice much difference for flat veneer work, but for form work I very much prefer them over vinyl bags.

Good luck!

 

[Giff]

Steve I have the larger Bagpress but an upgrade I made was fitting a non return valve on the bag. With the flimsy plastic ones supplied the vacuum escapes immediately the pump is switched off. With the non return coupling you can turn the pump off and it holds it's pressure, so long as there aren't any leaks . It made me think (possibly wrongly) that the pump was just peddling to keep up. G

 

[Steve Maskery]

I think it depends on whether what you had originally was a breach port or a breach valve. If it was just a port that would explain why the air leaks when the pump is switched off. If it was a valve, that should activate as soon as the atmospheric pressure hits it.

This isn't resolved yet, but I'll you know what happens. I'm optimistic.

 

[Giff]

This is the valve I use now. The ones supplied are straight through plastic. These use the same diameter hoses. G

http://www.vacinnovation.co.uk/page/1qx ... ctors.html

 

[Steve Maskery]

Yes, that is the sort I had on my Airpress. I do still have a bag, but not the pump or pressure line to evacuate it. I don't know if the breach valve is on the bag, I've not unrolled it. I had two bags but only one valve, so I swapped it over when I had to. It wasn't something I had to do very often.

BTW, do you know what it cost? There do not seem to be any prices on that site. Airpress has one at £40, Composites has one at just over £20. I can't find a direct Chinese supplier.

I do have a local supplier of pneumatic bits and pieces, I'll have to visit to see if they do vacuum stuff.

One of my questions is what the thread sizes are on this pump. There is a dual-port inlet, one bigger than the other. But I don't know whether this has British Standard threads or American standard threads on it. I've emailed Zensen but I guess they have already started their weekend.

 

[Giff]

Not sure of the price. There were quite expensive, but after I got the first male & female I ordered another pair for the spare bag so they can't have been that much !

I think the threads on the adapter are aerospace type threads. Possibly JIC or UNC. Threads on the pump ? If it's UK or european it will be BSP or metric coarse. If it's American
it could be anything !

 

[flanajb]

Be a bit careful with the oil pumps. They pull a better vacuum to that of a dry vane (becker pump), but the downside is that the also pump out oil mist into the atmosphere, unless they are fitted with an oil mist trap.

I have an Edwards lab pump which I use for degassing liquid polyurethane and that is vented outside for that very reason. For general vac bagging of wood, you don't actually need a full vacuum and that is why the Becker pumps which pull to ~ 25-28 Hg are ideal as you don't have the hassle of oil.

 

[Steve Maskery]

Yes, the Airpress one was the dry vane type.

There is something in the manual (written in Chinglish, I'm afraid) about that:

"The product design can reduce oil mist, and an oil separator at air exhaust outlet effectively treats and prevents oil pollution in atmosphere."

I've discovered today that the plastic foot of the unit is broken. It's not the end of the world, I bet some hot glue would fix it but it is disappointing. We have agreed a refund, but it is yet to appear in my account. I'd not noticed the damage when we agreed the refund though.

 

[flanajb]

Yes, the Airpress one was the dry vane type.

There is something in the manual (written in Chinglish, I'm afraid) about that:

"The product design can reduce oil mist, and an oil separator at air exhaust outlet effectively treats and prevents oil pollution in atmosphere."

I've discovered today that the plastic foot of the unit is broken. It's not the end of the world, I bet some hot glue would fix it but it is disappointing. We have agreed a refund, but it is yet to appear in my account. I'd not noticed the damage when we agreed the refund though.

So the Chinglish (chuckle, not heard that before) would indicate it already has an oil separator fitted. Worth checking though. The first time I used my Edwards vac pump I literally saw a slight fog emanating from the exhaust valve. Not good for your health, but the flip side is that the fine oil coating that gets deposited on your machinery will stop them going rusty.

 

[Steve Maskery]

Update.
After series of frustrating emails, all of which were answered promptly but acted upon tardily ("I'll do it tomorrow" x 3) I have received a refund. So I have in my possession a brand new, though slightly damaged, vac pump for the princely sum of £11.54.
If it does the job (and from what I gather here it will) I have a bargain, if it doesn't I've not lost much at all.

He did make a simple process very arduous though, at one point asking for my bank account details!

That cracked foot has broken off completely, though, I'll have to see how well I can fix it.

 

[Brentingby]

I expect you'll make a better foot than the original and be happy you did.

 

[Steve Maskery]

It shouldn't be too difficult. The hardest part will be shaping the cradle bit to fit the circular body of the pump. I might take it with me to the Community Workshop tomorrow and do it there. The lady I usually take is in hospital so I'll probably have a bit of time.