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John H

Vacuum Pump advice please

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John H

Has anyone experience of the cheap Vac pumps as sold on eBay for about £50 (a typical advert is “Vacuum Pump Rotary Vane Single 1 Stage 1/4 HP 2.5CFM, Refrigerant HVAC degassing”)

I want it for Vac Bagging Composite (glass/carbon onto foam) wings.  I currently have dry pump but the vac it pulls is a bit to low.  The spec of these looks OK but I would like to hear it anyone uses this sort of device before purchasing.

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Shedofdread

In general, those pumps work quite well but they are *quite* 😉 loud. You might also want to look to see if they are continuously rated. The better air con pumps will be.

If you use a vacuum reservoir (old compressor tank) you can get away with a pump that delivers less cfm of air movement.

Not terribly 'eco' but a pump from a fridge or freezer will work and can be had for very little / free. These do work well with a reservoir as the don't move much volume but will down to ~ -24"Hg . Mind you, re-use is 'eco' so maybe Greta would approve.....

Best of luck!

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Lloyd_d

R-G composites do a great pump. I bought one it was like £400 I think. I thought "That's expensive", but I have definitely got my moneys worth out of it already after about 2 years. It runs constantly but just hums away downstairs with me asleep upstairs. Its about half the size of a shoe box and is good enough for a 2m long bag or longer (not tested). Vacuum bagging and composite molding cannot be done properly 'on the cheap'.

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Witch_1

If your existing vacuum pump pulls too "low" for a vac bag, then you can reduce the vacuum by putting a tee in the line with a valve or a clamped piece of tube.  Adjust the valve to bleed air into the vacuum line and achieve the vacuum you want.  Helps if youhave a small reservoir and also a vacuum gauge, but it is not too critical in my experience.   I usually apply full vacuum for the initial pull-down, check there are no leaks, then reduce the vacuum with this method so the bag doesn't fail in the subsequent few hours.  You can try  the method out "dry" to see if it will work for you.

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Witch_1
On 15/12/2019 at 21:33, Shedofdread said:

a pump from a fridge or freezer will work

I use a fridge type compressor for moulded tailplanes etc.  It is a bit slow on larger items.  They theoretically have limited life as they slowly pass their oil out of the discharge tube, and you have to cover it with a cloth (and keep the compressor upright).  i have run mine for about 80 hours so far with no problem.  You are not legally allowed to remove them from a fridge these days without recovering the gas.  I came tho this thread because I am thinking of buying a low  cost double stage pump - interesting point about noise etc.

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Shedofdread
On 17/12/2019 at 22:37, Witch_1 said:

I use a fridge type compressor for moulded tailplanes etc.  It is a bit slow on larger items.  They theoretically have limited life as they slowly pass their oil out of the discharge tube, and you have to cover it with a cloth (and keep the compressor upright).  i have run mine for about 80 hours so far with no problem.  You are not legally allowed to remove them from a fridge these days without recovering the gas.  I came tho this thread because I am thinking of buying a low  cost double stage pump - interesting point about noise etc.

I should have mentioned; on the fridge pump I use, I have an air line water trap to collect the oil - as you already know [but this bares re-saying for others who may be reading...] you don't want that vapour in the air. I get round the speed issue you raise by having a vac reservoir so when the tap is opened, even 2m long wing bags pull down in a matter of seconds.

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