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What will multiple vacuum pumps do to a vacuum system, namely to PSI? Answered

Long story short, I'm looking to make a vacuum forming table, and have most of the thing designed. However, I am looking to use two (maybe three) cheap vacuum pumps until I have the money to get a decent vacuum pump. I know that the pumps (4 CFM) if stuck in parallel will get me roughly 8 CFM, however, what will that do to the PSI? The pumps have a 90 PSI pull (if thats the right phasing to it) and I'm unsure what grade of pip/tubing to get for this. Thanks in advance!! 

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Josehf Murchison

6 years ago

Are you building a suck and blow, not a joke?

Some forming table’s blow hot pressurize air under the plastic as it heats the plastic and then when the plastic is heated to the desired temperature they trip a valve and it sucks the plastic into the mold.

If you use vacuum motors use identical motors connected in parallel, the differential pressure between the ambient air pressure and the air pressure inside the chamber should only be 24psi, however the amount of air moved is crucial to the size of the table and the depth of the mold. So the bigger the more air to move, the more motors.

The 90 is probably 90 cubic feet per minute which is actually quite slow for a large table.

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DoctorWooJosehf Murchison

Answer 6 years ago

The plan was (and I think may still be) to build just a basic vacuum former with a oven box and suction table.

As far as the second point, thats also so handy info to have. I've said it a few dozen times on this question now, but my pneumatic knowledge is virtually non-existent.

And it is 90 PSI. The CFM is 4.2. However, the pump I was looking out is cheap (not only in price, but quality, recent googling showed) and I may be abandoning it.

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Josehf MurchisonDoctorWoo

Answer 6 years ago

And the blind man picks up his hammer and saw.

I take it the vacuum pump you want to use is the same kind you would use with a bell jar.

This is the vacuum molding machine I use.

It has a heat lamp to heat the plastic and I power it with a shop vac.

Plastic is very soft when it is hot so you don’t need 90 PSI to form it, but you do need air flow to form it before the plastic cools to the point it won’t form to the mold.

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steveastrouk

6 years ago

No vac pump call pull 90PSI
What you'll need is generous piping that can take a lot of flow, and withstand the pump pressure. Even a decent shop vac might pull adequate vac for what you want.

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DoctorWoosteveastrouk

Answer 6 years ago

I just looked more into it: you (as you already know) are right about PSI. My knowledge of pneumatics systems of any kind is slim to none...if it changes anything, the air intake of the pumps is rated at 90 PSI, and there is no pascal rating to it at all.

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rickharrissteveastrouk

Answer 6 years ago

+1 No need for massive vacuum You need flow and a shop vac is fine. Even better if you remove the filter and let the motor have better air flow.

The hardest thing in VAC forming is getting the pattern right and getting the material to the right temperature.

Get either wrong and your plastic will web and spoil the form.