Advice compressor & vacuum

[Sapre]

Long time reader here and proud owner of an old compressor which i converted to a compressor/vacuum pump. Works fine in compressor mode still, pulling 4 bars ok. But as a vacuum, gague only reads -1/2 bar or so…

Dont even know what -1/2 bar means tbh, but it doesnt feel like a strong vacuum.

I tried it for vacuum packing which wasnt great and hope to do some fibreglass work with it.

Im thinking to service the motor and pump, especially valves. Dont know how much better it will get? Think its about a 700w - 1hp motor.

Any thoughts, hints or advice? Im wondering if i should just get a seperate vacuum? Would be a shame after all the plumbing!

 

[brightspark]

the valves arent designed to pull a vacuum on the pump

 

[Barking Mat]

Welcome to the forum.

I was thinking before I zoomed in that looked like gas pipe.

I'd use a vacuum pump for specific needs like fiberglass work.

 

[Bornfree]

You will never get a very high vacuum level with a conventional piston pump.

 

[Sapre]

the valves arent designed to pull a vacuum on the pump

Thats what i feared

Welcome to the forum.

I was thinking before I zoomed in that looked like gas pipe.

I'd use a vacuum pump for specific needs like fiberglass work.

thanks - it is high pressure gas pipe, upto 10bar i think.

Shame i cant do both with one machine, no mods to the piston pump possible/practical i suppose… Back to the drawing board!

 

[Barking Mat]

Thats what i feared

thanks - it is high pressure gas pipe, upto 10bar i think.

Shame i cant do both with one machine, no mods to the piston pump possible/practical i suppose… Back to the drawing board!

Yep, maybe, but not under negative pressure.

Might constrict.

Won't help.

 

[Misterg]

With all that ^ said,

as a vacuum, gague only reads -1/2 bar or so…

The most vacuum you can ever, ever get is -1 bar, so it's not doing too badly. -0.5 bar is ~7PSI of vacuum.

You will never get a high flow rate through those small tubes though, so it will take time to pump air out and any leaks will affect it badly.

 

[m_c]

Dont even know what -1/2 bar means tbh, but it doesnt feel like a strong vacuum.

Atmospheric pressure is 1 bar (or at least it is averages around that at sea level).
A perfect vacuum is obtained by reaching 0 bar absolute pressure.
Those are the "absolute" pressures.

However when dealing with low pressure stuff like vacuums, you'll often see "relative" pressures used, which are typically the pressures relative to atmospheric pressure.
So in the case of your -0.5bar, that means the reading is 0.5bar below atmospheric pressure aka 1 bar, or 0.5bar absolute pressure.

Regardless of how you measure it, for your application, you really want to aim for as near perfect vacuum as possible, and depending on the size of item you want to vacuum, you may need quite a large pump.

 

[Morrisman]

Measuring vacuum doesn't use the same units as pressure, but is usually in inches of mercury: how far up a tube it can suck a column of mercury. mmHg: millimetres of mercury.

 

[Sapre]

Thanks for the advice explanations, i follow the measurement now.

looking into a seperate vac pump, was hoping to get away with this set up mainly to save space in my small and overloaded work space!

Cheers all..

 

[voipio]

An ordinary household vacuum cleaner is probably better for vacuum packing of large-ish items, especially for the initial draw down of the bulk of the air in the packaging, as it can reach quite high flow rates, and fet down to about 0.75Bar absolute (0.25 Bar below normal ambient pressure), which is plenty for most vacuum packing. A separate vacuum pump isn't going to take up a huge amount of space, as it doesn't really need a tank for most use cases.