Vac maxing out at 27 inch hg

Hey guys,

I am 738feet above sea level, so i should be getting 28.9 - 29.4 inches hg from what i understand from the chart at engineeringtoolbox (via skunkpharmresearch)

I have a robinair 15500 5cfm 2stage 35 micron pump, and a vacuum chamber assembly purchased from ebay that i just got last night. When i vacuum it stops moving at 27in hg as per the title of this thread. When i close the valve where the hose meets the chamber, it stays at 27 and doesn't drop off or lose pressure, so doesn't this mean that it's sealed well? What can i do to determine why it's not going past 27, as from reading threads here and elsewhere, 29 is what i want to achieve.

Please advise and help me figure this out, i really want to produce some nice stuff, thanks in advance!

Is the gauge reliable? I'm thinking your doing the job and the gauge is off.

SnapsProvolone said:

Is the gauge reliable? I'm thinking your doing the job and the gauge is off.

Click to expand...

I am not sure. It came built into the lid that came with the vacuum chamber assembly i purchased off of ebay. It is glycerin filled and the seller says its a good quality guage - but i have no idea. I do have another guage somewhere, trying to figure out how i can add that one into the mix

Further to this, when i tried vacuuming some oil last night - i had the stock pot in a water bath of around 130F, and the oil was around that temp as well, when i spread it thin on a slick pad and vacuumed, it would make make little tiny bubbles but when it just stops at 27 it stops creating bubbles and they just sit there as bubbles and dont pop or go down unless lock the check valve, stop the vacuum, and let in some air. Im not sure if im supposed to just leave the vacuum running or just lock it and turn it off and let it sit - can someone advise me please

i went and looked at the guage, and there was a small sticker that says to cut the nipple of the rubber stopper because its a pressure relief valve. So i did that, and now instead of 27 i get 27.5 - I will be attempting to physicaly calibrate this weekend if i can get some free time.

I have another few questions, since this is all i have for now until i can figure how how to remedy this whether its just the guage or something else - When i vacuum, i have the heat on around 130 - 140F - my first question is - is this hot enough?

When i am vacuuming, when the needle stops moving i cut off the vacuum with a valve, and turn the pump off. Should i be doing this and letting it sit? Is something happening when like this?

Alternatively if i'm supposed to leave the pump run - do i leave it run continuously, or keep allowing air in, and re-vacuuming it repeatedly? can i let a tiny bit of air bleed in from the pressure release valve while its vaccing?

This is what it looks like when it is at [my]full vac, and the bubbles dont pop anymore they just stay there. It's just a very small amount. edit: i turned the haet up a bit and they were popping for a second..very slowly

no expert but that's hot. 120 tops closer to 110
and what is your current elevation? subtract 1" for every 1000' above sea level. if you are at 2500-3000 feet then 27.5 is max vac

R&RHashman said:

no expert but that's hot. 120 tops closer to 110
and what is your current elevation? subtract 1" for every 1000' above sea level. if you are at 2500-3000 feet then 27.5 is max vac

Click to expand...

783 feet above sea level - so i should be getting 28.9 - 29.4

well then, leak? or faulty gauge maybe? did you swap out the gauge with a different one?

I haven't as it came screwed and glued into the lid and i have been trying to vacuum - also the other guage i have i dont think will fit into that hole even if i removed the existing guage - i started a new thread called bubbles not popping because i wasnt able to change the name of this one