Robinair 15500 only pulling to 29" - is it toast?

General Composites Discussions Equipment Talk
#1

My Robinair 15500 vacuum pump (two stage rotary vane) is only pulling down to 29" hg, according to 3 different analog gauges (albeit of the same manufacture), whether the gauge is connected to my vacuum plumbing or directly to the pump through a barb (but hey, I guess that means at least my vacuum plumbing is good…)

Is this too low for infusion? Is the pump toast now? I originally did have a leak in my vacuum plumbing and the pump probably has 50 hours of running at 28" with a leak (continuous oil misting) before it was found and plugged.

I’m really bad at converting units of vacuum pressure, but according to this chart (http://www.engineeringtoolbox.com/vacuum-converter-d_460.html) 29" is only 20,000 micron (20mbar?). Is that correct? Should I buy another pump for my infusion purposes?

I also have a Robinair 15310, which is a single stage pump (clarification on that would be appreciated too - I’ve heard some people say that multiple stages doesn’t actually improve achievable vacuum level, but rather just makes for a higher cfm…anyone know what’s up?) This single stage has seen better operating conditions since it’s never been exposed to a leak and only operates out of spec for a minute at a time while the degassing chamber is airing out. However, this guy only pulls down to 28.5" on my analog gauge.

I’m asking these questions because I have a pin hole problem that I’ve really not been able to solve.

#2

29 is perfect :smiley: nothing wrong with your pump.

35 micron is 29 hg

Tim

Check link

http://www.engineeringtoolbox.com/vacuum-converter-d_460.html

#3

And is that regarded as being enough to pull a pinhole free infusion? Thanks for the reply!

#4

Put a partial cup of water in your degassing chamber and see if you can get it to boil.boil, great! Doesn’t boil, toss your pump into the bin…

#5

So I can get it to boil (I did that test last time you recommended it ;)) but I’m not sure if a vacuum low enough to get RT water to boil is enough for a perfect infusion. Based on many threads throughout the forum, I can’t tell if anything above 25" is enough, or if you need as close to perfect vacuum as possible to truly guarantee a repeatable, pinhole free infusion.

#6

At my elevation (200m,600ft) it boils at approx 15 mb.you are 150m,450 ft. Would boil at even lower . Once your level reads in single digetss, water is boiled out,infuse. Buy absolute guage from our favorite german :slight_smile:

#7

29.92 inHg is atmospheric pressure at sea level. I think your pump is fine.

#8

I am not too impressed by the performance of your pump, a 2 stage pump should pull well below 1 mbar when plumbed without leaks, but then, for infusion you do not need too much either. If water boils, you are fine.

Also, the analogue meters are all crap. Very hard to tell what the actual vacuum is. For determining if a vacuum pump is OK, use a digital one. (and if you do not have it, the water boil test is fine)

You might want to change the oil, it can work wonders. Make sure you get the right oil for the pump.

#9

HVAC grade rotary vane pumps are supposed to pull below 1 mbar/1000 micron? Are you sure? That sounds quite low. Anyways, I am definitely able to boil water in a vacuum chamber, so at least I have that going for me. I topped off the oil (actually, over filled - not worried about excessive misting because I run the pump outside) and I was able to get the gauge to move a bit further in the right direction…

Thanks for all the advice so far guys.

#10

HVAC pumps pull about 1/100th of 1 mbar, so 0,01 mbar. Especially the dual stage pumps.

But for composites, be happy with 10 mbar.

#11

So I finally bought a digital gauge. TPI 605 is the model, which I picked up from Amazon for 120 bucks, and it only reads from 12000 microns to 15 microns, which is less than 20mbar to essentially 0. I plugged it into one of my pumps and the reading came up blank (the manual says it will read as blank if the level is above 12000 microns), and then when I plugged it into another one of my pumps that I had just re-oil, it spat out a reading of 11500 microns which is about 15.5 mBar. So I guess that’s good enough for infusion? Can I expect to have pinhole free parts if I infuse at that vacuum level, with MTI hose? My degassing chamber is hooked up to a pump that doesn’t pull low enough for the gauge to read but does read down to 28.5 on one of my analog gauges, 29 on another.

I’m thinking about returning this gauge and picking up a Robinair RAVG-1 which can read from atmosphere down to the 10s of microns. I’ve found it for 150 bucks online so I might go ahead with that purchase soon.

And damn is it hard to find the correct fittings for these vacuum gauges. They use “flare” style brass fittings (as opposed to NPT style which is the most common for barbed fittings), and while home depot carries some flared fittings, they didn’t carry a 1/4" female flare to NPT which is what you’ll need for most vac gauges. I went to two HVAC specialty stores, a plumping store, 2 home depots, and even Grainger before finding the right fitting at a local mom and pop hardware store…go figure…