Vacuum coltroller for absolute pressure gauge- Composite resin infusion

[ZeroMass]

I hope your all well and enjoying the holidays at foot.

I work with closed molded Carbon Fiber utilizing vacuum assist resin transfer and would like to improve from using the more reliable absolute pressure gauge instead of analog.

I'll say up front that I cannot currently afford a new/retail system such as a new Heise digital.....but I do find them in my budget on auction sites on occasion and have considered them instead of say the cheaper handheld Vacuum digitals. Those seem to range in the $200-300.00 zones. The Heise can be had with tranducer and cables for $1000.00 or less used.

My question is when researching which perameters are out there I become confused on what will work best for what I do?

I require to go as deep as -29.9" hg and I'm lucky to be at sea level. My pump is a Leybold D16a with kw2555 fittings. I see controllers, transducers,digital gauges in seperate auctions and I don't want to get the wrong componets.

Ayone here have experiance with this type of system? Your advice is very much appreciated.

 

[danw2]

>using the more reliable absolute pressure gauge instead of analog.

1) Does that mean you are currently trying to read 29.9"Hg on an analog pressure gauge?

2) Does that mean that you want to move to a digital readout?

3) Are you aware of the difference between an absolute pressure measurement (which references absolute zero) and a gauge pressure measurement which references atmospheric pressure?

4) Are you using absolute or gauge pressure measurement now?

5) Why do you think that absolute pressure is more reliable?

6) > I'm lucky to be at sea level. Why is that? What is so lucky about sea level?

7) What's an example of 'cheaper handheld vacuum digital'?

8) Which Heise gauge are you considering?

 

[ZeroMass]

Hi Dan,

Firstly,thanks for your time.

I'll see if I can answer concisely.

1)-I'd like to read as accurately a vacuum my pump can perform. Preferably, I hope my pump can obtain/maintain at least 29.9"hg.
2)- Yes, I'm being told that a digital handheld or cabinet system will be an upgrade.
3)- Yes. I understand that gauge measurement and absolute are different. I'm told that absolute will provide me with what is actually occurring day to day and to rely on this, not an analog dial gauge. But it is all new to me still.
4)- Most of my gauges are standard issue dial/vac gauges. Zero on the right side, -30 on the left. Although I do have a few Wallace-Tiernan absolute units, but I feel they'll need calibration beforehand.They range from the 200-500-800 to Zero mm mercury.
5)- Barometric changes etc. Do you not feel that are?
6)- Better ability to pull full vacuum at the gauge I'd guess. Are you laughing yet,lol.
7)- Testo #522-( I think that is its number).About $200.00.
8)- I was looking at the series 700-900 for 0-30". But I realize they were used and ordered per requested ranges. If I'm lucky-(I thought) I could piece together a decent system to start out with that would support my needs and possibly last long enough where I could earn a living and eventually buy new when I better grasped what I needed.

Whew! Ok, your turn.All good questions!

I bought a used VAI SMA-CC2 (Valtek) dual vac controller center with flow meters in hopes of figuring things out. But I'm in over my head at this point I've found.Trying to learn new equipment while designing and building parts has proven overwhelming somewhat. Boohoo, I know.

 

[danw2]

Just back from a project.

Reliability is usually used to mean "doesn't break down". Repeatability means to produce the same reading under the same conditions day after day after day. Accuracy means how close the reading is to what NIST would measure it at.

Both reliability and repeatability can be influenced by something like off-gassing that coats a convective vacuum sensor which inhibits heat transfer and alters its reading. Actually, absolute measurements are likely to be less reliable only because the hard vacuum that is referenced can leak over time, whereas gauge pressure is just an atmospheric reference. Even so, I strongly suspect that absolute readings will provide you more meaningful and repeatable readings because of the lack of barometric pressure influence on the reading.

Technically, 29.92"Hg is absolute vacuum. So when you're saying you need 29.9"Hg, that's a vacuum level does get well resolved on a 0 - 30.0" Hg mechanical gauge.

Wouldn't a gauge with better resolution work better for you?

Torr is a unit of absolute pressure.
1 Torr is 1 mm Hg.
760 Torr = 760 mm Hg which is atmospheric pressure at STP (sea level)
0 Torr = 0 mm Hg is absolute zero.

Higher vacuums are measured in milliTorr (mTorr).

The 0.02"Hg difference between 29.90" and 29.92"Hg is 0.508 Torr or 508 mTorr.

There are commercial electronic convective vacuum gauges that measure in Torr or mTorr

Our shop runs a vacuum chamber for evacuating capillary tubing, seals and pressure sensors. It's an ordinary roughing pump that pulls the chamber down to about 300mTorr or 0.3 Torr.

I asked the shop technician how much the electronic vacuum gauge that reads out in Torr/mTorr cost but he didn't know. It's an Instrutech model 201 Super Bee. I suspect it's more gauge than you need (meaning it goes down to fractions of a mTorr), but I think a digital electronic absolute gauge is what you should be looking at. I'm sure that there are other vacuum gauges that read in Torr to a couple decimal places that will work for you.

If it were me, I'd look at the electronic absolute units.

 

[ZeroMass]

Again, Thanks Dan.
I bought a TESTO #552 digital gauge that also shares the screen read-out with ambient temp, which is helpful. When powered up and set to read units in Torr, I get 756.7 idle.( I'm maybe 5075' above STP). It will pull down to 3.36 torr when Leybold D16a pump is running cold within ten minutes runtime. It should do better with a fresh oil change as this batch is due. Using Vinylester resins and unsealed cloth releases styrene and moisture which of course degrades the oil.

One confusion I had when using the unit of inHG was that it does not read as a standard dial gauge incrementally as in say….29.5", rather 0.130. Is that a psi conversion ?