View Full Version : Testo 552 vaccum gauge

Daz man
04-07-2014, 12:29 PM
Hi all,

quick question! Have any of you on here got the Testo 552 digital vaccum gauge?

I seem to be struggling to get mine to hold a torr reading?

I've even tried a simple test of connecting one of the 1/4 outlets of the gauge onto a gauge line then onto my vac pump.

Ran the vac pump so that the Testo gauge pulls down to 0.30 Torr yes I managed to get it that low! Isolating my vac pump with a quarter turn inline valve and watched on as my readings steadily rose!

This with a brand new gauge line! And a second one tried just in case!

Are they known to have loose connections inside?

Just asking for feedback before I contact Testo to ask to send them back for checks.

04-07-2014, 05:09 PM
What sort of seal material is used in your hoses?

monkey spanners
04-07-2014, 08:54 PM
I'm told it is because the volume of vacuum is so small, it needs to be on something like a cylinder or system. They don't work the same why as the other style vac gauges with i think use temperature.

I have one too but am not convinced with it, though i think my vac pump is worn out too!

04-07-2014, 10:10 PM
Those lines with the shut of valve leak slightly when you operate them,best to have an inline hand valve.

Rob White
05-07-2014, 04:43 PM
Those lines with the shut of valve leak slightly when you operate them,best to have an inline hand valve.

I agree with that, I'm starting to suspect the valves on gauge lines,
I have started to see combinations of poor vac levels, poor vac pumps
and poor vac gauges in lots of different combinations and I'm talking
about new or relatively new equipment.

I'm starting not to trust the gauge line valves, when in a vacuum.



06-07-2014, 08:40 AM
Charging hoses are designed for positive pressures and not for vacuum. They are permeable.
You should use metal hoses for vacuum, or special hoses designed for 20 microns of holding vacuum like these:
In these ranges of vacuum (1 torr and below), there is whole lot of issuses, and one of them is tightness of fitings.
You should use some sealant on fitings like NYLOG.
Check these videos:

Vacuum holding test is best if you using properly flared copper pipe (and maybe some NYLOG if your flare tool is not perfectly polished).

The MG Pony
06-07-2014, 03:53 PM
As said, charging hoses are no good for vacuums, I build a rig for vacuming using all 1/2 inch copper, brazed as much as I can, flared to the vacum guage and pump then a custom hose that is 1/2 all the way up to the last point of 1/4inch flare!

futur unit I will make and include cold trap! make for happy pump!

Daz man
06-07-2014, 09:13 PM

appreciate all the feedback - some really good thoughts there. Will try various ways tomorrow on site.

install monkey
06-07-2014, 10:24 PM
be careful sending stuff back to testo- i got the 550's and after 4 mth they wouldnt zero- even left with ports open , they still powered up with 2 bar difference- as i paid cash for them - sent them back, 6wks later they said there was nothing wrong with them and wanted to charge me 46 quid for calibrating them!!, got them back and they have been ok since

Daz man
07-07-2014, 09:14 AM
SORTED THE ISSUE THANKS TO YOU GUYS! you'll never guess how I sorted it?

as from previous posts, I removed all my standard charging lines and also the quarter turn in line isolation valve (mine was a separate valve) but I know you can get these built into standard lines.

the only hand wheel isolation valve I own is built into another analog torr gauge but I don't really use that torr gauge as the readings are in Kpa. But for this exercise I've used it just for the hand valve.

I've only used it as my Javac vac pump has no isolation valves built in and if I don't isolate the job from my pump the torr reading rises through my pump.

from my vac pump I've used a standard yellow charging line to the wheel valve. From the wheel valve I've come off of it with 1/4 soft drawn copper pipe (flared connection) to the left hand side of the Testo 552 vacuum stick also flared that end too. Switched on the pump vacced down to 0.03 of a torr then isolated wheel valve. It rose to 0.04 and is now holding a torr of 0.05 for pushing on 45 mins!! Looks like the copper pipe has done the trick! Always learning. It was either a leaking isolation valve (which was brand new) or the gauge line (which was also brand new) Note to self charging hoses are only good for charging - to purchase torr approved/tested lines ASAP. HOPE THIS HELPS PEOPLE?