100mm differential pressure guage

On eBay i won a 100mm differential Bourdon pressure gauge 0-50 in Wg. about one division is equal 1 torr. I think I could read it to about 1/4 of a division, that's 0.25 torr.

I screwed up. To use it to measure even 50 torr (absolute pressure), I would have to put a good vacuum on one input and the vacuum to be measured on the other input. I think I will have to be careful not to expose it to a differential of atmospheric pressure as that will be about 8x greater than its full scale reading which I assume will damage it i.e. bend the pointer on the stop or permanently bend the Bourdon tube. I will need a valve on each input to isolate the gauge and one valve to connect both input together when I release the vacuums.

Could the Bourdon tube have hard stops just outside of full range ???

Below is a pic of the gauge. The second pic of an odd looking lever with a + sign on the side at the top of the gauge. Anyone know what it is or does ???.







[Edited on 10/8/2024 by wg48temp9]

Quote: Originally posted by Sulaiman

I have an old Magnehelic differential gauge that was working before I killed it. (a tool from the 70's for diagnosing and setting up positive or negative pressures or pressure drops across air filters for 200 IPS tape drives) When working I could suck one side or blow the other with atmospheric pressure in the unused side. My gauge displayed pressure difference of 0 to 100 inches of water with max pressure 15 psig. Why is a manifold and bypass required? ,................... .

So I assume your meaning was your gauge could withstand a diff pressure of one atmosphere. That's about 4x full scale. In the case of my gauge, its 13.3x full scale. Perhaps it can survive it.

Did you kill your gauge with over pressure, then what was that pressure?

I assumed rainwater meaning of manifold is a set of valves similar to the manifolds used in gassing refrigerants into air conditioning units.



As I described in my original post, its required to prevent a diff pressure of one atmosphere.

https://www.bourdon-instruments.com/us/en/product-overview/d...

Manual for a close match to your gauge. Being graduated in wg is the only difference I see. Might be an older model.



_{image taken from the linked manual}
Normally this type of instrument requires servicing without shutting down the process chain being monitored.

Part of routine service is verification of operation.
Supose the gauge reads a clear 10wg.
You then simultaneously close both isolation valves.
You should not observe any change in the reading.
Now you open the bypass valve, you should observe a reading of 0zero.

Non routine procedures may require isolating the valve to prevent damage.
Process such as backflow/back washing will cause a reverse polarity.

And then sometimes you just need to approach absolute rated maximum to clear out the goop

[Edited on 10-10-2024 by Rainwater]

Quote: Originally posted by wg48temp9

Did you kill your gauge with over pressure, then what was that .

I dropped it
Pressure gauges and thermometers seem to have suicidal tendencies when in my care.
I have more than enough collected treasure to repair.
(Although during my last house move the removal guys labeled the boxes for most of my treasure as "shed, junk"
I was upset but my family found it funny (/true) ! )

Quote: Originally posted by Sulaiman

Pressure gauges and thermometers seem to have suicidal tendencies when in my care.