How to measure water level in a vacuum...

[thehoneybadger]

Good point, the transducer should should be level with or below the pump suction, with a way for air and/or vapor in the tap to rise or purge to ensure the tap is full of liquid only.

But OP is going with float switches, so this analogue approach, which would bypass and solve the problem with the WIKA breather, is moot.

LOL. Hey bitboy. Not quite what i meant.

I meant in the drawing, the vertical line is like the only straight line in the entire drawing. Which is why it was out of place. (Just a little comedy relief)

 

[drbitboy]

LOL. Hey bitboy. Not quite what i meant.

I meant in the drawing, the vertical line is like the only straight line in the entire drawing. Which is why it was out of place. (Just a little comedy relief)

LOL, yeah.

 

[PreLC]

Kind of OT, but maybe not: What does the boundary of liquid and gaseous material look like when a fluid is boiling? Can we put a float with a particular counterweight and expect it to stay at the boundary with precision?

 

[drbitboy]

Kind of OT, but maybe not: What does the boundary of liquid and gaseous material look like when a fluid is boiling? Can we put a float with a particular counterweight and expect it to stay at the boundary with precision?

Any "boiling" (to equilibrium) will probably take place in the spray(s) when the water enters the vessel (high surface area), so the sump water will be cold because it already lost latent heat of vaporization to make the vapor.

 

[Tom Jenkins]

I've been joining Peter in the desire for popcorn.

One thing only Dr. Bit Boy has mentioned is that water temperature drop will be a limiting factor on "boiling". It takes energy to turn liquid to vapor - this is referred to as the latent heat of vaporization. Taking this energy from the liquid water causes the temperature to drop. This is the cooling effect that caused nature to evolve perspiration to help control body temperature.

At some point, the water will cool to the point where its temperature matches the boiling point at the internal pressure and vaporization will cease. Incoming water will raise the temperature, vaporization (boiling) will continue, and at some point, steady-state balance will be achieved.

Another neglected aspect in many of the posts is that pressure, like voltage, is always measured as the difference between two points. Absolute pressure is measured with one point being a perfect vacuum.

Ignoring the change in water density with temperature, the difference in pressure from the top to the bottom of the liquid is the same. So you can measure depth with a submersible gauge pressure transmitter with the vent tube open to the inside of the vacuum tank. Or, you can use an absolute pressure transmitter and correct for the vacuum, assuming it is being measured.

 

[Steve Bailey]

I've been wondering how much the scavenger pump actually has to do. Presumably there is a vacuum pump in the system working to maintain the 20 torr vacuum level. To do so, won't it have to extract all the water that gets added to the vessel?

 

[NetNathan]

I think this is being WAY too over thought...
Doesn't the OP really just need 2 level switches for on and off?

 

[PreLC]

The vacuum is measured and goes to the PLC.
Desired accuracy should be say to the nearest cm, so we can use the high and low setpoint of the water level to turn on/off the scavenge pump.

I think this is being WAY too over thought...
Doesn't the OP really just need 2 level switches for on and off?

According to the post above, OP needs a cm precision. Maybe this is a self-inflicted issue and we can simplify the input to a couple switches?

 

[Mas01]

Engineers guide to tank gauging...
https://go.emersonautomation.com/rmt-en-l-resources-tank-gauging-guide?utm_content=22E_NA-en_NWS_RMTB_Measure_Instrumentation_JUL_EM01_0S&utm_medium=emle&utm_source=mso_nam-elqemnws-mei-zs&utm_medium=emle&utm_campaign=22grmtl-lvel_resources_eg15&elqTrackId=8bf1f8bc969243cda8afcd64bf0b6c4b&elq=77676850399a4dbf9c00684239fed887&elqaid=32370&elqat=1&elqCampaignId=21895

Tanks very much.

 

[drbitboy]

So you can measure depth with a submersible gauge pressure transmitter with the vent tube open to the inside of the vacuum tank. Or, you can use an absolute pressure transmitter and correct for the vacuum, assuming it is being measured.

OP had that system, but the vent (breather) tube seems to have ended up with moisture inside. It's discussed here, but many many posts earlier. Measurements of PSIG at the pump suction and of the vacuum could be combined to the same effect i.e. to get PSIA at some level datum, per the right side of @Tom Jenkins' sketch.

Tanks very much.

I think this is being WAY too over thought...

But we made it to a hectopost!

 

[Mas01]

I've been wondering how much the scavenger pump actually has to do. Presumably there is a vacuum pump in the system working to maintain the 20 torr vacuum level. To do so, won't it have to extract all the water that gets added to the vessel?

Yes, there is a vacuum pump.
The scavenge pump is used for purging the water in the vessel.

 

[padees]

I've been joining Peter in the desire for popcorn.

Try chips with various cheese, toppings and dips. Dentist told me to stay away from popcorn. LOL

 

[Tom Jenkins]

Try chips with various cheese, toppings and dips. Dentist told me to stay away from popcorn. LOL

Being in Wisconsin that sounds pretty good.

 

[I_Automation]

Try chips with various cheese, toppings and dips. Dentist told me to stay away from popcorn. LOL

I have a rather nasty case of acid reflux and have to watch spicy foods - but popcorn is an absolute killer for me. Can't touch it, or anything with corn flour in it.


Cheese is worth the trip up to the Pinconning Cheese Factory a couple times a year. With a stop for Frankenmuth chicken for dinner.



Too bad real Mackinac Island fudge is soooo far away. EDIT: I said "real", I know ACE Hardware sells a sort-of copy at the store across the street.

 

[Peter Nachtwey]

So now we know the 20 torr is relative to atmospheric. OK, but that isn't the way vacuum pumps are rated which is absolute. Given that, there have been a lot of good suggestions that have been turned down for one reason or another. So, maybe Mas01, or his engineers, are going about the all wrong. We know what Mas01 wants to do but we don't know why after 100+ posts. There might be a simple answer.

But we made it to a hectopost!

That is nothing to be proud of. This thread still hasn't matched Paula's "learning by doing" thread which I think was longer and all she wanted to do is cut wire at different lengths if I remember right.
It should have been an afternoon project.


Also, I want to add my own original and off the wall way of measuring the water level in the tank.
Use sound1 Just like the pitch of water in a glass increases with how much water is in the glass. I bet the pitch of the sound in the tank will increase with increasing water level.
It might take some research to correlate the sound in the tank with level but I think it can be done. The advantage is there is no need for active devices in the tank or extra holes.
It might not be that accurate but but that needs to be tested too.


I still would like to know what is being tested.