I need to monitor the water level in a pressure tank - How?

In My Humble Opinion (IMHO)
#1

This is for an old tanker truck. The old system for telling how much water is in the tank was a semi-clear hose that ran the height of the tank. But due to the clarity of the water, which is commonly sucked out of mud holes, that tube has discolored and no longer see through, not cleanable and not replaceable (long discontinued).

The truck can pull a vacuum inside the tank to suck up water, and also pressurize the tank to discharge it, the hose must be able to withstand substantial vacuum without collapsing (able to ‘suck’ water UP 25+ feet, whatever that works out to ), and 300+ PSI pressure.

Because this truck is a pressure vessel on wheels I am looking for a solution that does not involve actually penetrating the tank with wires or other openings. I am looking for a simple, reliable, foolproof and foul-proof method of monitoring the water level.
Thanks

#2

Could you disconnect the top of the hose and drop in a small, brightly-colored wood or light plastic bead to float on the water column, then reconnect it? If the hose is translucent enough, you might be able to see a neon-yellow or orange object much better than the water itself.

#3

Thanks Q.E.D., I was thinking of that also but told that this was tried in the past and didn’t work. Due to the politics involved I don’t think this will be tried again.

#4

Vacuum will only produce about 14psi of pressure differential, but how much pressure are we talking about here?

I assume that the taps into the tank are standard pipe thread. If so, then you might want to chuck the old sight glass and fab up a new one with level sensors attached. I’m familiar with using Omron capacitive sensors for this sort of stuff, but you could probably figure something out with the applications people at Grainer or your local industrial supply. If nothing else, you could put a tee at the top of the column and drop a sensor tree down to output high and low signals.

You would have to replace the pipe. If you want a clear riser, then a supply house should be able to recommend a material that would stand up to the pressure, and supply fittings that would not leak (besides, most hard plastics can be threaded.)

If you don’t need to check the level while filling the tank, I wonder if a stud finder would detect the change between where the column is empty and where it is full. Sure, it would have to be a type that detects the diffence in mass of a wall, not an inductive type that looks for nails.

#5

Quickly back to a bright float in the tube - the float explodes in a vacuum and colapses under pressure - so that’s why it failed.

cornflakes The working pressure is 300 PSI, but sometimes this is exceeded by rapid filling under pressure (sometimes the truck is filled with a pressurized line, sometimes the truck is filled by sucking, sometimes the truck just sucks) When filled with a pressurized line the pressure experences when the tank fills to the top must be intense.

I was also thinking of a stud sensor, but checking the level when filling is the primary reason, mainly so we can shut off the flow before the tank tops off (and has that intense pressure shuck).

Replacing the top most site glass with a sensor might be the way to go. Yes it will be only on/off, but it may be all we need.

Dropping the sensor tree down the tube introduced some problems as to how to get the wires out of the tank.

#6

I don’t think that I understand the design. The sensor trees I’ve seen mount through a bulkhead fitting; the wires leave on the outside. I was thinking of dropping the tree down and through the tube from a fitting on top.

#7

That’s why I suggested you use a solid float–like wood.

#8

I was considering a solid float too, but I don’t think wood will do, doesn’t wood float due to trapped air pockets? And when those fail the wood becomes waterlogged and sinks?

Well I think part of the problem is I don’t understand how these sensors work and how they are placed inside the tank.

It may be possible to get a sensor inside the tube, I’ll have to take another look at what are the options for getting a wire through.

#9

Sorry, here’s an example of what I’m talking about. The float has a magnet and tube has a magnetic reed switch that turns on and off as the float goes up and down. The sensor logic can be reversed by either turning the float upside down or by adjusting where the float travels.

We use “trees”, made of several switches in one tube, with multiple floats to trigger each switch to monitor and control liquid levels at my work. We all know what we’re talking about and I didn’t stop to think that the phrase is as obscure as it really is.

I don’t know the pressure ratings the sensors linked to above, but Newark part #92C8680 is rated to 750PSI but is much larger and will probably need and extension. These sensors can drive a light or buzzer through a relay, or you could set it up to control filling (with 500psi or that much water on tap, I’d have a backup of some sort.)

Alternately, you could use an electro-optic sensor (note the 2500psi pressure rating!) While the ones on the linked page are short and need to be mounted horizontally, I have seen sensors that extend about nine inches past the threaded fitting and drop in from above.

#10

After thumbing around on GEM’s website, I see that they sell to the water and wastewater industry. Their applications folks probably deal with this sort of stuff all of the time.