Hydraulic Fluid Level Detection.

Good Evening Everyone,

I am attempting to monitor the level of hydraulic fluid in a tank. The tank is 50 gallons. For insurance purposes we need to monitor to detect if we have a hose burst. What I am looking is for a sensor, that i can detect when the fluid level starts to drop. And is safe to use. I am told the Hydraulic Fluid is not combustible.


Tom

I'm not a hydraulic expert and really don't have recommendations on a sensor, but I'm sure you will need to handle initial start and stop of the pumps as the level will change.

First don't ever let somebody tell you hydraulic fluid is not flammable
its oil based and it gets worse when it gets under pressure then it can blow out in fine mist
its just like an oil burner
many years a go I worked in a steel mil that used water as hydraulic fluid to keep it from staring fires
for you problem a simple float would do the job
or if you need more accuracy
then try this
https://www.jowa-usa.com

Gems Sensors has a wide array of level sensors/switches.

there are capacitive probes that will detect oil, for example Endress, Siemens some can be used with Zener barriers if there is an explosion risk but hydraulic fluid although combustible if mineral oil based there are others that are water based, the flashpoint of mineral oil is generally just over 214 Deg. C I believe there are 4 classes A,B,C,D.

parky said:

there are capacitive probes that will detect oil, for example Endress, Siemens some can be used with Zener barriers if there is an explosion risk but hydraulic fluid although combustible if mineral oil based there are others that are water based, the flashpoint of mineral oil is generally just over 214 Deg. C I believe there are 4 classes A,B,C,D.

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Just to point out that it's not as simple as throwing in a Zener barrier to prevent an explosion or that the Zener barrier is the way to protect it. It's a system where all parts play a role and they need to be matched to work correctly.

The GEM, Temposonic or Balluff MDT rods will work. The Balluff and Temposonic rods work in oil all the time. I am pretty sure the GEM ones will too.

@Cardosocea, Yes that goes without saying, perhaps the OP should look at Vega 66 they are made for hazardous areas, I did point out that it depends on the type of hydraulic fluid as to whether zone protection is required.

Is continuous/analog measurement required? Or do you just need to know if it goes below a certain level? If the latter, a point-level/digital switch might be a good solution, we've used vibrating fork switches (by Vega) to detect oil successfully.

You must be dealing with the same insurance company as one of my customers. They approached me about this, a few years' back.

As far as sensors go, GEMS is a good product. I'd look for something in a 4-20mA and be prepared for some in depth programming.

I don't believe a switch would work because it won't sense the rapid loss of oil that a burst hose "could" cause, unless you set the level so low that you've already shot fluid out and started the fire. Bubba hitting the Estop would probably be quicker reacting.

You might be able to use a continuous, analog level signal and monitor a rapid change of reservoir level. Remember that reservoir level may change significantly during normal operation. So you might have to get sophisticated with the programming. "A rapid level change while The Big Ram is extending IS NOT a fire". "A rapid level change while nothing is moving...call 911". Of course hoses don't generally burst when nothing is supposed to be moving. But perhaps you could memorize the normal level changes in a normal cycle and something outside of that profile is an alarm?

I ran all this by my customer and they decided to not go this route. If you get something working please provide feedback.

In the first post it states "monitor to detect if we have a hose burst"

So this implies looking for a drop in tank level. The level of your tank will go up and down during normal operation as cylinders extend and retract and if you have an accumulator in the system it will also make the tank level go down when the accumulator is charged and go up when it is discharged.

You just need to analyze your cycle and determine what the normal fluctuations are. Then have the program shutdown the pump(s) when the level goes out of this range (plus some tolerance).

Because maintenance can add oil to the tank periodically or after doing component changes, it's best to log the current level when starting and then look at the difference from this starting point. That way you are not slave to hard levels and your code adapts to the current level each time the system starts.

ndzied1 said:

In the first post it states "monitor to detect if we have a hose burst"

So this implies looking for a drop in tank level. The level of your tank will go up and down during normal operation as cylinders extend and retract and if you have an accumulator in the system it will also make the tank level go down when the accumulator is charged and go up when it is discharged.

You just need to analyze your cycle and determine what the normal fluctuations are. Then have the program shutdown the pump(s) when the level goes out of this range (plus some tolerance).

Because maintenance can add oil to the tank periodically or after doing component changes, it's best to log the current level when starting and then look at the difference from this starting point. That way you are not slave to hard levels and your code adapts to the current level each time the system starts.

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We've done some projects on oil leak detection, doing a running average over the first 15-30 seconds of runtime and then having that set as the setpoint with +/- 0.5" of level (user-adjustable) trip the process. Operators can disengage protection to add oil and re-engage and it will re-initialize using the new level as a setpoint.

a few things to note...

If you are trying to detect a hose burst or some other anomaly, then you should look into adding a pressure switch, one after the pump before the pressure relief, and one after a valve close to the cylinder in question.

at that point you would just need to figure out when to check for proper pressure (after a machine starts to cycle), and then determine if the proper pressure is met, or if it is lower than normal, etc.

too see the level and to know if hasn't move from it's normal level would require knowing when best to take the measurement and determine if it's low.

like some have said, if you just go by a hard level, the system running will fluctuate some and throw false positives all day long. just putting the sensor on and monitoring the level through a trend could give you an idea of what the average level is, and when it is best readable.

There's a lot of guesswork being done in these posts.

If the hydraulic system is open-center and uses a positive displacement pump driven by a constant speed motor, as is common, then a pressure switch at the pump discharge or rate of change in level won't do the job. The flow rate (and rate of level change) will be the same whether the hose has broken or a cylinder is extending. The system pressure will be minimal whether the hose is broken or the valves are in neutral dumping flow back to the reservoir.

Peter's suggestion of a level switch is probably the way to go. You could also use a pressure switch teed into the reservoir drain tap and avoid modifying the reservoir.

Tom Jenkins said:

Peter's suggestion of a level switch is probably the way to go. You could also use a pressure switch teed into the reservoir drain tap and avoid modifying the reservoir.

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They aren't switches. Some have resolution down to 0.1 microns although that not necessary here.
Here is an example.
https://new.abb.com/products/measurement-products/level/magnetostrictive-level-transmitters

Magnetostrictive displacement transducers are common in the hydraulics industry.
Most don't look like this but this picture is the first that came up when I did a search.
https://new.abb.com/products/measurement-products/level/magnetostrictive-level-transmitters

I would have a few limits to monitor. I would have a low level alarm and also a low level rate alarm. To keep from having too many false alarms I would change the set points based on what the rest of the system is doing. If the pump is sucking a lot of oil out of the tank/drum then it would be wise to make the limits a little wider. Getting a little history would provide some formulas on how to widen the alarm limits as a function of machine operation.


Oil can burn but in normal operation the oil doesn't get anywhere close to that. In normal operation the oil should be in the 110 to 130 degree range which is no where close to the 350 degrees that might cause the oil to burn.