Tough Nut...

First off, it is entropy that increases.

If you are doing some re-plumbing anyway, I would add top and bottom taps so you can add a DP transmitter if you want. There are a couple of things you can do to extend the life of the poor transmitter, even if you get one with high shock ratings.

First, a gauge snubber is simply an orifice that attenuates the pressure spike. Many of them are made of porous sintered metal, and are quite resistant to failure. They can, however, get plugged by dirt and slime and general crud, so you want to put an isolation valve between them and the pressure vessel so you can remove and replace them.

Second, a guage isolator is a diaphragm type device that keeps the process fluid away from the sensor. They don't have much damping ability, but might not be a bad idea. Red Valve and many others have them.

Finally, you could install an accumulator or attenuator, similar to the ones used in hydraulic system. Put one in each of the taps between the pressure vessel and the sensor, again with isolation valves. They are essentially like the water hammer attenuators a lot of people have in their basements, but obviously of heavier construction.

One other comment about 'High Water Content' hydraulic fluids such as 95/5....

In addition to being prone to water hammer, the fluid tends to erode valves, fittings, etc, since the fluid will literally act like a fluid jet cutter.

Trying to automatically detect a low air pressure fault can be a challenge on a system that is always in use. It is relatively easy to detect a low precharge state during the inital power up (the hydraulic pressure will immediately spike up to the precharge pressure and then gradually climb as the accumulators are filled with fluid. Fault logic can be added to check during the inital power up (monitor initial pressure spike, and also time how long to fill the accumulators with pressurized fluid).

Once the system is up and running, these tests can't be performed but another possibility is to provide a real-time trend graph of the pressure discharge characteristics during a cycle. A press cycle with normal air pressure will have a specific pressure use pattern, where as a cycle with incorrect air pressure will have a uniquely different pattern i.e. a much quicker drop off in pressure and a much quicker recovery cycle.

On some of our hydraulic systems, I have trained the maintenance people to use the diagnostic monitoring features that we build into most of our controls and try to recognize a normal pressure use graph from an abnormal one. We also monitor the lowest pressure reached during each cycle and trend this information, since a drop off in precharge pressure will result in a gradual decrease in the peak minimum pressure sensed during the cycle. This does assume that the press cycles are consistent from cycle to cycle i.e. similar press strokes, speeds, final pressing tonnage setpoint, etc during a particular production run. This can also point to a problem with the pumps (as the pumps wear and system slip increases, the pressure recovery cycle will take longer). This type of training allows for manual intervention by the operator or maintenance personnel, but unfortunately it doesn't provide an automatic recovery solution.

So Terry.......

What Happened??????

Ok, this is the last time I am askin' I promise.

Terry what did you end up doin' if anything?

Sorry about that...

Nothing has been done... the coffers are empty... so they say.

Things might look brighter after the 2^nd of November.

I came up with a make-shift way to follow the trend and provide an indication that such-n-such needs to happen.

The situation is that there is Press that closes on compressible material. About 95% of the closure is accomplished with a large volume of low-pressure water. The final 5% of closure is accomplished by means of the high pressure accumulator and by a pair of high-pressure, low-volume pumps. It amounts to only a few gallons of water.

If things work out properly, the pressurized fluid in the accumulator is adequate to perform the final 5% of closure to the High Set Point. In that case, the pumps no longer need to be applied to the Press. Instead, they are immediately redirected and begin to recharge the high-pressure accumulator. Since there is still working pressure available in the accumulator, the fluid from the pumps, and the accumulator, becomes available, via the accumulator, to maintain the Set Point pressure on the Press.

However, when things do not work out properly then the accumulator runs out of oomph before the Press reaches the High Set Point. In that case, the pumps have to bring the Press the rest of the way to the High Set Point.

Since the accumulator is out of poop, the High Set Point must be maintained by one of the pumps. Once at the High Set Point, one of the pumps turns off. Using both pumps to hold the High Set Point is too much (too much volume). In this case, the High Set Point is regulated more by decompression than by supply. That is, the pump is over-driving the pressure on the Press and the High Set Point is regulated by opening a decompression valve now and then. It's a huge waste of time and energy.

As long as either pump is directed at the Press then neither is directed to the accumulator (it's in the plumbing).

So, as long as the pumps are not recharging the accumulator, the accumulator has to wait that much longer to become recharged. This directly affects cycle-time.

So... with respect to the water level issue...

There needs to be a particular balance between water and air in the accumulator at any given pressure (in the accumulator).

When fully charged, the accumulator needs to provide a certain volume of water before the accumulator pressure falls below the High Set Point pressure.

If the accumulator has too much water and not enough air then the volume delivered by the accumulator will be small... too small.

If the accumulator has too much air and not enough water then the volume of water will be all of the water available (not much) and the closed "water-valves" will "pass-gas", as it were.

So the deal is... to follow the trend, that is, make a judgement as to whether the process is getting worse, doing OK, or getting better.

I'm now watching for when accumulator pressure is equal to Press pressure, and how soon that is occurring. I'm also watching how long it takes to get to High Set Point.

If the accumulator pressure doesn't fall below Press pressure and High Set Point is attained at the expected time then things appear OK.

If the accumulator pressure does fall below Press pressure then I know that things are not well. If the time to attain High Set Point is still within reason then things ain't so bad.

However, if the accumulator pressure falls below the High Set Point and the time to attain High Set Point is unusually long... things are very bad.

If "things ain't so bad" then I provide a warning that things might get worse. The operators then need to force the air compressor to run for a while.

If "things are very bad" then I nag them with an obnoxious horn every cycle until they bring things back to OK.

And that is where things sit...

Even if you can't get the bucks to do what you need to do... there is usually a way - while still getting the job done - to make it painful for others... then, they too will be arguing for your cause!

DAMN!!! I LOVE THE POWER OF PROGRAMMING!

And I really, really, really, love that it is limited only by a lack of imagination! I've got lots of imagination!

(Tut-Tut... I'm really not a control freak... at least, not with respect to people... but with respect to machines... you're damned right I am! GOD, I LOVE THIS STUFF!)

(1818)

Terry Woods said:

Sorry about that...

Nothing has been done... the coffers are empty... so they say.

Things might look brighter after the 2^nd of November.

Click to expand...

I don't get it. What happens on November 2nd????

Hopefully, the Planet Earth comes to be more in tune with the Universe and the future, as seen by Harry Seldon.

Terry Woods said:

Hopefully, the Planet Earth comes to be more in tune with the Universe and the future, as seen by Harry Seldon.

Click to expand...

Many things can be acheived trough the analytic use of psychohistory.

Oh Great!
Now you made me go and google Hari Seldon

I don't get it. What happens on November 2nd????

Click to expand...

Uhh, election day. You are voting, yes?

Ok so what of any significance happens on Novemeber 2nd?

Yea icky, I already voted, but I'm not at all confident that things will turn out my way. The framers really had it right. They knowingly created a juggernaougt that is really run by profressional bureaucrats. So yea the faces change but the MO always stays the same.

No revolutoin on Nov 2nd..... Still you and I do have a responsability, (not a right) to vote. So I have fullfilled my responsability.

Whatever your politics, please do go and vote.

Maybe too late, maybe too little, maybe I just didn't have the to read the monster thread but here's something...

This sensor is good to 8700 PSI.

http://www.balluff.com/MicropulseCatalog2002/New_pdfs/singlepagepdfs/btl_022.pdf

They are regularly used inside hydraulic cyinders (the piston rod is gun-drilled to provide clearance for the waveguide rod and a magnet is manufactured into the piston). The end of the cylinder has a port made to accept the thread under the head of the sensor.

There are several styles:
http://www.balluff.com/MicropulseCatalog2002/BTL_W_intropage.htm

I vote for more plc projects.

Haven't really seen any canidate push for that.

I wounder who is the AB canidate, the Siemans canidate.

Too bad there isn't someway to have the election and everyone be happy.

Perhaps Vote (NONE of the above)?

I hope every one wins, no one loses, peace and prosperity for all, and a few Miller's too!

Make my two Miller Litess with a Coca-Cola chaser!

regards.....casey

Siemens LC300 capacitance probe is rated to about 3,000 PSIG standard and can be specially made to withstand 7,500 PSIG, at a price.

https://pia.khe.siemens.com/efiles/feldg/files/broschueren/sitrans_lc500_en.pdf

see page 5 in the brochure for pressure rating in process conditions.

Dan