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Waveguide Dehydrator Pressure Reading

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Jan 7th, 2011 at 5:08am  
Sir do you have any idea on what should be the pressure reading of a dehydrator for waveguide?
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Reply #1 - Jan 9th, 2011 at 2:39pm  
My days as an earth terminal operator are long behinds me, so I don't have a specific answer to your question, More info as to the type of dehydrator would likely be required by someone more current than I. Like whether it's inline or external, is active (own pump) or passive. The fact that you got no responses might have something to do with the time of day it was posted, so I bumped it back up to the top for you.

Typically, I'd expect the answer you seek to be in the documentation that came with the dehydrator. Generally I'd say that an inline dehydrator pressure would be neutral; that is, equal to that of the waveguide. And it would make sense that an external would need slightly lower pressure to ensure throughput rather than bypass.

//greg//
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Eric Johnston
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Reply #2 - Jan 9th, 2011 at 4:59pm  
Get hold of the dehydrator operating manual and the antenna manufacturer instructions.   Is is most important not to blow out the feed window or pump water/moisture into the waveguide.  A pressure of between 0.25 to 0.5 psi may be appropriate.

The dehydrator motor should run for only a small proportion of time, with a very slight leak. Read the manual about recommended flow rates and the possible use of a calibrated leak at the far end.

If a dehydrator has been out of use, is possibly faulty or has been allowed to run continuously for a very long time, get it serviced.

Motors may need replacing evey few years.

Ref: http://www.networketi.com/pdfs/adh3com.pdf

The common problems with dehydrator systems are:
Excessive leakage.
Completely sealed.

Best regards, Eric.
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Reply #3 - Jan 10th, 2011 at 12:02pm  
ok sir thankyou, the motor of the dehydrator is working when the pressure reading is 0.21 psi below. But my problem now is that the pressure drops below 0.21 psi almost every 10 mins. Is it normal? or does that mean we have a leaky system?
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Eric Johnston
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Reply #4 - Jan 10th, 2011 at 12:48pm  
That sounds quite normal to me.   The system should (and must) have a small leak.

I would expect something like 15 - 30 seconds to pump up, then 5 - 20 minutes silence to leak down, then pump up again and so on.   You don't say how long the pump runs for.  If is taking 9 min 30 sec pumping time to pump up and then leaks silently back down to the 0.2 psi trip level in just 30 sec then the leak is too large.  The duty cycle would be 570/600 = 95%, which is far too high.   If the leak is too small it might take more than an hour of silence between pump ups.

1%- 5% duty cycle is ideal.   18 seconds of motor on and 9 min 42 sec motor off = 18/600 = 3%
More than 50% duty cycle is bad.

Every few days the dehydrator may do a heating cycle where it switches over from one canister to the other and dries the off-line canister by heating and blowing the wet air out to the atmosphere.  During the heating process the motor may run continuously for a while. Read the manual for your unit.  There are significant differences between different manufacturers and model types.

Best regards, Eric.
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« Last Edit: Jan 10th, 2011 at 3:38pm by Admin1 »  
 
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Reply #5 - Jan 11th, 2011 at 2:12am  
Thnkyou sir I understand now how the dehydrator works. I'm really impressed how you were able to answer all my questions accurately. The duty cycle of our unit is 52-54% according to its reading. And the motor pump up almost every 2 mins. I will try to inspect the wave guide for some leaks.
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Eric Johnston
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Reply #6 - Jan 11th, 2011 at 9:36am  
If you reduce the leakage, the motor-on pump-up time may decrease a little, but the motor-off time will increase significantly - perhaps to 10 - 20 minutes.

You may find a small adjustable leak device at the far end of the waveguide run.

Best regards, Eric.
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