iDRY Vacuum Kilns

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Parked at 9%

Started by HORSELOGGER, February 22, 2004, 03:21:04 PM

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HORSELOGGER

Well back in the early days of this new forum ( bout a month ago  :D) I posted I had just loaded my kiln chamber ( Nyle 200 ) with 2500 bft of frozen solid white oak, fresh sawed. Heres the specifics... I started the kiln on Jan 25, kiln temp 24 degrees. Kiln up to 85 by the 27th. Moisture meter readings today run 12 s to high 7s. Benn around 10% average for 4 days. The kiln temp is 125 degrees, and just a little dribble of water now and then. Cant bump the temp any , cuz the 200 is a low temp dehumidifier. ( went to 127 today any way) Question... do the high temp dehumidifiers or conventional type kilns run into this problem of "stalling" or is it a low temp problem? I seem to hit this wall on every load I run, regardless of size or amount of pre drying.
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

East_West_Dan

Horselogger,  I've run into the same problem and was told it was the "low" temps. I ran a few loads in a Nyle 300 and did better at 160 degrees. It's frustrating to watch all that juice being used and not much happening. On a 200 I was able to open vents to keep the temp down and used a 90% run.  time on the commpressor, but I did get some surface checking when the humidity dropped to 15%. With White Oak you could have the same problem.

Dan  

HORSELOGGER

Hi Dan,  What MC was the lumber when you got the checking?
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

Norm

Horselogger I have the same problem with white oak, I don't have much luck getting it below 9%, if I get an average of 10% I call it good. For what we do that's ok but if I remember right you make flooring and may be too high a level for that.

To get below that takes forever this time of year, but the differences in moisture may have to do with the air flow in your chamber. I've wondered if a heat exchanger would help by getting higher temps in the chamber with the dh unit still running in addition.

Den Socling

I've read that all surface checks are in place at high MC whether you see them or not. The problem starts when the core is above 40% and the shell is under 25%. The shell shrinks over the core and stress occurs. It's hard to get water out of the core of white oak because of it's non-permeability. You have to go slow. And, if you get the RH too low, you overdry the shell.

I would guess that the stalled MC is due to the way water moves. At low MC, it moves with a process called diffusion. Heat greatly improves diffusion. Lowering RH doesn't create enough 'force' to get the last couple percent out of that non-permeable white oak.


Brian_Bailey

Horselogger,  

Is that 9% reading taken with a pin type meter @ 120* + ?

I find my meters will read high @ those temps.  If you let the lumber cool down to normal room temp, I think you'll find your reading to be about 6 to 7%.  

I run a Nyle L-150 and dry mostly hardwoods.
I AD before kilning.  
Many times I'll hit a sticking point at about 14 to 16%@ 120*, Dang meter just wont go any lower !!  
What I'll do at this point is shut off the compressor and raise the temp. to 140* and let the lumber cook @ this temp with just the fans on for about 24hours.
This does 2 things. 1) it sterilizes the lumber. 2) it gets the water moving in the core.
In many instances,once the temp. gets back down to 120* I'm at my target mc and can finish the load in a day or so.

Hope this is of some help :).  
WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

Don_Lewis

It is okay to let the temperature climb up to 130-135F at this point. We limit the temperature to 120 because you should not go higher when the water is moving freely.  But when the air is very, very dry, these temperatures are okay. That will usually solve the problem. The high temperature systems do dry faster when the MC is below 25%.But there are other things to consider. Also be sure to correct for temperature on your meter. If it doesn't automatically correct, there is a table available at the Dry Kiln Operator's Manual download site.

HORSELOGGER

Well, The load is done 8) I had decided to call it good at readings of 8- 10% so I turned off the compressor and turned on the heater, and ran it up to 140 to sterilize the load. After a day of those temps , i went in the chamber and it felt a little muggy in there, and I thought about your post Brian. I turned the heat off and let the fans run for a day and the temp drifted back down to the low 120s .I turned the compressor back on and got a nice little trickle of water. After 1day of this all my readings are 7%. That was a great suggestion, Brian and really makes sense as a way to get the water moving again to finish off with these low temp kilns. Thanks! ( oh yeah, all readings are with a delmhorst R2000 pin type meter)
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

Brian_Bailey

HorseLogger,  

That's great ya got yer load done.  

I'm a little bit leary of running my compressor much past 120* since I blew most of the gas out of it last year.  Maybe, one of the new L-200's can handle the heat better than my old L-150 can :D :D. Maybe it's time to let some moths out of the wallet an get me an L-200, but before I do, I wanna see the results from the vacuum kiln thread first  :).

I use a Mini - Ligno DX - C with external probes.  I've checked it against a scale and microwave oven and know it reads approx. 2% higher @ 120*. I hate to cut up good lumber for kiln samples, so I just rely on the meter's readings. I know that goes against conventional wisdom but it's my lumber and it works for me.

  
WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

HORSELOGGER

Yeah, I do the same ( run my kiln by the meter) I know its wrong, but I just cant help myself :D
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

FeltzE

I havn't run my Nyle 200 past 120 degrees for fear of damaging the pump or system. Is it ok to turn the heat up higher for steralization? Should I select a  0 cycle time for the pump during temps over 120?

Eric ???

Joe_Beaulieu

Set the compressor run time at 0% to prevent the compressor from operationg, then turn up the heat.

Don_Lewis

If you run the temperature too high with either an L150 or an L200, it will not damage the compressor because there is a high pressure safety that will trip before it reaches the point where damage to the compressor will occur. The switch is a manual reset so if it trips, reset it when the kiln cools somewhat. But don't worry about blowing the charge or compressor from that. It can happen but not from that reason

FeltzE

Thanks for the info Don

Brian_Bailey

I had a slow leak developed around the fittings and it went unnoticed by me for some time. When I ran the temp. to 140* and left the compressor running the high pressure caused enough gas to escape and tripped the low pressure switch. I replaced both switches and recharged the compressor and it has been running like it was new.

Moral of the story, if you've been running your DH for awhile, it might be a good idea to check for leaks.

WMLT40HDG35, Nyle L-150 DH Kiln, now all I need is some logs and someone to do the work :)

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