Dear Sir.

I am currently experiencing a problem with the validation of one of our Fedegari autoclave which is mainly controlled by pressure (verified by drain temperature).
Lately, we have observed temperature "blip"/droppage on 1 or 2 of 36 TCs during our qualification run (for a very short amount of time) despite a very consistent and acceptable RTD temperature in the drain.
Instrument used to record is the KAYE Validator 2000 (TC recorder), which are pre and post calibrated prior and after each qualification run (It has also been tested for 16 hours straight to produce accurate result in a temperature bath)
I have not yet rule out the possibility of instrumentation error, however would like to hear some insight on the possibility that these "blip" could be caused by wet steam. Note that this autoclave is not used for European market - hence steam quality was never tested.
Would a steam quality problem be consistent with the symptom of the problem I have been experiencing? or would a wet steam problems caused a more consistent drop in temperature throughout and for a longer period of time.

See below for example:

00:00:00 121.5
00:00:20 121.5
00:00:35 118.5
00:00:40 121.5


Any input, suggestions, insight would certainly be appreciated.

Regards,
Edo Dasuki

Without seeing a trace and much more data it is difficult to draw any firm conclusions BUT.

1. Check the steam supply capacity. Sometimes the capacity of the supplu system is overcome by steam demand and so pressure falls resulting in a concomitant drop in temp. If this is only momentray then sensors with a large thermal mass may have sufficient heta capacity not to see this.
2. NCG's in steam may be coming through the pipework at this particular time, locating at some points in the load and causing a momentary temp drop.

Dear Edo.

1. Do you monitor the steam supply pressure? Are there significant pressure flactuations? If positive, add a check valve on the steam supply line.
2. Did you check the chamber steam trap? did you replace the capsule? if positive, is the capsule "close to temperature" type? (Delta 5 Centigrade)

miki

First, I would like to thank both [email protected] and Michael Meyer for their input.
As for the steam supply pressure, it is not monitored. However, the autoclave does control through pressure hence the pressure inside the chamber is maintained to ensure saturated steam is present. Since data on the chamber pressure shows no fluctuation during the dwell, I would assume that supply is always available.
The chamber steam trap was also checked and they were functioning properly.
As for the NCG, could a present of NCG really caused such a significant drop in temperature within such a short period of time?
Follow up or more input are definitely appreciated.

Regards
Edo Dasuki

Dear Edo.

Idont believe it is the KAY Validator. To assure it, connect 2 TC's at the same location. If both will "blip", it means that you have to look for the problem somewere else. If only one "blips", - reject the TC.
The "blip" as you explained is a short moment of cooling. Can it be that put the TC at a point where the steam condensate? Do you get the steam from a Steam Generator or from steam plant? Could it be that water (condensate) is primed to this point? If your steam is provided from a steam generator, is the supply water pre-warmed (Hot well)? If you get the steam from a steam plant, - is the piping vented properely? is the condensate displaced fast enough? Is the piping at the correct dia?

miki

I have seen this phenomenon in some of the sterilizers we produce (resistometers and air overpressure sterilizers). We attribute it to a droplet at the thermocouple or even on the drain RTD (we use RTDs with very fast time constants). It seems to correlate with the complexity of the chamber hardware and/or a too-large steam pressure at the boiler. Either place a shield above or around the TC/RTD, lower the steam pressure (especially if you are seeing ANY superheat at the onset of the exposure/sterilize phase), or both.

Jonathan A. Wilder, Ph.D.
President
H & W Technology, LLC
www.stericert.com
http://members.aol.com/ehwco