Lyophilizer Vacuum Problems

[weeeds]

We are looking for information on a typical lyophilizer system.
What can cause a loss of vacuum?
How are vacuum leaks located?
Is it unusual to have a loss of vacuum on average once per year for this type of equipment?

 

[quark]

External air leaking into the chamber and residual moisture in the chamber etc. You can have your lyophilizer helium tested to find out leaks. First of all you should check whether the vacuum breaks due to permanent leaks or temperary leaks. If the pressure rise is constant over a period of time then it is the external air leaking in. If the pressure rise decays over a period of time then it is moisture inside the chamber. What leak rate you are observing? If you can't quantify it, give the dimensions of the chamber, initial pressure, final pressure and duration of pressure increase.

There is one good article in Pharmaceutical Engineering magazine(probably Jan or Feb issue)

It may not be unusual for your lyophilizer to leak.

Regards,

 

[weeeds]

Thank you for the information quark.
We are looking at purchasing a used lyophilizer and we have not yet confirmed a size.
Any idea as to the "normal" operating vacuum level for this type of equipment?

 

[quark]

Generally, that depends upon the eutectic point. The sublimation should take place just below the eutectic point. As a general rule, the final vacuum ranges between 50 to 300 mTorr(0.067 to 0.4 mBar).

The leakage rate should be maximum 0.01 mBar-L/sec.

Regards,

 

[MedicineEng]

Dear widla:
I don't have so many experience with lyophilizers, but I would just like to leave you some toughts/cares when to buy used lyophilizer/pharma equipment:

1-Qualification. Is the equipment able to be qualified? If it is too old you will pass a hell of a time trying to qualify it. So try to check this first before you make a decision;
2-Piping work. Vaccum leaks are very difficult to find specially if they are tiny. So all piping/welding work should be reduced to the minimum and done by proper staff with X-ray verification;

I would like just to share with you a story that happened with me and with my former colleagues and a lyophilizer when I was working in a previous job:
We had quite old lyophilizers and they were quite prone to leaks. I remmebr that one time we had a vaccum leak that was puzzling us: In the beginning of the process after some time we start to have vaccum leak, then sudenly as the process continues with the cooling step, the leak stop and then restarted again in the heating step. It was an headache!!! After some rough nights we finally realized that the leak was in a welding joint that freezed during the cooling step and then the moisture in the air was forming an ice layer over the leak and closing it.That is why the leak was appearing and disappearing.
Hope that helps
PR