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Pre - vacuum Autoclave Process

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akhilfrancis

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Hi,


Currently i am working on an autoclave device.

In that I have three major stages
1. Pre-vacuum
2. Sterilization
3. Post Vacuum / Drying/ cooling

For getting Steam I am using Heater and Water.


Next I am, coming to point.
I will explain the process.

1. I have to insert vacuum for removing the air
2. Then pouring the water
3. Heating until the inside temperature reaching the set point.
4. Then cooling

Here my doubt is After inserting the vacuum can I pour the water into chamber, because I am confusing about density relation between these two?
Or should I maintain separate reservoir for the water?

Thanks in Advance
Akhil Francis
 

You are using steam for sterilization. There is no need for vacuum.

The common temp is around 121C - that is the boiling point of water at one atm pressure (gauge). The whole device works like a giant pressure cooker.

If you are using a batch process, the boiling water will displace the air inside and the pressure regulator will keep the temp const (approx).

There is no need to insert the vacuum and the water need to be present from the beginning.
 

Hi,

water in vacuum will freeze (at room temperature) and then it will sublimate...


Klaus
 

You are using steam for sterilization. There is no need for vacuum

There is a common belief that the presence of air inside the autoclave can create regions where water vapor would take longer to reach. I do not share this view, but I believe that the greater concentration of only water inside makes the sterilization process more efficient.
 

Hai,

Thanks for your reply.
actually in my process i have to remove air using gravity and also, dynamically.
Dynamically means i have insert vacuum, and need to remove all the air from this.
How can i know the air is removed completely?

is there any constant pressure value for free space/complete vacuum?
 

How can i know the air is removed completely?
I believe that the absolute vacuum is not a safe decision, since the variation of positive and negative pressure may increase the material stress. Keep in mind the inherent risk of explosion that an autoclave represents.
 

water in vacuum will freeze (at room temperature) and then it will sublimate...

If you look at the phase diagram of water, then at room temp (say 300K) water cannot exist in the solid phase. If the vacuum is good, it will be in vapour phase or else it will be in the liquid phase.

- - - Updated - - -

actually in my process i have to remove air using gravity and also, dynamically.
Dynamically means i have insert vacuum, and need to remove all the air from this.

1. What you mean by "remove air using gravity"?
2. It is not possible to remove ALL THE AIR from any vessel; but you can get very high vacuum using modern tools.

It is not necessary to remove all the air for an effective autoclave. What is the real objective?
 

actually in my process i have to remove air using gravity
What you mean by "remove air using gravity"?

Just guessing, but; at the end of the sterilization process, once the water valve is open, all water and 'gases' (air+vapour) are ejected out due to the high pressure inside. If the valve is closed before the inner and outter pressure get equal, and if more water are added, at the new cycle much less air will be present. I never noticed any product doing that (I have not even researched this), but I had this insight at the time when my ex-boss asked me for a cheap solution to remove the air.
 

Hi,


Thanks for your reply .


In my process i have to sense the water level also. I am planing to use electrode type water level sensor.
But the maximum operating temperature should be 250 degree Celsius.
which sensor i could use for this?

Thanks in Advance
Akhil Francis
 

No need to do this way; You can take the water level at some external reservoir, measuring the minimum and maximum value, from where would drain to the vat.
 

In my process i have to sense the water level also. I am planing to use electrode type water level sensor.
But the maximum operating temperature should be 250 degree Celsius...

1. 250C may not be desirable temp for autoclave; what kind of items you are planning to sterilize? You need wet steam and that will correspond to a pressure of about 100 atmosphere (very high for a large object).

2. What is the max size of the planned autoclave? That will determine the construction parameters.
 

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