Sheldon SHEL LAB SVAC1, Installation And Operation Manual, Page: 66 / 78

66 | P a g e
MAINTENANCE
Note: Does the car actually have gas in the tank? Have you physically verified the computer is
plugged in? Yes, we are going to ask some very basic questions. Please bear with us.
Methodical verifications and the elimination of potential causes of failure are often the
quickest means of getting a unit back into operation.
Unit Vacuum Conditions
Verify the items below to ensure a fault in the oven rather than the pump or external vacuum plumbing or
contamination is preventing the unit from achieving its specified performance levels. During normal
operations, the oven can be vacuumed down to -3.0 to -29.9 inHg depending on the performance of the
pump, the oven chamber temperature, and the volume of outgassed byproducts. For most applications,
the vacuum pump must remain on and connected to the oven chamber to remove outgassed
byproducts.
• Is the chamber being quickly pumped down to -3 inHg or lower? Yes or No?
o
The door will not seal completely at pressures higher than -3 inHg.
o A slow evacuation may not be sufficient to seal the door.
o
The vacuum pump must be rated to a minimum flow capacity of 1 cubic foot per minute (cfm)
per cubic foot of chamber volume. Example: a 2 cubic-foot chamber should be connected
to a pump that can evacuate at least 2 cubic feet per minute.
•
Is the vacuum pump type suitable for your application or process? Yes or No?
o
The vacuum pump must be resistant to byproducts outgassed during the baking process.
Otherwise, the integrity of the pump can be quickly compromised.
• Is the gasket type suitable for the application? Yes or No?
o
Each gasket type is resistant to and vulnerable to different outgassed byproducts. A
gasket that is vulnerable to byproducts from your applications may fail after only a short
period of use.
o See page 76 of the user manual to verify that the installed gasket is suitable for your
application.
•
Is the oven chamber clean prior to being pumped down? Yes or No?
o
Outgassing from contaminants can cause a rise in chamber pressure. At very low-pressure
levels, the oven may register outgassing from fingerprints.
• Is the chamber being evacuated for the full duration of your baking application? Yes or No?
o
If the vacuum valve is closed during the baking application — isolating the chamber from
the vacuum pump – outgassing from samples or products will raise the chamber pressure.