Shellab SVAC4-2 - Manual (Page 11)

11
VACUUM OPERATION
6.1 The vacuum pump is the heart of your vacuum oven system. The selection of a vacuum pump is critical to
match your overall performance expectations for time to evacuate the chamber and the maximum obtainable
vacuum levels. As well, the type of pump should be considered depending on the material that will be
placed in the chamber. Common types are Chemical Duty PTFE Dry, Standard Duty Dry, Compact Direct-
Drive, and other specialty pumps for Corrosive gases. Selection of application specific pumps can improve
the overall oven performance as the right pump ensures cost effectiveness and minimizes pump
maintenance.
In general, a dry pump with a pumping capacity of 100 l/min. can be used to evacuate 840 liters volume
(0.84 cubic meters) in a reasonable time. High vacuum pumps based on oil sealed rotary vane technology
use the rule of thumb of 1 to 1.5 times the volume of space to determine pumping capacity (300 liters
volume needs a 300 to 350 l/min. pump). The reason for the differing rule on oil sealed pumps is that the
evacuation needs to be below 10torr in less than 10-15 minutes to avoid poor lubrication and overheating
the internal pumping mechanism. Oil-
free piston pumps don’t overheat while evacuating larger chambers;
however the time to maximum vacuum takes longer the smaller the pumping capacity.
6.2 IT IS IMPORTANT TO USE VACUUM TUBING FOR ALL THE VACUUM HOOKUPS. OTHER TYPES OF
TUBING MAY COLLAPSE AND PREVENT COMPLETE EVACUATION.
6.3 To Apply Vacuum to the Chamber:
There are two ways to apply vacuum.
1. Attach the hose from the vacuum pump to the 3/8" hose connection on back of the oven. Close the
VENTILATION valve (clockwise) and open the VACUUM valve. Latch the door shut and start the
vacuum pump. This action will hold the door shut and against the gasket until the pump creates a
vacuum in the chamber. Once a good vacuum seal is accomplished, the door will hold itself shut and
sealed until the chamber is returned to ambient atmospheric pressure.
2. The unit is equipped with a KF- 25 flanged 1” port. This can be used for faster, higher volume vacuum
pump down. When the large port, close both the VENTILATION and VACUUM valves.
6.4 Watch the VACUUM GAUGE and when the required vacuum is obtained, close the vacuum valve and turn
pump off. The digital vacuum gauge is factory set to display inches of mercury. The display will show 0
—29.92
inch. If the vacuum exceeds 29.92, the display will show “_ _ _”. The 0 indication represents present
atmospheric pressure. See Reference 2 for details for digital gauge settings.
6.5 Vacuum Release: To return the chamber to ambient atmospheric pressure, open the VACUUM valve very
slowly and allow the chamber to re-pressurize. The speed of pressurizing can be controlled by how much the
valve is opened.
Section 6