Adjusting the Vacuum Switch
Inches of mercury (“Hg) is a unit of measurement for gauging pressure or vacuum that is exerted.
What is a Vacuum Switch?
A vacuum switch is used to regulate the vacuum pressure during the vacuum bagging process to ensure uniform vacuum throughout the part during the curing process.
ACP’s vacuum switch is an inexpensive and reliable full range miniature vacuum switch with good sensitivity, repeatability and set point tolerance. The switch is adjustable from 1.5-30”Hg with a dead band of 2-3”Hg. It comes preset to shut a vacuum pump off when vacuum reaches 18” Hg, and then if the vacuum drops to 15” Hg is starts the pump back up automatically.
The amount of pressure being applied during the vacuum bagging process can vary depending on what is being vacuum bagged. Settings for the switch can be adjusted by changing the Hg settings at which the switch operates. The ideal settings are 5”-8” Hg when bagging low density white foam, 12”-14” Hg for gray and pink foam and 15”-18” Hg is recommended when bagging higher density foam, such as blue foam or Spyder Foam. If required, higher vacuum up to 30” Hg can be used when bagging solid lamiates into a mold.
Adjusting the Vacuum Switch?When different settings are required, the vacuum switch can be adjusted to start and stop between 1.5-30” Hg with a 2-3” Hg dead band. This means that the switch can be adjusted to start and stop within no less than 2” Hg of each other (i.e. it will stop the pump at 18” Hg and start it again at 16” Hg.)
Adjusting the switch can be achieved by raising and lowering the set-point, or set screw. This is done by loosening the steel lock ring and turning the electric switch housing clockwise to raise the set-point or counter clock-wise to lower the set-point.
Recommended process for adjusting the switch to have a 16”-18” Hg setting is as follows: