Vacuum Sentry
TM
safety Valve
5
Valve closed - Mechanical pump vented
The piston is fully down and Vacuum Sentry
TM
is fully
closed. The higher pressure above the piston forces it
against the valve seat, where the Viton O-ring makes a
vacuum tight seal. Air from the higher pressure area above
the piston continues through the small orifice in the top of
the piston into the inside of the piston, and through a second
small orifice in its side into the mechanical pump’s inlet port.
This vents the mechanical pump to atmospheric pressure
gradually. When the pump is fully vented, the pressure
above the piston, inside the piston, and in the mechanical
pump are the same (atmospheric). The pressure below the
piston, in the vacuum system, is still lower and the piston
remains down (closed), retaining the vacuum system under
vacuum.
Note that , given enough time, the pressure in the
vacuum system will rise due to outgassing, leaks, etc.,
or venting by the operator, and when the pressure is
high enough, the spring will open the piston and the
vacuum system will be at the same pressure as the
mechanical pump (atmospheric).
Power restored
The solenoid coil is energized causing the solenoid to
close, isolating the inside of Vacuum Sentry
TM
from the
outside atmosphere. The mechanical pump evacuates the
inside of the piston through the small orifice in its side and
the area above the piston through the small orifice in the
top of the piston via the inside of the piston. When the
pressure above the piston is approximately equal to that in
the vacuum system, the spring pushes the piston upward,
fully opening Vacuum Sentry
TM
. The vacuum system is now
back in normal operation and exposed to the full pumping
speed of the mechanical pump.
