VACUUBRAND PC 600 LAN NT - Manual (Page 56)

page 56 of 102
If the pressure in the network exceeds the preset pressure of an applica-
tion operated in parallel, the non-return valve of that port closes in order
to protect the lower-pressure application against backflow or contamina-
tion. When the non-return valve closes, it is no longer possible to evacu-
ate or control the application until network vacuum is restored to a level
below that needed by the application.
Remedial action: In order to restore control or resume evacuation of the
application, the gas flow at the open port must be reduced until the net-
work pressure is decreased below the lowest process pressure of the
parallel application.
Automatically controlled vacuum applications:
An increase of system pressure (that is, some loss of vacuum) due to
formation of gas (e.g., pumping down) and/or programmed preset pres-
sures can occur if several automatically controlled ports of a vacuum
network are operated simultaneously. Such an increase of pressure usu-
ally occurs in form of a pressure peak. Therefore the vacuum supply of
applications operated in parallel is cut off only temporarily; the non-return
valves counteract the mutual interference.
In general: It is recommended to reduce the pumping speed at automati-
cally controlled ports as well by using an additional flow control. By that
means, pressure bursts on the application side or in the vacuum network
are minimized. The hysteresis ( Δp) at the vacuum controller at the port
should not be set too low ( Δp= approx. ±10%p
Set
), if possible use the au-
tomatic hysteresis preset at the controller.
Notes: If the system pressure is increasing, the port with the lowest pre-
set pressure is closed first. With decreasing system pressure the port
with highest preset pressure is opened first.
Effect of the integrated non-return valves:
At each port, a non-return valve is integrated to avoid an increase of
pressure or contamination. The preset pressures of the different applica-
tions are related to the system pressure in the vacuum network as shown
below: