User guide

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 backow 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 ow 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 ow 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 rst. With decreasing system pressure the port

with highest preset pressure is opened rst.

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: