© Edwards Limited 2018. All rights reserved.
Page 31
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Installation
B722-40-880 Issue H
After a DX pump has been assigned a multi-drop address, it will ignore any messages in the format for single pumps.
An individual DX pump will remain silent and ignore all command messages unless the multi-drop address matches its
own address.
3.8
Vent options, vent valve connection and control
CAUTION
If the pump is vented when it is at full rotational speed and the rate of pressure rise is too high, the pump could
be damaged and its life may be reduced. Edwards therefore recommends that either the rate of pressure rise is
limited (refer to
) or that the vent valve is only opened after the DX pump speed has fallen to 50% of
full rotational speed.
To maintain the cleanliness of the vacuum system, Edwards recommends that, whenever the pump is switched off,
the pump (or vacuum system) is vented when the speed of the DX pump is between full rotational speed and 50% of
full rotational speed. Over this speed range, the rotor spins fast enough to suppress any back streaming of
hydrocarbon oil from the backing pump.
Do not connect the vent valve to the backing pipeline, this may lead to contamination. Connect the inlet of the vent
valve to the vent gas supply (refer to
for the vent gas specification).
Venting may be accomplished by using one of the following methods described in
to
3.8.1
Manual vent valve
A manual vent valve is supplied with the DX pump. It is not possible to accurately control the rate of pressure rise
using the manual vent valve so take care not to open it too quickly. Edwards recommends opening the manual vent
valve only after the pump speed has fallen to 50% of full rotational speed.
3.8.2
TAV5 or TAV6 solenoid vent valve
The TAV5 and TAV6 solenoid valves can be purchased as accessories – see
. The solenoid valves can be
used in the following ways:
Use a TAV5 or TAV6 solenoid valve in place of the manual vent valve on the pump
Use a TAV5 or TAV6 solenoid valve connected to a convenient flange on the vacuum system
If a vent valve is connected to the vacuum system, select a point upstream of the DX pump to prevent back streaming
of oil from the backing pump.
If using the TAV5 vent valve, the pump may only be hard vented when it is at full speed if the vacuum system has a
volume of 5 litres or more. If using the TAV6 vent valve, the pump may only be hard vented when it is at full speed
if the vacuum system has a volume of 10 litres or more.
If the volume of the vacuum system is less than 5 litres (when using a TAV5 vent valve), or if the volume of the vacuum
system is less than 10 litres (when using a TAV6 vent valve), incorporate a suitable vent restrictor and vent the pump
when it is at full speed.
gives an indication of the appropriate orifice size to be fitted to the vent valve for
given vacuum system volumes in order that the rate of pressure rise remains within the limits shown in
Note:
If a vent restrictor is used, the time required to vent the vacuum system is unacceptably long. The time
may be reduced by using a vent valve without a vent restrictor and waiting until the pump speed has fallen
to 50% of full rotational speed before opening the vent valve.
3.8.3
Controlled venting
The TAV5 or TAV6 solenoid valve can be controlled by the Podule electronics. To use this function, fit the electrical
connector supplied with the pump to the lead of the TAV5 or TAV6 solenoid valve. To ensure cable cores and screen
