© Edwards Limited 2013. All rights reserved. Page 47
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Installation
B800-00-880 Issue D
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 nEXT pump is between full rotational speed and 50%
of full rotational speed. Over this speed range, the rotor spins fast enough to suppress any backstreaming 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 Section 2.3 for the vent gas specification).
Venting may be accomplished by using one of the following methods described in Section 3.9.1 to 3.9.4.
3.9.1 Manual vent valve
A manual vent valve is supplied with the nEXT 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 that the manual vent valve
is opened only after the pump speed has fallen to 50% of full rotational speed.
3.9.2 TAV5 or TAV6 solenoid vent valve
The TAV5 and TAV6 solenoid valves can be purchased as accessories – refer to Section 7.4. 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 nEXT pump to prevent
backstreaming 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 or else use the controlled venting option. Table 20 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 Figure 7.
Note: If a vent restrictor is used, the time required to vent the vacuum system may be 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.
3.9.3 Vent valve control
The TAV5 or TAV6 solenoid valve can be controlled by the controller 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 are wired correctly, follow the electrical connection instructions given in the Accessories Manual
(supplied with the TAV valve) and refer to Figure 9. Plug the connector into the socket at the side of the controller
(refer to Figure 12).
The controller is capable of controlling a number of different venting options. These are defined in Table 19.
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