B344-21-880 Issue N
Page 24 © Edwards Limited 2007. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Installation
3.6.2 Connect the cooling-fail thermal snap-switch (optional)
This component can be supplied as an optional accessory to protect the Diffstak against damage due to failure of the
cooling-water supply. If the temperature of the Diffstak increases above the normal operating level, the switch will
operate to disconnect the heater from the electrical supply. The switch is preset during manufacture and
automatically resets when the temperature of the pump returns to normal. The switch can be mounted on the fixing
plate which is permanently attached to the cooling-coil on the Diffstak body (see Figures 1 to 4).
If you use a PPE fluid in the pump (see Table 2), you must fit the cooling-fail thermal snap-switch and interlock it
with the pump heater electrical supply.
A typical electrical circuit with the thermal snap-switch connected in-series with the Diffstak heater is shown in
Figure 15.
Figure 15 - Cooling-fail thermal snap-switch electrical connections
3.6.3 Connect the pump-ready thermal snap-switch (optional)
This switch can also be supplied as an optional accessory to indicate when the pump is in a fully operational state.
The switch will operate at a preset temperature level when the jet system in the pump has reached operating
temperature. The switch can be positioned at the end of the ejector-stage housing. Installation data is provided in
the instruction manual supplied with the switch.
If you use polyphenyl ether (PPE) pump fluids in the Diffstak pump, you must fit a cooling-fail
thermal snap-switch and interlock it with the pump electrical supply. If you do not, the thermal
breakdown temperature of the fluid could be reached if the cooling-water supply fails. The
thermal breakdown products of PPE fluids are dangerous.
1. Cooling-fail thermal snap-switch (optional)
2. Diffstak heater
3. Heater switch
4. Rotary backing pump
5. Fused isolator or contactor
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