© Edwards Limited 2007. All rights reserved. Page 31
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Operation
B344-21-880 Issue N
4 Operation
4.1 Introduction
The following sections are applicable to the Diffstak 63/150, 100/300 and 160/700 pumps which are operated in
conjunction with a combined backing/roughing-valve to provide a fully valved system as shown in Figure 18.
The Diffstak 250/2000 pumps are similar in operation but they have separate valves in the roughing and backing
pipelines (see Figure 19).
4.2 Pump start-up
The following procedure assumes that the Diffstak pump and your vacuum system are at atmospheric pressure.
1. Close the high-vacuum isolation-valve and air-admittance valve(s). Close any other openings to atmospheric
pressure.
2. Select ‘Backing’ on the combined backing/roughing-valve.
3. Switch on the cooling-water supply to the Diffstak, then switch on the rotary backing pump.
4. When the backing pressure reaches 0.5 mbar (5 x 10
1
Pa) or lower, switch on the electrical supply to the
Diffstak.
5. With the backing/roughing-valve in the backing mode, leave the pump a sufficient time for it to warm up. The
following warm-up times are recommended for the Diffstak pumps:
6. Check that the backing pressure is below the critical value for the pump fluid being used. Select ‘Roughing’ on
the combined backing/roughing-valve.
7. When a system pressure of 0.3 mbar (3 x 10
1
Pa) or lower is reached, select ‘Backing’ and then open the
high-vacuum isolation-valve slowly. If you open the valve too quickly, you can stall the pump.
If the cooling-water supply fails during operation, steam or water may be ejected from the
couplings if they are disconnected. If the cooling-water supply fails, allow the pump to cool before
you disconnect the couplings, or you may be injured.
Do not touch any part of the pump when it is switched on. Avoid contact between the pump and
combustible materials, plastic materials and electrical cables. Surfaces of the pump are very hot
(see below) and can cause injury to people and damage to equipment:
z The temperature of the pump base can reach 400
o
C
z The temperature of the pump body can reach 250
o
C.
Diffstak 63/150 pumps - 15 minutes
Diffstak 160/700 pumps - 30 minutes
Diffstak 100/300 pumps - 20 minutes
Diffstak 250/2000 pumps - 40 minutes
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