Maintenance Reassembling the Lower Jet Assembly

Maintenance

3-5-3 Reassembling the Lower Jet Assembly

aCarefully replace the fourth stage jet on the jet base.

bReplace the third stage jet shield.

NOTE

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Before completing the following step, check that the gaps are even and tighten the screws uniformly and in a cyclic pattern. Jet spacings are preset at the factory and controlled by the spacers secured to respec- tive stages.

c Replace and tighten the securing screws between the third and fourth stage jets.

3-5-4 Reassembling the Jet Assembly

NOTE

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Before securing the jet assembly to the pump, check that the lower jet assembly is firmly seated on the pump with the ejector correctly posi- tioned. For proper alignment, a pin is provided in the base of the pump; the large slot in the jet base must register on this pin.

a Complete the steps in para. 3-5-1 in reverse order.

NOTE

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If the jet coupling became loose during step 3-5-1c, refer to Figure 3-3,

Jet Coupling.

3-6 HEATER REPLACEMENT

The HS-20 diffusion pump heater array consists of six elements arranged to give as close a balanced load as practical over the three supply phases. The heater design employs a long, convoluted tubular heating element which is clamped directly to the boiler plate. A thin, stainless steel membrane with a number of elongated dimples, referred to as a crush plate, is placed in contact with the opposite side of the heating element. A stiff clamping plate forces the membrane against the heating element. When the clamping nuts are tightened, the dimples on the membrane are deformed at the points of contact with the heating element. This permits adjustment to dimensional variations in the boiler surface and/or in the thickness of the heating element.

During a replacement of heaters, only the crush plate and element must be purchased. These part numbers are listed on the Replaceable Parts List. The crush plate should be replaced if the heaters are removed for inspection or maintenance.

To replace the heaters, proceed as follows (refer to Figure 3-4).

3-7