2013/04/08

A Leybold sales engineer (Jim Hupp) forwarded our questions to a support engineer (Rich Tremblay) for the TRIVAC pumps. It appears as though there is nothing unusual about the shaft seal getting stuck in the centering disc (Fig. 1). Rich informed us that Leybold pry the shaft seal out with a screwdriver. Occasionally, a heat gun or solvent is used to loosen the bond between these parts. As soaking the centering disc in isopropyl alcohol overnight had done nothing but remove the vacuum grease, a screwdriver and plastic hammer were used to pry out the shaft seals. Rich informed us that each shaft seal included an imbedded metal ring that supports the outer diameter, thus requiring a little more aggression to remove. Fig. 1 is a photograph of the centering disc after the shaft seals were removed.

Figure 1: He-3 pump's centering disc, shaft seal removed.

What is surprising is that there were two shaft seals (Fig. 2). We suspected as much, and this had been mentioned to Jim in the first email. Rich informed us that the D16BCS (corrosive service) pump uses two shaft seals that have a PFPE-grease filling between them. However, our pump is the larger D65B, and there is no D65BCS model.

Fig. 2 (left) shows the extracted shaft seals side-by-side. The shaft seal on the left appears to be of the same outer diameter (40 mm) as that supplied in Leybold's shaft seal repair kit for TRIVAC D65B pumps (part no. 110002629). The one on the right is of diameter 42 mm, and lay closer to the electric motor. Fig. 2 (right) illustrates how they were connected together, with open ends facing away from each other. Much of the seal was destroyed during extraction, however according to Rich, this is nothing unusual.

Figure 2: Shaft Seals side-by-side (left) & connected together as they were (right).

The centering disc in Fig. 1 is 22 mm thick. It has an outer diameter of 105 mm, and inner diameters of 43 mm, 42 mm, 40 mm & 30 mm. According to Rich, this centering disc was used in helium-tight pumps around 15 years ago, and was unique for this purpose. A different centering disc is used in Leybold's present generation of helium-tight pumps. The centering disc we own is no longer sold or manufactured.

Both Leybold helium-tight and BCS pumps feature two shaft seals are installed next to each other with PFPE-grease filling the volume between them. Although different orientations of the shaft seal have been used in the past, currently both shaft seals point in the same direction with the open side facing the pump module. In addition to the regular 40 mm outer diameter shaft seal supplied in the repair kit for TRIVAC D65B pumps (part no. 110002629), a special shaft seal of outer diameter 42 mm is required.