Change the 3He Circulation Pump Oil

The 3He circulation pump oil should be changed every 6 months in principle, though we usually wait longer. It should be changed if it appears significantly darker than new oil.

The main difficulty is that normally the pump always has some mixture in it - this needs to be removed from the pump and secured in the dump or elsewhere. We use the cryopump for this - a long stainless steel vessel that can be lowered into a LHe Dewar to pull in helium gas. The cryopump has a black valve isolating it from a flexible hose with a KF-15 flange at the end.

1. Connect the cryopump hose to the Vent port at the back of the IGH.
2. Pump out cryopump hose, using the scroll pump connected to the 1K Pot pump line, through V5a, V2a, and the Vent speedivalve. Also have V7 and V2 open to monitor the pressure on G1.
3. Open black valve on cryopump to also pump out the cryopump.
4. Close V2a, V5a, and valve on 1K Pot pumping line. Turn off scroll pump.
5. also: we will be moving mixture through LN Trap 2, so this should also be pumped out. It is assumed to be warm.

1. It is assumed that the mixture has been pumped to the dump, V9 is closed, and the 3He pump is off.
2. Record the reading on G2. This is the 3He pump outlet pressure.
3. The following valves should already be open: V2, V7, vent speedivalve, black valve on cryopump. Thus cryopump pressure is seen on G1.
4. Open V12b+speedivalve. This connects Trap 2 volume to cryopump volume.
5. Open V13b. This lets mixture out of 3He pump outlet into (warm) Trap 2 and (warm) cryopump. Record G1 and G2.
6. Insert cryopump into LHe Dewar.
7. Wait for G1 and G2 to settle. Then record pressures. (G2 is apparently insensitive below 10 mbar, simply reads 0. So we will depend on G1 after first cryopump cycle.)
8. Close V13b to isolate the 3He pump.
9. Open V4 to connect Cryopump to Dump. Then immediately begin removing cryopump from LHe Dewar. Remove Cryopump completely and let it warm to room temperature.
10. Wait for G1 to settle. Record G1 pressure.
11. Close V4 to isolate dump.
12. Insert cryopump into LHe Dewar. Wait for G1 to settle. Record G1 pressure.
13. Open V13b. This lets mixture out of 3He pump outlet into (cold) Cryopump.
14. Return to Step 7 and repeat. With each repetition, G1 at Step 7 (the pump outlet pressure) should decrease. The goal is to reduce the pressure in the pump to a negligible value, so that almost all of the mixture has been removed. (Two cycles is probably sufficient.) On the final cycle, stop after Step 10.

The procedure for changing the oil is in the Pump manual. Here is a version of the procedure with some additions specific to our setup.

1. It is assumed that all mixture has been removed from the 3He Pump, and is currently being held in the Dump, the Cryopump, LN2 Trap 2, and several volumes inside the IGH. The 3He Pump is evacuated. It's also assumed that the pump has not been run recently for extended times - if it has, the pump and oil will be hot and extra care should be exercised to avoid burns - or better yet, wait for the pump to cool.
2. Open V6 100%. This opens the 3He Pump inlet to P1, and will allow for gas to be let into or evacuated from the Pump inlet via a port in a T-section of KF plumbing.
3. Remove the KF-15 blanks from the two ports to the inlet and outlet of the 3He pump, which lead to speedivalves.
4. Build a manifold with KF-15 to KF-25 converters and other KF-25 hardware to connect the inlet and outlet ports to a single KF-25 port.
5. Connect a hose from the N2 gas supply at the wall to the manifold connected to the 3He Pump inlet and outlet. Bleed the hose by running N2 through it before connecting.
6. Open the speedivalves on the ports to the 3He Pump inlet and outlet. Then let in N2 gas. Let in gas in several-second bursts and monitor G2 (the pressure at the 3He Pump outlet). Let N2 gas in until G2 is about 900 mbar. Do not exceed 980 mbar.
7. Find the rectangular oil pan - a steel pan with a short rim, about 1/2 inch. Place this under the back of the 3He Pump, the side facing the back wall wite the Pump's oil level sight glass. This will collect the old oil as it drains from the pump.
8. Remove the oil plug from the 3He Pump. This is situated below the oil level sight glass and requires an 8mm Allen key. Make sure not to lay the plug anywhere where it can get dirty from lint or dust.
9. The pan will not hold all the oil. When the pan is just a little full, replace the oil plug to stop the draining. Then pour the oil from the pan into a bucket. Wipe up any drips on the floor with paper towels.
10. Continue draining until the rate of draining becomes low.
11. Replace the oil plug. Close the speedivalve to the 3He Pump inlet. Open the manifold to air so that the 3He Pump outlet is not blocked. Then turn the 3He pump on for about 1 second - no more than 5 seconds - then turn it off again. Drain more oil. (More oil should come out.) Repeat this a couple of times to get as much oil out as possible.
12. (Optional) Measure the volume of oil removed and record this value.
13. Find a bottle of Leybold LVO 210 vacuum pump oil. If it is an already opened bottle, check the color of the oil to make sure it isn't cloudy. If it is, use an unopened bottle instead.
14. Clean a funnel with methanol and dry it. Remove the oil fill plug, which is situated above the center of the oil level sight glass. Place the funnel in the oil fill port. You may want to tie string to the funnel to hold it close to upright.
15. Pour new oil in through the funnel. It will take time with each pour for the oil to flow into the pump.
16. Use the level in the bottle to estimate how much oil you have put in. The manual says the correct amount is between 2.0 and 3.3 L. Since there may be some old oil left in the pump, the min/max amount of oil to add may be slightly less than these values.
17. Observe the oil level sight glass as you are pouring in oil. As the oil rises it will push up a patterned plastic rectangle - the oil level is the bottom of this plastic piece. The final oil level should be between the two levels marked by ridges on the pump surface. Fill till the level is about 50% between the marks.
18. While filling the pump with oil, also disconnect the flange to the 3He Pump inlet. Attached to the o-ring for this flange is a mesh dirt trap. Remove and inspect this dirt trap, and clean it with methanol. Then replace it and reconnect the flange.
19. An oil level in the sight glass of about 75% up between the marks is probably a good target. When this level is reached, replace the oil fill plug.
20. Close speedivalve to 3He Pump outlet and open speedivalve to 3He Pump inlet. Use Scroll Pump to pump out 3He Pump inlet for about 20 seconds. This will allow for less strain on the 3He Pump when it is first turned on. Close speedivalve to inlet to finish pumping.
21. Turn off Scroll Pump and disconnect from manifold. Open speedivalve to outlet so that 3He Pump outlet is not blocked.
22. Turn on 3He Pump. If it makes terrible noises, turn it off again. Otherwise let it run and record qualitative observations of the sound level.