Doc #: 3500-AD Revision: Rev 1. WHIRC Molecular Sieve Replacement. Author(s): Dick Joyce

Transcription

1 Doc #: 3500-AD Revision: Rev 1 WHIRC Molecular Sieve Replacement Author(s): Dick Joyce

2 Contents Revision History Purpose Applicable To Scope Definitions Training Safety Personnel, Equipment and Material Required Procedure Procedure Review Records References AD Docx Page 2 of 8

3 Revision History REV Date Approved Sections Affected Reason for Change Remarks and/or Change Details Initiated RRJ Modified some procedural details RRJ Name Approved by: SigEng Name, ME Title SigEM Name, EL Maint SigSci Name, SciOps Signature 28 August 2018 Tammie Lavoie, Safety Manager Date 3500-AD Docx Page 3 of 8

4 1.0 Purpose Document the procedure for replacing the molecular sieve (vacuum getter) in WHIRC. 2.0 Applicable To KPNO 3.5-m WIYN telescope, WHIRC infrared imager 3.0 Scope To be done whenever there is evidence that the existing molecular sieve has become saturated 4.0 Definitions 5.0 Training Clean room procedures High vacuum procedures ESD procedures 6.0 Safety 7.0 Personnel, Equipment and Material Required 2 people, one of whom is familiar with high-vacuum and ESD procedures Clean room attire (bunny suit, shoe covers, head cover, gloves) Allen wrench set High-vacuum pump (mechanical + turbomolecular pumps) N 2 cylinder with regulator Vacuum oven 8.0 Procedure 1. WHIRC must have been removed from the WIYN telescope with the Monsoon controller disconnected and shorting plugs installed on the connectors, installed on its transport cart, and transported to the Instrument Handling Facility (IHF) 2. A fresh batch of Zeolite ZSM-5 should be heated in the vacuum oven under vacuum at a temperature of 100 C [TBC] AD Docx Page 4 of 8

5 3. Clean the exterior surfaces of the instrument and move into the clean tent. 4. Move the dewar on its cart to the edge of the clean tent to permit the vacuum pump to be attached to the KF25 dewar vacuum flange (Figure 1). Figure 1 5. Turn on the mechanical vacuum pump and evacuate the entire pumping line up to the vacuum valve on WHIRC. Close the valve to the mechanical pump. 6. Open the WHIRC vacuum valve and carefully backfill with N 2 from the pressurized cylinder. Use a low regulator pressure setting to avoid overpressurizing WHIRC. This must be done gradually and carefully. 7. Once WHIRC has been backfilled, disconnect the vacuum pump line, install the protective KF25 cover flange, and move the cart back into the center of the clean tent AD Docx Page 5 of 8

6 8. NOTE: Steps 4-7 may also be done prior to moving WHIRC into the clean tent. 9. Using a 9/64 Allen wrench [TBC], remove the six 8-32 screws securing the Fill Line Clamp to the top surface of the dewar (Figures 2 and 3). The clamp is split, with three screws on each half. Figure 2 Figure Using a 3/16 Allen wrench [TBC], remove the twelve screws securing the top plate of the dewar (Figure 4). 11. Very carefully, lift the top plate off, making sure not to stress the fill line (Figure 5). This will expose the molecular sieve cage on top of the LN 2 tank. 12. Unscrew the single captive bolt holding the molecular sieve cage to the tank and remove the cage (Figure 6). 13. Unscrew the six 2-56 screws securing the top plate of the molecular sieve cage, discard the old material, and clean the cage with isopropyl alcohol. 14. Carefully fill the cage with fresh Zeolite ZSM-5 which has been previously heated in the vacuum oven (step 2) AD Docx Page 6 of 8

7 Figure 4 Figure 5 Figure Replace the top plate of the molecular sieve cage, taking care not to crush any pellets in the process. Once the top plate is secured, wipe down the cage to remove any residual Zeolite dust. Bolt the cage securely to the top of the LN 2 tank with the single captive screw. 16. Carefully inspect the O-rings on the dewar top plate and vessel flange. They should be carefully wiped clean or replaced if significantly flattened or damaged. 17. Carefully wipe the mating surfaces on the top plate, lower it into place maintaining the original clocking, and replace the bolts securing the top to the dewar case. 18. Insert the fill line clamp pieces into position and replace the bolts securing it to the vessel flange. This should complete the reassembly of the dewar. 19. The dewar and cart may now be removed from the clean tent. Hook up the vacuum pump to the KF25 flange on the dewar vacuum valve AD Docx Page 7 of 8

8 20. Turn on the mechanical pump (bypassing the turbo pump for now) and pump out the line. Slowly open the WHIRC vacuum valve and pump out the vacuum jacket until the internal dewar pressure (measured with the Convectron gauge on WHIRC) is 100 mtorr or less. 21. Valve off the mechanical pump and slowly backfill the dewar with N 2 from the regulated cylinder until the pressure is near atmosphere (600 Torr). Then repeat the pumping procedure in step 21. Repeat this procedure two more times. This will help flush out any residual water vapor in the dewar. 22. On the third pumpout cycle, once the pressure in the dewar is less than 100 mtorr, reroute the pump through the turbomolecular pump and power it on. It will take several minutes to come up to speed, but it should rapidly achieve a high vacuum. 23. Pump on WHIRC with the turbo pump as long as necessary to achieve a good, stable vacuum. 9.0 Procedure Review Update after initial sieve replacement to include any additional information from carrying out the procedure Records 11.0 References DOCUMENT NUMBER NA DOCUMENT TITLE KPNO Emergency Manual 3500-AD Docx Page 8 of 8