Cryopump Cold-head rebuild
- 1 Cryo Rebuild version 3
- 2 Future Cryo Cold Head Maintenance
- 3 When to Perform Maintenance
- 4 Cryo Preparation
- 5 Disassembling the Displacers
- 6 Disassembling the motor
- 7 IPA wipe down all parts
- 8 Valve Plate Seals
- 9 Motor Assembly Bearing replacement - Disassemble
- 10 Motor Assembly Bearing replacement - Re-assemble
- 11 Replacing the Displacer Seals
- 12 Reassembly, General
- 13 Parts for the repair (1 of each per repair)
Cryo Rebuild version 3
--EMK 6/2010
--SDS 7/15/2013
--NTS (w/ SDS and AK) 2/6/2014As always... RTFM
Share > library > MBE-manuals > Commercial > Helix - Cryopump Installation Operation and Maintenance
Share > library > MBE-manuals > Commercial > Helix - CTI Cryo-Torr Drive Unit and Displacer Assembly
There is light, medium, and heavy cryo cold head maintenance
Light is just replacing the Displacer Seals
Medium is also replacing Part 15 (generally)
Heavy is replacing (almost) everything (add in Drive and Valve (motor assembly) Bearings replacement, etc.)
The juncture between these procedures is in Section 7: Valve Plate Seals
Future Cryo Cold Head Maintenance
The next time the Bravo CAR cryo or the Echo cryo heads are pulled, replace the crankcase with a windowed crankcase. There are two spare cryo cold heads in the Bat Cave with windowed crankcases. A full maintenance kit is required for this work. It is part #RK-CT8 from Austin Scientific. (SDS 13FEB2014)
When to Perform Maintenance
If the cryo is seizing up or making the noises in the following video: Ratchety Cryo (auto-plays)
This is indicative of heavy contamination, so purging the cold head, lines, and compressor is likely necessary. You will probably also need to replace all seals and o-rings.
Spikes in cryo temperature
Pressure "burps"
Usually accompany cryo temperature spikes, but not always.
Cryo Preparation
Venting the cryo and disconnecting the He lines
This needs to be edited and is beyond my expertise - NTS
With the roughing manifold and load chamber at UHV, spin down the turbomolecular pump.
While the turbo spins down, pull the power plug to the cryo head. Remove the helium cooling lines. For loosening the line:
Disconnect the supply first, then the return line
Need to clamp down on the base of the connector and rotate the top, otherwise will have inner rubber lining rubbing on the metal
Be careful not to cross-thread or hit the threads with the wrenches
The special wrenches are in the hammer and cryo parts drawer
Turn off the nitrogen backflow to the turbo pump. Let the pressure in the load chamber/roughing manifold reach a steady-state.
When the cryo head reaches 77 K (N2 boiling point), crack the all-metal valve between the cryo head and the bellows to the roughing manifold. Open the all-metal valve all the way.
Let the roughing pump pump on the system while the cryo head warms up to room temperature.
EMK Notes below
Vent the load chamber and roughing manifold
Close cryo gate valve
Unplug cryo and bring up to room temperature
For loosening the line:
Disconnect the supply first, then the return line
Need to clamp down on the base of the connector and rotate the top, otherwise will have inner rubber lining rubbing on the metal
Be careful not to cross-thread or hit the threads with the wrenches
The special wrenches are in the "hammer and cryo parts" drawer
Will see the temperature slowly climb up to 77 K and then sharply increase to 300 K
Wait until cryo is at RT !!!!!
The connector will hiss, but continue to loosen past this point
Cap the ends with foil
Use the pressure release connector on the return line
Tighten until it hisses and releases the pressure in the motor/Drive Unit, then remove
Remove Drive Unit
Use the (5/32") stubby allen to undo the bolts that hold the Drive Unit in place
The Drive Unit will stay in place as it is being removed, then pull straight back
Wipe the inside of the cryo with kimwipes to remove Teflon dust. Do this til almost no dust comes out on the kimwipe. You may need to wrap kimwipes around a tool to get inside the displacer housing.
Disassembling the Displacers
When finished disassembling the displacers, wrap them in paper kimwipes followed by loosely wrapping them in foil and placing them in a desiccator until you are ready to reassemble the cold head. This will prevent the displacers from absorbing too much water or other contaminates.
Remove the dowel pin connecting the two Teflon displacers of the inner cryo using a 1/8" punch pin and rubber mallet
The bent spring between the two pieces is important! (it keeps the tension between the two displacers)
Undo the allen bolts attaching the larger displacer to the motor, and pull off the large displacer
Take out the pin and pull off the Collar (the piece the large displacer was on, parts 10, 11).
Pull off the Cap, large displacer (part 12)
Remove pin from middle of small displacer (part 4)
Separate trunnion pin and wipe with IPA (part 5)
Disassembling the motor
Undo 4 (3/16") allen bolts holding the Valve plate
With a rubber hammer, tap the top from behind to loosen (use the supply line as a torque arm)
Use a (7/64") to undo the bolts next to the valve actuators. There is a spring under this assembly.
Underneath this assembly are the valves. Remove.
They are non-identical, one inlet and one outlet (the outlet has a notch to fit a pin in the actuator assembly)
Underneath the valves are the springs, one larger and one smaller (concentric). Remove.
IPA wipe down all parts
Use IPA and cloth kimwipes to wipe down all appropriate parts
The cleaned actuators should move freely (and click when shaken)
Apply Krytox lubricant on the actuators and shaft of the motor
Inspect all parts for any wear and tear, cracks, breaks, or worse that would necessitate replacement. Inspect all parts going forward with the disassembly as well. There are some spare cryo parts in the spare cryo rest stop under the batcave table.
Valve Plate Seals
Remove the two seals to be replaced: Seals for the No. 1 and No. 2 displacer (Parts 1 and 9, and any sub-parts)
If we are replacing any of Parts 13, 14, or 15: Use a small flathead screwdriver and pin pliers to remove the spring clip
The seal under the Retaining Ring (aka spring clip) Kap-Seal-Gland (Part 15) wears down slower than the two Displacer Seals and does not need to be replaced every time. This is the part we expect to replace out of Parts 13, 14, and 15, so save parts 13 and 14.
First documented in 2014
If being done: Remove the retaining ring (part 13) from the valve plate. This is a PITA, and may require the right pliers and a flat head screwdriver or two. Do not bend the ring or let it fly away when removed.
If being done: Remove parts 14 and 15. They should come right out after the ring (part 13).
If we are doing medium maintenance, you can potentially skip from here to Replacing the Displacer Seals
If we are not taking apart the Motor Assembly, and just replacing basic Displacer and Valve Plate Seals, skip to Replacing the Displacer Seals
If we are doing Motor Assembly Disassembly, for bearings or what not, continue here
Remove parts 16 and 17 from the valve plate. This is also potentially a PITA. Try to get these parts out with pliers or a flat head first. Other techniques: put a large allen wrench through the hole of the valve plate from the back side and firmly hammer it a few times to try to dislodge, then retry removal with pliers. Parts 16 and 17 should come out together.
Remove part 18. Another potential PITA. Try to get this part out with pliers or a flat head first. Other techniques: Firmly pound it to dust with a hammer, allen wrench, and punch.
Motor Assembly Bearing replacement - Disassemble
First documented in 2014
You need a/the bearing puller to replace the drive motor assembly bearings.
Remove 4 allen bolts (3/16") on drive motor assembly motor front plate (part 55) to remove drive motor assembly from crankcase.
Remove the plug, o-ring, and bushing (parts 40, 39, 38) from the back of the crankcase. The bushing might be hard to get and if it can't be plied, punch it out.
IPA wipe non-replaceable parts as you go. Now is a decent time to wipe the plug (part 40), scotch yoke (part 22), and crankcase. Wipe the crankcase inside, including the port for the plug (use a thick allen wrench and kimwipe as a pipecleaner). Wipe the crankcase outside as needed (due to it getting crud on it as you work, wipe the inside, etc.).
Remove Retaining ring (part 49, it's tiny) from drive motor assembly using spring clip pliers. (Image above)
Do not damage the Crankshaft and Valve eccentric (part 51 and 54); we're keeping them.
MAKE SURE TO REMOVE BOTH SET SCREWS BEFORE USING THE BEARING PULLER. Set screws are located on part 54. (AMG 2023)
Remove Drive bearing (part 50 et al.) from the Crankshaft. You need the bearing puller tool. Tighten the jaws between bearings. Put 1/4" socket head onto center screw and 1/4" bolt into the socket head, with the other end in the bearing. The bolt is located in the cryo tool box. Twist until drive bearing is at least flush with the crankshaft pin. Pull it all the way if you can, otherwise, carefully but strongly use force to remove completely. [Old method: Land center screw on the exposed crankshaft pin and twist until the drive bearing is flush with the crankshaft pin. Put aside bearing puller and use pliers to remove drive bearing.]
Remove the Crankshaft (piece 51), Valve bearings (52) and Valve eccentric (part 54) together, using the bearing puller tool. The Key (part 53) should stay in the drive motor assembly. Use the socket head and bolt to help with removal. [Old method: To help the bearing puller, put a 3/8 to 1/4 adapter and 1/4 extension under the center screw and into the crankshaft center hole (to land on the key).]
To separate the bearings and valve from the crankshaft use leverage tools and/or pliers. 52 and 54 came off the crankshaft together using leverage. (Now 52 and 54 are together, and 51 and 52 are together.)
Use a vicegrip, 1/2" socket head, and mallet to separate 52 and 54 (pic 7). Use a similar technique for 51 and 52 (pic 8).
Motor Assembly Bearing replacement - Re-assemble
First documented in 2014.
Skip to the relevant part if you did not replace the motor assembly bearings.
Put it back together with new replacement parts.
Go to machine shop and use big vice (and protective wipes) to put 52 and 54 together. Repeat for 51 and 52. Make sure they are all the way together! When press fitting bearings, alternate where you're applying pressure (rotate the part), especially when pressing the crankshaft (Part 51) because it has an off-center post. Seriously, make sure they're all the way together.
Slide 52/54 assembly over key (53). Slide 51/52 assembly over key and press-fit them (firmly hammer with a mallet to ensure snugness). Make sure they are all the way together! Otherwise the cryo will make bumping noises when it's all reassembled and charged and you have to take it apart again.
There are two set screws (long and short) that go inside 54. The short one will abut the pin (right, POV from external side). The long one goes in the other hole (left). Screw in until they won't go anymore.
Put a little bit of IPA on exposed crankshaft shaft/pin and place drive bearing (50) on. Firmly hammer it on with mallet, hitting it in the center, to the point where it's (almost) flush with the crankshaft shaft/pin. Then hammer it off center to get it on all the way, without hitting the crankshaft shaft/pin.
Put Retaining ring (49) onto crankshaft shaft/pin, by spreading it a little using spring clip pliers and placing it on. Be careful, do not spread it so far as to deform it; just enough to get it on crankshaft pin.
Insert a Bushing (38) into the crankcase (26) from the internal side. Make sure it's flush with crankcase back wall. A little bit of Teflon dust will occur, so IPA wipe inside 26 again.
Put o-ring (39) on plug (40) and insert into same port the bushing went into, but from the external side.
Insert Scotch yoke into 26 and into the bushing (38). It has a grooved side that you need to put in properly.
Make sure you end with the scotch yoke in the most released position (all the way out).
Put O-ring (56) onto drive motor assembly and put drive motor assembly back onto the crankcase. Put in the four allen bolts and tighten.
Replace Bushing (part 18) into valve plate (part 19) from the internal side. Line up bushing with its home hole and get it started in there. After it's in a bit, use 7/16" socket head and rubber mallet to insert it flush with inside edge of valve plate. The socket head should stop when it's flush.
Put O-ring gland (17) onto the Gland scotch yoke (16) and insert into valve plate with o-ring facing down.
Put in Parts 15, 14, and 13. Can use 7/16" socket head and mallet to aid insertion.
Flip over valve plate and insert a big spring and small spring (concentrically, parts 30 and 31) into the two inlet and outlet ports.
Put valve stems (32) into valves (34 and 35) and o-rings (33) onto valves.
Put valves into ports. The round one is the inlet, the funny shaped is the exhaust. The inlet valve might not go down all the way due to the o-ring.
Put inlet valve seal (37) onto inlet valve stem.
Put on Rocker assembly (parts 23-29) and screw on. The inlet valve should now go down.
Put an O-ring onto the crankcase and reattach valve plate.
Proceed with rest of reassembly.
Replacing the Displacer Seals
Go up a few steps to the step that talks about Parts 15, 14, and 13 and continue from there if needed (Insert the little Teflon gasket, then the metal washer, then the spring clip; reassemble the Valve Plate)
The big Teflon gasket goes over the groove of the large Teflon displacer
The springed Teflon gasket goes on the small displacer with the metal ring over the spring, Teflon ring. Slide the Teflon gasket over the displacer, don't spread it to get it on. "Helpful" video on installing the metal ring over the gasket and spring:
Reassembly, General
Reassemble all parts
Actuate the Drive Unit until the shaft is in its extreme Out position and re-insert into cryo
Parts for the repair (1 of each per repair)
Purchase from Austin Scientific (Oxford Instruments)
Light or Medium Maintenance
+ L900698 / ASSY, SEAL, Displacer #2, CP-8 (4060-0011) Cryo
+ L900697/ ASSY, KAP SEAL, Displacer #1, CP-8 (4060-0010) Cryo
+ L900709/ ASSY, KAP SEAL WITH O-RING (4060-0014), CRYO
+ L900710/ SEAL, INLET VALVE EA (4060-0015), CRYO
Heavy Maintenance
+ RK-CT8/ REPAIR KIT for CT8 or CP8 (PN 98-00407-00)
Includes (Part #): SEAL, Displacer #2 (1); SEAL, Displacer #1 (9); Kap-Seal, Gland (15); Bushing (18); O-Ring, Crankcase (20); O-Ring, Vessel (21); O-Ring, Valve (33); Seal, Inlet Valve (37); Bushing (38); O-Ring, Plug (39); O-Ring (43); O-Ring, Sight Glass (46); Retaining Ring (49); Drive Bearing (50); Valve Bearing (52); O-Ring (56); Motor Bearing (57); O-Ring, Motor (58).