Scroll Pump Maintenance
This LASE Wiki Page is intended to supplement the Varian/Aligent recommended procedures for scroll pump maintenance.
Last Updated by: SDM 08/18/2015
Introduction
Regular scroll pump maintenance is key to well-behaved performance. Properly maintained scroll pumps will provide low ultimate pressures, cool running temperatures, and a quiet operation. New to scroll pumps? Scroll pumps are mechanical pumps that utilize spiral compression to generate vacuum pressures down to the mTorr. For more info, this [Wikipedia page Scroll compressor ] does a good job introducing the basics of scroll pump technology.
These pumps are used for three purposes: (1) backing the turbo pumps, which require at most 1 Torr of backing pressure for proper operation (we prefer in the mTorr range) (2) atmosphere to rough vacuum pumping, usually when the chamber is vented for maintenance purposes, and (3) the high vacuum cross overs, typically from turbo/scroll to cryo pump control.
Edwards Pump Maintenance
The LASE Group currently has 4 Edwards scroll pumps: 3 nXDSi6 (named "Gauss", "Euler", and "Newton") which are used as turbo-backing pumps in the MBE lab; one is used as a spare or for the BOS. The 4th pump is a nXDSi15 (named "von Neumann") and it resides in the FTIR lab to pump out the FTIR system.
A page from the Edwards company and for these particular pumps are here:
When to do maintenance?
Similar to the Varian pumps (described below), these pumps are spec-ed out to an ultimate pressure of 10 mTorr, although we have gone as low as ~4 mTorr. If the pump starts to wander to far from the ultimate pressure measured during a pump's last re-gen, it is time to replace the tip seals on the pump. The Edwards pumps require maintenance every 10-12 months. It is suggested to put a reminder on the group calendar so you remember when to perform an annual maintenance. Check the scroll pump status page (Current Scroll Pump Specs) for the latest maintenance information, and keep that page up to date with maintenance developments!
The Edwards pumps have on-board logic that can indicate when the pump is experiencing problems or needs service (image below). Note: the "!" indicator starts flashing after the pump hits a certain operational time threshold, e.g. 5 years of running for bearing replacement. This indicator does not let you know if there is a problem, rather that it is time for routine maintenance -- don't rely on the indicator to know if there's a problem!
To get the number of days/hours of run time for an Edwards pump, connect the Edwards pump to a computer with the nEXT nXDS Support Toolkit software. See diagnostics section below.
Pump Diagnostics
Installing nEXT nXDS Support Toolkit software
After entering name, company, and address info, there's a page with an option to 'copy to clipboard'
Copy to clipboard and paste into an email to the Edwards software license group
It takes ~2 days for the license team to activate your software
Use the key provided by the license team and complete software activation
Reading data from pump
Use A/B to USB cord between the pump and the computer
Open scroll pump software
nEXT nXDS Support Toolkit
Under Serial Comms,
change to COMM 4 and 'detect'
Baud rate should be 38400
Navigate the tabs and menus to find info
'Operational History' --> run hours
Edwards Pump Maintenance Procedure
Use the Edwards tip seal replacement manual, as reference. RTFM before starting, but keep in mind the procedure below is a slight modification/optimization of the procedure described in the replacement manual.
Supply list
Air respirator
1 small pair of wire cutters/pliers
Metric Allen wrench size 4 (i.e. 4 mm)
Small torque wrench, found in the box plastic box in the tool chest.
1/4" square drive Hex Bit socket that drives a metric size 4. This can be found in a zip lock bag within the Edwards pump maintenance box located in the Bat Cave. This hex bit is for the torque wrench
2 flat-head screwdrivers with fat head
1 of the largest flat-heads in the box (used later for leverage)
Many (dry) cloth Kimwipes
Large Plastic bag for Teflon-related trash
A lab partner
A few pieces of clean foil (to make foil boats for screw holding and to cover up any exposed ports, e.g. exhaust)
Scroll re-build kit, which can be found in the Edwards maintenance box in the Bat Cave (nXDs tip seal replacement kit A73501801)
Small tube of Krytox lubricant, found in the Edwards pump maintenance box (may have to borrow some from the Varian pump maintenance box if the Edwards box does not have any Krytox)
Procedure
Perform this maintenance in a closed off room, such as the Batcave, with respirators ON. Put up appropriate warning signs.
Place scroll on a Kimwipe-layered surface that is large enough to support 2-3 scroll pumps next to each other
Remove VPI from the top of the pump (if not already removed)
Support VPI with free hand or with your lab partner, because the VPI is slightly-heavy and off balance when loose
Place VPI off to side.
Foil off the bottom of the VPI
Remove plastic housing (AKA "cowling") from front of pump.
Use the metric 4 wrench to remove the two screws at the top and bottom of the cowling, located at positions 12 O'clock and 6 O'clock, when facing the cowling. Place in a foil boat or somewhere nearby such that they will not roll away.
Remove any foil or other covering on the exhaust port
pull the plastic cowling off, starting from the side that is farthest from the exhaust port. It'll take some finagling, but the cowling should slip off over the exhaust port. NOTE: there is an electrical jumper connection on the bottom of the cowling that connects to the rest of the pump. Be sure to remove to disconnect the connection before completely removing the cowling from the pump.
Place the plastic cowling off to the side
Inspect the inside of the cowling, checking that the fan and electrical wires appear normal. The cowling houses a fan that is used to cool the inner scroll faceplates of the fan which get quite hot while the fan is operating
Remove the 4 screws on the front face plate (located at the four corners) using the metric 4 Allen wrench. Place the screws (with their washers) in a foil boat or container off to the side
Remove the fixed scroll (see manual for the location of the part)
Apply the large flat-head screwdrivers to the notches located at the 3 O'clock and 9 O'clock positions between the fixed and orbiting scrolls.
Slowly wedge the fixed scroll off of the orbital pump. This will take a few minutes, so be patient. The key is to evenly separate the two scroll plates. Use the largest flat-head screwdriver to get extra leverage as needed.
Place the fixed scroll plate off to the side after it is removed
Inspect the two scroll plates and the green rubber gasket around the edge of the fixed scroll plate
See the pictures below as examples of scrolls after moderate/normal usage
Generally, you should see:
A light coating of Teflon dust on every surface
The tip seals might unseeded from the orbiting scroll, when you remove the fixed scroll plate, but that's normal
All the Teflon tip seals should still be in one piece, and there should not be any major pieces of debris on either plate
The green rubber gasket should be slightly worn, with small sparkly pieces of metal that dot its surface. There might be cracking or de-coloration.
IF replacing the Teflon tip seals... (sometimes you only care about simply inspecting the scrolls after a few months of usage -- skip the next part if so)
Triple glove, because you're about to get your hands coated with Teflon dust
Gently remove the tip seals already on the scroll plates using a very small flat-head screw driver. Place in Teflon trash once removed
DO NOT USE IPA for any of the cleaning. Wipe off all surfaces of the scroll plates using dry cloth Kimwipes until no more dust seems to want to come off. Be sure to remove any small pieces of debris that may have gathered on the scroll plates while wiping the surfaces.
Dispose of all Kimwipes used for cleaning in the Teflon trash bag
Insert new tip seals
Get re-triple-gloved, since your gloves are probably covered in Teflon dust
Get the two baggies of new tip seal from the scroll re-build kit. NOTE: both of the new tip seal baggies work for either scroll, i.e. they are not scroll plate specific
Starting from the center of the scrolls on both the fixed and orbiting scroll, insert the tip seal into the tip seal channel. Ensure that each tip seal starts as close as possible at the start of the scroll channel. See Figure 1 from the manual.
Using your lab partner to secure the newly inserted tip seal in the center of the plate, slowly work/seed the tip seal around to the outer part of the plate
Cut the short the tip seal using the wire cutters/pliers at the end of the scroll channel. There should be at least 20 mm between the end of the channel to allow for expansion of the tip seal while the pump is operating. NOTE: there is a small mark/groove in the metal that indicates where to tip seal should be cut
Using your gloved-fingers, run your finger along both plates' new tip seal, starting in the center, to ensure that the tip seal is properly seeded in the tip seal channel
Remove any debris that may have accumulated while installing the new tip seals
Dispose of any Teflon dust-covered wipes in the Teflon trash bag
Put the extra pieces of Teflon in the "Extra Teflon" box that is in the Edwards pump maintenance box in the Bat Cave
IF replacing the green rubber gasket ... (again, sometimes you only care about simply inspecting the scrolls after a few months of usage -- skip the next part if so)
Remove the rubber gasket and dispose of it in the Teflon trash bag
Get the new gasket from the re-build kit. Wipe off any debris that may have built up
With a new set of triple-gloved hands, put a small dot of Krytox on the index finger of one of your hands. Rub it with the thumb on the same hand until the two fingers are uniformly Krytoxed
Take the new gasket and slowly work the entire length of the gasket between your Krytoxed fingers, such that the gasket has a thin uniform coating of Krytox. This will help it seal the two scroll plate together
Fit the new gasket/O-ring onto the fixed scroll. There is a channel around its circumference where the gasket should sit
Remove your Krytoxed gloves and apply and apply get new triple-glove layer. Dispose of the Krytox gloves in the Teflon trash bag
Reassemble the fixed and orbiting scroll plates together. Check that the alignment dowel located on the bottom of the orbiting scroll lines up with the hole on the bottom of the fixed scroll plate.
Mate the two scroll plates together by starting with the bottom part of the plates and dowl/dowl hole lined up, but the top part of the plates are more separated. With the bottom part of the plates still together, slowly bring the top part of the plate into contact
Once the plates are together, the green gasket should still be visible and the plates should be evenly ajar on all sides. If not, un-mate the two plates and try again
Press the two plates together, such that the green gasket is no longer visible and the two plates are flush together
Tighten the fastening screws (the 4 screws with the washers) back into position
Evenly distribute the tightening of the screws to ensure a good seal
After the screws are finger tight using the metric 4 wrench, use the torque screw with the metric 4 bit fitting to torque each screw to 9 N-m
Re install the plastic fan cowling
Reconnect the electrical jumper between the cowling and the bottom of the scroll
Remove the foil from the exhaust port
Work the plastic cowling over the exhaust port and black leak valve, then make the cowling flush with the rest of the pump
Re-cover the exhaust port with foil
Re-screw in the two remaining screws at the top and bottom of the cowling
Clean up (respirators still on)
Put the fully reassembled pump next to a testing area, like near the BOS
Clean off any tools or (non-Kimwipe-)surfaces that may be coated with Teflon dust using IPA and dispose of cleaning wipes in the Teflon trash bag
Put away all tools
Remove the top layer of Kimwipes from any work surfaces and put in Teflon trash bag.
Remove the outer layer of your gloves and put it in the Teflon trash bag
Close the Teflon trash bag and put it in the regular trash
Take down warning signs from doors
Remove respirators and give partner a high-five. You're done!
Testing procedure
Connect the pump to an open exhaust port, such as on the BOS, using the appropriate KF 25 fittings. Without the VPI attached to the top of the pump, directly connect a Pirani gauge to the port input (on the very top of the pump). Listen for any strange or loud noises coming from the pump. This would indicate that the pump was not reassembled correctly, leading to a pump leak.
After the pump is confirmed to be working correctly, let the pump run for 10 minutes and monitor the pump Pirani gauge on one of the control panel. It should get into the mid-10s of mTorr range. Next, open the black leak valve on the side of the pump allowing air to leak into the pump. The pressure should spike up several 10s of mTorr. Per the pump instruction manual (not the tip seal replacement manual) from Edwards, let the pump suck on the leaking air for 20 minutes. After that, close the leak valve, and leave the pump running for 2-3 days. After that time, record the pump pressure, as it should have bottomed out as this point, i.e it will have achieved its "ultimate pressure". Record this pressure and the date of the tip seal (or any other maintenance) on the pump status page.
Varian Pump Maintenance
The LASE Group currently has 5 Varian/Aligent TriScroll 300 Series Scroll Pumps in the MBE lab. These pumps used to be used as the primary scroll pumps. Now, we primarily use the Edwards pumps. The Varian pumps are still used as backup pumps, but should not be used for extended periods of time, because (1) they are older and (2) they are a more of a pain in the ass to fix/maintain as compared to the Edwards pumps. This being said, avoid using the Varian pumps as primary pumps to back the MBE turbos unless you're in a pinch!
When to do maintenance?
Agilent recommends tip seal replacement when poor performance is observed, generally when the scroll pump is incapable to reaching an ultimate pressure of 10 mTorr. In their view, poor ultimate pressure is a sign of worn tip seals (like wore tires in a car), and thus need to be replaced. The LASE Group has stricter maintenance scheduling based on previous experience.
After 6 months, it is good practice to replace the tip seals, even if the ultimate pressures is good. Why? The simple answer is tip seal degradation. As part of the tip seal design, a teflon coating is applied to the end of the tip seal, for a low friction seal. However. over 6 months, tip seals shed significant amounts of are teflon dust within the blades of the pump, eventually get into a main set of shaft bearings, causing bearing stress, eventually failure (unfortunately from experience) You could just clean everything out and put everything back together without replacing the tip seals; however, since solvents are used in the cleaning, it's safer to replace the tip seal while you are at it risking failure
What determines maintenance?
Here are list of possible events:
Broken/bad tip seal that has been shredded, leading to teflon dust all over the inside of the pump
Teflon dust has reached the pump bearings
Key point: teflon dust can form around the bearings only after 6 months of use. Cleaning these out prevent the teflon dust from reaching the bearings, maintenance efficiency, and cool operation.
Before starting maintenance
Before scroll pump maintenance begins, it is important to record its performance specs. Previous cycle maintenances are logged at Current Scroll Pump Specs on the LASE Wiki. Chiefly, scroll pump must achieve the baseline performance spec determined by Agilent after maintenance as the following:
Ideal Operating Conditions:
Ultimate Pressure: < 10 mTorr
Faceplate Temperature: < 131 F
Noise: Quite as possible (should sound as it did before maintenance)
Varian Pump Maintenance Procedure
Use the Varian tip seal replacement manual, as reference. As always, RTFM before starting, but keep in mind the procedure below is a slight modification/optimization of the procedure described in the replacement manual.
Supply list
Air respirator
Scissors
Metric Allen wrenches 3, 5, and 6
2 small flat-head screwdrivers
Many cloth Kimwipes
Large Plastic bag for Teflon-related trash
A lab partner
A few pieces of clean foil (to make 2-4 boats for screw holding)
IPA
Scroll re-build kit
Procedure
Perform this maintenance in a closed off room, such as the Batcave, with respirators
Place scroll on a Kimwipe-layered surface that is large enough to support 2-3 scroll pumps next to each other
Remove VPI
Support VPI with free hand or with your lab partner, because the VPI is slightly-heavy and off balance when loose
Place VPI off to side. NOTE: VPI is still connected to the back of the pump
Foil off the bottom of the VPI
Remove plastic housing (AKA "cowling") from front of pump
Allen #3
3 screws
Set removed screws in a foil boat or spare container off to the side
Remove the 6 screws from the exposed plate. Now calling this first plate "plate 1"
Allen # 5
Remove plate 1
Note the build up of Teflon dust on the inside the scroll. It will look like yellow cheese powder form macaroni and cheese. The Teflon comes from the degradation of the tip seal (since the tip seal is made from Teflon)
The exposed face still connected to the rest of the scroll is a second plate. Now calling this second plate "plate 2"
Remove rubber O-ring from plate 2
Dispose of the O-ring in the Teflon trash bag
Remove plate 2 from the pump
Allen #5
4 screws
NOTE: Center of mass will change for the pump when removing plate 2. Use lab partner to support the backside of the pump
Set the remaining part of the pump off to the side
Remember the VPI is still connected to the rest of the pump
Gently remove fan blades from plate 2
Use Allen #6 to loosen the center set screw
Note: there is a black throwing star. Don't throw it away or lose it!
Set off to the side
Check that the key and rubber gasket are still in place
Turn plate 2 upside down and separate into two pieces (plate 2-a and 2-b, see figure)
Examine the tip seals
If tip seal is pulled out -- BAD! Tip seals are shredded
If black grease-like gunk is present -- BAD! Krytox leaked. (Recall: Krytox is a lubricant for the bearings)
Cleaning (takes ~ 1 hour)
Gently remove ALL tip seals from plates 1 and 2 by using the small flat-head screw drivers -- over-aggressive removal can accidentally bend the tip seal fin, which you don't want to do!
Remove all Teflon dust by using IPA + small flat-head screw driver in the following areas:
Tip seal valleys
Tip seal fins/seeding
Anything that looks like it would cause a tip seal to fail
Let all the cleaned surfaces dry for 30 minutes, to assure that all IPA is gone
Regrease the bearings inside 2nd half of plate 2
Remove Teflon dust from small plate from plate 2-b on top of bearings
DO NOT use IPA, because it will degrade the rubber seals! Instead, use a dry Kimwipe
Apply more Krytox to the bearings
If Krytox is translucent, it has gone bad! It should be white in color
Reapply Krytox to bearings and rotate them to allow the Krytox to mix into position
Wipe excess Krytox off the top of the bearings
Bearings should feel smooth/easy to roate; otherwise, the bearings are bad
Add a small amount of Krytox to your glove, rub Krytox along the 3 rubber seals for the bearing housing (i.e. small plate removed from plate 2-b). This helps with thermal expansion of the rubber so the seals are not stuck when they heat up during pump operation
Install new tip seals on the first part of plate 2
Grease crank shaft/key with Krytox
Apply tip seal to single tip sealed plates first before apply it to the multi-tip sealed plates
Do NOT remove tape from the tip seal package, because it holds the new tip seal in place
Cut at the outside first, making a good, square cut
Insert the tip seal into the cleaned grooves between the fins, with the dark side down and the white side up (the white stuff is Teflon)
Leave 1/4 inch gap at the edges of the tip seal fin starting and stopping points
After the tip seal is in place, go over it once more with your glove to assure it is well seeded
Re-mate the 2 pieces of plate 2
Might hear a "Ca-Chuck" sound once the plates fall into place
Re-add fan
Check that the key is correctly orientated
Check the washer is in place
Re-add large screw
Check that the black throwing star is in place
Bring the backside of the scroll + VPI back to the table
Re-add plate 2 to pump by simultaneously:
Correctly align throwing star
Positioning the fan exhaust toward the bottom
Carefully handling the blades
Aligning the 2 side studs
Re-add the 4 side screws (Allen #5)
Add new tip seal to the now-exposed side of plate 2
Re-grease with Krytox the 3 shafts on plate 1. Also add one dot of Krytox on the 3 holes of plate 2 where those shafts will go
Grease new rubber gasket O-ring with Krytox and install the O-ring onto plate 2
Align the 3 shafts on plate 1 with the 3 holes of plate 2 and orient the writing on plate 1 vertically (so it can be read from the front of the pump) and re-join plate 1 and plate 2
Re-add cowling cover
Test the pump
Should be quiet and not too hot, otherwise something is loose from the re-gen process
See how low the pressure gets. It might be 50 - 100 mTorr
Let the pump suck air for 3-5 minutes (through the Pirani gauge hole)
The pressure should now be much lower while maintaining a low pump temperature
Testing procedure
Once put back together plug in the scroll. It should as it did previously. Running the pump on air will (i.e. remove pirani gauge and leave the bellow hole open to air) help blow out any loose dust during the the clean, and help set the seals. Closely monitor the temperature using the handheld laser thermometer. While tip seal breaking, if the scroll pump's face temperature rises above 131 F, turn pump off, let it cool, then proceed. Note: it will take several turn on, pump exceeds 131, turn off cycles until the pump settles to a stable temperature near 131 F. Also, the pumps will run hot for the first week or two in operation, but eventually they will settle to a lower operating temperature as the tip seal seeds better.