Repairing Edwards E2M30 vacuum pump
The E2M30 is a high-performance 230-volt rotary-vane vacuum pump found on many pieces of lab equipment such as mass spectrometers. It has been replaced by the E2M28, which has virtually identical performance characteristics. Although they are very reliable, every time you turn a vacuum pump off there is a risk that it won't start up again. One day we turned off our E2M30 pumps to move our LTQ six inches to the left. When we tried to power it back up, one of the pumps seized. After much stroking of our beards trying to decide what to do, we decided to try to fix it ourselves.
To repair a seized vacuum pump, the pump has to be completely dismantled and every part checked for corrosion and scoring. If you're lucky, it might only be dirt trapped between moving surfaces. There could also be metal parts that have jammed against each other and become badly scratched or scored. These parts have to be polished back to their original condition before the pump will rotate. In the worst-case scenario, a part will need to be replaced.
There are many excellent companies that can rebuild vacuum pumps, but it is a labor-intensive task that can cost over $1000 when you include shipping costs. These pumps weigh over 100 pounds, so you can't just put them in a box and call FedEx. The pump has to be bolted to a sled and shipped by a freight truck. Sending a vacuum pump out for rebuilding can take several weeks. These pumps cost about $6000 when new, but the cost of instrument downtime can be many times that. So it can be cost-effective to do the work in the lab.
Disclaimer: The procedure below is not official. I am not an expert on vacuum pumps. The procedure below worked for us, but might not work for all pumps. Follow it at your own risk.
The main problem is: "it won't go!" No vacuum. Pump does not spin. Motor gets very hot and periodically trips the motor's thermal protection. When the motor tries to spin, it pulls over 30 amps. If your mass spec is on a UPS, this will most likely overload it or trip a breaker whenever you turn it on. It will also shred the rubber shock absorber between the pump and the motor. If the motor still works, the problem is in the pump and it will have to be stripped down and rebuilt.
- Edwards rebuild kit (contains mainly O-rings and rubber parts)
- Set of metric hex wrenches
- Several boxes of paper towels
- Sandpaper (600, 1000, and 2000 grit emery paper)
- Aluminum polishing kit (Mothers or equiv. and a cloth rag. Although marketed for aluminum, it also works well on steel.)
- Hammer and rubber mallet
- 1 quart of vacuum pump oil
Level of difficulty: medium
Level of mess created: high
Time: 1–2 days
- Unplug pump and drain out all the oil.
- Remove the 4 long metric bolts on the outer oil reservoir. This is the large rectangular cast aluminum piece on the right side of the photo above. Pull it off and clean any dirt off the sight glass.
- Remove the 3 short metric bolts on the thick steel end plate protecting the vanes on the end farthest from the motor.
- Remove the thin stainless steel top plate that holds the three valves in place.
- There is also a metric bolt on the side near the motor, under the plastic "30." It needs to be loosened to get the pump away from the motor.
- Now it is possible to remove the three long metric bolts that attach the pump to the motor.
- As each part is removed, check whether the pump begins to turn freely. This will provide a clue as to which part is causing a problem.
- Rotate the pump by hand, if possible, until the vanes are maximally extended, then carefully pull them out with your fingers. They are made of a very soft plastic. DO NOT use a metal tool to grasp them or pry them out. The vanes are pushed apart by two springs, each of which has a small pin inside. The notched side of the vane goes toward the inside. Clean the springs, pin, and vanes in acetone and polish all six sides with 2000 grit emery paper and aluminum polish if they are scratched, taking care not to change the shape or curvature of the end of the vane.
- Polish the inside of the rectangular slot which the vanes fit inside of to remove any dirt or corrosion, using 1000-grit emery paper wrapped around a small piece of wood.
- Clean and polish the circular rim contacted by the vanes. Dirt often collects in the corners. If the surfaces are brown, they are corroded and they need to be polished with aluminum polish until they are reasonably shiny. Steel wool is not recommended, as bits of it will get stuck between the rotating surfaces. Ask me how I know this.
Replace the vanes in their slot. If pump is still hard to turn,
the problem might be in the second stage. If so, it will be necessary to
separate the two pump sections.
CAUTION: The next steps require taking the two halves of the pump apart. This requires removing the large center bolt behind the vanes. Separating the two halves must be done very carefully to avoid creating gouges in the ground metal surface, which will prevent the pump from being re-assembled properly. One person has reported that when he re-tightened the center bolt, even slightly, the pump would not turn. On our pump, we left the bolt just loosely tightened, and the pump has functioned perfectly for over a year and a half so far. It seems that tightening this bold is not essential. But no guarantees ...
- The pump is in two sections held together by 3 more metric bolts plus a large metric bolt behind the vanes. This bolt is glued in place and requires lots of torque to loosen. Remove the large bolt and pull out the vane housing. Once the vane housing is out, clean, degrease, and polish it to get rid of anything brown or black.
- Gently pound on the protruding surfaces of the pump with a hammer to separate the two halves, which are precisely fitted together. Do not pound on any of the smooth ground surfaces, or it will prevent them from forming a good seal later on. It's necessary to pound evenly on all sides. The two halves have very tight tolerances, and must be pulled apart perfectly straight, or they will get jammed. Don't try to pry the two sections apart—this will create score marks. If the two halves get jammed, push the two halves back together and start again.
- Check the second-stage vanes. They are not on springs and should slide back and forth freely. Pull out the large roller bearing assembly, clean any dirt off it, and verify that they spin freely. DO NOT strip the bearings in acetone. Some bearings have internal plastic parts and will be ruined by exposure to organic solvents.
- Check the metal parts for scoring and sand them if necessary, taking care not to widen the gaps between rotating parts.
Now for the hard part: getting the pump back together.
- After cleaning the insides, reassemble the pump and replace the rubber shock absorber (if it's broken) between the motor and pump with a new one from the rebuild kit. The two pump sections are precisely ground and don't need O-rings, but watch out for two small ones in the bolt holes. They will be brittle and deformed into a square cross-section if they're old. Replace them with new ones from the rebuild kit. Use a rubber mallet to gently pound the two sections together. They must be inserted perfectly straight or they will get jammed. If this happens, pull them apart and try again. If it is still difficult to fit the two pump sections together, check whether one of the rotating joints is scored. If so, use 600, 1000, and 2000 emery paper followed by aluminum polish to remove all scratch marks. Polishing must be done evenly around the entire surface.
- Add a light film of oil to the surface of each moving part before putting it back in.
- It can be tricky to keep large O-rings in their slot, especially when coated with oil. One trick is to hold the O-ring down with a piece of paper and pull the paper out while pressing the steel pieces together. Or if it is a steel plate, you can slide it horizontally to keep the O-ring in place.
- After replacing the large center bolt, re-tighten the bolts holding the two sections of the pump together. If these are not tight enough, the pump will jam up when you tighten the center bolt. This can be very difficult. It's important to make sure the two ground faces are spotlessly clean, there are no gouges, and all the O-rings have been replaced. Once the two sections are together, tap them a few times with a mallet to ensure a close fit. Even a millimeter of space will cause binding. Note: it seems not to be necessary for this bolt to be tight. I have run a pump for over four years with no problems after leaving this bolt only minimally tightened.
- Make sure the three valves are correctly oriented and that their springs are inside the center pin of the top plate before bolting it back on.
- Don't forget the little stainless steel Brillo pad on the left.
- Put the green O-ring in the slot of the oil reservoir and re-assemble. This can be a challenge. Be careful not to break it, because there is no extra one in the rebuild kit. Some pumps may use a cork spacer instead of an O-ring.
- If any oil gets on the floor, clean it up immediately with alcohol (don't use acetone on linoleum!).
- Rotate the pump several revolutions by hand. If it turns easily and smoothly, proceed to testing. Add oil to the lowest level, attach the mist filter, and start the pump for a few seconds. The oil level will drop as oil is flushed into the second compartment. If it seizes again, disassemble and polish some more.
- Turn the pump off and add oil to bring the level midway between the two marks. Re-attach the mist filter and vacuum hose.
- With two vacuum pumps attached to an LTQ, and no vacuum leaks, the LTQ's turbomolecular pump should be able to bring the vacuum, measured by the convectron gauge, to 1.00 torr. The ion gauge should go below 1e–5 torr within 30 min, and eventually go below 0.7e–5. If only one pump is working, the convectron will eventually come close to 1.00 torr, but the vacuum will never be high enough for the turbo pump to start.
- If there is a vacuum leak, squirt methanol at the suspected location and watch for the vacuum to decrease on the computer screen. Alternatively, direct a small amount of helium at the suspected leak while watching the mass spec for a peak at 4 amu. (Ionization isn't necessary to observe this.) These tricks only work if there is enough vacuum for the turbomolecular pump to start up.
- Pump heat fins should be about 50° C. The motor heat fins should be below 35° C. If the motor feels hot, it is being overloaded.
- Let the pump run a couple of days before running any valuable samples.
- Tell the boss you just saved the company six thousand bucks.
Update (nov 15, 2013) Our repaired pump has been running continuously with no problems for over a year and a half, including oil changes and several on/off cycles. In fact, it works better than before. We are tempted to rebuild the other pump.
Update (sep 30, 2016) The rebuilt has been running continuously for 4½ years now with no problems.