From sam's laser faq http://www.repairfaq.org/sam/lasercva.htm#cvadipd Disassembling and Inspecting a Pfeiffer Duo 1.5A Rotary Vane Vacuum Pump The following should apply in general to other model Pfeiffer rotary vane two stage vacuum pumps with obvious changes in the details. For single state ("Uno") pumps, only the stage against the pump bulkhead (the vertical piece that separates the pump from the motor) will be present but otherwise, the procedure is similar. The complete operation and service manual for the Uno/Duo 1.5A used to be available at the Pfeiffer Vacuum Web site. But they now only have manuals for pumps still in production. However, I can provide a PDF of the Uno/Duo 1.5 manual if needed. It is recommended that at least the pages with the exploded diagrams be printed out for reference as well as the disassembly procedure in there (though the one below is somewhat more detailed). The Uno/Duo 1.5A is considered an obsolete model but that doesn't make it any less useful as long as major repair parts aren't needed. However, this may be why the manual includes complete service info and exploded assembly diagrams - not present on the Pfeiffer models in current production. CAUTION: This procedure may not apply even in the generalities to Welch or other rotary vane pumps as many of these require special procedures for rotor centering. Pfeiffer pumps use precision steel dowels to align everything and are about as simple as is possible in terms of the number of individual components and the ease of servicing. The reason I decided to go inside was mainly an unexplained noise best described as a sputtering or stuttering even at high vacuum. The base pressure of 4 to 5 microns wasn't terrible but is higher than the spec in the manual - 0.66 micron (though I was told by a Pfeiffer repair technician that 2 or 3 microns is really what to expect if everything is perfect. And that is the base pressure specification on current model Pfeiffer Duo pumps). The real reason was the noise. If you like to skip to the end of the mystery novel, I eliminated some of the noise by plugging the noise damper leak nozzle totally, though I'm not sure the new type of noise is an actual improvement. I have since acquired a second Duo 1.5A and while this one had a somewhat similar noise audible from the exhaust port, it is lower intensity and virtually undetectable when covered. So, there is something different about the two pumps but I have not determined what it is. Here is the step-by-step disassembly and inspection procedure of everything readily accessible externally or within the oil case. Descriptions assume looking toward the pump from the pump-side of the entire assembly. (What I call the "bulkhead" is the vertical piece with the vacuum and exhaust connections separating the motor from the pump itself.) A set of metric hex wrenches, a medium size flat blade screwdriver, an adjustable wrench, needlenose pliers, and a few other common hand tools are required. Also have an ample supply of lint-free rags available to deal with the unavoidable oil that will try to go everywhere. (There's no way around losing a few percent of the oil so some extra will be needed when refilling even if reusing the old oil.) For actual disassembly of the inner pump assembly, provide a padded area where parts can't roll away. I used a shallow tray with typing paper as a cushion. Pump oil should be used liberally on all parts during reassembly. Gas ballast valve (if present) Unscrew the knurled valve handle. This may not actually be attached to the needle itself but if it isn't, the needle and spring should pop out when it is removed. (The "needle" is actually a wide metal piece with a tapering end.) If the needle and spring pops out, it is a simple matter to inspect the seat, needle, and spring. If the needle sticks inside, then use an adjustable wrench to unscrew the entire gas ballast valve assembly. On mine, I had to whack it on a wooden board to use inertia to free the stuck needle, then cleaned and polished the parts with steel wool. Reassemble and confirm free movement of the needle as the knurled knob is turned. Safety valve electrical testing (if present) If your Duo 1.5A has the "safety valve" feature, there will be a 4 pin connector on the lower right side of the bulkhead (facing the pump side). A dirty or defective safety valve is a common cause of poor vacuum performance or almost no vacuum at all. The safety valve consists of an electrically operated solenoid valve powered by a small generator on the rotating shaft of the pump which vents the pump when power is removed. At the same time, air entering the valve also closes a separate valve which seals the vacuum chamber maintaining it at some decent vacuum after shutdown. How good it is will depend on the size of the evacuated volume relative to the small amount of air that leaks in before the valve closes (assuming it is in working order). For an inlet capped with just a vacuum gauge, a few dozen Torr may be typical. There is no need to go behind the connector if the following tests have acceptable results: With the pump running, the voltage across pins 2 and 4 should be 4.5 to 5.5 VRMS AC. With the pump running, the voltage across pins 1 and 3 should be 3.5 to 4.5 VDC. If both voltage are much higher, the solenoid of the safety valve is open or there is a bad connection in the wiring to the solenoid. If both voltages are much lower, there may be a short circuit in the solenoid coil or a shorted diode or capacitor. If (1) is high but (2) is low or 0, there is a problem with the diodes or their wiring. CAUTION: It is possible to remove the connector by taking out the two screws, but take extreme care not to break the wires running up into the pump - there is no way to reattach them. You would have to drill a hole in the pump bulkhead and feed new wires through there, sealing them in place. Not a disaster but certainly annoying. For the following, the safety valve is assumed to be present. If your pump does not have this feature, just ignore those steps which deal with it. Refer to the on-line manual for other differences. Note: For testing, the safety valve can be forced into the "vacuum" position by using something to block the valve seat. This will confirm whether the vacuum performance is being affected by a defective safety valve. However, leaving it like this may result in pump oil being sucked into the vacuum chamber after shutdown and may also prevent the motor from restarting if the system is under vacuum. Safety valve vacuum chamber valve inspection and testing (if present) Remove any vacuum system components attached to the inlet port. Protect the inlet flange from tool damage and use a suitable wrench to unscrew it. Inspect the O-ring for damage or deterioration. The bottom of the flange assembly is the seat for the vacuum valve. Inspect it for damage. Grip and remove the moving part of the vacuum valve with a pair of tweezers or other similar tool that won't damage it. It should come off easily and move freely up and down when in place freely. Inspect the seating surface for damage. Replace the parts in reverse order. Initial pump disassembly Drain the oil by removing the drain plug. After most of the oil had drained, run the pump with the inlet open for about 15 seconds to clear oil from the pump chambers. Tilt the pump toward the drain hole and continue to drain the oil until no more comes out. Replace the drain plug. Using the proper metric hex wrench, slowly loosen the two large cap screws that hold the cover in place just enough to determine if the gasket will detach cleanly from one or both surfaces. On mine, it came free from both. However, if the pump has seen a long and hard life without service, a putty knife or something similar may be required to free it - hopefully without too much damage. Since an exact replacement may no longer be available, preserving the gasket is particularly important. If it should tear, you may have to carve a replacement out of suitable gasket material. Once the gasket is free, remove the screws completely and set the cover (and gasket if it comes off the pump bulkhead) aside face-down on a soft surface. Place a lint-free rag or stack of paper towels under the pump assembly to collect any oil that continues to run off the components. Safety valve disassembly and inspection (if present) Carefully pull off the two spade lugs which attach the wires to the solenoid valve. Avoid damaging the wires. (Though these can be resolder or replaced if necessary - just don't overheat the feed-through terminal since that might cause the wire on the other side to come loose and that cannot be reattached. You'd have to drill a hole in the bulkhead, feed a new wire through, then seal it.) Use an adjustable wrench to remove the bolt holding the metal tube running horizontally from the solenoid valve. Use the same wrench to unscrew and remove the solenoid valve. DO NOT attempt to remove the hex nut attached to the bulkhead, this is NOT removable and doing so will ruin your entire day. Wrap a turn or two of cellophane tape or something similar around the threads of the pipe (to protect the O-ring) of the solenoid valve and roll the O-ring off of it. This pipe can now be removed from the solenoid. Protect the threads with several layers of paper or something similar and carefully clamp the threaded portion in a vice. Use the adjustable wrench to unscrew the hex nut revealing the magnetic plunger assembly of the solenoid valve. Inspect the surface of the hard rubber "washer" at the end of the plunger that was nearest the pump bulkhead. It should be flat with perhaps a slight depression where it contacted the small valve seat. Inspect the ridge of the seat for corrosion or other damage. If there is a significant depression from the valve seat in the rubber or the valve seat is damaged, these parts or the entire assembly may need to be replaced. The washer in my pump had a depression slightly off-center with a slightly rough surface. There was some erratic behavior before disassembly. When I reassembled the pump, it would not pull any significant vacuum due to the washer not seating properly. I tried to repair the washer on mine. First, I carefully pried out the soft rubber retainer at the other end of the plunger freeing the spring and washer. Using a small file, some material was removed from the shoulder to allow the washer to poke a bit further through the plunger (perhaps 0.2 mm). Then, with the washer reinstalled in the plunger to maintain alignment, 600 grit sandpaper, crocus cloth, and then just a bed sheet (!!) were used in succession to smooth the end flat (flush with the plunger) and then polish it. Unfortunately, it would seem that this is not good enough. The pump will eventually pull down to its base pressure of a few microns but takes a very long time as the washer probably isn't seating quite perfectly despite being parallel to the end of the plunger and almost mirror-smooth. Once it gets there, venting the vacuum and repumping is very quick suggesting that the washer needs to be hot to be pliable enough for a good seal. Once it cools off, this long pump-down delay reappears. What I have called "hard rubber" may have originally been much softer and is now aged and too inflexible to work effectively. Next day I fabricated a replacement from a short piece of 1/8" O-ring stock. I drilled a 40 mil hole most of the way through it and used a metal washer held by an 0-80 machine screw to form the shoulder present on the original piece. Then, with this installed in the plunger, I used 600 grit sandpaper followed by rubbing on cloth to smooth it flush. Even though the surface isn't mirror polished, the O-ring material is quite soft and the valve seals reliably. Whether it is too soft and will degrade eventually is not known but for now, it appears to work as well as the original. Reassemble the solenoid valve in reverse order tightening everything just snugly enough to they won't move on their own. The copper tube should be positioned with its end just below the aluminum exhaust pipe. Install the two spade lugs. Make sure the wires are routed so they won't be squashed when the cover is replaced. Pump assembly removal Using the appropriate size metric hex wrench, remove the two large cap screws that hold the pump assembly in place. CAUTION: Don't let the pump assembly fall on the floor!!! Both stages of the pump can now be pulled free (the only thing holding them to the pump bulkhead and to each other once the screws are removed is the oil!). Set the cross coupling disk aside that you will find between the pump assembly and drive motor. Immediately set the pump assembly aside in the safe padded location you have provided. Noise damper leak valve inspection Just below the long exhaust tube at the top-right of the bulkhead, there is a small plug with either a slot for a screwdriver, or flats for a wrench or needlenose pliers. There may be a number stamped on the plug indicating the size of a hole in its center in microns or mils or maybe it's just a part ID. On mine it says either "15" (most likely) or possibly "75". Use the appropriate tool to unscrew this plug, taking care not to lose the rubber O-ring and metal centering ring. Inspect the hole with a bright light, magnifier, microscope - whatever works - to check that the hole is not obstructed. If it is blocked, use a solvent and compressed air to clear it. DO NOT use a metal wire which may change its size. This is the so called "noise damper" leak valve. It is supposed to allow a small amount of air to enter the oil circuit - the passage in the bulkhead behind the plug leads to a tiny hole near the center of the second stage pump assembly. Reinstall the plug snugly but not overly tight. Note that I eliminated some of the noise from my Duo 1.5 by actually replacing the leak nozzle with a solid plug. At high vacuum, it still makes noise but I think it is less annoying than previously. I don't know if the hole was too large (it looked unmodified and undamaged) or if this "repair" is actually masking some other problem. I really don't even know for sure that the noise I was complaining about is abnormal for this pump (though my second Duo 1.5A does make much less noise). I also don't know whether there will be any long term wear or reliability issues with no airflow through the noise damper leak valve. Aside from what I don't know, everything else is obvious. :) Since I didn't notice any difference in base pressure or pump-down performance, I will probably reinstall the original leak nozzle next time I have an excuse to go inside. Pump assembly disassembly Carefully detach the two stages if this hasn't already happened. The only thing holding them together is the oil surface tension. Inspect the cross coupling disk which is between them and then set it aside. The unit closest to the pump is actually the second stage. There is a hole clear through it which feeds to the first stage. Set the second stage aside for now. First Stage Using the appropriate metric hex wrench, remove the three screws holding the first stage together. With a block of wood and a small mallet or other suitable tool, carefully separate the front or back piece from the pump chamber (doesn't really matter which). Take care that the rotor with the vanes doesn't come out with parts flying everywhere. While holding onto the vanes, carefully extract the rotor and vanes. DO NOT allow the vanes to come off unless you mark them with a Magic Marker or something similar to indicate orientation. Inspect the vanes and springs for damage. Inspect the inside surfaces of the end-plates and pump chamber for scoring and other damage. Serious scoring would indicate the need for replacement. A coating of varnish might be removed with a strong solvent. Making sure the springs are in their proper holes, press the vanes together and reinstall the rotor. Make sure it is in the proper direction! There is a very small hole for an oil channel (1 mm or less) in the end-plate that faces the second stage. Using a non-metallic probe like a piece of nylon fishing line, make sure it is not obstructed. Replace the end-plate that was removed and use the wood block to carefully tap it back in place. Replace the three screws and tighten securely in a rotating pattern in several stages. Confirm that the rotor turns easily without obvious sticking or hard spots. Second stage Using the appropriate metric hex wrench, remove the screws holding the "valve crown" on top. Inspect the valve plunger and spring for damage. Replace if no damage is found. Using a medium size flat blade screwdriver, remove the three screws holding the second stage together. With a block of wood and a small mallet or other suitable tool, carefully separate the front or back place from the pump chamber (doesn't really matter which). Take care that the rotor with the vanes doesn't come out with parts flying everywhere. While holding onto the vanes, carefully extract the rotor and vanes. DO NOT allow the vanes to come off unless you mark them with a Magic Marker or something similar to indicate orientation. Inspect the vanes and springs for damage. Inspect the inside surfaces of the end-plates and pump chamber for scoring and other damage. Serious scoring would indicate the need for replacement. A coating of varnish might be removed with a strong solvent. Making sure the springs are in their proper holes, press the vanes together and reinstall the rotor. Make sure it is in the proper direction! There is a very small hole for an oil channel (1 mm or less) in the end-plate that faces the pump bulkhead. Using a non-metallic probe like a piece of nylon fishing line, make sure it is not obstructed. Replace the end-plate that was removed and use the wood block to carefully tap it back in place. Replace the three screws and tighten securely in a rotating pattern in several stages. Confirm that the rotor turns easily without obvious sticking or hard spots. Pump assembly reassembly Install the cross coupling disk onto either stage, rotate the other stage so it lines up, and put the two together. They should fit easily flush with the bulkhead without force, else check that they are lined up perfectly. CAUTION: Attempting to tighten the screws with improper alignment may cause damage. Install the cross coupling disk on the second stage and install the entire pump assembly on the pump bulkhead. Again, this should fit easily without force. Finger tighten the two cap screws, then tighten securely using the proper metric hex wrench in increments alternating between the two screws. Power up the motor for a couple of seconds just to make sure nothing is binding. Place the cover with gasket against the pump bulkhead and finger tighten the large cap screws. Check the position of the gasket and then use the proper metric hex wrench to tighten the cover snugly alternating between the two screws. Err on the side of looseness for now, tightening further only if there is oil leakage. With luck, the gasket will last for 5 to 10 disassemblies but each time may require successively greater tightening of the screws. Replace or add new oil until at the middle of the sight glass. With the pump running, add oil if needed to maintain the oil level around the middle of the sight glass. Periodically check for oil leakage around the gasket and tighten as necessary. I'd like to find a supplier who will sell me just the Duo 1.5A case gasket as mine is probably on its last life, just barely sealing with the screws tightened down as tight as I dare tighten them down. Else I'll may have to make one myself out of cardboard or thin rubber stock. :) It may take longer than usual to achieve the base pressure after disassembly due to moisture and other contamination of the oil unless everything has been cleaned and only new oil is used. Opening the gas ballast valve slightly during a portion of the initial pump-down may help. Subsequent pump-downs should proceed at the expected rate unless there are other problems.