Rotary vane vacuum pumps are dependable and durable. After many years of service, many pumps are often neglected and unused. We recently inherited a few pumps, and in this webpage we document a full rebuild using a 1970s Welch 1402 as a model pump.

Service includes replacement of vanes, exhaust valves and baffles, intake and oil tank gaskets, and oil. The internal components and overall design of the Welch 1402 has hardly changed since the 1970s. Late models acquired changes to the shaft, where the collar is replaced for a pair of woodruff keys, and fusing of the center plates. If you are rebuilding a late model pump, these minor changes will be apparent during the rebuild process. This guide is an excellent reference for rebuilding both early and late model pumps, or pumps of rotary vane design. With enough preparation and the appropriate tools, a rebuild of a pump can be completed in less than 8 hours.

The rebuild kit (PN:P102024) was purchased from pchemlabs.com, although our chemistry stock room has some authentic Welch parts. A full rebuild and repair kit includes a V-belt, exhaust valves and springs, phenolic vanes, shaft seal, and gaskets. If you are massaging an old pump, you might also have to replace the motor if the bearings have gone bad or if it is spewing the magic smoke. The motor brackets should be left in place to avoid having to make major adjustments to the pulley ratio and V-belt tension.

CAUTION: The mating surfaces and internals of the pump are made of soft steel. Do not scratch or marr any surfaces, as this will ruin the performance of the pump.

Corrections, comments, and suggestions can be sent to me, Ignacio Lopez: ilopezpe AT ucsd DOT edu

Tools and Materials

  • Standard Wrenches
  • Standard Sockets
  • Standard Allen Keys
  • Gear Puller
  • Rubber Mallet
  • Putty Knife
  • Copper Brush
  • #0000 Steel Wool
  • Petroleum Ether
  • Vacuum Pump Oil
  • Vacuum Pump Oil w/ detergent (optional)
  • Replacement Oil Drain Valve (optional)

Literature

  1. Owner's Manual (1975)
pump image

Step 1

Large end plate disassembly

  • Remove the V-belt and major pulley from the pump (not shown, reference reassembly).
  • Remove pump from the platform (not shown).
  • Remove the four hex head screws securing the intake chamber with an allen key.
  • Remove the chamber by tapping on it with a rubber mallet, if stuck.

Go to cleaning

Go to reassembly

pump image

Step 2

Large end plate disassembly

  • Remove the intake gasket.
  • Remove the intake filter.
pump image

Step 3

Large end plate disassembly

Remove the shaft seal

pump image

Step 4

Large end plate disassembly

Remove gas ballast from the oil case.

pump image

Step 4 (cont.)

Large end plate disassembly

  • Remove 10 perimeter hex nuts securing the large end plate to the oil case with a wrench.
  • Lift and seperate front end plate from oil case.
pump image

Step 4 (cont.)

Large end plate disassembly

Side view of large end plate and exhaust stage assembly

pump image

Step 5

Large end plate disassembly

Remove 4 remaining hex nuts securing exhaust stages to the large end plate using a socket wrench.

pump image

Step 5 (cont.)

Large end plate disassembly

We used a bucket with a hole in the bottom to hold the shaft and front end plate in place. The exhaust stages were then lifted and seperated from the front end plate. You should probably have an assistant for this part. We chose to do it this way to avoid damaging the pressure plate on the small end plate.

pump image

Step 5 (cont.)

Large end plate disassembly

The backside of the large end plate. The ports for intake, exhaust, and shaft are now visible.

pump image

Step 6

Exhaust stage disassembly

Remove the nut securing the exhaust baffle with a wrench.

pump image

Step 7

Exhaust stage disassembly

Remove the nut securing the baffle post to the stage.

pump image

Step 8

Exhuast stage disassembly

  • Remove the screws securing the exhaust valve cover.
  • Remove exhaust valve cover.
pump image

Step 9

Exhaust stage disassembly

  • Remove nut securing the valve block.
  • Remove valve block and valves.
pump image

Step 10 (older models)

Exhaust stage dissassembly

An Aside. The exhaust valves for the first stage are mounted to a plate on early models (~<1975). There are two metal gaskets between this plate and the first stage (shown in Step 43). Rebuild kits for late model pumps do not include these gaskets, because this plate is integrated into the stage. At this point it lifts off of our model, but I'll leave it in place here.

pump image

Step 11

Exhaust stage disassembly

  • Remove the two nuts securing the shields for the 2nd stage exhaust valves.
  • Note: the upper exhaust valve for our second stage was broken! There it is off to the right.
pump image

Step 12

Exhaust stage disassembly

Remove steel screw and valves.

pump image

Step 12 (cont.)

Exhaust stage Disassembly

First and second stage valves have been removed at this point.

pump image

Step 13

Exhaust stage disassembly

  • Remove the 5/16" Hex bolt that is securing the pressure relief valve cover to the small end plate.
  • Remove screws securing the valve cover.
pump image

Step 14

Exhaust stage disassembly

  • Remove the hex bolt located inside the valve cover, and remove valve and cover.
pump image

Step 15

Exhaust stage disassembly

  • Remove the steel ball, and 4 hex bolts.
pump image

Step 16

Exhaust stage disassembly

  • Remove the end cap.
pump image

Step 17

Exhaust stage disassembly

  • Remove the small end plate
pump image

Step 18

Exhaust stage disassembly

We had to skip removing the end plate for a minute, because it would not come off easily and we were very frustrated. We flipped the stages around and removed the thurst washer.

pump image We revisited the endplate. Argh..
pump image ARGH..
pump image With the end plate removed, we can see the second stage rotor.
pump image

Step 19

Exhaust stage disassembly

Remove Exhaust Ring

pump image

Step 20

Exhaust stage disassembly

Remove small vanes, vane springs, and vane spring holder.

pump image

Step 21

Exhaust stage disassembly

Remove woodruff keys and exhaust rotor. Do not destroy or discard the woodruff keys, as we discovered that the new keys didn't fit well into older model shafts

pump image

Step 22

Exhaust stage disassembly

Invert the exhaust body to reveal the intake rotor (first stage).

pump image

Step 23

Exhaust stage disassembly

  • Remove intake rotor
  • Remove large vanes, vane springs, and vane spring holder,
  • Remove shaft
  • pump image

    Step 23 (cont.)

    The first stage and shaft, in all their glory.

    pump image

    Step 25

    Exhaust stage disassembly

    • Remove hex head screws
    • Remove center plates
    pump image

    Step 25 (cont.)

    First center plate
    pump image

    Step 25 (cont.)

    Second center plate
    pump image

    Step 26

    Cleaning

    Dunk the intake ring into pet ether.

    Go to disassembly

    Go to reassembly

    pump image

    Cleaning

    Use a copper brush to remove debris and gunk.

    pump image Give parts a nice petrol bath to remove oil.
    pump image Immediately rub parts with clean pump oil to prevent oxidation.
    pump image Like new.
    pump image Use steel wool to clean all gasket mating surfaces, such as in this example of the intake filter cover.
    pump image

    .

    pump image This one had the texture of a thin tortilla chip.
    pump image

    Use a putty knife to remove any left over gasket, but avoid gouging or scratching the mating surface with the blade edges.

    pump image

    Our rebuild kit did not come with window gaskets for our model pump, so we avoided removing them from the case.

    pump image Use steel wool to clean the metal frame of the window, and a paper towl to wipe down the glass.
    pump image A magnificent scene.
    pump image

    Another satisfying picture of cleaned parts.

    pump image

    Step 27

    Reassembly

    • Place the intake ring on the table, so that the intake side is face down.
    • Place the first center ring onto the intake ring. The large relief should face towards you.

    Go to disassembly

    Go to cleaning

    pump image

    Step 27

    Reassembly

    Place the second center ring on top of the first, with the small relief facing outward and the large relief facing inward.

    pump image

    Step 27 (cont.)

    Reassembly

    Note: the center piece in late model pumps is machined into a single part, as opposed to the two pieces found in our pump.

    pump image

    Step 27 (cont.)

    Reassembly

    Note: the center piece in late model pumps is machined into a single part, as opposed to the two pieces found in our pump.

    pump image

    Step 28

    Reassembly

    Put then two hex head bolts into the center rings to join them to the intake ring, but do not tighten them down. A turn or two will suffice.

    pump image

    Step 28

    Reassembly

    Flip the assembly in preparation for adding the first stage.

    pump image

    Step 28

    Reassembly

    • Assemble shaft
    • Assemble vane spring holders, vane springs, and vanes
    • Note: Replacement vanes are phenolic vanes instead of metal. These replacement vanes form superior seals with the ringed exhaust chambers.

    pump image

    Step 28 (cont.)

    Reassembly

    Vane spring post goes in first.

    pump image

    Step 28 (cont.)

    Reassembly

    Vane springs go onto posts

    pump image

    Step 28 (cont.)

    Reassembly

    The stage is ready for the vanes

    pump image

    Step 28 (cont.)

    Reassembly

    In go the vanes.

    pump image

    Step 28 (cont.)

    Reassembly

    Make sure the vanes are springy.

    pump image

    Step 29

    Reassembly

    Drop the stage in with the shaft collar facing out. We used an inverted bucket with a hole in the bottom to hold the other end of the shaft in place.

    pump image

    Step 30

    Reassembly

    Tighten the two hex bolts down.

    pump image

    Step 31

    Reassembly

    Add woodruff keys to the shaft. You may have to angle them to better accept the second exhaust rotor.

    pump image

    Step 32

    Reassembly

    Add exhaust rotor

    pump image

    Step 33

    Reassembly

    Add vane spring post, vane springs, and vanes to the exhaust rotor.

    pump image

    Step 33 (cont.)

    Reassembly

    pump image

    Step 34

    Reassembly

    Add exhaust ring

    pump image

    Step 35

    Reassembly

    Turn shaft to ensure that rotors can freely move and are not bound.

    pump image

    Step 36

    Reassembly

    Add small end plate.

    pump image The stages are now assembled.
    pump image

    Step 37

    Reassembly

    Secure the pressure release tube and valve in place by partially screwing in a hex bolt on to the end plate.

    pump image

    Step 38

    Reassembly

    Place the rest of the hex bolts in, but do not tighten them.

    pump image

    Step 39

    Reassembly

    Do not forget to insert the steel ball and place the valve over it.

    pump image

    Step 40

    Reassembly

    Torque bolts evenly, except you will remove this bolt once all bolts are secured.This bolt will be used to secure the pressure relief cover.

    pump image

    Step 41

    Reassembly

    Secure bolt and secrews into the pressure relief cover.

    pump image

    Step 42

    Reassembly

    Secure the end cap to the end plate with screws.

    pump image

    Step 43

    Reassembly

    For early models (pre-1975), there are two gaskets that sit below the mounting plate for the intake valves. We cleaned the original parts, because the rebuild kit does not come with these gaskets.

    pump image

    Step 44

    Reassembly

    Add the mounting plate.

    pump image

    Step 45

    Reassembly

    • Add valve spacer.
    • Add hex nut used to secure baffle plate.
    pump image

    Step 46

    Reassembly

    Assemble valve spring, valve block, and valves onto valve spacer.

    pump image

    Step 46 (cont.)

    Reassembly

    First exhaust valve assembly

    pump image

    Step 47

    Reassembly

    Secure valve mounting plate if you have one.

    pump image

    Step 48

    Reassembly

    Secure valve assembly with a screw post

    pump image

    Step 49

    Reassembly

    Secure valve plates

    pump image

    Step 50

    Reassembly

    Secure valve mounting plate and adjust second hex nut the screw post used to set the height of the exhaust valve cover.

    pump image

    Step 51

    Reassembly

    Secure baffle in place with a nut on to the screw post.

    pump image

    Step 52

    Reassembly

    Prepare the lower and upper exhaust valves for the second stage.

    pump image

    Step 53

    Reassembly

    Secure valves in place with the screw post and hex nut.

    pump image

    Step 54

    Reassembly

    Add a spacer for the second screw post.

    pump image

    Step 54 (cont.)

    Reassembly

    Add a second screw post

    pump image

    Step 55

    Reassembly

    Secure the second baffle in place at both posts with appropriate nuts.

    pump image

    Step 56

    Reassembly

    Thrust washer. Do not forget this part!!

    pump image

    Step 56 (cont.)

    Reassembly

    Did you remember the thrust washer?

    pump image

    Step 57

    Reassembly

    Secure the large end plate and filter bracket to the exhaust stages with 4 bolts.

    pump image

    Step 58

    Reassembly

    Pack the shaft seal with silicone grease

    pump image

    Step 59

    Reassembly

    Grease the shaft gasket.

    pump image

    Step 60

    Reassembly

    Use the alignment tool to secure the shaft seal in place.

    pump image

    Step 60 (cont.)

    Reassembly

    Shaft seal in place.

    pump image

    Step 60 (cont.)

    Reassembly

    Remove the alignment tool.

    pump image

    Step 61

    Reassembly

    Replace the intake filter.

    pump image

    Step 62

    Reassembly

    Replace the intake cover gasket.

    pump image

    Step 63

    Reassembly

    Replace the intake cover, and secure it with four hex head screws. Remember to apply torque evenly and inspect the gasket.

    pump image

    Step 64

    Reassembly

    Replacing the gas ballast seal. A picture of the oil case with the gas ballast seal removed.

    pump image

    Step 64 (cont.)

    Reassembly

    Pack the new gas ballast seal with silicone grease. The gasket off to the side is original, and we did not have a replacement. We made sure not to tear it when we removed it from the oil case.

    pump image

    Step 65

    Reassembly

    Fasten the seal cover with only a few turns, until we are able to insert the gas ballest.

    pump image

    Step 66

    Reassembly

    We also replaced the oil drain valve. You have to order one in advance, as it is not a standard part in rebuild kits.

    pump image

    Step 67

    Reassembly

    Align the gasket with the oil case, in preparation for joining the large end plate.

    pump image

    Step 68

    Reassembly

    The best method to join the large end plate to the oil case is to put the bolts in place...

    pump image

    Step 68 (cont.)

    Reassembly

    and tilt the unit forward. Mount the gasket onto the bolts.

    pump image

    Step 68 (cont.)

    Reassembly

    Put the bolts into the oil case, but do not fasten them in place.

    pump image

    Step 69

    Reassembly

    Tilt the unit back and secure the bolts in place. Use original or copper washers to ensure a tight fit.

    pump image

    Step 70

    Reassembly

    Insert the gas ballest and secure the seal in place.

    pump image

    Step 71

    Reassembly

    • Secure the pump to the base platform
    • Secure belt shield
    • Replace woodruff keys on the shaft. We found that the original keys fit best on our shaft
    pump image

    Step 72

    Reassembly

    Replace pully.

    pump image

    Step 73

    Reassembly

    Secure pully in place with set screw.

    pump image

    Step 74

    Reassembly

    V-belt replacement. The picture shows a modest deflection in the belt. This suggests that the belt is over tension. The V-belt tension should be just enough, so that the belt doesn't slip during rotation. We adjusted the motor pulley ratio, and thus the belt tension, using a percussive method. We loosened the AC motor bolts, and used a rubber mallet to make minor displacements to the motor position. You should avoid making major adjustments to the motor position unless you have force gauge to properly set the V-belt tension.

    pump image

    Step 75

    Reassembly

    OIL FILL. We filled the oil case through the intake, atleast twice, manually cranking the oil through the first two stages. This is crucial for getting oil into every void. The rest of the oil capacity was brought to regular level by filling the oil case through the exhaust.

    pump image

    FIN

    After a couple of minutes, we were able to obtain a 5 micron (Hg) or 5 mtorr vacuum as measured using a McLeod gauge. Awesome!

    I'd like to thank a certain hand model who wishes to be unnamed, and the boss.