Introduction: Repair and Rebuild a Deep Vacuum Pump, the JB Industries DV85.

About: general bloke type of tinkering

This deep vacuum pump was made in 1988 and most of the parts are obsolete.

I'm doing a complete tear down of the pump body, including the valve cartridge and I'll show you how to re align the 5 steel plates that make up the unit in step 2.

The previous owner had seized the pump and it had destroyed the flexible coupling and caused considerable damage between the vane impeller and front cartridge cover plate.

I cover the process to make a new flexible coupler, called a Guardian 20, in step 3.

The reason for the seize was due to it being run on an ammonia system, there's a warning on the manufacturers website regarding ammonia and sodium bromide(salt), not only do they rinse the oil off the impeller walls, they also contaminate the oil causing it to go green and lumpy. To compound the neglect, the oil level was at the bottom of the sight glass, no longer cooling or sealing the valve cartridge.

Judging from the blued SS valve in step 2, the unit reached a temp of approx 300°C in a device that runs normally at 70°C.


These are the tools mentioned by the manufacturer.

  • Hammer

  • Medium Screwdriver

  • 5/32" and/or 1/8" and 3/16" Allen Wrench

  • 11/16" Socket Head 3/8" or 7/16" Wrench or socket

  • Thread sealant

  • Vaseline or grease

  • I used vac pump oil to lubricate all the moving parts before re assembly.

  • Carb cleaner for all the dirt and grime.
  • Wet and dry sandpaper to lap the damaged surfaces, 600 800 1000 1500.

Step 1: The Pump Body.

First drain the oil, then remove the front cover housing with the oil sight glass. Then remove the coupler from the pump shaft, you can leave the one on the motor shaft on. Next all the bolts of the square valve cartridge can be removed if you're going to rebuild the unit.

If you're just changing seals and orings then leave the 2 center bolts in and just remove the 4 corner bolts, that way you don't disturb the alignment. I've labelled the bolts in the 2nd photo of step 2.

Its important to center the impeller shaft with the housing body when you remount the valve cartridge, before you tighten the cartridge bolts. I hang the body upside down so that the shaft is facing up and then lightly tap the cartridge around with a small hammer to get the shaft centered while eyeballing the shaft from above.

My smallest rod was 1mm drill bit which didnt fit anywhere around the shaft and seal hole.

Finally, I removed all the fittings, cleaned the filter of hair and debris and blew out all the passages using a compressor.

Step 2: The Valve Cartridge.

This is officially Part # D10087 DV-85 and is obsolete, meaning you can no longer replace it and rebuild is the only option.

I pulled the plates apart and measured all the tolerances, it seemed that the 0.2mm gap between the round disks(vane impeller) meant that there was a running clearance of 0.1mm. This gave me a limit as to how far down I could lap the damaged surfaces on wet and dry paper.

After lapping and re assembly I found that the shaft spun freely but wouldn't when the plate bolts were tightened.

It turns out that the end plate (No 5) had a warped surface with a high center and my lapping was only rounding it over more.

I solved the issue by flipping plate 5 over and using that as the new sealing surface, naturally after more lapping on the wet & dry paper.

For aligning plates 2,3,4,5 you'll need a 3mm rod to slide into the gas bypass hole until it seats into a dimple in plate 4.

A 7.7mm bolt worked for one corner mounting hole, hold the assembly shaft up and tighten the 2 align lock bolts.

Plate 1 can be lined up with the corner bolts when re assembling the cartridge, give the unit a little shake when centering the shaft so that all corner bolts wiggle into a centered position other wise there's a chance of pulling the cartridge over to one side when tightening the bolts down.

Once all together see if the shaft turns freely with nothing binding, there's a slight metal rubbing noise, but thats from the vanes sliding on the housing walls.

Step 3: Rebuilding a Flexible Coupler.

This particular flex coupler is called the Guardian 20 and I used PUR80 urethane poured onto the 2 zinc halves in a mold.

My technique involved using a syringe filled with urethane and injecting it into the top fill port, this created lots of small bubbles even after pouring the mix into the top of the syringe and inserting the plunger afterwards.

This was where a vac chamber came in handy to remove all the bubbles before the part started setting, takes about 90 seconds before gel, so 30sec mix 30 pour and inject and 30 for a quick vac, then vac release to make any left over bubbles shrink again.

I initially had issues with bubbles till I drilled a 2mm riser hole above each tooth valley. The 3rd try almost worked but the urethane started setting while vac was applied which produced 2 large bubbles.

Number 4 released easily, all surfaces had epoxy release agent applied and it looked good.

I'm presently using the 3rd sleeve with the large air bubble and it works well with no vibration. If it fails then I have a decent replacement.

In the meantime, no4 is being used to create a silicone mold to make more urethane sleeves.

The 2 zinc coupler halves are butted up against each other in the mold and then pulled out by 3mm on each side when mounted on the motor. This allows the part to flex properly during running.

Step 4: Some Mods and Replaced Parts.

I replaced the 3 main maintenance seals in the 1st pic, but not the housing cover seal which wasn't available. It was still working with no oil leaks.

I acquired an after market knob with a round hole that I needed to file square to fit the vac open/close valve.

All 6 low grade black oxide bolts on the valve cartridge were upgraded to stainless steel.

The oil drain valve in the front cover was extended with a custom brass tube made for me by a hydraulics company.

I changed the brass vac intake fitting which was loose and leaked. I flared the end of a copper tube and fitted it instead, I want to use reinforced auto fuel hose so that plan will work well.

I installed a splash shield, 0.9mm SS plate 100mm x 100mm and folded a 10mm lip in the vise to mount it to the pre existing unused bolt hole. There is no visible oil mist out the handle exhaust port while running, but you can smell the vac oil if you put your nose there.

I removed the oil sight glass and milled 2 extra slots, next I soaked it in a caustic soda mix to remove the oil film, then soaked it in acetic acid to clean some of the tarnish. The unit was installed using red high temp auto gasket sealer and has remained in place, even after I forgot the rubber exhaust plug, when that popped out under pressure.

The only other mod I considered is cutting some heat sink fins and thermal gluing it onto the case sides, however I don't use the pump for extended periods so it would probably be a bit overkill.

Step 5: Very Necessary Maintenance.

Another neglected area was these 2 holes for oiling the motor shaft. Its recommended for 10 drops but mine needed about 30 in each hole before the felts looked nice and oil wet.( I opened the motor to check the bearings)

The oil level must be at the proper level in the sight glass for it to cover the cartridge housing, this not only cools down the unit but also seals it against air leaks.

After rebuilding my pump body, I drained the oil twice and ran it through my Harvey filter to remove any metal particles from the lapping process. I also performed 2 power flushes, where you slowly pour a cup of oil into the vac intake while the pump is running, for the same reason.

Step 6: A Quick Test and a Story.

A quick check using the vac gauge from my chamber vac build and the DV85 pegged the gauge in about 3 mins. This tells me that the repair went well, I don't have HVAC gauges so I cant tell if the pump still pulls down to the 50 micron original spec, but its adequate for my needs and I'm well pleased with the end result.

I've wanted one of these devices since 2004 when I was into vacuum bagging model aircraft wings, but the best I could afford was a rotary piston compressor from the scrapyard. It worked well enough, but needed lots of oil top ups due the fine oil mist out of the exhaust. They're not meant for my use scenario and are designed for closed aircon systems so I guess that was to be expected.