Rotary vane vacuum pump repair? / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Rotary vane vacuum pump repair?

1 2 next

Move Thread

LAN_403

klugesmith

Fri Dec 04 2009, 07:54PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Anyone here have experience with broken RV vacuum pumps?
Lots of chatter here about vacuum this week, but none of the existing threads seem to fit.

Last night I took my first close look at a 2-stage rotary vane pump that a friend scrounged years ago.
J/B Industries model DV-85, pre-2001 version. Found user manual and service manual online.

The oil looks clean & at right level, but pump seems to be seized or incredibly draggy inside.
When switched on, the motor behavior is something I have never seen before!
Violent torsional shaking and flashes of blue light as the centrifugal start-winding switch opens and closes about twice per second. My wife says it made lights inside the house flicker.

The motor separated from pump runs normally, and I can't turn the pump with my fingers on the splined connection. Have drained the oil in preparation for opening the case. Don't know if the "cartridge" with chamber, rotor, and vanes is a user-serviceable part. Anyone think there's hope of restoring this without a new cartridge? (list price $179 -- more than a cheap new RV pump)

MinorityCarrier

Fri Dec 04 2009, 09:24PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

For the rotary-vane pumps I am familiar with, the vanes are a consumable part, and need to be replaced after so many (thousands?) hours of operation.

The vanes are pressed against the chamber by spring-loaded pins. If the vanes are not repaced in time, surface wear thins the vane material (phenolic composite) over the pressure points of the pins and then the pins punch through the vane.

The pins will score the pump chamber wall, ruining it, they also catch on the chamber outlet and inlet ports doing further damage, and they make a lot of racket when this happens.

What does a RV use this style of pump for?

klugesmith

Fri Dec 04 2009, 09:53PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

MinorityCarrier wrote ...
What does a RV use this style of pump for?

Sorry for the confusion. I foolishly had written "RV" for Rotary Vane. The thread title is correct now.
The product is made for the refrigeration service trade.

Thanks for the hints. I'll know soon enough what's going on inside my defective pump.
Rich

klugesmith

Sun Dec 06 2009, 05:19PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I have come to know this pump rather intimately, and think it may yet be of service. Here's the case without motor, and opened up to expose the "cartridge". Somebody was here before me, and left a part missing -- sheet metal oil deflector between cartridge outlet and the case exhaust (through handle).

The regular service instructions say to clean everything visible at this stage -- it's even OK to wire-brush the cartridge -- but "don't touch those screws" except to replace the cartridge.
Well, what did I have to lose? The f***er was still seized! After loosening the corner screws, I went to remove the drive coupling from shaft on the motor side. To my surprise, the shaft could now be turned by hand

causing little sucking noises and oil oozes. When I retightened the screws, the shaft was again locked! Let's take this all the way off & figure out what's wrong.

The cartridge is a stack of hard steel plates with precisely ground flat surfaces and cavities. Shaft turns easily now, with rotor and vanes visible through inlet opening -- but the vanes don't project. Top plate comes off easily, and we see vanes apparently in good condition, without springs -- must depend on centrifugal force. Being impatient, I wipe off the oily flat surfaces with a paper towel, at the risk of leaving paper fibers in the works.

Nothing looks worn or scored, so I start putting it all back together (w/ plenty of oil).

Same problem as before -- shaft locks as soon as the screws are tightened a little. Is the cast-aluminum case tweaked, perhaps from being dropped, or is some joint in the cartridge stuck out of registration?
Re-install the shaft coupling and motor. Run motor in 1-second bursts -- fine when the screws are loose, but start/stall/start/stall as they are tightened.

The remedy that worked: tapping the back of cartridge with a steel hammer during brief motor runs & wrench turns. Now the oil cover is back on, sump is filled up, pump sounds OK to my untrained ear. Got no vacuum gauge at hand, nor flare fittings for either of the inlet ports, but maybe I have a useful pump.

IntraWinding

Wed Dec 09 2009, 01:16PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I fixed a 2 stage rotary vane vacuum pump that had really severe corrosion of the first stage steel cylinder that the vanes seal to.
Fortunately the corrosion was in the form of pits with undamaged metal in between. I thoroughly cleaned the metal and filled the pits with best quality high temperature solvent free epoxy, just proud of each pit. Then I carefully hand sanded the epoxy level with the steel cylinder. Seems to have done a really good job after a few tens of hours running in to correct for the different expansion of the epoxy compared to steel as the pump heats up. It might have been worth using the epoxy filled with steel powder, but then sanding it without changing the original cylinder would have been harder.

klugesmith

Fri Dec 18 2009, 10:32PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Just got a chance to measure the vacuum from my repaired pump, and it looks promising. A compound gauge from A/C service rig indicates a vacuum of slightly more than 30" Hg. So it won't be a waste to get set up for low torr and micron measurements.

Longer story: At work I found a manifold gauge set (like at

connected to a water chiller. Turns out it belongs to my buddy, the facilities manager, who invited me to bring my vacuum pump in for a test. By the way, the pump pictured in that link appears to be the same ancient model as the one whose guts are illustrated in this thread, but the outside looks even worse for wear.

[edit] Can any of you experts tell if one of the first-stage vanes is upside down? Perhaps re-assembled wrongly by the person who took this apart before me, and screwed something else up. In the last photo of my previous post, the vanes appear to have tips chamfered in opposite directions with respect to clockwise rotation. Maybe this is just a trick of lighting. I'm not eager to go back in for a closer look, but would hate to damage a good pump now that it's able to run again. Thanks!

IntraWinding

Sat Dec 19 2009, 03:52AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I can't claim to be an expert but I think you're suspicion that one of the vanes is the wrong way around is right. I wouldn't know which one to change for sure though. I would look for clues as to which way they spent most of their life. There may be scratch patterns that only match one way around for example, but the thing that strikes me is the orange (rust?) stain on the end of the lower vane in the photo, which looks as though it might come from the similarly stained end plate. Don't jump to conclusions though.

Depending on which of the vanes you reverse, they will either both tend to scrape oil from the cylinder walls or both tend to aqua plane (oilqua plane?) over the oil film. I suspect the later is the intended mode, but since it seems to be coping with both orientations at the moment, you could just try it both ways and see which pulls the better vacuum!

After I'd repaired my pump I 'ran it in' (with a fresh filling of oil and the inlet sealed) for progressively longer periods with long breaks to cool down. At first I could tell that as it got hot (after an hour or so) the motor was straining/slowing (which increases heating) but it didn't take many runs to loosen up. I successfully recycled my oil by filtering through a very fine filter paper. It removed both debris and any water droplets, after which the oils looked brand new.

Proud Mary

Sat Dec 19 2009, 10:43AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Something of this ilk could occur in the case of failed bearings, or eccentricity in the shaft.

Dennis Rogers

Sun Dec 20 2009, 11:28PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

Proud Mary wrote ...

Something of this ilk could occur in the case of failed bearings, or eccentricity in the shaft.

to elaborate I would be especially suspicious of a thrust bearing, sounds like axial clearance issues. Perhaps a thicker gasket or spacer could buy you some time if the bearing is not worth replacing.

klugesmith

Tue Dec 22 2009, 06:11PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I can't claim to be an expert but I think your suspicion that one of the vanes is the wrong way around is right.

Thanks for the support. But, oops, it looks like I fooled myself before anyone else. The apparent chamfers are with respect to the eccentric chamber wall (duh!). In a picture looking through inlet port of assembled cartridge, a vane tip looks pretty symmetric wrt the rotor.

Before realizing that, I posted a question about vane chamfer direction to JB's Technical Support department.
[edit] Prompt and helpful reply arrived while I was wasting time here. "Both sets of vanes, 2ea in the exhaust stage and 2ea in the intake stage, start out with the same surface radius on the vanes surface that rides on the statorâ€™s wall. The appearance of the ends is from wear. There wouldnâ€™t be any difference in the performance if someone switched the ends that ride on these walls. The vanes would wear in after a while. Iâ€™m sending an attachment that will help keep the pump in good working order. The main caution is not to take the cartridge apart other than lifting the intake plate off." My hat is off to J B Industries!

So no strong reason to disassemble this again. As for the original cause of seizure, I've seen no bearings other than steel shaft in one closely fitting steel hole. Maybe other plates in the stack have inserts of bearing metal. There should be no significant axial force. I bet the previous "fixer" put the cartridge stack together with plates skewed a little, creating a shear force in the journals.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob