Anatomy of a Vacuum Pump

[201Steve]

Can someone enlighten me as to the anatomy of a vacuum pump. Taking a look over my engine, I noticed that in each corner of the base plate of my vacuum pump, where it attaches to the access case, there are skeletal like notches "cut out." You can see the spinning shaft through the opening, when you pull the prop through. What is the purpose of this? Pics attached. 77 j / IO360 A1B6D

 

 

[Dialed In]

The pump is a dry pump, the shaft driving it through the adapter has engine oil to lubricate it. There is a seal on the drive shaft, the windows are there to allow oil to seep out so if that seal is compromised you should see oil dripping out and making a mess. 

[Guest]

Older style pump had open portions, newer style are fully sealed.  The open style makes it very easy to verify when the drive coupling shears.

[EricJ]

+1 that if the pump fails it gives an easy visual indication that the drive has sheared, verifying the failure mechanism (seized pump).

[N201MKTurbo]

It’s amazing how many people want to buy a new shear coupling when it shears…

FWIW, I have disassembled every failed pump I ever dealt with. Back in the 80s I bought a pump rebuild kit, I still have it. 

[carusoam]

Biggest failure of dry vac pumps…

Worn carbon blades….

They wear with every rotation, and slide down a channel, to refresh the seal with the outside case…

After millions of rotations… the blades are too short or something causes them to snap…. Probably lots of carbon dust inside the case after hundreds of wearing hours….

Carbon blades are brittle… and easy to snap…

once a blade snaps, it is easy to destroy the other blades in the ensuing melee….

 

Pumps are often exchanged at 500hrs when used in IMC…

Shaft failures are not very common around here… but the shaft coupling can fail if the pump jams up…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Guest]

I’ve seen the drive fail when the pump gets very stiff and hard to turn, but more common failure is worn blades causing completed failure of the rotor.

[N201MKTurbo]

The only time I’ve seen one get stiff is when it gets contaminated with oil. It turns the carbon dust into a mud like gunk. I have taken it apart and cleaned all the parts with brake parts cleaner and put it back together and had them  run for years afterwards. 
 

In most cases, the vanes get too short until one cocks sideways in its slot causing the rotor to jam and crack. So far it has always damaged the housing beyond repair when this happens. Not only do the end of the vanes ware away, but the sides of the vanes and the sides of the slots wear away, the increased clearance allows the vane to cock sideways in the slot leading to its sudden death. 
 

After 60 years of building dry pumps, they finally decided to put an oil seal on them. I haven’t seen one with an oil seal ever get contaminated. 

[Fly Boomer]

1 hour ago, M20Doc said:

I’ve seen the drive fail when the pump gets very stiff and hard to turn, but more common failure is worn blades causing completed failure of the rotor.

Given that I'm not on the clock, I wonder if there is any potential benefit to pulling the pump to at least check for rotational resistance, and possibly disassembling to look at the vanes?

[N201MKTurbo]

12 minutes ago, Fly Boomer said:

Given that I'm not on the clock, I wonder if there is any potential benefit to pulling the pump to at least check for rotational resistance, and possibly disassembling to look at the vanes?

No harm taking the pump off to check it, but I wouldn’t take it apart unless you have to. The problem is the gaskets in the pump. They are very fragile and probably can’t be reused more than once, if that. It is hard to get new ones. You have to salvage them from old pumps. 
 

It would be a waste of time to pull it to check if it is stiff unless it is oily. About the only thing that will get them oily is a bad seal in its mount, or a leak above it, but considering they are usually the top accessory, there is nothing above them to leak on them.

[A64Pilot]

11 hours ago, N201MKTurbo said:

It’s amazing how many people want to buy a new shear coupling when it shears…

FWIW, I have disassembled every failed pump I ever dealt with. Back in the 80s I bought a pump rebuild kit, I still have it. 

I rebuilt one once, it’s sort of a fools errand.

The reason is the pump body is aluminum that the carbon blades run on, carbon is abrasive, the aluminum is coated in something slick, maybe teflon? But eventually the blades wear through the coating then wear is rapid. I don’t think the coating will last through two sets of blades, I don’t think these things were designed to be repaired, I have a hard time calling blade replacement rebuilding.

After seeing just how cheap and fragile these things are, I bought an Air Wolf (Pesco) wet pump and installed an Airliners standby elec Att indicator we had at the plant.

The wet pump is heavy but it a very well built thing and outlasts an engine, 

The dry pumps are cheaply constructed,  if it wasn’t an aircraft part I would think it would cost $50.

If you fly IFR and have vacuum instruments I strongly recommend a Garmin / Pesco wet pump, they do emit an oil mist as they are a wet pump so ideally you have an air / oil separator, but it’s not required.

My personal belief is that both electric and vacuum instruments are the way to go, independent redundant systems. A battery backed up AHARS and an Ipad is actually pretty darned good for standby use

[PeeJee]

Yesterday my standard engine driven vacuum pump on my Ovation 2 went down. What would be my best option? New one of same make and model or check if repair is possible?

[Guest]

3 hours ago, PeeJee said:

Yesterday my standard engine driven vacuum pump on my Ovation 2 went down. What would be my best option? New one of same make and model or check if repair is possible?

Install a new pump, it’s a very simple job, four nuts, four lock washers, and a new gasket. An hours work on your airplane.

[Fly Boomer]

On 2/26/2023 at 3:32 AM, PeeJee said:

Yesterday my standard engine driven vacuum pump on my Ovation 2 went down. What would be my best option? New one of same make and model or check if repair is possible?

Welcome to MooneySpace!  Get a new pump.  These days, there is no rationale for a rebuilt one, or worse, trying to rebuild it yourself.

EDIT:  I need to start reading these topics all the way to the end before commenting so I don’t embarrass myself by re-posting what @M20Doc said.  Sorry.

[PeeJee]

Thank guys! New pump is ordered

[cliffy]

Get the special wrench from Rapco   Makes the job easy

[GeeBee]

On 12/27/2022 at 9:32 AM, A64Pilot said:

If you fly IFR and have vacuum instruments I strongly recommend a Garmin / Pesco wet pump, they do emit an oil mist as they are a wet pump so ideally you have an air / oil separator, but it’s not required.

I'm not a fan of vacuum pumps, but if you got to have one, a wet pump with a separator is the way to go. They last forever.

 

[T. Peterson]

On 2/26/2023 at 8:16 AM, Fly Boomer said:

Welcome to MooneySpace!  Get a new pump.  These days, there is no rationale for a rebuilt one, or worse, trying to rebuild it yourself.

EDIT:  I need to start reading these topics all the way to the end before commenting so I don’t embarrass myself by re-posting what @M20Doc said.  Sorry.

Two witnesses just adds credibility. I am grateful for the reposts. Since, generally speaking, no one restates exactly what was previously written, there are various nuances which can be helpful.