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How to stop oil going into a motor from the attached pump? Answered

I am fighting a little war with some oil pumps.
Attached to a 1/2HP motor the construction is quite simple.
To prevent leaking there is a spring loaded oil seal between pump and motor.
But this seal is never 100% if you deal with 180°C hot vegetable oil....
At these temps the stuff is literally thinner than water and sooner or later finds a way out.

Main problem I am facing is the drying of the vegetable oil.
Over time it turns intoa really hard resin.
But before that it manages to creep all the way into the motor bearing in the front part of the motor.
It drives out the grease and slowly replaces it with drying resin util the whole thing seizes.
Rebuilding is a true pain in the back as it is a 180V DC motor with build in rectifier and regulator to run on 220V AC mains.

Things I tried so far:
Adding a good amount of high temperature grease bewtween oil seal and motor housing - only a marginal longer service time was achieved.
Making a custom sleeve to go over the motor shaft that is glued onto it - worked well, or so I thought until I realised the silicone oil content in the oil slowly destroys all gues I tried so far.
Adding a shim disk right on top of the bearing - this worked best so far and almost doubled the time until the motor failed. Downside is that it takes me over 4 hours to fully rebuild a motor just to get said dik in and I have no replacements anymore.

It was suggested to me to set the back of the motor slightly higher than the front so the oil would not go anywhere near the bearing.
This I tried to implement about 8 weeks ago and as the motor got noisy last week I took it all apart for a service again.
Despite the motor mounted at an angle of about 5° the oil still creeped past the shim disk and into the bearing.
So I did some simple tests with the hot oil and indeed it forms a slowly creeping film tha travels upwards on a shaft.
I guess the rotation helps here as well to spread the drops around.
And yes, last time I used "fully sealed" bearing with an build in cover and still it fails :(

I would love to try something flexible but long lasting to seal the bearing against the rest.
Something in the region of a rubbery stuff that can be applied like a sealant.
But hard enough to survive a few weeks of shaft rotations.
Are there any really sealed bearings available?
Bearings that, for example would be fine working submerged in liquid without any liquid being able to enter?
It is clearly a desing fault of the machine to make money through spare parts but that's not the point here.
I can not replace the pump as it is an intergral part of other things attached.
And not really that easy to find a pump capable of dealing with hot oil anyway.
Is there any grease available that does not turn into a liquid at these high temps and would it be possible to get ito into a bearing?

Running out of ideas here guys, so feel free to throw in whatever comes to mind even if it seems odd!
I just need a way to keep highly viscous, boiling hot oil from entering a bearing ;)


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Jack A Lopez
Jack A Lopez

1 year ago

There is a design I have seen for some kinds of motor-driven pumps and mixers.

The essential feature of this design is a long shaft, connecting the motor to the pump, so that the motor can be placed a far distance above the pump.

The pump kind of has to be down in the muck it is pumping, but the motor would prefer to be in a place that is high and dry.

The only thing left, is for me to attach some example pictures.

I have seen this design in water pumps found in swamp coolers, although it always seemed to me the shaft should be even longer. The pictured version of this pump with the crazy long shaft, was produced via photo-editing.

Immersion blenders, which are mixers rather than pumps, are built using the same philosophy: put the motor in a place high and dry, and keep it out of the muck.


Reply 1 year ago

I see we are on the same page design wise ;)
Sadly I can not relocate the motor even a longer drive shaft could only be about 5cm longer and that wouldn't help much as the pump is mounted directly onto the 1/2HP motor housing.
Imagine a standard sized 1/2HP motor with a fist sized pump on the shaft - plus the mounting flanges.
It is clearly a desing flaw of the machine deliberately aimed on making revenue through spare parts :(

I contacted the makers of the pump and was informed they are good for about 2 years of service before they need a new seal on the housing and new teflon runners in the pump wheel.
The motor manufacturer stated the motor is neither designed to work in an envrioment getting sometimes to over 120°C as the operating limits is just over 80°C.
And the desing of the motor is for "dry" use only as no part of the motor is in any way protected against liquids getting in.

Will check with my local bearing shop again next week to find more options for bearings and additional (very thin) seals.
Since I care for the machine (about 3 years) we had 8 motor replacements and all due to the bearings seizing.
The last I took apart had the carbon brushes not even worn by 3mm - with being 15mm long...

Jack A Lopez
Jack A Lopez

Reply 1 year ago

What about if one of the old motor housings could be turned into a shell, with just a single pulley inside, in the place where the motor windings used to be.

Also this old motor housing would have a big hole in one side, to accommodate the long belt, which is connected to another pulley, on the shaft of a working motor.

I mean, basically, this is the same idea as before, instead using a long belt, in place of a long shaft.

Actually, long belts and pulleys, and a turning shaft on the ceiling... this used to be the state of the art, a long time ago.



Reply 1 year ago

Not too bad as an idea, have to check if there is enough room for a solution like this inside the machine.
On a plus side my local bearing shop is quite supportive.
There is tripple sealed bearings available in the size I need, special order though and not in stock.
Benefit of those is that you can pay extra for wide range of lubricant fillings - for both the ball part and the filling of the sealing areas.
Currently waiting on a reply from the manufacturer in regards to options with hot vegetable oil that has up to 5% of silicone oil in it.
Another neat thing they showed me in the bearing shop was what they called vibration cap, am sure there is other names for it.
It is literally a seal that goes into the motor or axle housing to hold the bearing in place.
What makes it special is that on the outside there is another seal that only leaves room for the inner diameter of the bearing - and additional dust seal.
Downside is they are made for a specific bearing size but not to accomodate a slightly smaller bearing in an original housing.
For the next smaller outside diameter I would need a shm-ring or similar to make it fit.

One thing that might work if I waste a lot of time and wrecking my back would be to cut the shaft of an old motor.
By doing the same on a working motor and some extra machining I might be able to fit a coupler between pump and motor or at least to extend the axle a little bit.
Needs major surgery on the internals of the machine though to get the motor moved only by 5cm :(
And means I would need to make a custom mount for the pump or a suitable extension for the motor housing to hold it in a secure fashion.
Don't care about of leaking oil once the seal start to fail as long as it will go on the floor and not into the motors bearings.
Whatever the final solution will be it needs to be short LOL