Let’s talk about vents

[WaterH]

First, let me clarify that I’m talking about diff of gearbox vents. Engine vents have blow by to deal with and fuel tank vents have massive changes in volume. But a differential just heats up and expands the oil and air some. After cool down, it sucks the exact same volume back in. It has been explained to me that when it expands, it can leak or blow an axle seal. Also, when it contracts, it can suck in water or other shit. This all makes logical sense to me.

Then there’s my tractor.
It has a belly mower with a right angle gear box. It’s basically a square box with two shafts, one from the center PTO and one that drives the pulley that drives the blades. It has a two plugs to allow you to fill it half way with oil. When I start mowing, it’s obviously the same temperature as the out side. After 20 minutes, that box is easy 150 degrees or more. How does it do this without a vent? Better seals? While my tractor box happens to be a handy example, it is not the only one I know of. There’s lots of examples of gearboxes with no vents. So why do they have them? This brings me to my next question, just how much pressure is there in a hot gear box?

I decided to do some math. When it come to math, Im not “in to” getting it perfect. So I’m hoping one of you guys will correct me. Here’s what I came up with.

First, I took an old 8.8 diff that was sitting in my shop and filled it with water. It took approximately 4 gallons to fill. There were no axles or gears in it, so that may be a bit much. I’m thinking that number might be about the amount of a larger axle. (Like a Sterling or 14 bolt)

Second, I don’t think we have to be concerned with a couple thou that metal expands. So that leaves oil and air. For this calculation, I’m going to say there’s one gallon of oil and three gallons of air. I’m also going to say the starting temp is 70 degrees and the diff gets to 150 after running down the highway. I don’t actually know how hot a diff gets, so correct me if I’m wrong.

Then I went searching the net and found this site.

Volumetric (Cubic) Thermal Expansion

So 231 (cubic inches in a gallon) x 1.06 gives us 244ci. That takes care of the oil.

I didn’t find a handy calculator for air expansion, but after a bit of research, it would appear that the 70 to 150 gives us an increase of volume of 12 percent. Starting from 3 gallons of air (693 ci), that would give us 776 ci. So the total increase in volume (air and oil) would go from 924 to 1020.

Now maybe I got this completely wrong, but that doesn’t seem like much expansion. Doesn’t twice the volume only equal 15 psi? Are we saying the seals can’t take less than 15 psi?

What am I missing? Am I way off? Based on this, I’m inclined to just install a plug. Anybody done this?

 

[Winchested]

You've got it completely wrong. On a low speed rock Crawler you can get away with those dumb bellows things. On anything high-speed/ road driven you're blowing seals.

And no the seals can't take much pressure they aren't designed to.

I've measured temps on my 14 bolt upwards of 185-200 is normal after a road trip, running 85w-140.

As far as hot diffs going into water, again not a big deal on rock crawlers but on touring rigs (overlanders) hot diffs can def suck in water as the axle shaft will contract just enough when the water hits the steel. Not necessarily a huge amount but plenty enough hence why every owners manual for a 4x4 says to change diff lube and hub grease after fording water higher than said diff or hubs.

I'm first hand experience that water quickly takes out wheel bearings after a few trips of forgetting to regrease after fording deep water.

 

[arse_sidewards]

You've got it completely wrong. On a low speed rock Crawler you can get away with those dumb bellows things. On anything high-speed/ road driven you're blowing seals.

And no the seals can't take much pressure they aren't designed to.

I've measured temps on my 14 bolt upwards of 185-200 is normal after a road trip, running 85w-140.

As far as hot diffs going into water, again not a big deal on rock crawlers but on touring rigs (overlanders) hot diffs can def suck in water as the axle shaft will contract just enough when the water hits the steel. Not necessarily a huge amount but plenty enough hence why every owners manual for a 4x4 says to change diff lube and hub grease after fording water higher than said diff or hubs.

I'm first hand experience that water quickly takes out wheel bearings after a few trips of forgetting to regrease after fording deep water.

Reading comprehension much?

He's basically asking how his mower gearbox can stay sealed with no vent whereas an axle fucks off at a few psi.

 

[ThePanzerFuhrer]

Reading comprehension much?

He's basically asking how his mower gearbox can stay sealed with no vent whereas an axle fucks off at a few psi.

Mower gearbox has a vent somewhere he just doesn’t see It. It will be a 1/16 or smaller hole drilled in a bolt head somewhere.

 

[Poke]

Mower gearbox has a vent somewhere he just doesn’t see It. It will be a 1/16 or smaller hole drilled in a bolt head somewhere.

This was my guess. It’s vented and he hasn’t seen it yet

 

[ThePanzerFuhrer]

This was my guess. It’s vented and he hasn’t seen it yet

Yes because they would blow the seals out immediately if it wasn’t.

 

[Winchested]

Reading comprehension much?

He's basically asking how his mower gearbox can stay sealed with no vent whereas an axle fucks off at a few psi.

Sorry it's hard to explain easy to people who overthink life, there's no way it doesn't have a vent.

Maybe easy we should just let him plug it and find out the retard way.

 

[WaterH]

Not saying your wrong about axle seals but I’ve had my mower box completely apart. There is no vent.

Edit, Here is a tail rotor gear box. I’ve had 20 of these apart. There is no vent.

 

[ThePanzerFuhrer]

You may be able to get away with no vent in a grease based gear box. Oil filled no way can you get away with no breather.

 

[WaterH]

You may be able to get away with no vent in a grease based gear box. Oil filled no way can you get away with no breather.

Both my mower gearbox and the tail rotor box use gear oil.

Its funny you mention grease because the only time I have ever blown a seal is greasing a bearing with a grease gun. Of course now your talking hydraulic pressure.

Edit, I have about 5000 hours in the helicopter type above. They very, very rarely leak And I’ve never seen a blown seal. The seal on the output side would be hard to fail because it is pressed from the inside to a shoulder. The seal on the input side is pressed from the outside and would be easy to blow out. To my knowledge, it has never happened. I know at least 50 people with this chopper.

 

[MoparMoe]

For discussion purposes, my John Deere 110 TLB has a Spicer front axle , it is a non vented unit.
Its a common issue to have the seals weep at the king pin area as the fluid they spec for the diff is Low Viscosity Hygaurd hydraulic oil, its very thin.
this along with the pressure build up causes the weeping around the seal areas.

Its been replaced by a regular syn gear oil ( Mobil SHC 628 ) and hasnt been a trace of leakage since.
after a good days work I can take the fill plug out and release a fair amount of pressure.

I

 

[Winchested]

You can clearly see oil has leaked past that seal on the tail rotor. There are also several different styles of lip seals some far better at containing pressure than others.

 

[ThePanzerFuhrer]

Both my mower gearbox and the tail rotor box use gear oil.

Its funny you mention grease because the only time I have ever blown a seal is greasing a bearing with a grease gun. Of course now your talking hydraulic pressure.

If they are oil filled they have to breathe. As soon as they warm up the pressure will blow oil out the seals. You’re just not seeing how it breathes.

Fuckit I vote plug it up tight. Report back with what happens.

 

[WaterH]

If they are oil filled they have to breathe. As soon as they warm up the pressure will blow oil out the seals. You’re just not seeing how it breathes.

Fuckit I vote plug it up tight. Report back with what happens.

I use to be part owner in the company making that helicopter. I know it like the back of my hand. There is no vent. We bought the design and I recall remarking about how the main gearbox has a vent but not that one. We didn’t fix what wasn’t broke.

You can clearly see oil has leaked past that seal on the tail rotor. There are also several different styles of lip seals some far better at containing pressure than others.

No, you can not clearly see a leak. I have that helicopter at the airport right now and it doesn’t leak a drop. I zoomed in and maybe you are looking at the swash plate bushing. (It is not the exit of the gearbox)

 

[arse_sidewards]

If they are oil filled they have to breathe. As soon as they warm up the pressure will blow oil out the seals. You’re just not seeing how it breathes.

Fuckit I vote plug it up tight. Report back with what happens.

There should be a range of temps where there's not enough pressure to blow out the seal. I think most applications have too wide an operating temp range for that.

I have a cheap worm gearbox (like snowblower sized) kicking around that only has a fill plug, no vent. It's like 40:1 and 1000rpm input. IDK how it works but it does.

 

[ThePanzerFuhrer]

There should be a range of temps where there's not enough pressure to blow out the seal. I think most applications have too wide an operating temp range for that.

I have a cheap worm gearbox (like snowblower sized) kicking around that only has a fill plug, no vent. It's like 40:1 and 1000rpm input. IDK how it works but it does.

I’m guessing it’s because the low amount of oil. Both gearboxes waterhead showed are small and prolly take less than a quart to fill.

 

[arse_sidewards]

I’m guessing it’s because the low amount of oil. Both gearboxes waterhead showed are small and prolly take less than a quart to fill.

Someone should try plugging the vent on an ecobox.

 

[WaterH]

I’m guessing it’s because the low amount of oil. Both gearboxes waterhead showed are small and prolly take less than a quart to fill.

The gearboxes mentioned are small, but the oil doesn’t expand with heat as much as air, so not sure why that would matter.

 

[Donk]

The gearboxes mentioned are small, but the oil doesn’t expand with heat as much as air, so not sure why that would matter.

Are the gears straight cut or hypoid? Volume of air compared to oil quantity? Also that gearbox is exposed to a huge amount of cooling air compared to a diff. I'm also a little surprised it's not vented because of the pressure changes due to altitude.

 

[Weasel]

Quad lipped seals can be had to hold up to 300-750psi.

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Why would you want a vent on a gear box that is the air? How you gonna refill it if any oil pukes out? What keeps oil in when your not flying level? What keeps contaminates (dirty air/dirt/sand) out of that (assuming ) high precision gear box?

 

[BDK]

When I rebuilt my differentials (8.8 and HP D44) I used those accordion expanding caps. Blew the seals on the D44, which are a pain in the ass to replace, on the first trip.

Next time, I used long hoses with little lawn mower fuel filters on the ends to keep dust out. Hoses are up at the top of the firewall and inside the tail light well, which is high enough because I don't really do deep water crossings. Deepest one so far was at the top of my 35" tires. Atlas vent hose is on the firewall as well with the same little fuel filter. No more blown seals. I think the 8.8 didn't blow the seals because there is a lot more empty space in them with the seals at the end of the axle tubes.

 

[Winchested]

When I rebuilt my differentials (8.8 and HP D44) I used those accordion expanding caps. Blew the seals on the D44, which are a pain in the ass to replace, on the first trip.

Next time, I used long hoses with little lawn mower fuel filters on the ends to keep dust out. Hoses are up at the top of the firewall and inside the tail light well, which is high enough because I don't really do deep water crossings. Deepest one so far was at the top of my 35" tires. Atlas vent hose is on the firewall as well with the same little fuel filter. No more blown seals. I think the 8.8 didn't blow the seals because there is a lot more empty space in them with the seals at the end of the axle tubes.

This is how I do all mine too.

 

[WaterH]

Are the gears straight cut or hypoid? Volume of air compared to oil quantity? Also that gearbox is exposed to a huge amount of cooling air compared to a diff. I'm also a little surprised it's not vented because of the pressure changes due to altitude.

I believe they are spirl-bevel gears. When flying in the sky, it just gets warm, but if I’m hover training, it’s gets plenty hot.

When I rebuilt my differentials (8.8 and HP D44) I used those accordion expanding caps. Blew the seals on the D44, which are a pain in the ass to replace, on the first trip.

Next time, I used long hoses with little lawn mower fuel filters on the ends to keep dust out. Hoses are up at the top of the firewall and inside the tail light well, which is high enough because I don't really do deep water crossings. Deepest one so far was at the top of my 35" tires. Atlas vent hose is on the firewall as well with the same little fuel filter. No more blown seals. I think the 8.8 didn't blow the seals because there is a lot more empty space in them with the seals at the end of the axle tubes.

I was thinking the more space for air, the less pressure could develope.

 

[BDK]

More volume takes more heat to create the same amount of pressure.

 

[vetteboy79]

Mower gearbox has a vent somewhere he just doesn’t see It. It will be a 1/16 or smaller hole drilled in a bolt head somewhere.

Yes because they would blow the seals out immediately if it wasn’t.

You may be able to get away with no vent in a grease based gear box. Oil filled no way can you get away with no breather.

Well, wrong. Correct on the TXT stuff you run that's designed to be maintained by neanderthals (not a dig at you or the gear, in any way) but there are plenty of industrial and food/beverage applications where the gearbox interior needs to be isolated from the atmosphere. 🙂

Check this thing out. It's called a carcass winder, think flexible metallic conduit but a few feet in diameter, to protect deep sea pipelines. It gets a strip of continuous flat steel, has a forming section where the profile gets rolled in, and that entire giant thing rotates around at up to 30+ RPM to form a continuous length of the shielding.

You can see the three gearboxes in that photo, there are two more hidden behind the framework. That thing is 30ft diameter so those boxes are trying to be flung into orbit. Not my machine, we just supplied the gearboxes.

I spec'd all those gearboxes, and we had a utility to calculate the self-heating of each one at the rated load and duty cycle, and based the oil fill level off the anticipated temperature change and volume of the gearbox cavity as to not exceed the internal pressure the lip seals could handle. Splash lube at its best (I had to emergency mill some slots in a support bracket in DozerDan82 's basement one night to supply for a motor brake after the customer decided they wanted a little extra)

We'd have stuff like this too, gearmotors that were able to be completely submerged indefinitely, but sized for open-air operation if the application called for it.

A lot of that was wastewater where you might have a dry spell in summer and the thing would be out in the hot air, or you might get a winter storm that floods the works with cold water. No worries.

Worst cases, if we absolutely had to have pressure relief and where we didn't want to use one of those ugly external expansion bladders, we had this internal thing that was basically a small balloon inserted through the fill plug. The plug was vented to the balloon but the inside of the gearbox was totally isolated.

Point being, yes it's common in many industries to have an oil-lubed gearbox not interact with the atmosphere...just probably not the one you're gonna get off the shelf at your local Motion branch. We never had 'fill level' plugs on our stuff for a reason, because the oil level was as engineered as the rest of it. (sight glasses sometimes, but those things are generally worthless and another leak point) You get the millwright who just rides around on the lube cart to 'top things off', that's when you're gonna run into problems.

 

[ThePanzerFuhrer]

Well, wrong. Correct on the TXT stuff you run that's designed to be maintained by neanderthals (not a dig at you or the gear, in any way) but there are plenty of industrial and food/beverage applications where the gearbox interior needs to be isolated from the atmosphere. 🙂

Check this thing out. It's called a carcass winder, think flexible metallic conduit but a few feet in diameter, to protect deep sea pipelines. It gets a strip of continuous flat steel, has a forming section where the profile gets rolled in, and that entire giant thing rotates around at up to 30+ RPM to form a continuous length of the shielding.

You can see the three gearboxes in that photo, there are two more hidden behind the framework. That thing is 30ft diameter so those boxes are trying to be flung into orbit. Not my machine, we just supplied the gearboxes.

I spec'd all those gearboxes, and we had a utility to calculate the self-heating of each one at the rated load and duty cycle, and based the oil fill level off the anticipated temperature change and volume of the gearbox cavity as to not exceed the internal pressure the lip seals could handle. Splash lube at its best (I had to emergency mill some slots in a support bracket in DozerDan82 's basement one night to supply for a motor brake after the customer decided they wanted a little extra)

We'd have stuff like this too, gearmotors that were able to be completely submerged indefinitely, but sized for open-air operation if the application called for it.

A lot of that was wastewater where you might have a dry spell in summer and the thing would be out in the hot air, or you might get a winter storm that floods the works with cold water. No worries.

Worst cases, if we absolutely had to have pressure relief and where we didn't want to use one of those ugly external expansion bladders, we had this internal thing that was basically a small balloon inserted through the fill plug. The plug was vented to the balloon but the inside of the gearbox was totally isolated.

Point being, yes it's common in many industries to have an oil-lubed gearbox not interact with the atmosphere...just probably not the one you're gonna get off the shelf at your local Motion branch. We never had 'fill level' plugs on our stuff for a reason, because the oil level was as engineered as the rest of it. (sight glasses sometimes, but those things are generally worthless and another leak point) You get the millwright who just rides around on the lube cart to 'top things off', that's when you're gonna run into problems.

Show my the math I need to do to turn my txts into a ventless box. I have like 100 of the and the vents are the stupid issues. The best fix I have for them is to put the taconite external seal kit on them and the external bladder ballon breather.

 

[arse_sidewards]

Show my the math I need to do to turn my txts into a ventless box. I have like 100 of the and the vents are the stupid issues. The best fix I have for them is to put the taconite external seal kit on them and the external bladder ballon breather.

And don't forget to drill yourself a new fill plug at the right level because "employees"

 

[Muckin_Slusher]

How did you vent your Osh-Bronco to keep water out of the axles?

I recall reading that those Alvis-Stalwarts had positive pressure to the gearboxes and diffs to keep water out. I've been dealing with a situation at work where a 20 hp motor is gonna get flooded probably monthly and have been thinking about plumbing instrument air at about 3 psi to the peckerhead. Would keep us dry to 6 feet submerged.

 

[WaterH]

How did you vent your Osh-Bronco to keep water out of the axles?

It never got in during my tests. I guess The vent hole is too small. Could be if I got it hot and than dunk it, it could cool and suck in water.