Replacing another Wheel Motor.

[BobRip]

I could not find the flow rate. It is just something in my memory. Looking at the wheel motor circuit I see that some flow from the variable volume pump goes to the oil cooler. The outlet of the oil cooler then goes to the tank. The charge pump then must pump from the tank into the wheel motor circuit through the hydraulic oil filter to make up what is lost from the wheel circuit through the hydraulic oil cooler. I don稚 know how much flow goes through the oil cooler, but it must be more than a trickle given the size of the hoses and oil cooler tubing. It appears that the charge pump is an integral part of the VVP.

Of course I agree that particles in the wheel circuit could damage the VVP. But they will be filtered out eventually.

 

[MossRoad]

That's where I'll disagree... I don't think metal parts from the wheel motors will be filtered out eventually. I think they'll be sloshed back and forth between the next wheel motor and VVP, lodge in the wheel motor case, or the VVP case, and, at best, sink to a corner in the tank if they make it that far.

Of course, fine shavings and such will have a better chance of making it to the tank and eventually the filter. But I'll guess that the main PTO pump will have a better chance of pulling shavings out of the tank and recirculating them than the charge pump would have of getting the shavings through the filter.

So, fine shavings maybe. Large pieces from a failied bearing, probably won't ever make it to the filter. But again, I could be completely incorrect. Just guessing.

 

[BobRip]

Since all oil eventually returns to the oil tank (although it is hard to see since flow through the valve bank is on two separate drawings) and the hydraulic oil filter draws from that tank, then all oil is eventually filtered. I hope I have explained this clearly and that I am correct. I have made some assumptions since oil flow through valves and pumps is not shown. However the steering/PTO pump and PTO pump do pull from the oil tank.

 

[BobRip]

I think the heaviest particles may settle to the bottom of the tank. At this point I am guessing. I am not an expert on hydraulics, just an electrical engineer. I certainly understand your points. Any hydraulic experts here? Somebody call Terry at Power Trac.

 

[Barryh]

The way I understand it is any hydraulic oil that enters the tram circuit is filtered as it leaves the tank, then goes to the charge pump in the tram pump. Anything that leave the tram circuit returns to the tank. So if you're driving along forward, the tram pump is pushing fluid forward, through all of your wheel motors and back to the tram pump. The 400 series wheel motors don't have case drains (that I know of), so all fluid goes through all wheel motors and back around through the tram pump. Anything that leaks past the seals inside the tram pump is where it goes back to the tank from the tram circuit.

So, if a wheel motor tosses chunks of metal internally, they're gonna circulate around inside the motor, back and forth in the wheel circuit(s), and perhaps make their way to the next motor or the pump. To get filtered out, they'd have to pass through the tram pump, into the tank and manage to get picked up in the sucktion for the filter to get back into the tram pump.

As far as I know, the main and aux PTO pump circuits are never filtered.

Moss, My old motors do have case drains.. I have upgraded and replaced two of the old motors for the newer style along with the newer improved hubs.. One right front.. And now the left rear. but still have two of the older style motors in circulation with case drains. Including the one with the bad bearing, I had to cap off the case drain hose's on the newer motors.. How does that change the equation if any ? Thanks to all for reply's so far... Hopefully I have no unseen pump damage seems to running fine at this point.. Really never thought about it before. I'm now starting to get a better understanding of how the system works ..

 

[ponytug]

Bob- I think that you are correct. Some fraction of the oil in the wheel motor circuit flows out of the circuit via the cooler to the tank. The charge pump is responsible for charging the return (suction) side of the variable volume pump.

If you have a look at the first link that I posted above, it has a nice discussion of possible ways to plumb a charge pump. From the drawings, you can get a sense of the diversity of solutions; there are hydraulic systems where the charge pump is a separate pump. That's where the Danfoss calculations come in, second link in my prior post, to compute the necessary charge pump size.

The bit where I am confused is how much of the PT charge pump flow is added to the hydraulic drive system, i.e. how much of hydraulic drive system is diverted to the tank/min, and how much, if any, of the charge pump flow is returned to the tank via a pressure relief or variable volume pump lubrication blow by. That's why I was interested in where you got the 4gpm number, and what it represented. (total flow of the pump, flow into/out of the drive circuit, or just maximum flow)

That was just me being curious. My PT and this forum has taught me pretty much everything I know about hydraulics.

The oil is eventually all filtered through the suction filter on the charge oil pump. In the 425s, the hydraulic tank is 10gal. That means that 40% is filtered every minute, or in about 10 minutes 99% of the oil has been filtered. (to 10 microns) unfiltered oil remaining =(1-.4)**n, where n is the number of minutes (approximately)

Barry-
The case drains on some motors are there to simplify the design of the motor. By intentionally passing oil from the high pressure side through the bearings and by the seals, it is a way to a) cool the motor, b) sweep away dirt penetrating the seal, and c) have mechanically simpler, and lower cost, seals. I don't know that one way is intrinsically better than the other; there are tradeoffs. The volume draining though the case drains should be minimal, in the grand scheme of things. When I worked in food processing, I used to see lots of machines in that had a water flush/drain on the shaft before the motor. It kept food particles from contaminating the bearings, cleaned the seals, and kept oil and grease out of the food. Same idea.

All the best,

Peter

 

[MossRoad]

If the hydraulic tank was a long, thin, tube, all of the fluid would be forced through the filter eventually. However, the hydraulic tank is not a tube. It's a cube. With corners, baffles, etc... Fluid flowing into the tank will create uneven currents. Some of the fluid will get filtered more often and some will get filtered less often.

Look at it like the water behind a bridge abutment in a river. Throw your bobber in there, and it doesn't move. The water is calm. The sediments all gather under that spot. That's why the fish are there, to eat the food that falls out of the current there. Then a flood comes along, the current increases, and the sediments might get stirred up. Similar to if we jar our machines around.

And if we're running our PTO, which I'm guessing sucks a LOT more fluid than the tram pump, just by the size of the hoses, most of the fluid will be going into and out of the PTO circuit directly from and to the hydraulic tank. Most of the fluid won't be getting filtered that day.

 

[MossRoad]

I think I'd have more faith in magnets in the tank to grab metal particles. Some day, I may do that. But probably not until I'm forced to do a hydraulic oil change.

 

[SpringHollow]

The magnets pick up a lot of crap.

Ken

 

[ponytug]

Look through the hydraulic fluid cap sometime with the engine running. It is really well mixed, or at least mine is.

All the best,

Peter