External oil pump for gearbox 1

[frotojk]

I am designing a custom gearbox for an aerospace application. It will only be run for a few hours of testing on the ground.

It is a high performance assembly, very small and tight due to space constraints, with relatively high power going through it. We will pumping gear oil to and from the gearbox provide spray for the gear mesh and to provide active cooling.

The suction or drain port is at the lowest part in the gearbox, however there won't be a maintained oil level due to lack of space ( one of the gears is just a fraction of an inch away from the suction hole).

So if you can imagine the conditions inside the gearbox will be very turbulent, oil and air could likely mix at times at the suction port.
My question is, would a gear pump be ok for this application? If not are there suitable options? All input is highly appreciated.

-John

 

[MikeHalloran]

A gear pump with an intake screen and a simple relief valve would seem appropriate. You might want to include a small spin-on filter.





Mike Halloran
Pembroke Pines, FL, USA

 

[micalbrch]

I think an intake screen will even worsen the situation.

Your gear housing is already designed, right? If not you could perhaps add a small sump at the bottom of the housing. Or a small tank in front of the gear pump? Dry running is indeed bad for a gear pump but for the alternative (vane pump), too. Pumps with dry running capability are not used for that and most probably much too big. Try an oversized gear pump (slow running) with big inlet pipes. That's my only advise.

 

[hydtools]

Keep the pump below the gearbox to keep it flooded.

A gear pump will work.

Ted

 

[JJPellin]

For a very brief operation, I think a gear pump is a good selection. It will continue to pump even if there is a considerable amount of air in the oil. I will even pass a larger air bubble as long as the gears are coated with oil. The pressure and flow of oil may be wildly erratic. I assume that there will not be a low pressure trip. If the pressure is regulated with a full-flow relief valve, you may experience some bad chattering of the valve. But, this is for a very short run so long term reliability is not an objective.

Johnny Pellin

 

[MikeHalloran]

On second thought, you're really trying to run this gearbox in 'dry-sump' mode. ... which ideally would require a gear pump drawing from a quiescent reservoir through a bird screen, and pumping through a filter, a relief valve, and a cooler to the bearings and gear meshes. ... and a larger scavenge pump pulling oil and air from the gearbox sump and directing both to an air separator draining into the reservoir. Note that most of your oil inventory will be in the reservoir, not in the gearcase. You might be able to use the reservoir as a cooler by increasing its surface area. Most components except the scavenge pump can be located remotely from the gearbox. Within a certain power range, you can get kits of appropriate components from guys who sell to circle track racers.







Mike Halloran
Pembroke Pines, FL, USA

 

[frotojk]

Mike, that is almost exactly our planned setup.

I will plan for a larger scavenger pump, and upsize the suction ports.

Thank you all for the great advice.