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Hydraulic Pump drive Side load question.

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
Adding a hydraulic pump to an old tractor just for kicks.

The pump in hand is "designed" as a gear drive unit.
Will there be any problem using it with a pulley based vee-belt drive?

Base question, Which subjects shafts to more side loads? Gear drive or belts?

Consider, there are no parts in this example bigger around than 6 inches, and no longer than 8 inches. No sense talking about electrical generation plants with giant herringbone gear sets transmitting thousands of HP. ;-)
 
any markings at all on the pump ?
The bearing at the shaft end is what takes the loads, I have seen
simple brass bushing style with not much side loading allowed, to full on
timkens for large amounts of side loading.
 
DD

How can your observations be applied to the variation in side loads between Gear drive and Vee Belt drive? Considering this pump is much too small to expect tapered rollers in the input. (It has plane bearings all around, but is very well lubricated under high pressure, 2500 psi under some conditions! ;-)

Regardless of markings, the pump was fitted with a gear on the drive input to be driven off an engine cam drive. Now I wonder how the side loads compare with a vee belt pulley drive. 'Any guesses? Even more, the side loads trying to force the two pump gears apart under full hydraulic pressure must (?) dominate the forces on the pump shafts.

I can guess that the thrust loads with a pulley drive might be reduced to a very small value if properly aligned. That original skew toothed drive gear will never accomplish that. ;-)
 
Helical gear drives suggest radial forces proportional to tangent forces according to the formula Ft (Tan Alpha/Cos Beta) About 1/3 of the tangential force.

The tangental loading on an external gear pump is that of the area of a single gear times the pressure. The other aspects are in balance.

But that doesn't get me far in relation to a belt drive ;-)

I do know that the internal loading on the supporting gear shaft and bearings is biased toward the inlet port at about a 90 degree included angle ;-)
It would seem there could be something gained in compensating by orientation of the pump and the drive.
 
Belts rely on friction.

Gears, friction is something the best gear designers try to avoid.

If we replace the vee belt's friction requirement with a relatively friction free cog belt, will the gear designers still choose a 20 degree pressure angle?
 
Go for it! The seal will leak, but just add fluid as needed.

Just as automotive power steering pumps do?
Automotive units are "mostly" plane bearing construction, but often of internal gear or movable vane design. They seem to work well with belt loads.

2000 to 5000 hr lifetimes are typical from my experience.

The pump in example is a .5 in^3 /rev external gear device.
 
The gear drive will produce a side load equal to the torque required divided by the radius of the gear. So will a timing belt drive along with whatever tension is on the belt, which will be small. As long as the timing belt pulley is larger than the gear, the side load will be smaller. This is referring to pitch radii, of course. The pressure angle of the gear will introduce some more load, but not much. Gears have friction, too. The teeth do not roll against each other, but slide. The involute curve is to produce a smooth drive, not to eliminate friction.

Bill
 








 
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