"Anthony" wrote in message
...
"Moray Cuthill" wrote in
:

I have been thinking about this problem for a couple weeks now, and
have so far not found an ideal solution. Any input would be very
gratefully recieved.

The scenario- Currently got a timber trailer with crane mounted on it.
The hydraulic power is supplied by a PTO driven pump with gearbox
mounted on the tractors PTO shaft. Now due to the tractor it's mounted
on (MBTrac 1000), the PTO is alot nearer to the drawbar than a
conventional tractor. Originally the pump was mounted onto the PTO via
a PTO extension shaft, but this had the problem that if the tractor
went up a steep slope, the pump would hit the trailer chassis and snap
the tractors PTO shaft. This was remidied by doing away with the PTO
extension, grinding a bit of the top flat off the tractors pick-up
hook assembly, which allowed a flat of the pump gearbox to sit ontop
off the pick-up housing, eliminating the possibility of it coming into
contact with the trailer. This has worked fine for a few months of
intermittent use, but last week the end off the PTO shaft snapped off,
allowing sufficient room for the gearbox to be spinned around and the
gearbox casing smashed.

What we would now like to do, is to mount the pump onto the front PTO
shaft, which is never used. The current gearbox was geared so that the
pump ran at aproximately 2000rpm with an input speed of 540rpm (aprox.
ratio of 1:3.76). Now the PTO can be run at 1000rpm, which means a
ratio off 1:2 can be used. The pump output that the crane dealer specs
is 76.9litres per min at 3500psi. Now given these figures I work the
horsepower required at 2000rpm as 51hp allowing for 80% pump
efficiency (worse case), with required torque off136lb-ft.

Originally I had thought about using V-belts, but due to limited space
around the front PTO, pulley size is limited to 7inches diameter,
which would require the use off A-section belts. Having gone through
the various calculations/charts, this would require 6 belts to
transmit the required power, and would not realistically fit in the
available space.

I have also considered using a timing belt, but also due to the
limited pulley size, these would not be able to transmit enough power.

So I am back to using gears. My current idea is to utilise the gears
out the previous gearbox, and build a new casing, with the pump
mounted on the opposite side compared with the original gearbox, to
allow for the front PTO turning in the opposite direction. I may have
to swap to using smaller gears, and possibly altering the ratio to 1:2
due to space limits.

Do my belt results seem plausible?
The geabox would be construced by machining two plates to accept
bearings/seals, welding sides onto one off the plates, and bolting the
other plate on. Would this provide acceptable results?

Thanks In Advance

moray




Moray,
There are readily available, pumps made specifically to run off of the
front pto, or crankshaft. Look at any older backhoe for an
example........Would be much easier a task.

The catalogues I've seen so far only list the same style pump and gearbox
combination that has been damaged, which are too big to mount in the
available space. Crankshaft mounting isn't possible as the pump oil lines
will be disconnected when the trailer isn't in use.
The biggest problem I'm facing, is that when merecedes designed the
MB-Tracs, they took most of the components from Unimogs, and very little
seems to meet any off the established Tractor standards. Alot of this is
because the MB-Tracs use a conventional chassis with the components bolted
on.
Raising the rear PTO up to the standard height above the pick-up hook has
even been considered, but the prop shaft for it would then have to pass
through the rear axle.
Other problem is that in the UK, front PTOs are not very common, so anything
to fit them is very hard to come by.

Thanks
Moray