Variable speed transmission

[J_J]

I need some one that has a hydraulic schematic to check and see if the tram pump used in the PT's is a closed loop system. In a closed loop system, the oil is circulated from the pump through the wheel motors, and back to the pump. The charge circuit makes up for any losses in the system. We may have a modified circuit is our PT's. What this is leading to is that any foreign particles induced into the system goes directly to tank and only some of that oil is filtered. The PTO is sucking oil directly from the tank, and so is the steering and lift pump. The tram pump and wheel motors is always filtered, and therefore less prone to wear. There seems to be no reason why , if we have the space, to install input filters in all the circuits. I would estimate the cost to be about $50.00 to filter each circuit. On my 1445, the replacement cost for the steering pump is about $95.00, PTO pump, about $350.00, and the tram pump about $2200.00.

I have replaced both the steering and the PTO pump. The technician that looked at them said it was due to wear. In my opinion, this was caused by partially filtered oil. I don't know if any one could determine how long it would take the tram pump to filter 20 gal of oil, because at the same time, the PTO and lift pumps are recirculating partially filtered oil continuously. I don't feel that this is the best method that could have been used. What say you?

 

[Spiffy]

Maybe I need to look again, but I wasn't positive from my diagram.

I don't really have room for another suction side filter, but I'm still convinced at least one (PTO, steering or both) should have a return filter. Aside from requiring less room, you could use finer filters (perhaps 3 micron), also, a little back pressure would stress the pump much less than excessive vacuum on the inlet.

 

[J_J]

A return line filter would not help your pump, except in the long run, because you are still pushing any particles or trash through the pump. Over time the filter would help filter the entire system. They make high pressure filters that could plug in right before the hyd motor. A suction line filter is your best bet for protecting the pump. It could even have a shut down switch on it if it gets clogged.

My ideal system would have one suction line feeding a three output manifold which would feed each pump. or a manifold with three filters, one for each pump. A one micron bypass filter would also be a good thing.

 

[MossRoad]

I don't know where, but I read somewhere to beware the suction side filter. I've read it many times, too. So there may be some concerns. Best to research it well, before doing it.

 

[Spiffy]

I agree with you JJ that the suction filter is the best protection for the pump, but while a return would laught at 100 psi (though I think most hit bypass at 25 or something), the suction is plugged at 10 (causing the pump(s) all sorts of headaches), so I'd want a gage right before the filtered pumps.

Where does the most contamination come from? I can see 5 places: hydraulic connections (when you change attachments - not matter how clean you think you keep and wipe the ends), pump wear, motor wear, tank corosion, filling the tank.

If the last two are the concerns, the suction is the only prevention.

The rest would be kept in check with a return as easily - an added bonus if you run individual returns - you can tell which pump(s) are wearing out (they'll have aluminum floating in the filter - I thought it strange, but the FIL showed me one: pretty obvious /forums/images/graemlins/shocked.gif ). Also if you run a 1 or 3 micron on the PTO or any other high GPM combination, you'd have the system filtered by the time the engine is warmed up. It should also keep that 10 micron really clean (I'd like a guage there, I bet with 1 or 3 micron return filtration, the 10 micron would last 500 hours easy).

 

[J_J]

David, do you realize that the filter on the tram pump on your PT is on the suction side

 

[J_J]

I don't think you can draw much fluid through the small micron filter. They usually use them in bypass circuits to aid in the filtration over time.

 

[MossRoad]

Nope, I didn't realize that. /forums/images/graemlins/blush.gif

 

[BobRip]

JJ, here is the wheel motor circuit for the PT422/425. It is a little blurred, but I think OK. If you need a better version I will try again.

Bob

 

[BobRip]

Sorry about your problems. When I took the class on the 422 about 5 years ago, they told me that the wheel motor circuit was much more critical about contamination because of the variable displacement pump. At least that's their justification.
This does not mean that an extra filter on the other circuits would not help. I like the 3 micron filter that runs from an electric motor while the machine is stopped, but what the heck, I am not an expert here. What does your mechanic think would be the best thing to do.

Bob Rip