Variable speed transmission

J_J · Apr 12, 2006

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 · Apr 13, 2006

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 · Apr 13, 2006

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 · Apr 13, 2006

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 · Apr 13, 2006

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 · Apr 13, 2006

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

J_J · Apr 13, 2006

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 · Apr 13, 2006

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

BobRip · Apr 13, 2006

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 · Apr 13, 2006

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

Spiffy · Apr 14, 2006

( 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. )

No, I don't think a fine filter on the suction side would be good, but for the rated GPM of a PT (20GPM combined steering and PTO ?), you wouldn't even have to run a bypass on the return side for a 1" inch fitting filter head.

This one comes with a 10 micron, but, if I remember right from looking at this a couple monthes ago, you can get replacements in 25, 10, 3 and maybe 1 micron.

I also noticed the same site had suction filters with 5psi relief; they had suction filter gauges too.

Gravy · Apr 14, 2006

FWIW,

Inspired by a previous thread on filtration, I've bought a 3 micron filter assembly (surpluscenter.com), hoses and quick-disconnects (TSC) to make a main PTO filtration system. The plan is to plug it in in place of the mower after a mowing session. My thinking is that any contaminants should be in suspension at that time, so I should get good filtration efficiency without having to keep an eagle eye on a restriction gauge while mowing.

I would have preferred a 1 micron setup, but those seem to be made of unobtanium, and 3 microns beats the heck out of 10.

Of course, I only have about a dozen or so other projects that I REALLY need to finish before I actually assemble and test this one, so it might be a while before I can report my findings...

I'll let you all know how it works out...someday.

Gravy /forums/images/graemlins/tongue.gif

JerryG · Apr 14, 2006

I don't know if you guys have seen this site or not. He has some very information on filtration as well as other things.

J_J · Apr 14, 2006

Why not put the high pressure filter inline [ it can not be a regular filter ] with the pump to protect it from contaminants. I would also make sure that the filter can pass the GPM's that your PT is rated, A slow down of the mower would be a good indication of the condition of the filter, If you put in on the return line, the pump is passing unfiltered oil or slightly filtered oil.

The site that Jerry G provided to is a very good site for info. I have read through it many times.

KentT · Apr 14, 2006

As far as an auxiliary (sp?) filter, why not just build some sort of mounting plate for a filter that you could run through the PTO connections, when you're not running something that requires the PTO...

That's an existing high volume pump on a circuit that's only used part of the time... seems it would filter and recirculate the entire PT's hydraulic tank very quickly....

J_J · Apr 14, 2006

True, but the point is that you would want to filter the oil before it goes through the motor. If no motor is in use you could filter or not.

Spiffy · Apr 15, 2006

As far as an auxiliary (sp?) filter, why not just build some sort of mounting plate for a filter that you could run through the PTO connections, when you're not running something that requires the PTO...


That would be a very simple way to fine filter the oil, but I'd still put it permanently on the return so it's always filtering - the only problem being [assuming it's the same as mine was] that the return is different line whether the PTO is in use or "idle". Now if you put in that reverse valve [another thread, BTW I'm very happy with mine /forums/images/graemlins/smile.gif ], you only use one line so a filter would always have the PTO flow.

Of course [as I think JJ pointed out] that still doesn't protect the pump or attachement motor against tank introduced contaminates - but they'd only get to make the trip once! /forums/images/graemlins/grin.gif

Gravy · Apr 15, 2006

My filter setup will handle the flow, but won't handle high pressure. It's a return line filter rated for about 30GPM and 120 psi max. It will simply connect to the main PTO circuit in place of the mower or other hydraulic motor.

My plan is to plug it in after a mowing session and let the engine run, filtering the hydraulic oil while I wash the dust and clippings off the machine. This should give the entire volume of the oil several passes through the filter while its hot and any contaminants are still suspended.

Ideally, I'd like to ultra-filter all of the oil all of the time, but I think what I've got will clean the oil a whole lot better than the factory setup for a small fraction of the cost and effort of the ideal fulltime ultra filtration design.

One Of These Days, Real Soon Now, I'll actually assemble the parts that are sitting on a shelf, and try it out. I'll post photos shortly thereafter. Maybe even tomorrow. It COULD happen... /forums/images/graemlins/crazy.gif

Gravy

BobRip · Apr 15, 2006

Are you planning to keep the engine at idle to reduce the pressure, or will it be OK will full flow and the pressure will be low since there is plenty of flow capacity and no back pressure?

Bob Rip

Gravy · Apr 16, 2006

IIRC, it's rated for 30GPM. It *should* be able to handle full flow with no problem. Nonetheless, I plan to start out at idle with hot fluid, and watch the pressure gauge very carefully. The internal relief valve is set at about 25psi, so it should bypass well before anything blows out.

I'm going to try to put it together and run it today, so I may be able to report results this evening.

Gravy