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tommyg

Interpreting Hydro pressure readings

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Excellent writeup Andy. You should write a book on this stuff.

I'm with coldone on this, I think option D is probably the best.

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For what it's worth, there is a set of hydro valves on ebay at the moment. I know we should not post links to ebay, but the item number is 180901854800

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Wow. I didn't realize one follow up post would generate so much discussion! JamesB1, I tried the visegrip route but can't get a good bite on the shaft since it's hardened. The stuck valve has been this way since I purchased the machine and so has the pressure issues. Almost had my hands on a replacement valve yesterday, but waited too long. Hopefully another one will come up soon on eBay. I think that's going to be the most logical route at this point. But I was considering removing it and seeing if couldn't break it loose. Coldone, that's a good idea. If those caps come off easily, it makes good sense to drive it back into position from the bottom. That seems doable. I'm sure I'll need to remove the valve, though. It still perplexes me that the valve is rotated 90 degrees from the other one. I just might give that a try in the meantime.

Here's the question that I keep going over and over in my mind though... How does all of this translate into a lack of power? (Which was the real reason I dove into this discussion in the first place.) When I start out cold, the power I have seems acceptable. Might not be as good as it could be, but I don't know any better not having experienced what a functioning D hydro system should feel like. Within 15 minutes, though, I can already see a significant drop in power and the temp is barely at 150 degrees. Pressure is still 250-300 psi though. I'm just thinking that if indeed this implement valve is the problem, then why does performance drop continuously the longer I run the tractor? Shouldn't I see just poor performance from the get go? Just wondering. I really want this valve to be the proverbial "smoking gun", but I find I'm preparing myself for disappointment.

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I think this topic creates a lot of discussion because sooner or later, we are all going to have to deal with situations like this, so we all might as well participate and learn as much as we can. Good thing we have some smart people here to share their knowledge. Sorry you can't get vice-grips on it. I think coldone's suggestion is probably the next best strategy to free up the valve.

I hate saying this, but I think this probably isn't the cause of your lack of power problem. Many times in the past, I have been troubleshooting one problem, and stumble upon another unrelated problem. It's just a matter of your intense scrutiny of the tractor that revealed this stuck spool valve issue. But, I would be happy to be wrong.

I keep pondering the feasibility of using the holes in the side of the dash to affix a pressure gage more or less permanently. Something functional that doesn't look like a drunken monkey added it. Maybe I can find an instrument pod to attach that will look ok.

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I started with my 'D' a little less than a year ago and quickly realised I'd have to try and get to grips with how the hydro system works starting from a point of knowing nothing at all about them. Still reading and learning but I'll get there with the shared knowledge pool that we have here.

Here's the question that I keep going over and over in my mind though... How does all of this translate into a lack of power? (Which was the real reason I dove into this discussion in the first place.) When I start out cold, the power I have seems acceptable. Might not be as good as it could be, but I don't know any better not having experienced what a functioning D hydro system should feel like. Within 15 minutes, though, I can already see a significant drop in power and the temp is barely at 150 degrees. Pressure is still 250-300 psi though. I'm just thinking that if indeed this implement valve is the problem, then why does performance drop continuously the longer I run the tractor? Shouldn't I see just poor performance from the get go? Just wondering. I really want this valve to be the proverbial "smoking gun", but I find I'm preparing myself for disappointment.

Yep, you've gotta prepare yourself for this one (several of us have been there and experienced that) but.... you do have to work your way through the system fixing things that are clearly wrong as you go along. Running at those high pressures all the time isn't doing your hydro any good and to my mind needs sorting now in the frst instance. It may sort the problem out.

It still perplexes me that the valve is rotated 90 degrees from the other one.

The spool is able to rotate in the main valve body by design, what prevents it from doing so is the 'hook' that passes through the hole in the end of the spool shaft and that's broken off so your valve rotated after the shaft broke off but before it seized up.

Andy

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Playing catch up here (been on hols).

Mostly makes sense - but a few questions (mainly for Andy) :

Which pump are we on? sundstrand piston or hydrogear?

Assuming you are testing the pressure on the implement port?

If so then surely that has no bearing on the pump for the drive motor?

The charge pump is geared and runs at 700 psi doesn't it?

Am I missing something and being a bit daft here :confusion-confused:

mark

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Sundstrand piston piston - with permanently high charge pressure.

No, the charge pump runs around the 100 psi mark give or take, must never fall below 50 psi or cavitation will destroy the hydro pump and motor.

Pressures in the 700 psi range only occur in the charge system when implement ram reaches end of travel and control valve is held open.

At this point the implement relief valve opens preventing damage to the hydraulic pipes etc.

Andy

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Sundstrand piston piston - with permanently high charge pressure.

No, the charge pump runs around the 100 psi mark give or take, must never fall below 50 psi or cavitation will destroy the hydro pump and motor.

Pressures in the 700 psi range only occur in the charge system when implement ram reaches end of travel and control valve is held open.

At this point the implement relief valve opens preventing damage to the hydraulic pipes etc.

Andy

cool - now caught up, yes if piston pump/motor loses charge pressure then bubbles/voids appear and massive friction occurs... seen quite a few things destroyed by that.

This is the reverse - with over pressure causing high temperature...

back to the thread then :)

So problem could be down to relief valve or blockage/restriction in the system. Sounds like implement ports being blanked off might be a start to eliminate that part of the system.

Might even be worth removing the oil pickup strainer and filter to see if theres any debris. Shame a D sunstrand isn't as easy to remove and split as a GT14.

For what it's worth, mine gets warm after 20-30 mins of pulling a ton trailer at full revs / half speed. It only makes noise at low revs or high revs and massive load.

That much heat will always lead to low pressure and does not sound like a good sign - it's either working really hard to pump/suck or grind metal :hide:

fingers crossed it's not the latter. Did I read that right that it's running at 150 deg F - I'd hope mine doesn't get to 100 - unless I was really making it work hard.

mark

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OK everyone, the preliminary results are very encouraging! Got the implement valve out. Just disconnected the metal lines and was able to maneuver the valve to a position where I could tap the bottom of the valve stem and drive it back up. After 4 or 5 solid raps with a deadblow hammer, I was able to move it to the neutral position. It even turns freely. Took me about an hour to put everything back together.

Held my breath and started the tractor. To my delight, pressure held steady at about 100-125 psi. Didn't run it long, but even at lower rpm's the pressure held steady. No 400 psi! Moving the implement handle, it bottomed out either direction and hit about 425 psi at the end of the travel. Not the 550-700 that the manual says, but perhaps there are other reasons for that. Tomorrow, I'm going to take it for a spin and run it awhile and see what happens. I will report back!

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All right! It might not be perfection, but at least its progress. Major progress at that.

I am very interested to know what the results of your test drive will be tomorrow. Well keep our collective fingers crossed and even sacrifice a craftsman over a bonfire for good luck.

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Fingers are crossed that everything else is ok.

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If only one of the implement valves are bad you could just get a single C series valve and add it to the set. Just thought i'd mention that. I know a guy who is after the thimble on the bottom of the valve. I think he lives near Boovuc. Maybe you could sell that part and get a little money back or something.

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Well, mixed emotions on the trial run. Started out good. Ended up fair. Now the opposite seems true regarding pressure. All the way down to 25 psi when in operation. That can't be good. In neutral, I was able to maintain about 50. When cold, about 100. Temp slowly topped the 200 F mark. Still below the old number with the stuck valve, but still too high. Perhaps it's time to look at the pump or motor more closely? The stuck valve was definitely a piece of the puzzle, but not the last piece. Even when I wrapped up mowing the lawn, I still had more power than I did when the valve was stuck. So I guess that's a good thing.

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I am glad to hear that there is at least some progress. I guess it's the pump next. Good think is that Jeff and Paul wrote up a great rebuild thread. It should help a lot.

Might want to pick up an extra set of orings or two. Just in case.

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I know the feeling only too well Tommy - I was elated when I discovered a broken spring in the acceleration valves in the motor on mine then gutted to discover that replacing it didn't cure the fault. Welcome to the dysfunctional 'D' roller coaster ride.

The problem with pinpointing faults on hydros seems to be down to a case of dealing with too many variables to accurately interpret pressure readings and symptoms. I think we're all getting a pretty clear picture of why hydro places simply tear the whole thing apart, replace everything they can on the basis it's the only way they can guarantee the work they've carried out. Trouble is that approach makes the work very expensive and some parts for ours are unobtainable now.

I'm still racking my brains over Paul's curious readings and overheating but your new readings are equally 'odd' in some ways though very different. We know that your charge pump is good - its capable of producing high pressure so it would be easy to jump to the conclusion that wear in either the hydro pump or motor is resulting in the low charge pressure readings that you're getting now the implement circuit is working correctly. This would be based on the fact that the charge pump isn't able to keep up with larger than normal oil loss from the hydro pump and motor loop as the oil heats up and gets thinner.

This may be a contributory factor in all that's going on with you tractor but for me there's also puzzling feature. With the implement circuit effectively blocked by a stuck control valve and at 175 F you were originally getting 175 psi with the hydro in neutral and the engine running at idle You could also achieve 280 psi with the throttle open as I recall so here's the puzzle. With the implement circuit effctively blocked charge prssure was being limited by the implement relief valve and the charge pump could more than cope with losses from the hydro loop. Now that the implement circuit is clear, charge pressure should be maintained by the charge relief valve in the range 75 - 150 psi but this doesn't seem to happen.

The next thing I'd want to check before tearing into the pump or motor is the charge relief valve. You could try removing it to check that the seat's clean etc but if Paul has a complete valve and spring from a unit he's taken apart it would be worth cleaning the seat and swapping the valve and spring over as I'm not sure how else one could eliminate the spring being weak.

A word of caution re further testing though - don't continue to operate the tractor if the charge pressure drops below 50 psi. It's mentioned in the manual. Below this there's a danger of air pockets developing in the hydro loop (pump and motor) which can cause damage to the system.

Interested to know what others think re the pressure readings now the implement circuit is clear.

Andy

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The readings that you are getting now are almost exactly what I was getting when I started troublshooting the D200. I am going to say go ahead and pull the hydro motor and take a look at the valve plate.

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Andy, I'm trying to determine where the charge relief valve is located. Is it on the motor or the hydro pump? Coldone, you had success with polishing the valve plate in the motor, did you not?

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I suspect coldone is right and there may well be underlying hydro pump / motor issues. I'd still want to check out the charge relief valve though - in theory it's pretty easy to do and it eliminates another item before proceding to the motor. It's actually the first thing to check according to the Sunstrand troubleshooting chart before moving on to the motor.

gallery_4509_190_13485.jpg

The charge relief valve is located on the same side of the pump unit as the push (tow) valve - it's the one at the top on that side.

Unlike the check valve, it has a hex head cap and isn't down inside a hole so it shouldn't be too difficult to remove and inspect.

I'm not sure how best to make sure the valve seat is clean - looking for suggestions here from those who've been there and done it.

Andy

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the fact that you have had high pressures would semi-eliminate the pump wouldn't it for now?

I'd be looking at charge relief onwards...

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To check the charge relief valve, all you need to do is pull the left side panel under the PTO lever. The plug is an ORB so all you need is a socket. The hydro motor is a little more involved. I ended up pulling the entire rearend out to get to my motor since I was already setup to do that. Another quick check to make would be the "buffer" valves that are connected to the hydro motor. If they are leaking they will bypass high pressure fluid over the low pressure side. The accel valves in the motor are another quick check also. They have an extremely tiny bleed hole in them that can get clogged. The accle valves will have to be disassembled for a thorough check.

I performed all of those checks before I pulled the motor and restored the valve plate.

Britt

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As to cleaning the charge relief valve seat. I uses a bore brush from an rifle cleaning kit. it is copper so it won't damage the machined surface. I had my pump out and disassembled at the time. There is some risk of a piece of copper wire breaking off.

If the pump is still on the tractor i would limit my cleaning to solvent and Q-tips. If it doesn't clean up the it may be time to pull the pump for a complete go through...

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If cleaning with solvent, are there any seals that might get damaged?

Also, there are lots of different sized bottle brushes on the market. I would imagine that nylon bristles might be safer than copper ones. Not sure where to procure them locally. Working in labs all my life, they are sorta ubiquitous.

When cleaning things, don't use paper towels, use cheap coffee filters instead. Coffee filters are better to clean certain things with, as the are lint-less.

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