OT: hydraulic help needed!

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Messages 41 - 60 of total 96 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 11:34am PT
Ok Folks, the moment of truth is upon us. Picked up the spring for the relief valve this morning and finished it off, and by my calculations it should open around 1000psi. Heading over to install it...

Bill Mc Kirgan

Trad climber
Cedar Rapids, Iowa
Feb 7, 2013 - 12:11pm PT
Adatesman, I hope you get that rig running soon. I'm so impressed with the Old Schoolhouse project you've started, and am rooting for your success.

I can't help any, but...jes want to say

This thread is just more proof the the Taco is becoming the great repository of all that should be known about the universe.

On matters of the building trades, or computer repair, programming, photography, cooking bacon, coffee, car repair, chocolate, boat building, beer, MUSIC, ...whathaveyou? I tend to search the Taco first before resorting to the Google box. I don't think I'm the only one making this transition.

Very impressed with the power of the Taco.

Good luck with the hydro repair so you can get to trenching and frenchin' and stabilize the humidity and protect the plaster work in that amazing structure.


Ferretlegger

Trad climber
san Jose, CA
Feb 7, 2013 - 02:05pm PT
Hi guys,
This has been interesting to watch unfold. I hope the new solution works. For those with an interest in machining, especially "old school", and who enjoy crusty craftsmen at work, here is a link to Keith Fenner's page of (hundreds) of Youtube videos of his work. http://www.youtube.com/user/KEF791/videos?view=0. He is a real joy to watch and very generous with his advice and time. Beware: you may not get much sleep after you start watching these!!

Michael
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 02:19pm PT
First the good news- the backhoe's reassembled and it not only builds steering pressure when cranking over, but the wheels move!

The bad news- it didn't like sitting the past couple days and it refuses to start.

So close!!!!
hillrat

Trad climber
reno, nv
Feb 7, 2013 - 02:29pm PT
nice! try not to hold it over relief if you can. theyre usualy designed to handle full pump flow, and with the smaller hole it would be somewhat less. shouldnt be a problem as long as you dont keep it cranked to the stops.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 02:56pm PT
So close!!!

Got it running finally (forgot I had turned off the idle circuit in the carb), and it keeps a steady ~850psi to the steering valve. Even better, it will turn the wheels when parked with just a single finger on the steering wheel (which is a major improvement from not being able to turn it at all with both arms before).

Thing is, it only steers in one direction. And the direction is almost random, and based on the position of the spool at startup. Going to have to think on that.

adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 03:08pm PT
Hmmm... I think I follow, Hillrat.

And actually, I think we might have missed something that explains the goofy behavior. This diagram from before is based on actual measurements of the spool valve (read: relative positions are within a couple thou...), and looking at it again I'm not seeing how it isn't deadheading the pump if the relief is closed.



.... Which leads me to think that the problem wasn't a springless relief valve, but rather modern power steering fluid being a lot less viscous than the original "transmission fluid" called for and not seeing any restriction from the orifice in the original "relief" valve.

Easy enough to test this theory by removing the relief and splicing the gage and ball valve into the exhaust side of the spool valve (and use the ball valve to throttle it down/build pressure).

Not sure if this explains why I can't switch directions though...
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 03:32pm PT
A couple more clues... I'm 99% sure the spool is deadheading the pump and the new relief is not opening, as there's no flow apparent in the reservoir. If either the relief opened or the spool not deadheading, then there would be flow apparent. Additionally, closing the ball valve I have on the output of the pump has no effect whatsoever on the output pressure, so I'm pretty sure the 850psi I'm seeing is the max the pump is capable of (whether in total or by way of its relief valve).

As such I'm really beginning to think this whole mess is an oil viscosity issue rather than something mechanical. Any thoughts, Hillrat or anyone else? Seems to me that finding the right size orifice for the flow/pressure and fluid I'm using would be a simple matter of looking it up on a chart. At least, I hope so as I did terrible in fluid dynamics and really never want to open that book again.

Heading out of town for a couple days, but will be back on this Monday AM.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 03:41pm PT
Scratch that.... Can't mock it up by throttling down the exhaust port... That would leave no pressure differential to work the cylinder. Crap.
hillrat

Trad climber
reno, nv
Feb 7, 2013 - 04:25pm PT
i almost think its possible that pressure and return are backward at the inlet-
that would cause the cylinder to put more pressure on the valve in the direction it was steering and cause it to run to the stop.

Normally, when you move the wheel it opens the valve until the steering moves enuf to center the valve at which point everything would stop.

by your drawing, it does look like a closed center valve, which would mean pressure runs over relief all the time in neutral. Odd. have to think on that.

in any case, viscosity really shouldnt be a major issue here, and transmission oil vs power steer oil shouldwbe simikar viscosity anyway.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 05:31pm PT
Yeah, this sure seems a goofy way of doing it. Certainly would explain why they went to the more typical steering-column-mounted rotary setup a couple years later... Then again, the earlier models were all manual steering and this was certainly an easy way to graft power onto it. Unfortunately this model fell right after the change from manual steering, so does not have the steering box geared down far enough to make it work without assist.

Anyway, I just picked up the little one from an overnight at the in-laws and she's completely zonked, so pardon my talking this through while parked in the driveway...

If we assume that the valve is indeed a closed center (thx for the proper term!), then clearly there needs to be a restriction of some sort between the high and low sides to create the pressure differential to work the cylinder. Assuming the original springless relief was correct, it had to be relying on the combination of flow and orifice size to build pressure. From what I've read, the pump was rated at something like 1200psi and 6gpm, but best I can get it is 850psi at an unknown flow (don't have a way to measure it). Clearly the original combination of flow/orifice isn't working, as it wasn't building any pressure after rebuilding the pump. So I guess that leaves me guessing at what pressure it needs to run at, and then decide whether to obtain it by way of sizing of the orifice or spring pressure on a relief valve.

I'm thinking a spring loaded relief is a better option since it'll be relatively constant as the fluid warms, but a sized orifice much simpler.

Hmmm....


adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 05:33pm PT
Btw, Hillrat, absolutely feel free to use this in your class! Quite the interesting problem, having to reverse engineer everything to come to the solution. I probably even have more pics and a video or two of remachining the pump...

Oh, and what's the class?
hillrat

Trad climber
reno, nv
Feb 7, 2013 - 06:03pm PT
heh heh..
class is hydraulics.
Hard to say, this whole thing may not be original configuration, and it could be that smeones mixed and matched parts that dont fit together. Gear pump systems almost always use open center designs, unless its tied into the main hydraulics with a priority valve. Constantly ruming over relief in a closed center like this is going to build lots of heat, which will be bad in short order.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 06:25pm PT
Ha! Kinda figured hydraulics, was meaning more high school/college/etc. :-)

Fwiw, the pump, cylinder and spool valve body all appear to match the depictions in the parts manual (and/or have the correct numbers cast on them). Unfortunately no way to tell on the spool or it's relief, but it's clear someone had been in the pump at one point and did it correctly.

Little one's now awake and watching a movie, so currently throwing some dimensions on some pics to try and make sense of this (and prove one way or another if it's closed center).
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 07:18pm PT
Well, looks pretty decidedly like a closed center valve. Sorry about the goofy dimensions; it was a quick and dirty with a caliper (really doubting that 0.160"). And I've skipped a couple versions of my CAD software and haven't yet figured out how to get this one to do what I want it to, so gave up did it in MS Paint....



Not pictured is a pair of very small chamfers on 2 spots of each side of the center lobe of the spool (orange dots). At most they're 0.015" wide x .100" long, so nowhere near enough for much fluid flow. No chamfers on the other spool lobes. Oh, and one very small (~0.050" dia) hole going underneath each lobe on the spool, connecting the chambers on either side (brown lines).


EDIT- Occurs to me I never posted a pic of the pump... This is after an attempt to stone out the cupping in the mating surfaces, which didn't help with the pressure issues. The cover was subsequently drawfiled/stoned flat and the other piece turned flat and the bore for the gerotor remachined in the lathe, which helped immensely pressure-wise. Oh, and a completely new pump shaft was machined out of some A2 I had in the drawer.

hillrat

Trad climber
reno, nv
Feb 7, 2013 - 07:57pm PT
Were there any valves in the pump?
I don't see any discrepancies in the parts pictures you've got. All looks pretty straight-forward as to how it should be working. Basic kinda system. But I don't see any alternate flow path for the oil in the closed center system, which is weird.

I should have been more clear earlier... if the pressure/return were backward, it would steer in the opposite direction of steering input.

And I see there's a relief in the pump, just wondered if it's a straight relief or if it's something else.

It's a college class. I work as a mechanic by day, and teach a class once in a while part-time. Fifth class so far, 2nd hydraulics class. They've got a bunch of old books (or had some anyway) but i don't know if there's any on this thing. Was supposed to go up there today, but we've all been sick here, so haven't made it.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 08:21pm PT
Seems I didn't take pics of the finished but not yet reassembled pump. Oops. Here's the back of the housing though, which should make the relief fairly obvious... Basically just a linear valve that connects the high side (output is the flare fitting at the top) to the low side when the pressure on the high side becomes too great. Other than the relief and gerotor, the only parts are o-rings, bearings and the 2 halves of the housing.



And yup, steering direction was correct. Just that it wouldn't reverse without shutting down the engine and repositioning the spool.

Cool about the part time teaching gig. Would think that rather rewarding. Bummer about being sick though.

Oh, and:

But I don't see any alternate flow path for the oil in the closed center system, which is weird.

This is why I was thinking along the lines of the relief valve orifice size/oil viscosity thing. Nowhere else for the fluid to go, other than a small amount to cycle through the pump or the entire volume to cycle through the spool relief. Neither are great options, but the former much worse than the latter.
WBraun

climber
Feb 7, 2013 - 08:33pm PT
This is awesome guys.

Thanks so much for updating and good luck.

I love this stuff and I'm learning from you guys ....
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 7, 2013 - 08:42pm PT
You're not the only one learning, Werner. :-)

Hillrat must be one heck of a teacher, given his willingness to put this much time into this for me. Thanks again, Hillrat!
hillrat

Trad climber
reno, nv
Feb 7, 2013 - 08:42pm PT
so the relief in the pump is the same style as the spring/ball/seat as in the steering valve? Must be quite a bit larger then...?

Steers in the correct direction, but won't return until engine is shut down. There's no way pressure is getting in behind the end of the spool is there? Leakage, etc? I would think the cavities at each end of the spool should not have any oil in them, or should be vented to the atmosphere somehow so you can't develop a sticking spool somehow.

I'm the guy who hides in the back of the class, so teaching is a continual challenge. And if you want to learn something, try teaching it. Or, you know, threads like this. ha!

You don't have the parts diagram for the pump itself by chance?
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