OT: hydraulic help needed!

Search
Go

Discussion Topic

Return to Forum List
Post a Reply
Messages 21 - 40 of total 96 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 2, 2013 - 03:12pm PT
Hate to poke, Werner, but:

Thanks for the update adatesman.

I love your your stuff here .....

might be the first time I've even seen you say you liked something here on ST. I'm flattered!

:-)

-a.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 2, 2013 - 04:28pm PT
Hmmm.... So much for the "lengthening the stroke on the spool" plan. Looks like the stroke is limited by the housing and retaining washer, which allow only ~1/8" of travel. Weird, and has me wondering why they bothered making the slot for the pin so long.





I could get more travel by boring out the sleeve the pin is in, but dunno how much material would be left afterwards. And since the sleeve is clearly original, I'm hesitant to go that route. Perhaps 1/8" travel is all that's needed? And if so, that begs the question of why I didn't have any noticeable power to the cylinder yesterday, as I had the spool snugged up tight and close to where it was supposed to be and didn't see any pressure buildup when the pin was moved either direction....

Think I'll punt on this until tomorrow, as 8 hours on a Saturday is plenty for one day.
hillrat

Trad climber
reno, nv
Feb 2, 2013 - 05:09pm PT
Looking at the pictures helps a bunch. So, the spool is bolted solid to the housing actuated by the pin? Push pin left, spool goes left. Push right, spool goes right. Spring centered, always returns to center (neutral), correct?
As small as the cylinder is in relation to the valve body, and being directly attached, i'd say 1/8th is plenty of motion for the thing to work right. If you're uncovering the ports at all, you should get movement out of the cylinder. Most of the little ball bearing plugs are there for cross-drilling of passages, and yeah, you should really avoid removing them. Also avoid removing the pressed plug for the relief unless there's a way to verify that it's failed.
Remember that on a small cylinder like this, it only takes a very little volume to get a lot of movement, and fluid under pressure flows at a high volume.

The first two drawings represent what you'd likely see in an actual schematic, representing fluid flow. Ignore the first entirely, it's wrong. A reservoir is the only component that there are multiples of even though a machine only has one. (like Ground in an electronic diagram). On the spool valve schematic (2nd) there are 3 boxes that represent what the fluid is doing in the three positions of the spool and the paths the oil actually flows. In reality, the spool floats in between these positions with proportional flow in relation to how much effort you put in the steering and how far you move the spool physically.
The 3rd is like a generic cutaway of the internal guts of the valve, which should allow you to envision what happens as the spool is moved off-center and the ports connect. It's not exact either, but blue would be return to tank on that one, red is pressure, yellow and green are ports to the cylinder ends. I should have probably color-coordinated the lines on the 2nd drawing to match the third.

At this point, if you haven't got the cylinder apart yet, and you're pretty sure the pump is putting out flow (and thus pressure) then you probably ought to get the cylinder apart and replace the seals. Could be very likely that the piston seals are shot and the oil is simply bypassing the piston and flowing back the return to tank without moving it. If the seals are shot, you should be able to see that pretty readily on disassembly. Of course, this is not a gaurantee. Hard to diagnose from across the country. And I have no idea how hard all this is to perform from here.

I'm assuming, in saying that, that the spool is self-centering and firmly attached to the linkage like I asked above. Also assuming that the pump and relief are good at this point.

btw- your non-standard flow diagram looks spot-on.

How is this thing mounted?
photo not found
Missing photo ID#287742
hillrat

Trad climber
reno, nv
Feb 2, 2013 - 11:59pm PT
Ok. After re-reading this whole thing:

Your pump is rebuilt and producing up to 800psi. The steering system is separate from the main hydraulics for the loader/backhoe, and doesn't run anything else...?

You've mapped out the ports in the valve, pressure from pump at center, return on the outsides, cylinder ports between. Important to have the pressure/return hoses installed correct, as if they're backward they will exactly counteract whatever direction you try to steer, and the relief would not function at all.

You get lots of flow with everything running and in neutral (no steering input) so the valve is of "open center" design, meaning fluid simply passes through and returns to tank. Most gear-type pump systems run this kind of valve. That also means it's important to have a relief valve in the system so that when the cylinder bottoms out, fluid has a place to go. Gear pumps are positive displacement, meaning for every revolution they move a fixed volume of fluid. This by itself only creates flow. When you restrict flow, like closing a water faucet, pressure goes up. Without the relief, you end up finding the weak link... like slipping belts, blowing hoses, etc.

So if you have flow from the pump and the belts hold enough to create pressure, the plumbing is correct, and the spool is shifting side to side enough to open ports and divert fluid flow to the cylinder, we narrow down the possibilities:

1. The piston seals in the cylinder are shot and fluid is bypassing it, simply flowing through and back to tank.

or

2. The relief valve is stuck open or the spring is weak/broken essentially causing the same effect, allowing fluid to flow through it and return to tank at low psi when it should be moving the cylinder rod instead. Sucks it's under the swaged in aluminum cap.

The whole thing is kind of interesting in design, but without hoses between the valve and the cylinder it's a little harder to check things out. At least that part makes it impossible to cross the lines to the cylinder. Anyway...

relief valve, briefly... pressure acts against the check ball, which is held in place by a spring. When pressure overcomes spring force, the check ball/poppet/plug moves off its seat and allows fluid to flow by. on the right is a schematic representation of a relief valve. Fun stuff. You'd be amazed how a check ball the size of a BB can shut down an entire machine if it gets hung up. And in a fixed displacement pump system, the relief has to handle full pump flow, so if it's stuck open, there goes your pressure.
photo not found
Missing photo ID#287818
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 3, 2013 - 01:07pm PT
I think we found it Hillrat... At least, I'm 100% certain it can't possibly work the way it is currently and have something to fix.

But first, you asked how the thing attaches... In a nutshell, one end of the steering cylinder bolts to a bracket on the front axle, with the other end bolted the steering by way of the pin on the spool valve.


I got thinking about your post from last night and agree; it's got to be a problem with either the rod seal or the relief valve. And given it was 20 degrees out, I opted to drilling out that aluminum plug on the relief rather than heading over to the other house to take apart the cylinder.

Good news is that the aluminum plug will be easy to replace, as it's literally just a plug with an o-ring. New one will take all of 5 minutes to make, and I'll likely drill and tap the one side for a small screw to make removal easier in the future.



This also got me access to the relief valve, which now that I see it I can't imagine how this could possibly work as there's no spring to bias the ball and the oil is free to flow through unrestricted.





What this leaves me with is effectively this:



The way I see it, there's two options:
1. Make a new relief valve that incorporates a spring
2. Say screw it and plug the bypass, relying instead on either the relief on the pump to open or the pulley to slip.

Much as I'd prefer Option 1, I think I'm going to go with Option 2 because the relief in the valve only comes into play at the end of steering travel and because the pump's only putting out 2/3 of its rated pressure (should be 1200psi or so, but the pulley slips at 800). Plus making a plug will take 20 minutes or so, while a new relief will take the better part of the day (calculations, followed by machining, followed making the tooling to wind the spring, followed by actually winding it). The way I figure, if the plug works then I can decide whether to fix it properly or not.

BTW, I haven't yet looked at Grainger to see if they have a relief that will fit, but McMaster didn't.

Anyway, lunchtime!

-aric.
TGT

Social climber
So Cal
Feb 3, 2013 - 01:25pm PT
There's no spring in the exploded diagram.

Sure that isn't a check valve?

If it was a relief valve and had a spring in it, bits of that spring would have to be somewhere.
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 3, 2013 - 01:56pm PT
Sure does look like a check valve, and there's no evidence of a spring anywhere. That said, the o-rings were in fairly good shape so there's a decent chance it was rebuilt at some point (and possibly parts omitted, although there doesn't look to be any missing per the diagram).

FWIW, the parts diagram calls that bit a "Valve, Relief w/ Ball". And with nothing keeping it closed there's no way to build any pressure in the system short of overwhelming it with volume, which the small steering pump simply wouldn't have the flow for. At least, that's what I make of it....
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 3, 2013 - 04:49pm PT
Well, lost the bulk of the afternoon to playing with our little one (Helen, 2-1/2) while my wife took a much needed nap, so only got as far as machining the plug to replace the check/relief valve and a new aluminum plug to seal the passage, as well as getting it all assembled.

Pic of the replacement parts, and kindly excuse the overly-large slot on the plug... I already had a 1/8" endmill in the spindle of the milling machine and got lazy. Oh, and I upgraded the aluminum piece with a #6-32 tapped hole to make removal easier next time (happen to have a bunch of #6-32 stainless bolts handy, as well as the tap).

.

I'm sure I mentioned it elsewhere, but I'm *REALLY* loving this lathe. It's an old Clausing 5900-series (5917 to be exact), probably 1960's vintage, and 12" swing x 36" bed. Was an "upgrade" to my Atlas 12"x36" last summer (or the one before?), if you can call it that.... The Atlas weighed ~250 pounds. The Clausing is north of 1200 pounds, with the same work envelope. An absolute joy to use in comparison (not to say good work can't be done on the light and flimsy Atlas; just that it's easier and more enjoyable on the much sturdier Clausing). It's in the background of one of the pics above where I have the spool in the bench vice.

Man, I really wish they still taught this stuff in the general curriculum in schools.... Being able to make things is an important skill that everyone needs to have a degree of exposure to, IMO.

hillrat

Trad climber
reno, nv
Feb 3, 2013 - 10:04pm PT
Wow. Yep, the relief valve without a spring would be nothing but a check valve. That spring pressure is what the hydraulic psi has to overcome for the valve to open, and if you got no spring then you got no pressure.

Wouldn't it be nice to throw it back together and have the thing work?

Just don't tighten that belt too much or you'll find the weak link!

Sure is nice to have a lathe eh? I've got an antique (1917 or so?) Walcott in the garage. Too bad it's missing the 1 1/4x6tpi leadscrew and a motor. It was a basket-case when I bought it, so I'm making progress. Meanwhile, I went chukar hunting today. Football? What's that?
AP

Trad climber
Calgary
Feb 3, 2013 - 11:14pm PT
Never stand beneath a hoisted load. Damn right.
I was working in a pipe mill many years ago and the Pettibone operator came in to the shop after a near accident. He had stopped his machine and got out to throw a piece of lumber out of the way of where he was going to set this big scrap bin of steel. The hoist failed, bin crashed down and missed him literally by a hair. His jeans had a 6 inch rip from crotch to upper thigh.
bajaandy

climber
Escondido, CA
Feb 3, 2013 - 11:48pm PT
Man, I really wish they still taught this stuff in the general curriculum in schools.... Being able to make things is an important skill that everyone needs to have a degree of exposure to, IMO.

Not that I can help you with your hydraulics, but you'll be happy to know that we still have a fully functioning set of shop classes at the high school where I teach. We've got two machining classes, two fabrication classes, five woodworking classes, two construction trades classes, one CAD class and one Architecture class. The drafting and wood are my babies, with another instructor for the metal side of the show and one more instructor for the trades classes. In this day and age of schools closing shops left and right, it feels good to work in a district that sees the value of CTE.
WBraun

climber
Feb 4, 2013 - 01:16am PT
"Being able to make things is an important skill that everyone needs to have a degree of exposure to, IMO."

Just see

A real Yankee, with ingenuity ......
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 4, 2013 - 04:14pm PT
Not that I can help you with your hydraulics, but you'll be happy to know that we still have a fully functioning set of shop classes at the high school where I teach.

Absolutely ecstatic to hear it, in fact. Way too many of these programs have closed down due to liability issues...
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 4, 2013 - 04:29pm PT
Well, looks like perfectionism got the better of me again and I spent the day making a new relief valve anyway. I had given up on that approach when I couldn't find a spring anywhere near strong enough that would fit (less than 0.300" OD, 1" long and 30 pounds of force), but this morning I had a realization... The pressure on the ball bearing seal is a function of the size of the hole in front of it, so if I make that hole smaller I'll be able to use a much more reasonable spring.

A quick flip through the McMaster catalog didn't turn up anything, but Grainger sure did... 0.300" OD, 13/16" long, 11.9 pounds of force when compressed to 0.413". Plenty of physical space to fit that in the relief, and if taken all the way to 11.9 pounds of force would make the valve open at ~1500psi! Perfect!!!

So went ahead and ordered that spring and then machined a new relief valve, sporting a much longer body to make room for the spring:


Should be pretty self explanatory except for the little tabs on the back end... I figure I'll put a spacer inside behind the spring to compress it and then fold those tabs inwards to keep everything in place . Much simpler than trying to figure a threaded connection back there... Oh, and the cross-drilled holes are because this valve crosses in front of the main return line and I figured it best to reduce any restriction there.

Anyway, the spring will be here on Wednesday, so guess I'll have time to poke at the main hydraulics a bit... Will update this in a couple days to say whether the repair worked or not.

Thanks for all the help Folks! And Hillrat especially!

-aric.
FRUMY

Trad climber
SHERMAN OAKS,CA
Feb 4, 2013 - 07:33pm PT
adatesman It is an absolute pleasure watching you work through this.
Hillrat you are a treasure.
hobo_dan

Social climber
Minnesota
Feb 4, 2013 - 08:52pm PT
This is better than the super bowl--What's next? Did it work?
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 4, 2013 - 09:40pm PT
Thanks Frumy. Aside from the freezing temps and deadline, this has been quite an enjoyable project.

And yes, Hillrat's quite a treasure!
adatesman

climber
philadelphia, pa
Topic Author's Reply - Feb 4, 2013 - 09:44pm PT
Hobo-Dan- the spring won't be in until late Wednesday, so I won't know if it works or not until Thursday. I do have a nice pile of all sorts of sizes of spring wire sitting here (in both carbon and stainless), but simply have no interest in going through the iterations it takes to find the combination of wire size, mandrel diameter and coil spacing to get what I need. There's a day of trial and error right there, and when I can get a pack of them for $6 and have oodles of other work to do it's just not worth it.
hillrat

Trad climber
reno, nv
Feb 4, 2013 - 11:40pm PT
Well, I'm quite a something-or-other, but treasure maybe giving me a little too much credit. Now if you'd asked me about office management or something, that'd be outa my league. Just hoping the thing works for ya.
hillrat

Trad climber
reno, nv
Feb 6, 2013 - 04:37pm PT
Hey, if this all works out and the thing gets fixed, would you mind if I used this thread for a real-life example in the class I'm about to teach? I think the students could benefit from it. I'd leave out names and alter the content somewhat, so that it can be presented as a problem that they have to work on solving kind of along the lines of what we've been doing here.
Curious as to how this thing turns out when it's all said and done too.
Messages 21 - 40 of total 96 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
Return to Forum List
Post a Reply
 
Our Guidebooks
Check 'em out!
SuperTopo Guidebooks


Try a free sample topo!

 
SuperTopo on the Web

Review Categories
Recent Trip Report and Articles
Recent Route Beta
Recent Gear Reviews