Hydrolic Blade "hold valve"

ZGrant231 · Aug 15, 2018

My Sumitomo sh75 blade bleeds off from max height to ground level in about 2.5 seconds. Bleeds both ways up or down. I purchased the machine with this issue and I'm not sure how long it's been like this.

I have ran numerous tests on the cylinders come to the conclusion that both lift cylinders do not bypass, and are if good shape.
After consulting a hydraulics professional, he enlightened me that all cylinders like that need a "hold valve", but I can not find it.

Blade function is controlled by a cable activated sliding rod. The valve has 4 ports. Pressure,return to tank,A&B.

I've tracked the cylinder lines all the way from the actuator valve into the orbital valve, out the botom of the orbital valve, through the frame to the cylinders with no "hold valve" to be found.
Also no hold valve on cylinders, pipe thread to hydraulic fitting.
To be specific,
What am I missing?
Do all cylinders need hold valves?
Is the hold valve built into the actuator valve?

Any input is appreciated. Thanks

heymccall · Aug 15, 2018

Statistically speaking, since it drifts both ways, either cylinder, or both, are suspect.
Load check valves, if utilized, may be within the actuator valve.

You don't mention how many hours, and I cannot see the history of use/ abuse from here, BUT, bidirectional drift is "almost" always the cylinder.

StumpyWally · Aug 15, 2018

I agree with heyMcCall....& typically manufacturers do NOT put lock valves in the blade cylinder circuit, or the bucket curl circuit, unfortunately. Usually just in the boom & arm circuits.

If you have a service manual for your machine, you can look up the "allowable" drift for each circuit. It's usually a absurdly large number, on the order or 3mm/5 min measured right at the cylinder rod, but your drift is even way beyond that.

heymccall · Aug 15, 2018

The only other common point for bidirectional drift on that is the cable actuated valve. Whether the cable isnt putting it in neutral, or the control spool is scored are the ones that come to mind.

John C. · Aug 15, 2018

So how does a blade cylinder bleed up?

How were the blade cylinders checked? Were they dismantled and repacked? Was one end capped and the other end left open and force applied to the capped side? How was the swivel checked? Were the fittings feeding the functions above and below the ones for the blade capped and the top end left open and force applied to the blade from the implements? The first post says the hoses were checked looking for holding valves but not what was actually done to troubleshoot the problem.

heymccall · Aug 15, 2018

From what I inferred from the first post:
Blade raised above ground level drifts beyond noticeably
Blade used to raise machine allows machine to drop noticeably

ZGrant231 · Aug 18, 2018

Sorry for the late reply
No holding valves. Interesting.

-Heymccall, 4,200 hrs. Purchased from an estate sale. Unfortunately the previous owner passed and couldn't get much info. Other than it was used for his excavation busines installing septic systems. His receipts date back to 1998 @1,100hrs on the unit.

"Blade used to raise machine allows machine to drop noticeably"... yes but only if you lift the machine with bucket. What ever is bypassing is doing it so bad it won't lift the tracks, even at wide open throttle.

John C.
No I did not repack or dismantle the cylinders.
If you were referring to the cap and pressure of retracting side of cylinder like this

Yes I did.
Aside from a dismantle, what method would you use?

Was the swivel checked, no. It wasn't. Great idea, that didn't even dawn on me.

I'll take a video of the issue and post it tomorrow so you can see the symptoms.

ZGrant231 · Aug 18, 2018

And thanks for bearing with me. I'm definitely learning a lot about basic hydraulics and functionality of these ol' minis.

John C. · Aug 18, 2018

You can do that test but you have to unpin the rod end of the cylinder from the blade so nothing contains it. Are the packing on the ends of the cylinder barrel leaking?

ZGrant231 · Aug 19, 2018

Yes it was un pined.

No external leaks on any cylinders. Not even wet around the dust seals.

ZGrant231 · Aug 21, 2018

This video might explain the blade issue more clearly.

Ether a new symptom, or new to my attention. The left track travel in reverse seems to drop blade at a faster rate.
Orbital pivot valve leak?

John C. · Aug 21, 2018

That has to be a blown seal in the swivel.

ZGrant231 · Aug 22, 2018

Ok, thanks John. That's what I was thinking, but wanted second opinions before I pull it out. It doesn't look like fun.

ZGrant231 · Aug 24, 2018

Update on what was initially a problem with my blade bleeding off and not holding. Just in case some one comes across this same issue.

Blondie70 · Aug 24, 2018

What is it?

John C. · Aug 24, 2018

Nice job. How are the sealing surfaces?

ZGrant231 · Aug 25, 2018

Outer part of the excavator pivot valve.

My backyard/driveway mechanic experience said there ok.

At least they feel fine.

As I was using it, the travel function became extremely weak. That explains the rings totally gone. It prompted me to tare it down right there. I'm sure if I would have kept swinging it would have taken it out.

My next task is to find sealing rings and reassemble it with out nicking or cutting one.
Called all my local hydraulic shops within 150miles and no one has a clue for these 8 square sealing rings. The response is dealer item.

I contacted our listed Sumitomo dealer here in Oregon, Triad machinery in Portland and Eugene OR. Said
"Sumi..what? We're not a Samsung dealer."

Real confidence booster... Honestly I'm scared to death of this project. Sourcing parts and reassembly without screwing it up.

I'll resume the search on Monday, and post my findings.

John C. · Aug 25, 2018

You can get the rings at either a Case or Link-Belt dealer if you identify which model is the same as your SH75. It should be the same thing as a Link-Belt 75 Spin Ace. It also might a Case 9007B but the weights in the specs are a little different.

You will need something with some slow force to reassemble it. Try to line up the fittings and hoses to the same as it was when you dismantled it. The rings will be very tight and you will not be able to turn the halves by hand once you push it all together.

ZGrant231 · Sep 30, 2018

Just closure to a inconclusive post where I asked all kinds of questions, ranging from hold valves to hydraulic cylinder testing.

The rebuilt valve is in, and the unit is functioning great. Dug stumps and rock with it last week. What a beast!
Thanks again everyone!

Hydrolic Blade "hold valve"

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