Spool Valve Seals

[granitepeak]

The last of the external leaks on my Davis 185 backhoe are coming from a few of the spools. The diagrams show the seals press in from the top. Is it possible to remove them without pulling the spools? #18 in diagram.





Thank you,
Don

 

[the old grind]

When I worked repair in the transmission plant (THM-350) we would replace pressed-in selector shaft seals on a smaller scale than my BH's 6 gpm valve spools and in aluminum vs steel 'cases'.

With the stack as shown in the diagram use an awl & hammer to punch just enough thru' the metal face tangent to it that you can pry the seal out without the awl's point scratching the bore.

A driver might be improvised from a deep-well wrench socket etc. Size whichever as close to the diameter of the seal as is convenient. Add a short extension to help hold it straight going in.

 

[dfkrug]

Is it possible to remove them without pulling the spools? #18 in diagram.

Do you have access problems, Don?

It is usually not too hard to get the spool out, and that is the correct way to replace the seal. You need to remove retainer (#10) from the other side.

 

[granitepeak]

Thanks for the idea.

 

[granitepeak]

Access is not an issue. The valve is 65 years old and am concerned that I will open a can of worms without replacement parts available. Depending on other ideas, so far Plan A would be as the old grind suggested, plan B would be your suggestion and plan C would fabrication of a mount for a new unit. I am going to live with it until I get some work done and then tear into it.

Thanks,
Don

 

[mike48130]

So it has always been my understanding that hydraulic spools do not have "seals", but they are just dirt wipers basically. The seal is between the housing and the spool. They are honed to match at the manufacture and the seal is steel to steel. I think you are wasting your time replacing them, it will probably still leak.

 

[wdchyd]

So it has always been my understanding that hydraulic spools do not have "seals", but they are just dirt wipers basically. The seal is between the housing and the spool. They are honed to match at the manufacture and the seal is steel to steel. I think you are wasting your time replacing them, it will probably still leak.

They most certainly do have seals, and many......though there are no seals in between the ports inside the spool, only seals near the end of the spools, and in between sections (which the OP will not have because of the monoblock design).

 

[mike48130]

They most certainly do have seals, and many......though there are no seals in between the ports inside the spool, only seals near the end of the spools, and in between sections (which the OP will not have because of the monoblock design).

I don't think I have ever seen one with internal seals designed for pressure, at least in this type of application. I think what he has is just a dust/dirt seal. I know it is a monoblock and he was asking specifically about seal #18 in the picture. The diagram shows no other internal seals. The other end is a dust cap and centering spring cap.

 

[dfkrug]

The valve is 65 years old and am concerned that I will open a can of worms without replacement parts available.

If you can successfully remove the seal without taking out the spool, then you will have to slide it over the exposed upper part of the spool. That will require that the upper part of the spool is very clean and free of paint, rust, and other bad stuff.

At least your monoblock valve has no seals between sections, as stack valves do. I am dealing with inter-section seal leaks now, on a hoe valve.

 

[granitepeak]

Went trough this with my steering. On my power steering, the spool to the body wear was to great and therefore to much pressure escaped causing the upper seal to spray fluid and could not be repaired. It could very well be that the same issue(as you described) will surface on the backhoe valve as there is no way these seals could hold back the operating hydraulic pressure. It doesn't seem to have much pressure as it is a drip here and there from each. More reason to try and pop a seal out and replace it on one spool to see if it helps.


Thanks,
Don

 

[granitepeak]

So it has always been my understanding that hydraulic spools do not have "seals", but they are just dirt wipers basically. The seal is between the housing and the spool. They are honed to match at the manufacture and the seal is steel to steel. I think you are wasting your time replacing them, it will probably still leak.

It will not hold back operating pressure for sure.

 

[granitepeak]

If you can successfully remove the seal without taking out the spool, then you will have to slide it over the exposed upper part of the spool. That will require that the upper part of the spool is very clean and free of paint, rust, and other bad stuff.

Very true.

 

[the old grind]

Looking again at the diagram, #14 seems to be more a seal on both ends of the sleeve itself, the top one being perhaps changeable by just pulling the sleeve partway out. (O-ring?)

My advice on page one was with expecting #18 to be a lip seal with steel shell/face vs say a poly bushing/wiper, I now agree more likely. If that wore enough to let dirt gum up or mess #14 changing both would seem to vet whether the bores were worn enough that a good #14 wasn't enough to reduce the leak enough.

If what leaked between #14 & #18 could drain to return, would the top one have to contain much pressure? (unlikely :laughing Double-lip seals at both ends of crank/cam shafts contain oil pressure that I bet is fairly higher than return pressure in an OC valve/stack.

 

[granitepeak]

I looked up #14. They call it a ring seal, so your correct. I think I will pull 1spool and prepare myself for a new valve assembly and the work required to make it work.
Thanks
Don