Hydraulic spool valve clearance

[lfw618]

For high pressure, directional control valves, I have read that the diametric clearances from spool to bore are generally around .0002"-.0006". I was wondering what this refers to? Would this be both the spool and bore at maximum material condition? Or is that just the clearance based on the size limitations from both, and that concentricity and out of roundness are not included in that .0002"-.0006" clearance?

Thanks in advance.

 

[MikeHalloran]

GD&T may not apply.

I have the impression that good high pressure valve spools and sleeves are fitted to each other individually, and are not interchangeable, and that the clearance is damn small.





Mike Halloran
Stratford, CT, USA

 

[lfw618]

Ahhh that would not be ideal. If it makes a difference the assembly I'm concerned with does not have a sleeve, the valve slides directly in the bore in the block, with the bore being either ground, or lapped/honed.

Thank you.

 

[MikeHalloran]

I'd expect that a body that's not circularly symmetrical, would distort enough to bind under temperature changes or stress from external forces, like mounting bolts, if the clearance were small enough to seriously limit internal leakage.

If the clearance is large, i.e. internal leakage is not significant for the application, I guess it would be okay.

Are you working with actual production valves, or just math models?



Mike Halloran
Stratford, CT, USA

 

[lfw618]

Working with actual production valves. Internal leakage would be significant for the application. Temperature of the oil/ambient conditions would be regulated. I am concerned about binding though, it seems like it would take very little to potentially bind up with such small clearances.