Hydraulic Lock Question?

[svi]

Would one hole of 1.2mm have the same flow characteristics as three holes of 0.693mm? They have the same overall area, would they all hydraulic lock at the same time or would the small holes lock first?

 

[JTT]

Seems to me there is a mathematical equation for this, but not being a mathematician (or even able to spell it), I don't know what it is off the top of my head. I seem to remember that it is not as simple as the equal overall areas though...pretty sure the big hole still flows more.

 

[kevin5758]

Technically, I'd thing the flow characterists would change as soon as you alter the original hole.
From my experience, the three holes would lock first. There is more surface area for the oil to flow accross. (3.8mm vs 6.5mm) This will have some effect.
A simple way to find out might be to drill the two sets of holes, hook it up to the garden hose, count to ten a see which one fills a bucket the most. (if the hose would produce enough pressure)

 

[svi]

That's as I suspected, so I could drill a number of small free bleed holes in a piston to give reduced damping at very low shaft speeds without impacting on a wide speed range that one large hole would create.

 

[kevin5758]

Be sure to have a spare piston. Drilling holes is a fun way to learn things, but it's hard to go back.

For one experiment, I put a small bleed for the rebound. When riding, I noticed I had to run the rebound adjuster at about 11 out, while normally I would run it 14 out. It took awhile to figure it out, but eventually I learned it did the following:
At 11 out, the rear would rebound correctly for about the first 1/2 of wheel return and felt fine. But when launching of larger / abrupt faces of jumps, the bike would shoot strait up in the air. (almost looped out) It turned out the hs rebound was to slow and didn't pop the back of the bike up enough to level me off. At the normal 14 out, hs rebound was ok again, but the rear was busy and boingy over smaller stuff.