OK, Here we go......
The one factor I had to figure out was approximately how big the difference of the midvalve swept volume versus how much fluid is actually passing through the base valve. The answer I kept hearing is "allot more", "big difference". I believe that those generalizations are true, but I need numbers!
A couple quick notes;
1.I am using a 1999 KX fork for reference (28mm cartridge)for reason being it has the same size piston diameter as the base valve.
2.My calculations are the total volume difference after the fork has traveled the entire stroke (manufacturer specs this at 12.2in.) (309.9mm)
3.I also am not trying to calculate any fluid "leaking" by the bushing at the top of the cartridge.
1. I took 3.14(14x14)309.9 to find the volume of the empty 28mm cylinder. (190725)
2. I figured 3.14(6x6)309.9 to find the volume of the piston rod (35031)
3. 190725 - 35031 = 155694 (m.v. swept volume)
4. 155694/35031 = 4.44
Result - almost 4 1/2 times as much oil flows past the midvalve as compared to the volume that flows through the base valve.
Ok, back to the original question of why a high flow piston works better for a midvalve. I can see how the midvalve that flows 4.44 times the amount of fluid might cause a restriction if we use a low flow piston. But actually, with really light valving who knows?? I guess you have to figure out how much fluid can flow through a low flow piston at max shaft speed without causing a resistance.
Anyone ever try a low flow piston for a midvalve??
How about tossing this " bone into the soup".....
A late model WP fork with a 28mm cartridge and a 14mm piston rod. This set up comes out to about 3 times the difference of the amount of oil passing through the midvalve as compared to the base valve.
Now, since the difference isnt as large (as compared to the KX) Would a low flow piston design work for a midvalve????
Yeah, I know, I answered a question with a question......
Allright , I am tossing this to you guys........whaddaya think??
Take Care, John
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99 KX250
98 KTM50
88 LT250R
86 TRX70