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Check with the Guru's

Your question is probably best answered by Dougal (originator of the thread you referenced) or AshwinEarl (frequents this forum) -- both seem to be very knowledgeable with regard to Manitou forks. My understanding of the SPV valve is that it is normally closed until the fork encounters a bump large enough to overcome the SPV air pressure setting, which then forces the valve to open and allow a greater oil flow.
 

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FrankinMich said:
Your question is probably best answered by Dougal (originator of the thread you referenced) or AshwinEarl (frequents this forum) -- both seem to be very knowledgeable with regard to Manitou forks. My understanding of the SPV valve is that it is normally closed until the fork encounters a bump large enough to overcome the SPV air pressure setting, which then forces the valve to open and allow a greater oil flow.
I believe FM is right. Check out this link:

http://www.bikemag.com/features/gear/spv/index.html

By the way, also according to that link (and thanks to Stratocaster's suggestions) I realized that the air charge in the SPV valve is just at atmospheric pressure. I opened it up last night, took the blue and raw metal pieces apart from each other to equalize the pressure and it seems to be working now. I have to take it on a ride to see if I can get more support in the midstroke without too much SPV pressure. If that still does not work, I may have to devolve my Minute and see how it rides without SPV.

What was the consensus reached on rebound damping? Is it possible to speed it up a bit by playing with the shims on top of the SPV damper? I am currently using Finish Line 5wt oil, what oil are you guys running? Also, do you know if the air pressure in the SPV chamber affects the speed of the rebound?

Thanks!
 

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nybike1971 said:
I believe FM is right. Check out this link:

http://www.bikemag.com/features/gear/spv/index.html

By the way, also according to that link (and thanks to Stratocaster's suggestions) I realized that the air charge in the SPV valve is just at atmospheric pressure. I opened it up last night, took the blue and raw metal pieces apart from each other to equalize the pressure and it seems to be working now. I have to take it on a ride to see if I can get more support in the midstroke without too much SPV pressure. If that still does not work, I may have to devolve my Minute and see how it rides without SPV.

What was the consensus reached on rebound damping? Is it possible to speed it up a bit by playing with the shims on top of the SPV damper? I am currently using Finish Line 5wt oil, what oil are you guys running? Also, do you know if the air pressure in the SPV chamber affects the speed of the rebound?

Thanks!
Yes, Devolve! My Minute 3:00 is more active now, and like you said there is some compression adjustable with the SPV pressure now.

When I had it apart to devolve, I removed one rebound shim (there was one small, two large diameter shims, so I removed one large one). Rebound still feels a bit slow just pumping the fork, but on the trail it tracks well, doesn't pack down. See what rebound shimstack you have and think about removing at least one shim if you want faster rebound (like the Devolve mod it's reversable anyway, just sketch the current stack arrangement for future reference).

Oil - Motul synth 5wt - 1 liter bottle is cheaper than the (~300ml?) Finish line stuff.

Rebound - below somewhere around 30psi in the SPV, the rebound damping goes away completely. I haven't tested whether small changes in pressure around that point "adjust" rebound, I think it's more that the damper needs to be pressurized for the rebound to work.
 

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nybike1971 said:
I believe FM is right. Check out this link:

http://www.bikemag.com/features/gear/spv/index.html

By the way, also according to that link (and thanks to Stratocaster's suggestions) I realized that the air charge in the SPV valve is just at atmospheric pressure. I opened it up last night, took the blue and raw metal pieces apart from each other to equalize the pressure and it seems to be working now. I have to take it on a ride to see if I can get more support in the midstroke without too much SPV pressure. If that still does not work, I may have to devolve my Minute and see how it rides without SPV.

What was the consensus reached on rebound damping? Is it possible to speed it up a bit by playing with the shims on top of the SPV damper? I am currently using Finish Line 5wt oil, what oil are you guys running? Also, do you know if the air pressure in the SPV chamber affects the speed of the rebound?

Thanks!
Yes you are both on the right track.

If the SPV valve is open when out of the fork, it generally means you're at a lower atmospheric pressure (or higher altitude) than when the damper was assembled.

The air pressure added to the damper through the top valve holds the valve closed. When you hit a bump the oil flow works against the air pressure to open the valve and let the fork work.

The air pressure in the SPV chamber will have a small effect on rebound, but only because the trapped air works as an additional air spring. More SPV pressure = slightly stiffer spring and faster rebound.
The shims operation are not affected by SPV pressure.
 
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