Here is my post about it with additional links to post, the valve and video of before and after.

https://talk.newagtalk.com/forums/thread-view.asp?tid=549000

Get a hydraulic flow control valve that controls flow in one direction and plumb it to control flow raising marker.

http://www.surpluscenter.com/Hydraulics/Hydraulic-Valves/Flow-Control-Valves/1-4-NPT-5-GPM-PRINCE-WFC-400-IN-LINE-FLOW-CONTROL-9-7960-4.axd

The orifice where the hose goes into the frame of the planter only controls drop rate.

This way you can dial in the raise speed you want and take the slamming out of the markers. Works like a dream and saves a lot of abuse on the marker arm and steel bumper stop.

Here is a close up of the valve courtesy of Surplus Center.

Here is the photo album you should be able to click on the .wmv files and they will play directly without having to download. 

http://imageevent.com/vprb/hydraulicmarkerflowcontrol

(Valve.JPG)

Valve.JPG (24KB - 155 downloads)