i have a problem with some extending forks. The truck only has 3 hydraulic function with a change over manifold from the 3rd function to give a 4 th function. The truck has lift (1st function) tilt (2nd function) sideshift (3rd fuction) extending fork (4th function). 4th function is operated by a dead man switch on the floor plate. The switch operated 2 solinoids in a manifold fitted to the fork carriage backrest. The forks operate in and out ok, but when they are pulled all the way back to the heels, after about a minute the left hand fork creeps forward about 20mm. i have tried using a different spool (on the main valve block). and many other different things. i was there was some sort of back pressure in the system cause by a difference in hose sizes, so i was told to try putting a hose between both inlet and outlet with a restrictor in the equalise the pressures. This just made both forks creep forward but much quicker.
Has anyone had this problem before and is there a quick fix. looking at this on paper it shouldn't happen. The fault gives the impression that there is air in the system, but when looking at how the forks work this is very unlikely. The forks have the inlet and outlet going to each side of the forks and a hose linking the two forks together in the middle.
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I know this is a very old post but I'm having the exact same problem with the kooi reach forks. It's quite weird in that it seems the cylinders for each fork are setup in series. As in each fork has a hose coming from the mast and then a hose joining the two together if that makes sense. My guess is the piston seals are bypassing.
It's actually a real pain in the **** on this machine because it has a Hall effects sensor fitted so when the forks are extended the travel speed will be limited. So when the fork creeps forward it slows the machine down.
So anyone come across this and found the issue?
Hi Leon. I would check the D/A seal for bypass on one jack. With the forks right back you have pressure in the front of both jacks. This is trapped by the valveblock being closed (or Solenoid valve etc). If the pressure trapped in the front of either jack can ecsape via the piston (D/Actiing) seal it causes the other jack to move outwards just as you have described but within the limits of any mechanical hinderance. (Free play etc)
Also. I would check stroke length and fixing points on both jacks to make sure thay are identical. A pair of Tilt jacks will do the same as you describe if the D/A seal lets by. I would start again and remove any extra bits that have been put in to try to solve this, before starting your checks. Cheers. baz c.
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