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No pressure in pistons

Discussion in 'Fisher Engineering Discussion' started by Gicon, Dec 25, 2007.

  1. Gicon

    Gicon Senior Member
    from MA
    Messages: 989

    Whenever I go into a pile, the plow doesnt hold its position. I could have it angled all the way to the left, and it will go all the way around to the right. Anyone know what this could be? Its a 2 year old SS Xblade.
     
  2. snow7899

    snow7899 Senior Member
    Messages: 238

    I had a metal filing which was keeping the valve from completely closing. I pulled the valve assembly out and cleaned the port. No problems after that. The fisher website has the exloded view. I think it was the releif valve which was affected. I would udate the suction filter with the new style kit while your working on it. good luck.
     
  3. Gicon

    Gicon Senior Member
    from MA
    Messages: 989

    One of the relief valves on top where the motor is? Nothing to do with the piston down on the A-Frame?
     
  4. Gicon

    Gicon Senior Member
    from MA
    Messages: 989

    FYI Snow, I just had the fluid and filter replaced this season....
     
  5. rtm038

    rtm038 Senior Member
    from NJ
    Messages: 231

    There is a relief valve for each angle ram (i.e. cylinder) mounted inside the valve manifold. They are normally closed, which keeps fluid in the body of the cylinder when it's extended. These valves are designed to open and allow fluid to drain from the body of the ram back to the reservoir when the blade encounters an object (i.e. curb, hard-packed pile of ice, etc.) that could potentially damage the plow or truck This way, the impact doesn't damage the plow or your truck. Think of it as a "trip edge" for the hydraulic system. The amount of psi needed to open each valve is preset at the factory, however the valves are adjustable.

    There is a link to the mechanics manual for Minute Mount 1 & 2 plows that use the Insta-Act hydraulic units....http://www.fishersnowplows.com/pdf/27179_070001.pdf. In this manual you'll find information on how to properly clean and adjust these relief valves. But before you go through the trouble of either cleaning and/or adjusting the valves, make sure you weren't hitting anything "significant" (i.e curb, ice, etc.) beneath the snow that was causing the cylinder to retract. Important note: If you over adjust the valves (i.e set the relief pressure too high), you'll increase the chances of damaging the plow and/or truck if you hit an object beneath the snow.
     
    Last edited: Dec 25, 2007
  6. snow7899

    snow7899 Senior Member
    Messages: 238

    If you cannot find what you need, I have a factory service manual you can borrow. The fisher website is great and you should be able to find all tech articles there.
     
  7. Gicon

    Gicon Senior Member
    from MA
    Messages: 989

    RTM.......you the man. Thank you.
     
  8. rtm038

    rtm038 Senior Member
    from NJ
    Messages: 231

    No problem. Just be careful with the adjustments. Since you recently had the fluid changed, I'd drain the system, remove the valves and see if something (like a small piece of metal) is preventing the valve from closing fully. This is because, like the engine in your truck, when the pump itself runs (not necessarily the electric motor that powers it), it wears and as a result, very small pieces of metal are introduced into the fluid as it passes through the pump unit. As the fluid makes its way through the hydraulic system, a magnet in the bottom of the tank is supposed to catch and hold them (much like an oil or transmission pan) these metal particles. However, not all particles will be captured and held by the magnet. If one of these rouge particles travels through the system, it can get easily get lodged in one of the valves, whether its a poppet, relief, crossover or solenoid valve and prevent that valve from operating properly. This is why before doing any adjustments, I'd drain the system and check the valves.

    Also, you mentioned in your original post that if the blade is angled to the left, the blade will travel towards the right. Does the plow do the opposite- angled right, move left? With the plow raised off the ground, can you push against the backside of the blade and angle the blade manually? If so, either the crossover or S2 valve may be sticking or there might be air in the system. Is this the first time you've used the plow since the fluid change? If so, make sure you have enough fluid in the system. Too little will create air pockets in the system, which could prevent the rams from holding the blade steady. Just some extra things to think about before making those adjustments.

    Take it easy,
    Ryan