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  1. #1
    Veteran Member Mechanos's Avatar
    Join Date
    Aug 2010
    Roosterville, MO
    JD 955/70A/7 TLB

    Default Pressure Relief Valve on #7 BH boom swing

    Just wondering why the boom swing on the 7 backhoe has a relief valve set so low. The main relief is set at about 1750psi, but the boom swing has its own relief set at about 1025psi. Is there a weak point in the hoe that they are trying to protect or is this a case of corporate lawyers trying to protect us from ourselves? The boom swing uses two single acting cylinders plumbed together to act as a double acting cylinder.

  2. #2
    Gold Member
    Join Date
    Jun 2007
    Northern West Virginia

    Default Re: Pressure Relief Valve on #7 BH boom swing

    I have that same backhoe, but I didn't know it had its own relief valve. However I have noticed that it didn't seem to have much mmmfph in the swing, mainly when trying to push dirt from the spoils pile back into a hole with the side of the bucket, and occaisonally when trying to swing a bucket heaped full of wet clay uphill out of a hole when working on a slope.

    My guess is that a strong lateral swing with the boom and/or dipper extended might rack the boom (twist the rectangular cross section of the boom), and the special relief valve was engineered to prevent that.

    I've read several posts where people using other brands of backhoes have damaged them because the hydraulics were too powerful for the design of the hoe. I've used and abused my hoe a lot including things like using it to raise the rear of the tractor to move it a bit forward, backward or sideways for a better digging position. The only time I damaged it was when I accidentally backed up into a bank when the dipper wasn't fully folded (bent the hydraulic cylinder rod).

    While I wish it had a stronger swing, I'll assume the relief valve is there to prevent me from damaging the backhoe.

    As for "corporate lawyers trying to protect us from ourselves", I think if you were in a situation where 1750psi would kill you, reducing it to 1025psi probably isn't going to make much difference!

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