Pinhole leak B21 relief valve

   / Pinhole leak B21 relief valve #1  


Elite Member
Jul 29, 2013
Sacramento, California
Kubota B21
This relief is on the backhoe valve stack. About half of it looks like it has been gnawed by a rat. You can see the pinhole in that area. The relief is in a place where debris never accumulates and has a light coating of oil because I spray the backhoe linkage periodically. Never seen a corroded part that looks quite like that. There are six of these reliefs on the valve stack, one other has a bit of this kind of corrosion and the other 4 are still perfect. So six valves in the same place and one corrodes to the point that it springs a leak. There is no corrosion on the valve body or linkage or hose fittings either.


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   / Pinhole leak B21 relief valve #2  
That looks like galvanic corrosion caused by dissimilar metals in contact with one another, same as what you'd see on a boat that had no anodes. What's close to it that could be causing the reaction, any kind of odd metal? What is the valvebody made from, looks like steel, is it?.................Mike
   / Pinhole leak B21 relief valve
  • Thread Starter
OK I am sure you are right about the galvanic corrosion. The body of the new relief valve is steel, and it is magnetic, but shiny like some kind of stainless steel. That is the part that corroded away. Mystery why 1 of the 6 corroded badly, 1 a bit, and 4 not at all, in the same location. Anyway the new relief is installed and works properly. Will get a spare for the second corroded one. Thanks for the tip on galvanic corrosion.
   / Pinhole leak B21 relief valve #4  
I just went and checked my B21 BH valve stack and no corrosion signs at all - they are all black and look fine. Also looks like a bit of an exercise to change the valves out too!

Interesting corrosion on one of many under there - I suspect its bad steel to break down like that. Galvanic corrosion occurs when different metals are in contact with water or ground - like the sacrificial anodes in a water heater or a boat with an electrical connection to ground.

Thanks for posting - this is a mystery!