Check valves on my Backhoe?

/ Check valves on my Backhoe? #21  
I have seen somewhere a thermal releif valve that could be put on cylinders, but I am guessing each time they would bleed off pressure than where you set it at would than be at wrong height. I think they are non adjustable so you would need to allow 400 to 500 lbs. over pressure releif. Just thought I would add that!
 
 
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