Was going to ask but forgot till I was thinking about it today. Before I tore my machine down I noticed when I ran out of travel on the cylinders, something made a rapid "tapping" noise. Sounds almost like an air impact on a stubborn bolt, as fast, but not as hard. I thought it was the bypass valve, but wondered if that was normal. Just seems like an odd sound for a bypass. I've heard them hiss and squeel before, but never hammer like that. Just wondered, cuz if it needs to be checked or changed, now would be the time before I get all the hydraulic fluid back in it. I don't make a habit of running the cylinders out of travel, actually I'm pretty careful about such things. Figured if something was going to give I wanted it to go before I tore it down. Anywho, the noise was coming from behind me, which is where the bypass is located. The sound is what has me confused.
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It has those, but my 600 has a "master relief valve" in the pressure line just upstream from the pump. It's to the right, and just above, the hydraulic filter. When tripped it diverts fluid back to the suction side between the filter the pump. Also, I see there is a check valve in the system that holds 20lbs of fluid pressure to the drive clutches. My other thought was perhaps it was just the watered down hydraulic fliud causing the bypass to rattle like that. I'd hate to tear the whole thing apart and find nothing wrong. My biggest fear woth doing that, is working with nearly 40 year old fittings
Here is a cropped image of the system. Had to keep it under 500x375 max for clarity. #6 is the Master relief Valve. #8 is the Check Valve for the clutches.
