Insane Hydraulics

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Two Times in a Row!

This is the one kaboom story I've been craving to share for a long time, but having no pictures to illustrate it with forced me to wait patiently for the day X. Fortunately - the right pump popped up, and I finally can tell you the sad story called "twice in a row".

The story is about a Rexroth A7VO55 open-loop unit, and the pictures below are from my post about this model - A7VO55LR3E. I have no images of the actual scrap (this tragedy is from the old days - when I wasn't carrying my camera everywhere I went, and the phones weren't smart), but it's still a nice story, so I kind of hope that your imagination can fill in the missing details.

Rexroth A7VO55LR3E Hydraulic Pump
When you remove the torque limiter control, this loose pin can fall into the pump case!
The pin is not attached to the spool!

So, here it goes.

Once upon a time, a machine owner appeared at our doorstep, and he brought an A7VO pump with him (exactly like the one on the pics above). The complaint was - "it makes a funny noise, and the machine won't work". We opened the pump and discovered a completely trashed rotary group. The damage pattern suggested that something very hard got jammed in between the barrel and the valve plate, leaving a deep scar on the bronze surface, and pretty much mutilating everything else. It wasn't difficult to determine what it was since the torque limiter pin was missing. When the man saw the parts - he recalled that the torque limiter was dripping oil, so he gave the order to dismount it and replace the O-rings. Of course, when the torque limiter valve assembly was removed, the person who performed the task wasn't aware of the small pin behind it, nor he was aware that this pin wasn't attached to it - so it fell directly into the inlet, destroying the ill-fated unit! What's done is done, so the man cursed, stiffened up his upper lip, and paid for the expensive overhaul.

About a year and a half later, the same guy came to our shop with the same pump. When I said something like "Don't tell me that you removed the valve to replace the O-rings again..." he looked at me, surprised and puzzled at first, and then (and this was the most interesting moment of all) he didn't utter a single word, but for about five seconds his facial expression clearly relayed the following array of emotions:

The last phrase was pronounced out loud (in Portuguese), and I agreed with the man that he indeed was in a pickle... again. The following disassembly confirmed the diagnosis, and in the end, the man had to stiffen up his upper lip yet one other time...

I am so sorry that I took no pictures - the damage was extensive and picturesque.

I've been carrying this story for a long time, waiting for the right example pump. Many A7VO pumps with torque summation controls passed through our shop, but all of them had the connecting rod attached to the spool with a small spring pin - so I couldn't use them for proper illustration...

Finally, I can take this load off of my chest and pass this story to the privileged circle of IH readers.