Blew Out Hydraulic Chamber

I just rebuilt, in a way, a hydraulic pump. It
had some issues lifting, figured I'd see what I
could do about it. I dropped the pump, took the
whole thing apart, blew out all the channels,
replaced the side chamber gaskets, ground down the
valves and seats. I did a really nice job.
Replaced the safety valve. I replaced the lift
piston earlier with the newer style.

Everything was going great. Went out to test the
system. Test one (about 200#) worked great for
the lift and lowering. Smooth and held great.
Thought I might trying something a little heavier,
before I started patting myself on the back too
hard.

As I was lifting the heavier item, something in
the pump went BOOM!! Much to my surprise, it was
the side of the chamber, at the top, just below
the plug, as listed in the exploded view in the
I&T manual.

I was shocked to say the least. I can replace the
side chamber, as I've got spares, but not that
many spares. I don't want to make the same
mistake twice.

I can't figure out a few things: a) why didn't my
new safety valve relieve the pressure before the
metal blew out? b) did I tighten the cap screw
too tight. I didn't find a torque value for that
cap screw, and I've had them leak in the past, so
I really bore down when I put this together. c)
could the side chamber have been stress before,
had a hairline crack or something like that.

I did remove this pump from a parts tractor I
have. It is actually a steel pump, not a cast
aluminum pump (which surprised me). There was
some water in the belly as expected, but not that
much water. This blow out was right where the
plug (part #3 in the exploded view) meets the
valve chamber. Which would have been much higher
than any water that was in the belly.

I'll drop the pump later, and get some pictures if
that will help. I appreciate your thoughts. This
really woke me up this morning when it happened.

Bill........

How much weight did you have on the lift? The system is capable of lifting 800# or more without exceeding the pressure relief setting of 1600 PSI. So unless you had considerably more than that on the lift I would rule out a defective over pressure relief valve.

I'd be inclined to suspect something got caught between the mating surfaces of chamber and pump (e.g. piece of old gasket material). A high spot like that may have caused the housing to stress fracture when you tightened down the cap screws. Doesn't take much unevenness to fracture hollow cast iron sections......

TOH

It is interesting that you say that. When I
cleaned the old gasket off, it was tricky to clean
around the alignment pin on the pump base.
Couldn't use the razor blade, as I did everywhere
else. Scraped it best I could with a screwdriver.

I never would have thought that the chambers might
have a little twist or bend from a little extra
gasket material. Really a good thought there.
Thanks. Once I get a chance to drop the pump I'll
take pictures for other to see if interested.

Bill......

Oh, forgot to answer one of your questions. I was trying to lift a wagner loader frame, without the bucket. Just the front end of it, as the back was still on the ground. It was not mounted. I have no idea of the weight. Another person had told me that he had unloaded one of this in the past with a boom. I was using a boom at the time of breakage.

I just assumed that if the pressure was anything over the 1600 pound range, the safety valve would trip and I could never experience an over pressure situation, no matter what the weight. Just figured the weight wouldn't lift if the safety valve was tripping. I don't know if this is the right thinking.

I would say at the time I blew the side chamber, the loader frame was about 3/4 off the ground.

You realize that when lifting something at the end of the boom pole that weight is multiplied several times.

Are you sure someone has not tampered with the relief valve. The cap on the relief valve can be tightened down so it won't relieve at any pressure.

Zane

I did know that lifting something on the end of the boom can be problematic. Much of what I know about the 8N has come from a local friend or the hydraulic video that is available for purchase. Based on the video, I figured if the front end does lift off the ground, the hydraulics should lift it. I don't know if this is the right thinking. I had picked up this frame with another 8N that I have (who can have just one), with the same boom.

The safety valve was brand new, fresh out of the wrapper. As a rule of thumb, and in the interest of saving myself some hassle, I just replace them when I rebuild. I had wished I done it in the past. I never know exactly what they are set at. I trust that the "factory" has set these properly. I've got no way to test them.

Still haven't had a chance to drop the pump, yet and take pictures. As soon as I do, I'll post them.

Well, I dropped the pump. The pictures are
attached. One picture shows the section that was
blown out. In the same picture along the front,
from chamber to chamber, through the threaded
section you can see a good size crack.

Also, I did find a piece of gasket on the bottom
of the one side. I placed it on the top of the
chamber I found it in. I was shocked at the size
that was in there. I'm somewhat embarrassed,
because I thought I did better work and was more
careful than that. I had the whole thing apart
and sprayed the whole system before reassembling.

Did the gasket piece cause the cracks, or are the
cracks a result of the blowout or overall weakened
side camber? I don't know.

In my own mind, I'm thinking that the gasket got
in the way of the check valve, got bound up in
there and caused some unusual pressure on the
system.

I'm going to replace the chamber from a spare that
I have.

Thanks for all the help. If you have any other
thoughts, I would appreciate them.

I'm just guessing, but may be it was a combination of to much muscle on the cap screw and a piece of grit getting caught under there. Thanks for posting pictures might help someone like me.