Vicsec VC13 mini-excavator

[zwelch]

After more research, I believe that the pump outlet port fitting is DIN 3852-H (adjustable o-ring style); it has a locking nut, backup washer, and retaining ring. From that, I think a DIN 3869 profile ring (aka "D-rings") might be the best solution, particularly since the backup washer does not fit snugly on the fitting shank. The two o-rings that I installed have both been extruded through that gap between the backup washer and the fitting. The D-Ring profile has a flat top and outer radius; those surfaces would seat flush against the backup washer and retaining ring, respectively.

Assuming that analysis is correct, it looks like there are plenty of suppliers that provide these in Viton/FKM. But to pick the right one, I need to tear the machine down again and measure the fitting's OD and the washer's ID and thickness. With luck, I can find a local hydraulic parts supplier with the one that I need in stock, so I don't have another weekend or two of machine downtime.

If I can't find a suitable D-ring locally, I will try to find a standard FKM o-ring with 90A hardness. If I can't find either, I might try to limp along with another FKM o-ring (probably 70A) from the kit that I have on hand. Otherwise, I will be stuck waiting for suitable parts to be delivered.

 

[dfkrug]

After more research, I believe that the pump outlet port fitting is DIN 3852-H (adjustable o-ring style); it has a locking nut, backup washer, and retaining ring. From that, I think a DIN 3869 profile ring (aka "D-rings") might be the best solution, particularly since the backup washer does not fit snugly on the fitting shank.

Just looking at the spare metric O-ring fittings I have, and the DHH catalog, it seems the fittings that need to be "clocked" have to have a backup washer in addition to the retaining ring. So, in comparing a straight fitting to a 90-degree fitting (e.g. 6068 vs. 6069), the straight one has no backup washer.

All my spare fittings have a snug 0-ring.

 

[zwelch]

I just went out and pulled the fitting to measure the seal dimensions. This time, I brought my camera and took a photo of the failed ring in the fitting. You can see from the picture of that the O-ring was pushed between the gap between the backing washer and fitting. Again.

Based on some quick measurements with my calipers, the fitting OD is ~18.12mm, the retaining ring ID is ~23.6mm, and the retaining ring thickness is ~1.75mm. Based on those measurements, I’m thinking an 18.5mm ID o-ring with 2.0 (or 2.4?) mm cross-section will compress properly and fill the space.

 

[zwelch]

Just looking at the spare metric O-ring fittings I have, and the DHH catalog, it seems the fittings that need to be "clocked" have to have a backup washer in addition to the retaining ring. So, in comparing a straight fitting to a 90-degree fitting (e.g. 6068 vs. 6069), the straight one has no backup washer.

I just checked discount hydraulic hose, and it looks like this fitting is a 5069L? Viewing the various sizes available made me realize that I forgot to measure the thread pitch while I had it off the machine. Guessing it is M22x1.5?

I also had the thought that this failure might relate to engine speed? Specifically, is pressure proportional to RPMs? Could I be causing an over-pressure condition by operating the machine with the throttle wide open? Maybe the upper limit needs to be adjusted downward? I still need to do a pressure test and adjust the main RV, so this line of thinking might bump that up on my priority list.

 

[dfkrug]

I also had the thought that this failure might relate to engine speed? Specifically, is pressure proportional to RPMs?

No.

But everyone should do a pressure test when they first get their machine and set the main RV to 2400-2500psi. Most are set way too low.

 

[zwelch]

I have ordered some 90A FKM o-rings that I hope will be less prone to extrusion failure.

In the meantime, I realized that there might be a trick to installing this fitting in a way that reduces the chance of this type of failure. Since this side of the fitting installs into the pump horizontally, the backup and retaining washers will be pulled downward by gravity, so they rest on the top of the fitting. That means there will be zero gap at the top of the backup washer and double the average gap at the bottom. That’s probably where the extrusion happens. I need to be sure that the washer is centered (so the gap is even all around) before tightening down the nut.

 

[Carl_NH]

When I have used these ORFS fittings (o ring face seals) the washer and the seal are one piece with the oring as part of the washer like this one. 9500-08 | Bonded Seal (Buna) for 1/2" BSPP