mini ex thumb

[wdchyd]

JJ
the valve that runs the thumb is the one to the right of the single yellow capped one. (don't know what the caps are)

Bill

Duffs right, those yellow caps are work port reliefs for other functions, I see the valve section for your thumb is machined and plugged for WPR but they don't have them installed.....I agree with most others as the culprit is most likely blown cyl seals.....one big problem with thumb cyls is the "induced load" from your bucket cyl (usually the bucket overpowers the thumb cyl resulting in way too much pressure)....also your Volvo equipment has a higher pressure rating than the thumb add-on.....

after all is said and done if it were my machine I'd find out from VolvoOEM if those WPR valves are available separately, remove plugs, install 2 (there will be another spot directly under for the other) set the pressure for whatever the cyl manufacturer for the thumb gives for max pressure....if you don't, the potential for more trouble exists (i.e. bending hyd rod ect.)...there are other ways to add pressure controls for that circuit but the best would be to add those cartridges....

Just my :2cents:

 

[bcantell]

Whew! Alot of what you guys are talking about is Chinese to me, but I'm starting to get it. I believe this is what caused my problems. First of all, I installed the thumb, without real advise on the correct way of doing so. The thumb closes to far and pushes the packing, over time it starts to leak internally. I'm going to take the advise here and after replacing the packing, I'll put a manual stop on the arm to prevent the cyl from closeing all the way. I'll get the WPR valves if possible and install them as suggested. Sounds like wdchyd is right, more problems coming if I don't. Broke a pin in the thumb over the weekend. Gotta tell you, that little Volvo is a sweet machine. Thanks to all for the help. Bill

 

[wdchyd]

:thumbsup:I see alot of "Thumb Attachment Issues"over and over....of course I usually see them after bent and broken rods:2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents::2cents:

you get the picture?

 

[bcantell]

OWCH!!! Called Volvo today, they want over $560.00 EACH for the WPR valves. Over $1,100.00 is alot of cylinder packing.

 

[J_J]

Either rebuild it or get an equivalent cyl from Surplus Hyd, for less bucks. You could move your bracket back some and prevent the hard stop.

Either test the cyl as has been mention, or take the cyl to a hyd shop for a test.

 

[wdchyd]

OWCH!!! Called Volvo today, they want over $560.00 EACH for the WPR valves. Over $1,100.00 is alot of cylinder packing.

You can instead add a cushion valve (Parker - DWV, CROSSOVER RELIEF VALVE BLOCKS, 210 BAR (3000 PSI), INPUT FLOWS TO 94 LPM (25 GPM))

This will do essentially the same, you'll have to mount this somewhere(preferrably ,but not necessary ,)close to cyl...

mount this valve between cyl and main control valve (or one similar & smaller) and add hoses to fit....done.....

There is others that do the same....the nonadjustable type you can add shims internally (use pressure guage when do this!)

The result is the same.....too bad for them (Volvo)....but there is always other ways to skin a cat:laughing::laughing:

Good Luck, Bill

 

[yankeerider]

.....
2/ Thumb does not have a mechancial stop on it, so basically the piston is bottoming out all the time its pulled back. When pulling it back all the way, ensure the operators do not slam it back, make sure they do it smoothly or stop pulling it back before it bottoms out.
Or put in a mechanical stop, to stop the piston bottoming out on the cylinder.

Duff:thumbsup:

Since I'm finishing up the design to build a thumb for my mini-ex, could you please explain how the lack of a mechanical stop on the thumb when retracted creates a problem? Is it considered back practice to allow a cylinder to operate to the fully retracted position? I can understand that if an operator "slammed" it back, there would be a pressure pulse at the end of travel, but wouldn't the pressure pulse also occur when the thumb stopped suddenly because of an external stop?

 

[wvpolekat]

It is the piston bottoming out that is the problem, not the sudden stop.

 

[Stonehaller]

You can instead add a cushion valve (Parker - DWV, CROSSOVER RELIEF VALVE BLOCKS, 210 BAR (3000 PSI), INPUT FLOWS TO 94 LPM (25 GPM))

Unfortunately, a crossover relief will not work on a single rod cylinder. You can limit the force that the cylinder can generate with this valve, but it will not relieve the thumb cylinder when it is over powered by the bucket or the dipper.

 

[yankeerider]

It is the piston bottoming out that is the problem, not the sudden stop.

Why is the piston bottoming out a problem? The piston seals do not appear to be typically located on the surface which would contact the end of the cylinder.

I did a web search and found a National Fluid Power Association document which provides application guidelines for selection of hydraulic (and pneumatic) cylinders. Nowhere in this document does it specify that a cylinder should not be allowed to travel its full stroke in service.