Volvo EC15B swinging problem by arm move down

[wowe]

Boys and Girls - to find the reason for this boom down movement I removed both secondary valves of the boom valve element and put in plugs. With These plugs the boom-valve has no anti cavitation function and no 250 bar limiting, so I can test the elemetary valve function.


At first I removed some pipes, because they were in the way. To prevent Problems with dirt I use ballons and cloth.

IMG_0465.jpg


This both parts I changed. The same on the other side

IMG_0466.jpg

This is the anti cavitation valve which was originally at the boom valve

IMG_0473.jpg

I disassembled the valve. This is the outer and the inner part:
IMG_0468.jpg

IMG_0472.jpg

At the inner part you can see a "circle" which is the seat of the valve. But If I move with my finger nail over this area, I donīt feel much. So I think itīs not worn.

What I wondered, the inner part has a gap to the outer part. Itīs not an exactly matching. But This shoud not be caused by wear. I donīt know how to rate this circumstance.

So tomorrow I will test, if the boom will sink again. I think the anti cavitation valve was ok so I expect the same result.

[Mattir]

Interesting...

looking forward to the next phase

[Muz]

[ATTACH=CONFIG]3474[/ATTACH]

At the inner part you can see a "circle" which is the seat of the valve. But If I move with my finger nail over this area, I donīt feel much. So I think itīs not worn.

What I wondered, the inner part has a gap to the outer part. Itīs not an exactly matching. But This shoud not be caused by wear. I donīt know how to rate this circumstance.

So tomorrow I will test, if the boom will sink again. I think the anti cavitation valve was ok so I expect the same result.

Presumably its spring loaded ? has the spring become weak perhaps ?

[wowe]

Yes - there is a spring inside. But these spring needs not much power for a well function. The pressure pushes the movable part into the valve seat. The spring is only for a "perfect function" - I guess.

[v8druid]

looks like a balanced pressure type of cartridge valve to me ... the spring does not have to be much, just enough to exert additional pressure

[wowe]

Hello,

but now I have a real problem to understand this valve. Here ist a drawing of the hydr. valve:

Ventil2.jpg

And here I have put the inner part on the outer part. Certainly the inner part is cylindric - I removed my fingers from the pic.

AntiKav.jpg

Now put this anti-cavitation valve in the upper valve element. How can the oil stream? from "A" to "T" or vice versa?

[wowe]

Today I made a short test. For warming up I lifted 20 times the digger. Then I lifted the boom and .... it stillstands!!!!!!!!!! I hope this was no singular effect. So I believe the anti cavitation valve is the reason of the moving down. But at first I must clear the strange function of this valve. What do you think about it? Is this the real valve and how do you think about it?

Regards wowe ... a little bit happy today.

[v8druid]

Hello,

but now I have a real problem to understand this valve. Here ist a drawing of the hydr. valve:

[ATTACH=CONFIG]3478[/ATTACH]

And here I have put the inner part on the outer part. Certainly the inner part is cylindric - I removed my fingers from the pic.

[ATTACH=CONFIG]3479[/ATTACH]

Now put this anti-cavitation valve in the upper valve element. How can the oil stream? from "A" to "T" or vice versa?

Damned if I can see how that works .... deffo not a balanced type valve as no pressure both sides

Any numbers on the valve Wowe and who's valve block is it ?

[wowe]

Any numbers on the valve Wowe and who's valve block is it ?

The block is from Rexroth. Type: SX 12 Number: 08100930

Damned if I can see how that works .... deffo not a balanced type valve as no pressure both sides

You can immagine it. There is a pic where I hold the complete assembled valve. You can see through the holes the piston part. This part is pressed softly into the seat of the outer part (to the left at the pic). At another pic you can see the inner piston. You can push it to the left then the Piston is lifted from the seat an the fluid can flow between the front of the valve through the many holes around the outer part. If you look to the drawing of the complete hydraulic valve for the boom you can see that this is the flow from pressure-area to the tank. So I say that with tis valve the boom must sink.

[v8druid]

The block is from Rexroth. Type: SX 12 Number: 08100930



You can immagine it. There is a pic where I hold the complete assembled valve. You can see through the holes the piston part. This part is pressed softly into the seat of the outer part (to the left at the pic). At another pic you can see the inner piston. You can push it to the left then the Piston is lifted from the seat an the fluid can flow between the front of the valve through the many holes around the outer part. If you look to the drawing of the complete hydraulic valve for the boom you can see that this is the flow from pressure-area to the tank. So I say that with tis valve the boom must sink.

I agree .... can NOT see HTF that works or what it is supposed to do .... as you say it is in the pressurised gallery ..... but the schematic shows it as a one way/check/non return valve ..... so pressure should keep it closed ???????


It looked like Rexroth engineering and VERY similar to the balanced RV that I had out of the 'Drema's block a few months ago, which is why I asked and also why I queried whether it was indeed a balanced type cartridge, which it obviously isn't

there is quite a lot of good informative videos on you tube about Rexroth equipment .... might be worth trying to find something in there . there is also the Rexroth website ..... found it last August and IIRC there is a link to it in my thread .... everything in there, but takes some searching.

[Mattir]

Damned if I can see how that works .... deffo not a balanced type valve as no pressure both sides

Any numbers on the valve Wowe and who's valve block is it ?

Wowe,

spent some time last nite and this morning. Got enlightened. The functionality is actually straightforward. Think what happens when the spool moves from right to left. It opens way from A to T and at the same time opens way to the LS valve B-side to sense if there is too much load. Additionally, Pump connects to the B-side through the compensator. If the ram sinks, the reason for that is the main spool.

[wowe]

The block is from Rexroth. Type: SX 12 Number: 08100930



You can immagine it. There is a pic where I hold the complete assembled valve. You can see through the holes the piston part. This part is pressed softly into the seat of the outer part (to the left at the pic). At another pic you can see the inner piston. You can push it to the left then the Piston is lifted from the seat an the fluid can flow between the front of the valve through the many holes around the outer part. If you look to the drawing of the complete hydraulic valve for the boom you can see that this is the flow from pressure-area to the tank. So I say that with tis valve the boom must sink.

I must be more exactly:

You can immagine it. There is a pic where I hold the complete assembled valve. You can see through the holes the piston part. This part is pressed by a weak spring softly into the seat of the outer part (to the right at the pic). At another pic you can see the inner piston. You can push it to the left then the Piston is lifted from the seat an the fluid can flow between the front of the valve through the many holes around the outer part. If you look to the drawing of the complete hydraulic valve for the boom you can see that this is the flow from pressure-area to the tank. So I say that with tis valve the boom must sink.[/QUOTE]


I made a drawing:

Zeichnung Anti Cav Ventil.jpg

I made a technical study and I had some physics - but itīs hard to think that this valve is the right one. This valve must produce this sinking effect, or I am mad - may be.

[wowe]

Wowe,

spent some time last nite and this morning. Got enlightened. The functionality is actually straightforward. Think what happens when the spool moves from right to left. It opens way from A to T and at the same time opens way to the LS valve B-side to sense if there is too much load. Additionally, Pump connects to the B-side through the compensator. If the ram sinks, the reason for that is the main spool.

Hello Mattir,

what you describe is the normal function of an movement: The fluid can flow from Section "A" back to the tank and at section "B" the fluid is pressed so it can move the Piston in the RAM.

When my boom sank, the "main spool" (this complex hydraulic steering Piston) is in the shown neutral mid-position: "A" to "T" AND "B" to "T" is closed. Of course - a wrong secondary valve can bypass the hydraulic piston and open a way from "A" to "T".

regards wowe

[Mattir]

Hello Mattir,

what you describe is the normal function of an movement: The fluid can flow from Section "A" back to the tank and at section "B" the fluid is pressed so it can move the Piston in the RAM.

When my boom sank, the "main spool" (this complex hydraulic steering Piston) is in the shown neutral mid-position: "A" to "T" AND "B" to "T" is closed. Of course - a wrong secondary valve can bypass the hydraulic piston and open a way from "A" to "T".

regards wowe

Yes, if the spool (piston) leaks from A to T in neutral position, then there is a possibility for the Ram to sink. That happens in case the ram seals are leaking as well.

Take a look at this. It is quite enlightening. At least for a rookie like me.
https://youtu.be/4REdJIW6-Kg

[wowe]

Yes, if the spool (piston) leaks from A to T in neutral position, then there is a possibility for the Ram to sink. That happens in case the ram seals are leaking as well.

Take a look at this. It is quite enlightening. At least for a rookie like me.
https://youtu.be/4REdJIW6-Kg

But this is not my problem. The test has shown: If I replace this "anti-cavitation-valve" by a plug which separates "A" and "T" all time, then the Arm doesnīt sink. This means, that the fluid Controlling Piston in the hydraulic valve is positioned in the neutral mid and no "A" to "T" Connection is open.