Volvo EC15B swinging problem by arm move down

[Muz]

They are quite simple really, just a shut off valve that stops the ram dropping in the event of a burst hose. Mostly there be a ball spring valve in there and the spring controls the pressure that is allowed out of the circuit, Your machine will have to overcome the spring load to get the ram to move, but if the spring pressure is not correctly adjusted it prematurely shuts the flow to the cylinder causing the stop start motion, or at least making it seem worse to you. I imagine a 'decent' valve would have a damping mechanism built into I would have thought, but I wouldn't have thought volvo would fit something that 'comprehensive' to their machines, beyond that I can only speculate. It might be worth pulling it apart to see if a spring has broken , or some debris is preventing normal movement. In any event, its not 100% necessary to have it fitted, unless your client specifies that it is mandatory to have one.

[ianoz]

I removed the boom lift drop valve. Moving down the boom is done very softly now. But there is one change in the behaviour:

At jostick neutral the boom is sinking down very slow. If I move the boom up until the restiction followed by a down move and stoping - then the boom donīt sink further. But if I play a litte bit with the boom, the boom will sink again in neutral position. If I move the boom up to the restriction and move the boom down, the boom will hold the position until I play a little bit with the stick. Maybe air the reason? Nevertheless the big problem has gone.

regards wowe

If the boom is creeping down , i would think that the ram seals would be the cause , not air.
They do wear out . The debris Muz is saying could be causing problems in the check valve may have come from the seal. A faulty seal could cause the valve to think there is a blown hose ,

[wowe]

If the boom is creeping down , i would think that the ram seals would be the cause , not air.
They do wear out

But if the ram (ram = hdraulic cylindre with push rod?) seal would be leaky then the boom would be move down also with the valve. As I think the valve inhibits only a problem which is located ahead of it. If the cylindre itself has a Problem (Piston defect, seals defect...) then the valve is without any effect.

[Muz]

A bit of boom drop in that machine is not unusual because Volvo make very poor seals and small seal packs on their rams. Frankly apart from JCB they are the shittiest rams and seals I've ever seen .. very poor construction and quality .

[ianoz]

But if the ram (ram = hdraulic cylindre with push rod?) seal would be leaky then the boom would be move down also with the valve. As I think the valve inhibits only a problem which is located ahead of it. If the cylindre itself has a Problem (Piston defect, seals defect...) then the valve is without any effect.

The valve is there to stop the ram from moving if a leak develops . If the boom was not dropping before you bypassed the the valve ,it means it is doing the job it was designed to do. Stop the ram letting the boom fall .
I am not a fitter , but this is what my common sense tells me .

[Mick-the-fitter]

The valve is there to stop the ram from moving if a leak develops . If the boom was not dropping before you bypassed the the valve ,it means it is doing the job it was designed to do. Stop the ram letting the boom fall .
I am not a fitter , but this is what my common sense tells me .

It sounds like the piston or nut has come loose on the end of the rod and the o ring between piston and rod is letting Oil past, by using the control lever it moves the piston sometimes away from the rod end and other times against the rod end. If the ram is taken apart it could be fairly obvious.

mick

[wowe]

Ok - now the reason for the jerking is found especially the hint of Stock. But now the Problem of the sinking down boom in neutral Joystick position appears.

I made a drawing

Zeichnung Hydraulikzylinder.jpg

Before the remove of the BDV we had case 1: no drop down. But this assumes, that the RAM has no leaks. This means the seals are ok. If the seals are weak at a closed BDV, the pushrod will move in the cylindre although the valve is blocked. That means that the sinking boom now has a reason out of the cylindre.

[v8druid]

check valves/hose burst valves/(boom drop valves) have a cracking pressure ---- the amount of pressure required to be fed into their system to release their effect .... unless they are pilot operated .... which this does not appear to be

if the cracking pressure is too high, it will cause exactly this symptom as the pressure is suddenly 'injected' into the system and it is high enough to have an effect on the ram ..... a low cracking pressure would not do this.

cracking pressure is usually adjustable ..... some times internally in the valve with no visible sign of it being adjustable, until dismantled.

installing a test gauge in the circuit would give you an indication of the cracking pressure ... it will drop as the valve opens and pressure is released into the cylinder.

The boom dropping, now the valve is removed would suggest to me a faulty main valve spool ....... or a badly adjusted stick on the pilot valve, holding this service's pilot circuit slightly open, allowing a leak to circuit ???

[wowe]

@v8druid: The boom lift drop valve is disassembled. But at first I will now check, why the boom is lowering at joystick neutral position.

[wowe]

Hello,

I hope to get further help from this Forum. I will resume the Facts:

(1) The Problem now is the sinking boom in Joystick neutral Position.

(2) This Problem exists only at the hydraulic circle of the boom.

(3) The hydraulic has Power. Ist easy to lift the digger

(4) The RAM is NOT the reason of the Problem, because with the boom drop valve the boom was fix.

(5) So the Problem must been located ahead the RAM.

(6) There is no visible Oil leakage.

(7) The boom drop valve is removed.

So boys - come on and tell me how to locate the malfunction.


Regards wowe

[ianoz]

OK , seals can leak , not externaly ,but internaly .Oil goes from one side of the piston to the other side less oil on one side means the rod moves .
By removing the burst protection valve it lets the oil go down the hose . so the boom drops .
I would replace the ram seals . . Mick the fitter suggested the piston could be loose . once again . replace the seals at the same time .

[wowe]

I would replace the ram seals . . Mick the fitter suggested the piston could be loose . once again . replace the seals at the same time .

I wrote:

(4) The RAM is NOT the reason of the Problem, because with the boom drop valve the boom was fix.

You can take a look on the drawing some posts ago. I think that (4) is a correct conclusion. Or do I make a mistake???

[ianoz]

I just changed boom seals on my excavator .
Symptoms Boom would not hold in neurtal position .
Note there was no oil leaking out of the ram .
Pulled ram apart , found seals breakling up .
Replaced seals put ram back on machine .
Tested . Boom holds in position .
Machine has 5000 hours on it seals have been replaced a couple of times
Joysticks and control valves have not been touched .
let you decide where your problem could be based on the above .

[v8druid]

I wrote:

(4) The RAM is NOT the reason of the Problem, because with the boom drop valve the boom was fix.

You can take a look on the drawing some posts ago. I think that (4) is a correct conclusion. Or do I make a mistake???

Therefore, as said previously ..... the issue is with either the main valve block or the pilot control not centering properly and allowing backflow

[wowe]

Therefore, as said previously ..... the issue is with either the main valve block or the pilot control not centering properly and allowing backflow

I made an further perception: When the boom is sinking and I will fix it (so that is fix in heigh), so I must softly pull the joystick. In this Moment, I hear the hydraulic must work, because itīs louder. So I conclude that the steering valve has no internal Problem. Why? If there would be a Problem in the steering valve in this kind, that the internal Piston is not in itīs correct Position at neutral (e. g. a broken spring) then the Piston would be in correct Position, if I pull the stick softly. But then, the hydraulic Need not to work and should be quiet and the steering Piston of the hydraulic valve should be Close the pipe to the RAM. But the hydraulic isnīt quite when the boom is fix. I hear the working noise. That means, that the hydraulic pumps oil in the RAM to Keep the boom fix. That means, that the oil of the RAM or on the way to the RAM is flowing out of the hydraulic. The hydraulic area which is "under pressure" at boom Lifting must have a leak.


I hope you can understand my thinking. Ist not easy to take it in words.