Hymac 580d issues

[iain106]

Iain, I don't know what would cause the slew to wander but the rams creeping down I suspect would be one of two problems, the first of which is the most likely and that is that oil is leaking back past the spool valve that controls the boom hoist, or the relief valve in that part of the spool block, the other issue could be that although the rams are dry and not leaking oil, one of them could be leaking oil past the seals internally.

When I changed the two boom hoist rams on my 580BT to fit two reconditioned ones, as I knocked the top pin out at the piston end, the ram dropped by itself because the seals were worn.

I would suggest having a word with Tony Flint who was a Hymac trained fitter I will pm his number to you.

Jeremy

Thanks for the pm I will give him a call

[essexpete]

The ram would be acting like a damper, but rather than there being an orifice that the oil passes through, it would be going past the seals to the wrong side of the piston, activate the ram and that oil on the wrong side of the piston would be forced back again. The piston obviously couldn't go all the way down the bore, just some of it (just the equivalent of the spare volume above piston) and it would put a fair bit of load on the wiper seal...I had this happen to me last summer on a Yanmar excavator to the point of the wiper seal failing...was quite messy.

The wiper seal on a ram is just that, to prevent ingress of dirt on the rod being taken into the gland or pressure seal. The wiper seal will blow if the gland seal has blown.
My point about the piston seals is that assuming there is not air present in the hydraulic fluid and there are not leaks in the pipe work and the spool is not leaking then for an extended ram to close the total volume of oil must reduce. The working volume of the cylinder is fixed. Push in the rod and piston and the free volume in the cylinder is reduced by the volume of the rod returning into the ram.

[FOWLER MAN]

Hi,
I have read through the posts on this one and I think whilst it could be the seals in one or both rams my money would be an, (SLRV), service line relief valve fault.
I think too that the wandering slew is possibly a cross line relief valve fault. You need a pressure test to pinpoint and correct these faults.
Pete is not over thinking. There would be more oil displaced from below the piston than could be accommodated above on the rod side and the only place for it to go is an external leak or back to tank through an SLRV.
The oil could be just passing the ram seals if it doesn't creep far though, even the 580 I had would creep a little over night when new.