relief valve

[billymo]

i just got a new holland l 785 when i lift something heavy or come to end of travel the releif valve makes a screaming noise and could this have something to do with the amount of lifting and tilting power but the bucket and boom move real good with no load there ii a hydro valve on the left and the right you can see them when sitting in unit i get a noise from one side when i use the boom and the other when i use tilt i can wrench on alot of stuff but im green when it comes to hydros

 

[skidsteer.ca]

Relief valves tend to squeal or scream when you bottom the cylinders or over pressure the circuit by attempting to lift more then it can handle.
Find out what the relief psi spec is for that model and hook a 3000 psi guage into the front couplers and verify that your relief is in spec by pressuring up the guage.
But what you describe sound perfectly normal and should be nothing to be concerned about.
Ken

 

[Tazza]

The relief should make noise when you hit the end of the ram stroke or attempting to lift something thats too heavy. It shouldn't make any noise when lifting something heavy, only the pump will groan. Is it only lift or is it when the arms fall? Just thinking it may be a by-pass valve when there is too much flow as the arms are droping is all.
There should be one main relief for your entire hydraulic system and some times they install them on your lift circuit too. Its there to prevent damage if a heavy load is dropped on the arms.
Ken may have a better idea as to what the reliefs are for.