Stroking Spool Causes a High Pitch Whine

[dmroselx565]

Anyone know what might cause my New Holland LX565 skidloader to whine when stroking the control valve spool that operates the loader bucket? My control valve has three spools and one controls the auxilary hydraulics, the next one the lift arms, and the third controls the bucket. I get no noise when stroking the auxilary or lift arm spools, just when dumping or curling the bucket. I don't suspect air is getting into the system as it would probably do it all the time when running or when using the other controls. I called a couple buddies of mine and they told me to start looking for a pinched line as this apparently will cause a high pitch whine. It is very loud when the RPM's are way up and quiet when at idle. I assume it is because the hydraulic pump is increasing the line pressure. Recently, the control valve was replaced with a new unit and the lift arm cylinders were repacked to take care of another problem I was having. The problem didn't start until after we packed the lift arm cylinders which should have no impact on the spool that controls the bucket. I'm at a loss, please advise.

Thx. Mike /forums/images/graemlins/confused.gif

 

[Soundguy]

Does it only whine at the end of the cyl travel.. or during the cyl travel.

At end, I'd guess a relief opening.

During, I'd guess there was a restriction int he spool output.. like an orifice restrictor bushing.. etc..

Soundguy

 

[5030]

Interesting.

My big hay mower has a restrictor orfice in the lift cylinder inlety and it "whines" too. Could be just the restrictor rattling at high frequency with pump pulsations.

 

[dmroselx565]

It seems to do it through the entire cylinder travel. So, you would recommend disconnecting the pressure lines coming out of the control valve for that spool and looking for a blockage? When you say bushing do you mean like a rubber o-ring or something?

Thx. Mike

 

[dmroselx565]

Problem solved. I tore everything back down and disconnected the pressure lines and removed the fittings from the control valve on the bucket spool and found nothing. Everything looked great an no signs of blockage or contamination. I reasssembled everything (with covers off) and the pitch continued. I just happen to grab one of the metal lines coming off the control valve while stroking the spool and the whining dimmed down. Basically, at full RPM's there is enough flow through the line that it was actually vibrating and making a harmonic high pitch. I shut the machine down and checked to see if the metal hydraulic lines were touching any metal. No luck. To fix the problem, I took an old rubber heater hose and wrapped it around both hydraulic lines so the rubber hoses were touching each other. I fired it back up and the sound disappeared... I would have never of thought harmonics would cause that much noise... Anyhow, everything seems fine now and I appreciate everyones help and advice.