1st Stage Cylinder Whine

[MadMango]

First off, sorry for the abuse of standard terminology.

My company recently purchased a product line from a competitor. This product uses a telescoping hydraulic cylinder coupled with a chain reefing mechanism. During no-load operation the cylinders (2) are quiet, as expected. When the product is loaded (>300lb) there is a loud whine from some of the cylinders while the chain is in tension.

Looking into the problem, the whine seems to happen when the "1st stage" of the cylinder is extending. After the 1st stage is fully extended (~18") the whine stops and the 2nd stage begins to extend (~12").

The 1st stage is 1.75"bore, the piston has a u-cup seal and a wear ring about .50" wide. The gland nut that guides the .75" bore 2nd stage has a wiper. The cylinders are oriented vertically, with no obivous side-loading.

What could be causing the whine on about 70% of these cylinders? We believe the whine is being caused by resonance, but are not sure. We have tried different orifice sizes with no luck.

[green]"But what... is it good for?"[/green]
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
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[byrdj]

I am assumming the piston is double acting.
Is it possible that the whine is fluid leaking around the first stage piston u cup? (and stops when the piston reaches top stop). You may be able to feel the drain line when whining and note if there is higher flow than with the few that are quite.

When you change orfices, was this to restrict the opening supply flow? Have you tried orficing the opening drain flow from the above piston area?

 

[MadMango]

This is a single-acting cylinder, where hydraulic fluid extends the rod and opening a release valve allows the cylinder to collapse.

Upon inspection of the failing cylinders, there doesn't seem to be any leakage past the u-cup of the piston, everything looks dry and clean, including the wear ring. There is no "drain line" only a single hydraulic hose attached concentric to the bottom of the cylinder body.

Changes to the orifice size on the piston of the 1st stage were made to increase the diameter, from .026" all the way up to .048", no changes have been made to decrease teh orifice.

Have you tried orficing the opening drain flow from the above piston area?

I'm not sure I understand this.

[green]"But what... is it good for?"[/green]
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
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[byrdj]

If the piston was double acting, the fluid in the above piston area would have to be drained, when fluid was supplied under the piston for it to extend. Restricting the drain of this oil slow the opening rate.

Sorry but that all the ideals I had. But I would look to see how the air that would be in first stage above piston is vented, possible a small hole in the circumferance just bellow the gland nut.

 

[MadMango]

[blue]Byrdj[/blue], thanks for burning a few brain cells on this with me. The vent for the 1st stage is in the gland nut. We wasted a few parts to change the size of this opening too, but no luck.

We did find out that some of these seals and components have been sitting on a shelf in a warehouse for the past 2-3 years. Some of the white (unsure of material) u-cups are discolored. We think the material might have degraded over time and lost some of it's properties. We have placed an order for "new" seals to see if this helps any. They should be in by the end of the week.

[green]"But what... is it good for?"[/green]
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
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[byrdj]

My standard answer when ever something acts strange in hydrualics. AIR

After I sent the vent response, I then recalled the load being required for whine, and could not come up with a scenerio that I would believe.

hopefully it is friction caused by the cup with the higher pressure of load trying to push it out

 

[jrnsr]

I doubt seal would influence noise... white urethane u-seals last a long time, until they turn orange and crumble after 20 years. maybe switch wear ring materials...
Is rod chrome plated? Combinations of materials work
& wear different. Chrome rod on bronze gland is good. Aluminum glands are good (as long as they don't skimp on surface area). Bare steel rod in steel gland may not slide as smoothly.
You'd assume the pressure would increase with the smaller stage... what does your gauge say?
Noise obviously isn't conducting from pump, is it?
Make sure your tank is vented adequately- sometimes systems will develop a vacuum and start acting wierd.
Good luck!

 

[MadMango]

jrnsr thanks for the post. The rod is chrome and the gland nut is bronze, no pressure readings were taken to see any increase in pressure.

I should have updated everyone. We got the new u-cups in, and the noise did go away. We can only assume we have fixed the symptom, but probably not the problem. This is on one of our product lines that I am not involved with. As far as I know, everyone is happy, so no further effort is being exerted. Go figure.

Thanks again all.

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[EdDanzer]

The gland nut is a dry bearing! When sliding a dry material against tubing it will typically resonate. Most single acting cylinders have the seal in the head gland so that bearing area receives lubrication.