Hydrauic boat steering has air entering, How?

[oldestguy]

I have a friend in Sweden with who I communicate via Skype. He describes his boat hydraulic steering using copper pipes and some rubber hoses. Operations are jerky, with no movement of the steering cylinder followed by a jerk. Seems like air on the pressure side then. He maybe gets one drop of oil leak a week, yet apparently on the suction side of his steering wheel "pump", in one direction, could he be sucking in air? Is there the possibility that the viscosity or molecule size of the oil is such that it does not leak out much oil under pressure, but air can get in, under the suction condition?

Rudder is not stuck and moves freely when not h hooked to the steering cylinder.

The tests he has done certainly appear to show air in the system. Bleeding has not been done, but lowering the steering piston seems to solve his problem (letting air get to a reservoir).

I suggested locking the steering cylinder and seeing if he can expel anything via the pressure lines, looking for a leak.

thoughts or suggestions?

 

[msquared48]

Has he checked the condition of the rubber hoses to see if any are oxidized to the point of not being supple?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

A few ideas....

Check for drop in oil level. Turbulence at impeller with low oil volume can introduce bubbles in the oil.

Assume the cylinder is dual acting...in that case, could be pulling small amount of air past the seal.

Impeller could be wearing out as well.

I would also bleed the system.

 

[oldestguy]

No info yet on the type of "pump", but I would assume it is a typical rotatory pump with perhaps two inter-meshed gears. Swedish friend (no I.D.s here), if you read this, what does pump look like, A photo would help.

Hey Ron: sounds like you are a pretty well rounded engineer. I'd bet you have a ham license as well. I'm one, as does Svenska friend.

 

[Ron]

OG...never got the ham license. Couldn't afford the equipment at the time.

Pretty much grew up in a junkyard! Lots of varied experience there.

 

[Ron]

...and thanks for the compliment!

 

[Ron]

To show the relationship between Geotechnical Engineering and junkyards...

Back in the late 70's we were constantly underfunded in our geotech lab. Corporate office wouldn't let us buy a sample extruder (for shelby tubes). Went to junkyard and bought a hydraulic tailgate for a pickup truck for less that $100. Stripped it and built a foot-operated hydraulic sample extruder. Visited the lab a couple of years ago and they were still using it.

 

[unclesyd]

I would suspect the steering wheel pump. These are usually spur gear or gerotor pumps. Both styles of pumps pull a mean vacuum so I would change out the input shaft seal and wee what happens. I have seen many of these pumps that would suck air but would not leak oil
If the shafts penetrate the front and back plate I would also check them out.

 

[oldestguy]

Ron: I built a Shelby tube extractor also, but used new parts for the pump and cylinder. Now, some 40 years ,later it is in another lab and slightly modified, but doing the job. Made some other test gear, mainly to test peats in Shelby tubes for compression characteristics, still in use. Now I have moved to a house without a nice shop and have given away my welders, lathes, etc. and, of course already have had to go to them for some jobs. Can't give it up.

 

[Ron]

OG...fun stuff. Still have most of my tools, but don't get to use them as much. Probably a garage sale in my future!

 

[oldestguy]

Guys: The Swede did as I suggested, fixing the hydraulic cylinder and forcing fluid towards it. Found a joint leak, taking one turn to correct the leak. Prior to this test that joint appeared tight.