Hydraulic system over pressuring???

[richy_B]

Hello,

 

Nifty tracked MEWP. Starts up, track it a few metres starts to overflow hydraulic oil from the filler (with cap on and tight). If you open the cap it stops and seems to run fine for hours. If you turn the engine off it stops and restart the engine (without removing the cap) it seems to run fine. 

 

Trying to work out why it might be doing it. Why a sudden surge of pressure after start up from cold but at no other times. 

 

Any thoughts?

 

 

Edited November 7, 2019 by richy_B

[swinny]

is there not some sort of relief valve or vent in the cap? maybe blocked?

 

Start and run from cold with cap off for a little trial?

Edited November 7, 2019 by swinny

[richy_B]

I was thinking along the lines of a relief valve but surely if it's got the correct amounting of hyd fluid wouldn't it be air pressuring the system? A relief valve would surely just overflow, effect rather than cause.

 

My other thought was maybe oil was being returned to the tank quicker than it was being circulated out? On start up the pump (s) are pushing more in that is being pulled out.  Not quite sure if that's a thing? Partially blocked out pipe. If so why would be it be resolve  when the cap is off?

 

Bit of a head scratcher so far.

[monkeybusiness]

Sounds like it might be sucking air into the system possibly when cold - check all connections between the pump and the tank.

[Canal Navvy]

It would be interesting to leave the cap loose overnight as the tank cools and retighten just before you start it. 

[openspaceman]

10 hours ago, monkeybusiness said:

Sounds like it might be sucking air into the system possibly when cold - check all connections between the pump and the tank.

 

I've mentioned this several times before; as you say the oil is foaming because air is being sucked in. With cold oil  this can be from a seal failure  somewhere but also that the oil in the tank is being sucked into a vortex because it is viscous, just like the  vortex when the bath water goes down the drain, the air then get sucked down the middle. So the oil should be circulated at low rpm for a while to  get warm and less viscous. The other thing is that the oil may be being returned above the level in the tank and entraining air as it splashes around.

[richy_B]

On 08/11/2019 at 10:45, openspaceman said:

 

I've mentioned this several times before; as you say the oil is foaming because air is being sucked in. With cold oil  this can be from a seal failure  somewhere but also that the oil in the tank is being sucked into a vortex because it is viscous, just like the  vortex when the bath water goes down the drain, the air then get sucked down the middle. So the oil should be circulated at low rpm for a while to  get warm and less viscous. The other thing is that the oil may be being returned above the level in the tank and entraining air as it splashes around.

This makes a lot of sense. Once the machine has been running a few minute it is fine. I have noticed there is, what appears to be, some kind of suction around the join between the engine and the hydraulic block. I'm not 100% what is happening at this join but it looks like the reverse of bubbling. Doesn't exactly tally that this would be hydraulic oils though. 

 

Edited November 10, 2019 by richy_B

[richy_B]