Pressurized hydraulic tank - how important is this to maintain functionality? 490D

[TreeHogger]

Greetings - when I was looking at my machine to purchase (out of state, and beastly cold), it had been sitting and obviously not very well cared for - and all the fluids were down...

The hex release that was supposed to be there to unlock the cap for hydraulic tank was apparently not 'in there' and the long and short of it was that I broke up the cap getting it off to add fluid.

My two-part question is: Should I replace it (dealer?), or is it fine that it doesn't hold the 5 PSI as long as it doesn't let rain water in??

And, what makes this pressure? Is it simply the returning hydraulic fluid, or is the some sort of pressure-making system (E.g. air, or supplemental hydraulic pressure routed to the tank)?

I would add that the machine will be used around the farm, and not fasted paced production work like pipe laying...It is a 1990 490D with 9000+ hours

Thanks,
Mark

 

[Mobiltech]

The piston pumps last longer with pressure on the tank. Less cavitation and easier on piston slippers.
On some Cat hoes they feed turbo boost pressure to the tank through a regulator and the machine will be in slow mode until that pressure is built up.
The heat in the hydraulic system will naturally build some pressure if the tank is sealed.

 

[TreeHogger]

Thanks - no turbo on this old girl... Yes, I can see how a slight pressure would be easier on some part of the hydraulic system (wish I knew/could envision what piston slippers looked like!).

Anyone else have thoughts? I haven't priced a replacement cap, but I can only guess it'll be $100 bucks or more(?) Maybe good 'insurance?

 

[willie59]

Replace the cap. As stated, it's better for the system to have pressure in the reservoir. The cap has a one way check valve in it, allows air in, but not back out. Pressure is built by extending cylinders. When you fully extend the cylinders it draws down the oil level in the tank, this draws air into the tank via cap. Then when you retract the cylinders, oil level in reservoir comes up, air can't escape, voilà , pressure.

 

[kshansen]

Which would you want to replace a $100 cap or $1,000 pump? That's not counting the cost when pump fails and contaminates the whole system. And then you will still need to replace the cap!

 

[joispoi]

Positive pressure also keeps out dust.

 

[lumberjack]

+1 on replacement. You only get one chance to get it right the first time, the second time is much more expensive.

 

[td15c]

AT321249 KEY LOCKABLE AT323462 LOCKED WITH PADLOCK
these are the part numbers for a 490d fuel cap. if you put them in Google you will find prices. looks like $43 to $130

 

[typ4]

AT321249 KEY LOCKABLE AT323462 LOCKED WITH PADLOCK
these are the part numbers for a 490d fuel cap. if you put them in Google you will find prices. looks like $43 to $130

He needs a hydraulic tank cap. Also individual parts were available last year.

Check some used parts places.

 

[AndrewC]

Part number is 4326285

 

[td15c]

He needs a hydraulic tank cap. Also individual parts were available last year.

Check some used parts places.

sorry about that don't no why I had fuel cap on the brain.:beatsme
I no what your thinking what brain. ointhead