open atmosphere fluid tanks?

[TheBennyB]

So I'm a definite newb to hydra. Been wondering about this and researching for a bit. How come the Eagle Mach dozer and 870 have an open air and still get pressure? Both have essentially "over spills" off the fluid tanks stock that would allow air to both enter/exit. Is fluid level essential in keeping balance?
For me not. Just cruise till I hear pump motor differnence (higher rpm.) Man, sorry for the back to basics question, but I don't get it, far as I'm concerned it's voodoo like electricity or folding a fitted sheet.

[jack van]

my guess would be pressure is in the valve block to cylinder no pressure from block to tank intake is always below fluid level.that is my guess

[TheBennyB]

So no answer or everyone is too cool for school?

[Northern Farmer]

The reservoir has no pressure inside of it. The “overfill line” in reality is a vent/breather for the reservoir. Check out this link for more info on the differences of vented and non pressurized reservoirs.

http://www.ehp-eg.com/hydraulic-training/hydraulic-circuit-components/hydraulic-reservoirs/

[bigford]

I built the super dumpers hydraulic tanks just like my 1:1 kw's tanks with vents. It's gotta be vented or you get hydro block and fluid don't flow

[TheBennyB]

Thanks for the replies. Makes sense.

[frizzen]

If you don't run it vented at atmospheric pressure, you'd have to keep a big enough head pressure above ambient, with enough volume, on the reservor to keep the pump from pulling a vaccum on the reservor and making the pump cavatate when fluid is drawn out and sent to the cylinders.
When fluid is out in cylinders that volume isn't available in the reservor, pump, or return lines.
Even on a vented reservor, it's still sitting at 14.7 psi, plus weight of fluid column above pump pickup, for head pressure to supply the pump.

(My experience is mostly 3000psi aircraft systems charged with 1000psi head pressure, not construction models.)

[Lil Giants]

If you don't run it vented at atmospheric pressure, you'd have to keep a big enough head pressure above ambient, with enough volume, on the reservor to keep the pump from pulling a vaccum on the reservor and making the pump cavatate when fluid is drawn out and sent to the cylinders.
When fluid is out in cylinders that volume isn't available in the reservor, pump, or return lines.
Even on a vented reservor, it's still sitting at 14.7 psi, plus weight of fluid column above pump pickup, for head pressure to supply the pump.

(My experience is mostly 3000psi aircraft systems charged with 1000psi head pressure, not construction models.)

Great explanation Frizzen! :cool: