Good customer of mine has an end dump trailer he pulls to haul material to his concrete plant. He uses it everyday but once the outside temperature gets below 40 degrees F it blows oil out of the vent cap on the tank when he lets the bed down. It's got a tank mounted right behind the cab and it does have a baffle over the return line to deaden the spray coming back in the tank when the cylinder is returning. The oil never really heats up because he dumps a load then it's a 2 hour round trip before he gets back with another load when the PTO is engaged for 30 seconds then shut back off for another 2 hrs. I suggested a thinner oil. Any other ideas?
What viscosity of hydraulic oil is he using right now..?
I believe it's AW46 Nige. I'm sure that's what I've seen on his tank. He's going to double check for me.
If he is using a 46 now I'd go to an AW32 or even a 22. Let's face it the system's not complicated and because of the way it's operated there is no chance whatsoever that the oil is going to overheat.
A couple things come to mind. Is this problem something new? This would be the most important question. Is it possible someone over filled the tank? Last is he sure the baffle is still in place, assuming this is a new problem on a previously working system. Only problem I can see with going to lighter viscosity oil is it could allow the box to come down faster making the problem even worse. I'd almost be tempted to install a restricted fitting in the line to make the body come down slower.
What if he tries lowering the dump slower? Also does he have the PTO on when lowering?
Lowering it slower doesn't seem to make a difference. It's done it every winter the past 3 yrars. I thought it was air so I bled the cylinder and got quite a bit out. But it's still doing it. PTO is disengaged when he lowers it.
try with the PTO on
Can you take a picture or make a drawing of the tank and baffle design. Also, what is the diameter of the cylinder and the time it takes to retract? You may also be looking at an inlet leak on the pump. Aerated oil?
Most dump pumps come with a sleeve restrictor on the return side... maybe someone has removed that one to make the box come down faster?
In my experience the cause is suckling air into the pump, usually at the seal to the input shafts of the pump. It does do it more in the fold too. I have learned this one the hard way fighting with the problem and wasting oil, making a mess etc. I tried putting the body down slow as possible and two thirds of the way down here comes the oil. Replaced the seal with a double lip seal and problem solved. Have had this twice over the years.
Sucking air is what I've always thought but couldn't prove it. The cold weather would probably harden that seal up a bit and suck air. I'll try that.
Either sucking air or fluid was too low in tank, tank ran out of fluid and started pumping air into cylinder. Air went to top of cylinder and forced all the fluid back into the tank when let down, including fluid that was in the cylinder, which was more than what tank could hold, so excess_was forced out breather. Open bleeder on top of cylinder and raise bed until all air is pushed out, then top tank off.
I've done that multiple times. It's not over filled or too low. It will do it every single time, regardless of how slow you let it down or how many times you bleed it.
Are there baffles in the tank that the cold oil is not flowing past, causing it to be too high where the breather is located?
The only baffle in the tank is basically a spray deadener. And it is there and not damaged. I checked. It's very foamy when it comes out so I have to agree with guys suggesting that it's sucking air.