My front loader has Aux hydraulics. there are two lines ..Pressure and returne with a reversable valve. That makes sense to me but what's with my backhoe? It has three lines going down the Dipper. Not sure how or why that is. Only one foot pedal that rocks back and forth, I thought that would be like the Loader. Rock the pedal one way for pressure down one line, rock the other way to reverse pressure. Third line has a bit smaller Flat Head Coupler then the other two.
Hi, some attachments have an extra line such as a tarmac planer. When i used one on my backhoe i had to run the third smaller hose directly in to the hydraulic tank. I think it`s a relief line and it may be what yours is for
Some attachments have a component, such as a hyd motor, that requires a case drain line that goes directly to tank return line as cymro mentioned.
Most bobcats have a similar set up
Ah so it's kind of an 'overflow'. meaning if the attachment you are using cannot pass through as much fluid as the Aux is sending to it, it will dump back into this line? If the Gallons per minute is more then the attachment can handle, this third line is a return. Makes sense. Thanks
Yair . . . A bit O/T but can any of you hydraulics blokes clarify this case drain thingy. What is the go with case drain motors? Why are case drains necessary on some applications and on others not so much? I have two different make mowers, one is thirty years old with just a pressure and return line to the motor works fine . . . and then we get a new John Deere trying to do exactly the same job and it has the extra case drain plumbing, what am I missing here? Cheers
Usually piston-type motors require a case drain line because even when new some oil will get past the pistons and accumulate in the motor case. It's usual for the case drain line to have a screen or filter in it so that if the motor fails the resulting debris does not get back to the tank. Gear or vane-type motors on the other hand don't generally require a case drain because any internal leakage finds its way into the return line anyway.
Yes like others have said, we have a E50 bobcat that has several attachments, bush hog deck and US mower flail axe, the flail can not have back pressure on the motor and seal so it has it's own 3rd line with a filter to catch the trash if it let's go. We also have some other mowers we run on the other trackhoe and boom mower tractors that only have the two large lines.
The case drain is to protect the output shaft seal. There is a port on the inside of the motor that is connected directly with the case drain line going back to the tank. What I've seen generally is the motors that use cheap shaft seals run the case drain line. Motors that use a more expensive shaft seal tend to vent the case drain to the return side of the motor. Generally those motors also run a two sided check valve when the motor is bi-directional. I've also noticed that the more complicated motors will use a case drain line. Add a shaft brake and a two speed function and all those motors that I've worked on had a case drain.
If you attach an implement that has a motor with a case drain, make sure that the case drain line is connected to a no-restriction return to the tank. Having a blocked or restricted case drain will blowout the motor shaft seal, or burst and destroy the motor case. I've seen very expensive motors split apart when a case drain was plumbed incorrectly.