Is it necessary to bleed the hydraulics?

[jtheise4]

I recently changed the hydraulic fluid on my Massey Ferguson 1643. I have a DL120 loader on it and its a hydrostatic transmission. I've been using the tractor for the past 3 or so hours and every thing seems to be working just fine. I was glancing through the owners manual last night and noticed that several pages after the section on changing the hydraulic fluid, there is a section of the manual that recommends bleeding the hydraulic pump after changing the hydraulic fluid. I always thought tractor hydraulic systems were 'self bleeding'. Am I wrong? Is it really necessary to bleed the system? Thanks.

 

[oldnslo]

I recently changed the hydraulic fluid on my Massey Ferguson 1643. I have a DL120 loader on it and its a hydrostatic transmission. I've been using the tractor for the past 3 or so hours and every thing seems to be working just fine. I was glancing through the owners manual last night and noticed that several pages after the section on changing the hydraulic fluid, there is a section of the manual that recommends bleeding the hydraulic pump after changing the hydraulic fluid. I always thought tractor hydraulic systems were 'self bleeding'. Am I wrong? Is it really necessary to bleed the system? Thanks.

Depending on the system style they may require bleeding.

1) If this was a closed center pressure comp pump it may not prime properly since it is being "dead headed" at start-up. This can be over come by looping the work ports on direction valve and then holding the valve so flow can pass through it at start-up.

2) Problem with hydrostatic is they are a closed loop system so if they are truely drained they require a start-up sequence that bleeds the air out under very low load conditions. Since you did not drain the HST you should be good to go.

Roy

 

[jtheise4]

Depending on the system style they may require bleeding.

1) If this was a closed center pressure comp pump it may not prime properly since it is being "dead headed" at start-up. This can be over come by looping the work ports on direction valve and then holding the valve so flow can pass through it at start-up.

2) Problem with hydrostatic is they are a closed loop system so if they are truely drained they require a start-up sequence that bleeds the air out under very low load conditions. Since you did not drain the HST you should be good to go.

Roy

Actually, I did drain the HST. On my tractor, there is only one hydraulic reservior for the HST, power steering and hyrdraulic remotes.

 

[oldnslo]

Actually, I did drain the HST. On my tractor, there is only one hydraulic reservior for the HST, power steering and hyrdraulic remotes.

Yes you drained the reservoir for it but you did not open up any lines between the HST pump and motor. It is when you open these lines that air gets into the closed loop portion of the HST and can cause problems. Yes you can potentially get some air in the HST from the charge loop if it drains out but this is usually bled out when the charge goes over it's relief valve.

Sorry for the confusion or any concern this may have caused.

Roy

 

[jtheise4]

Yes you drained the reservoir for it but you did not open up any lines between the HST pump and motor. It is when you open these lines that air gets into the closed loop portion of the HST and can cause problems. Yes you can potentially get some air in the HST from the charge loop if it drains out but this is usually bled out when the charge goes over it's relief valve.

Sorry for the confusion or any concern this may have caused.

Roy

Got it! Thanks for explaining.