Why so high pressure in rod side during boom down operation in excavator?

I've an excavator, in this excavator i tried a new control valve block. After complete installation i found some jerks in boom up & down and arm in & out operation. So i put orifices both side of the pilot line of the boom and Arm spool, but due to this speed is getting very slow i tried little bigger orifice but same result i got. At last i removed all the orifices and try to run the machine but strange i found boom down is ok and boom up too slow. Then i decide to take pressure traces of all the services then some strange facts i observed that during boom down i found no back pressure in boom head and high pressure in rod side (250 bar) (generally it is around 130 to 150 bar). please REFER TO THE ATTACHED FILE OF PRESSURE TRACES OF BOOM DOWN [/B]OPERATION. Kindly ask me if any other information is required.

do you measure boom rod pressure downstream the control valve or upstream?

boom rod pressure measure downstream the control valve

It might be drift reduction valves causing those pressures.
Later Bob

So all you have to do is, remove the pin that connect the rod to the boom, and try to test once again.
Bt the way when you measure the boom head, is it also downstream the control valve or upstream?
is there any drif reduction valve that is throttling the boom head, like BOB said?

the wird thing is that above 32 sec you still have 250 bar at rod end, and the pump pressure decrease below 30 bar (the black line). Which means the load on the rod end is indeed 250 bar. By the way is there one cylinder or two for the boom?

Thanks for the reply. This is one cylinder boom machine. Pressure measure downstream the control valve.

By removing the pin, you mean removing the boom cylinder from the structure. And what is the objective of doing this and what should be the result after doing test once again? From my perception it will conclude that there is no mechanical resistance in Boom Up by doing unpin the boom rod.

Pardon my stupidity, but what problems are you attempting to resolve ??????? What does rod side pressure on boom down circuit have to do with an arm cylinder circuit ??????

So, it looks like the rod side was supplied pump pressure during boom-down and then stayed at pump pressure once the valve closed and the pump went into bypass?

Wouldn't that be expected? You supply 260 bar to the rod side, control valve closes....traps that pressure in that side. You can see it slowly drifting down...would that be slow pressure bleed-off around the piston/control valve seals?

You should probably provide make and model of the machine before we can give any more information.

Generally manufacturers provide some kind of control function in cases where gravity can make the boom or stick fall faster than the pumps can provide oil for. On older machines this was done by feeding two pump flow and return to tank where gravity doesn't affect the function, and single or two pump flow with single flow return to tank. That means the boom or stick won't just free fall faster than the pumps can provide oil for.

It kind of sounds like you have some hoses hooked up backwards.

Hi Friends,

thanks for showing interest in my query. Good news is that the issue is resolved now. actually the problem was due to missing load check valve spring in main valve block. Due to that spring the pressure in the system was not able to sustain.
Thanks a lot friends.