Counter balance system
Counter balance system
(OP)
I have a system i want to get some advice on. Large milling machine, hyd system = counterbalance circuit : 2 counterbalance cylinders, pilot operated check valve, pressure reducing valve and a nitrogen charged accumulator. pressure line going out to 1 other area of machine. My experience with this system is when hydraulics are shut off pump pressure immediatly drops to zero and counterbalance gage does not drop, holding system pressure at the check valve. What I have on this machine is pressure is maintained at the pump for a couple seconds after pump is shut off, then a noise like fluid rushing back reversing the pump. Hyd gage drops to zero. C/bal gage also drops to zero, then quickly return's to system pressure. Is a brand new machine, have replaced the pilot operated check valve and the pressure reducing valve. Initially with the original components the c/bal pressure was slow to creep back up to system pressure after shut down, now with new valves = quicker response to system pressure.





RE: Counter balance system
RE: Counter balance system
RE: Counter balance system
[IMG]http://i13.tinypic.com/6gbx8aq.jpg[/IMG]
[IMG]http://i8.tinypic.com/689jpmw.jpg[/IMG]
RE: Counter balance system
RE: Counter balance system
RE: Counter balance system
While the check valve is open, gravity induced load on the cylinders is pushing oil back through the system, motoring the pump. When the PO check valve eventually closes, the pressure rises because of the load on the cylinders.
The noise you can hear is high velocity fluid flowing over the PO check.
The schematic drawing shows the PO check with an external drain. If this drain is too small or blocked the PO check may be slow to operate.
First job would be check the drain line from the PO check.
The drawing shows that the PO check drain is connected to the Y-axis cable conveyor. High flows = high pressure. If the drian form the conveyor is full, it will stop the PO check resetting.
This post would be better in the Fluid Power Engineering forum.
'hope this helps...
Adrian
RE: Counter balance system
[IMG]http://i18.tinypic.com/54lwmzp.jpg[/IMG]
RE: Counter balance system
While the check valve is open, gravity induced load on the cylinders is pushing oil back through the system, motoring the pump. When the PO check valve eventually closes, the pressure rises because of the load on the cylinders.
The noise you can hear is high velocity fluid flowing over the PO check.
The schematic drawing shows the PO check with an external drain. If this drain is too small or blocked the PO check may be slow to operate.
Hydromech replied as follows :
First job would be check the drain line from the PO check.
The drawing shows that the PO check drain is connected to the Y-axis cable conveyor. High flows = high pressure. If the drian form the conveyor is full, it will stop the PO check resetting.
This post would be better in the Fluid Power Engineering forum.
'hope this helps...
Adrian [IMG]http://i18.tinypic.com/54lwmzp.jpg[/IMG]
RE: Counter balance system
RE: Counter balance system
You are correct...sorry I did not read the drawing correctly. There is a seperate drain line for the y port. It goes back to DR2 on the power unit. That would be the place I would look.
I am sure the problem is with the PO check not closing.
Is the schematic correct because it also shows the counterbalance pressure at 5-5.5 MPA which is 50-55 BAR. The pressure gauge in the picture only goes upto 16 BAR?
Adrian