The boom function on my john deere 310a works good enough for backyard usage,plenty of strength,but drifts really bad,whether running or stopped. i am pretty sure that the spool is probably worn out after many years of use,but was wondering if there was any type of valve i could add inline to stop this annoying problem.Any help would be greatly appreciated,thanks for looking.
Have you resealed the cylinder already? That's usually the first suspect.
have not done that yet,but it has no external leaks
First guess would be piston seals bypassing.
is there any test i can do to confirm that the seals are bad?
I have fixed this very problem on a county precinct rig. I had the boom cylinder resealed and it still wouldn't hold. I got a high pressure ball valve and adapter fittings from Surplus Center and installed it inline on the raise side of the cylinder. The it is close enough to the operator station that he opens it when in use then closes for transport or just to leave up. It has worked perfectly for an older machine versus a new valve $$$. The only problem I had was routing the hoses to allow for swing without too much bending.
Yeah, a ball valve as wrwtexan says, and for testing if need be a short hose to help install it, you can lift the boom and close the valve, see what happens. If it stops drifting it's the spool valve, if not it's piston seals. If the spool is worn a more elegant solution would be a single cartridge counterbalance valve to lock the cylinder until pressure is applied to move it downward.
lantraxco; interesting idea on the counterbalance valve. Would that be similar to the safety valve on something like the boom cylinder on a skytrack? If so, how well would it stand the constant cycling of a backhoe duty?
Yes, those may be a lock valve which is slightly different or they may actually be counterbalance valves. In any case the valve closes off the outlet of the cylinder until you build enough pressure on the opposite end to open up the outlet back to the spool valve. A small line or passage brings the pressure across to pilot the valve, and there are different pressure ratios to provide different braking curves. The same sort of valve in a back to back configuration is used on all excavator swing and travel motor circuits for braking, you can't get much more punishing than that.
thanks guys for all the response will be trying these ideas.thanks again, Steve
Cylinder leakage test My 410B/C; 510B/C tech manual (TM-1468; Oct-88) describes a cylinder leakage test that will show if fluid is leaking past the piston seal.