Posted by pete 23 on June 26, 2009 at 20:42:57 from (173.87.14.132):
In Reply to: 350 hydraulics posted by Bob 02 Martin on June 25, 2009 at 19:17:02:
Yes, a new perfectly manufactured spool type valve as used in the 350 will hold a load in both directions (up to a point) and that point is when the pressure required to hold the load and viscosity of the fluid reaches the point where fluid will leak through the clearance required to allow the valve spool to move freely in it's bore. A worn spool or bore will leak that much sooner. Like Dick said, that is why IH used a check valve on the hitch and made them available for the other valves as well. Some were single action, some double, and some were alternating check valves. One of the major complaints against IH by John Deere oriented customers over the years was always that IH tractors always allowed hyd cyl's to settle. Deere SCV's, had a positive seal and that is why you saw high pressure safety relief valves on deere cylinders as they would blow cylinders and hoses when parked out in a hot sun and the IH would not as they would seep enough to relieve the pressure. I found out the last few years I worked at a Deere dealership that this positive seal feature was very expensive to maintain as I repaired a quite a few SCV's and it was a money making deal for dealer. Could have bought a new aux valve on the IH for what was put into them as a regular repair. The thing I always like about a spool type valve is the control you have when inching a cylinder into a load and you don't have that precise control with a poppet type valve.
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