Absolutely RIGHT.....I did not want to bring that into the first post because I did not have enough time at that moment....
We have had a few cylinder drift threads lately, and all of them have been "low pressure drift", at little or now load at all....
If heavy load (high pressure on capped end of cylinder) is causing drift, AND the piston seal is leaking MORE than the natural spool leak 2-3c/c per min, pressure will equalize and pressure will multiply with the bore/rod diameter ration, (in my example 4:1).......a 2000psi pressure will become 8000psi.....and if neither of the bucket cylinder port have a WPR, something will burst, and we'll get our leakage, by a cracked CV housing, burst a hose or the cylinder...
Even if the load pressure is 500psi, and the piston seal is leaking, the steady state pressure will equalize and become 2000psi, but with FEL lifted up and travelling, hitting some bumps on the road, inertial force might create pressure PEAK's at 5000-10000psi, if we don't have a WPR, at high loads DRIFTING IS NECESSARY to protect the equipment structure from over load damages
This whole thing, cylinder drift from load, is a reason why some GREAT hydraulic designers, sometimes choose a WPR pressure setting on an application like this, a little HIGHER than the regular system pump pressure.
A knuckle boom crane, or an excavator, lifting a heavy load with the boom, and later reaching out further with the stick (longer leverage arm), would drop the boom from the increased pressure in the lift cylinder
(This scenario can NOT happen with load pressure on the rod side of the piston)
I can't more than agree, this will happen at higher pressure levels.....
If you read my previous post about drifting, you can see that I didn't not exclude the WPR leak option.....I just did not give it a lot of attention, because we had been talking about "low pressure" drift...
I can see here at TBN that most members is carrying around the misunderstanding that, a single rod double action cylinder, leak the same way from both sides of the piston.....when this only happens whit hydraulic motors, cross connected double action cylinder or double rod cylinders.....
I am from the logging world, and equipment wont even get rolled off the trailer if they do not have a proper design....but I can see the "light equipment" manufacturers taking short cuts to save some extra bucks (more profit)...It is also a very competitive market.....but some smaller equipment I learned to know about here at TBN, is definitely pretty well equipped on the hydraulic side....
Before buying equipment like this, buyer need to know what to look for on the hydraulic side.....WPR's and such.....it is a tough world to be a buyer with no hydraulic/electric engineer degree....you are in the hands of a sales man that probably DO NOT KNOW S**T about this, but still promises that hydraulics is properly designed....
