m-325 plastic vs rubber pilot lines

This topic contains 2 replies and was last updated by eric-simpson-2 7 years 3 months ago
November 18th, 2013 8:36pm
Hello everyone! New to this site but so far love it and its resources! Anyways down to business, we have recently been having trouble with our aging cat m-325 (approx. 23 000 hrs) it started out as a small complaint of having a faint jerking motion when operating boom and stick controls to getting as violent enough that it was almost impossible to hang on to controls after the jerking began which was usually either retracting the stick cylinder, swinging either way, and the boom cylinders were spongy. our spongy boom cylinders were cured after removing upper pin, and cycling cylinders back and forth removing the air. Now this next part is where id like help, after telling another mechanic about our symptoms on our machine he recalled an excavator having the same symptoms as ours, apparently the pilot control system hydraulic lines from factory were made from a plastic synflex line which were spec and made to handle the low pressure the pilot system uses. When one of these lines blew they were replaced with a rubber 2 wire hose which had the inside diameter matched as close to the plastic lines as possible and were installed instead due to the unavailability of the plastic synflex lines in the area and for the need for the machine to be up and running, and after 2 or 3 of these oem plastic lines were replaced the machines controls were affected just as ours was, the rubber hoses were soon after replaced with synflex lines and the machines controls were back to the smooth normal controls. After hearing this and realizing that we as well replaced some of our plastic synflex lines with conventional rubber 2 wire hoses the correct synflex lines were ordered and reinstalled and sure enough it solved the problem. So I guess what im asking is if anyone else has run into this problem or has any kind of explanation as to why construction of a hydraulic line could make such and impact on a machine, I know ive been doing some head scratching! thanks!
November 19th, 2013 9:23am
Welcome Rick to Mechanics Hub! We are so happy that you love the site and its resources...this is what Mechanics Hub is for :)

December 22nd, 2013 10:43pm
Interesting result! Could it be an accumulator effect? When a rubber hose is pressurized, it expands slightly (accumulator effect) and then when pressure is relieved, that slightly expanded hose collapses to its normal size. I'm scratching my head on this one too!

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