Stubby 19 #26 Posted June 12, 2021 (edited) On 5/21/2021 at 10:09 PM, Handy Don said: Several thoughts.... Simple stuff: Does the control lever fully move the valve spool in both directions (i.e. does the lever move the "piston" in the control valve the same distance in each direction)? Yes Has the system been cycled 10 or 20 times to be sure that all the air has been purged out of the lines, control valve, and both sides of the lift cylinder? And the oil level in the reservoir checked to be sure it is topped up? Yes When the cylinder has reached the end of its travel and you keep holding the control lever in lift/lower, do you hear the relief valve open up (it'll make a whistling/screeching sound)? (If not, then the pump may not be delivering enough pressure to the lift cylinder.) No screeching. Kinked or obstructed hose(s). No kinked but clogging not sure. Bad seals or excessive wear on one side of the valve spool internally, allowing oil to bypass the valve instead of going to the lift cylinder. Quirky thing: In which direction (lift/lower) is the rod moving out of the lift cylinder? It takes more oil to push the rod out of the cylinder than to push it back in (because the rod itself takes up space on one of the cylinder. If you have low fluid flow then extending will take longer than retracting. Lowering. My comments are in the quote at the end of the sentences. Edited June 12, 2021 by Stubby forgot explanation . Share this post Link to post Share on other sites
Handy Don 12,496 #27 Posted June 12, 2021 (edited) A couple things come to mind based on your answers. Is the lifting speed a lot faster than the lowering speed when there is a load on the lift? In other words, is there a deck being lifted/lowered or are you looking only at an unloaded system? Hydraulics are all about volume and pressure. The pump normally delivers a fixed volume at a given engine speed. Filling the "extend" side of the cylinder will take longer than filling the "retract" side--but the difference is a second or two, usually, when the engine is running at idle. So your expectation of nearly symmetric performance is correct. Something is causing the volume going to one side to arrive more slowly than to the other side. Pressure is probably the reason. On a well-sealed system, the pressure determines the maximum force that the cylinder can exert in lift and lower directions. That's why there is a pressure relief valve--to protect the pump when the cylinder is overloaded or reaches either end of its travel. Pressure is lost when fluid is obstructed or is going where it's not supposed to go. How? - Leaking seals in the control or the cylinder (in the control is more likely than the cylinder which has only one seal for both directions and yours fills correctly in one direction) - Obstructed flow to the "lowering" end of the cylinder caused by a blockage in the control valve or hoses (an improperly seated or torn seal or a foreign object in the valve are likely causes) - Pressure relief valve opening and letting fluid go back to the pump without going to the cylinder - a combination of the above! I wish I had an easy way to specifically diagnose the above issues. Hydraulics usually require specialized test equipment or time-consuming trial and error. Edited June 12, 2021 by Handy Don Share this post Link to post Share on other sites
