HYDRAULIC CYLINDER REBUILD

[smartguyz]

</font><font color="blue" class="small">( With all due respect to everyone, on the subject of leakdown. I talked to several hydraulic technicians at hydraulic supply and repair business. They say that a good hydraulic system should not leak. Pumps should not bypass, valves should not bypass in the raise and lower situation, and cylinders should not bypass. )</font>

I'm inclined to agree here. I know that my hydraulic car jack had better not leak down, or someone will get killed!

I have a brand new PT425 (purchased in July 2003), but it has always leaked down. I know, because right after I first used it (the first day), I put the mower up, and went 10 feet away to get the hose. I noticed that the mower was already starting to push down on the 4x4 I braced it with. Therefore, it was a leaker from the very start.

Hmm. I'd be curious to see if the 'rebuild' of both lift arms fixes it. I personally think it's the valve. Let's find out.

-Rob /forums/images/graemlins/grin.gif

 

[Charlie_Iliff]

<font color="red"> Assuming those are 100lb weights </font>

Stand on a scale; note your weight (w); pick them up; note the combined weight (cw); subtract w from cw and divide by 16. If the result is 100, your assumption's correct. /forums/images/graemlins/grin.gif

 

[J_J]

Does anyone hnow what brand of cylinders and valves PT uses on our machines. I will replace the valve as my last resort, as that is the control point, and the most expensive. I was even thinking of installing pressure gauge outlets. One on the output of the lift pump, one in the PTO pump, and one on the cylinder output block. The quick connect outlets will let you use only one gauge to check different areas of pressure.

J.J.

 

[jrlichina]

If your lift arms start leaking down in ten minutes you definately have a problem. It sounds like PT is using some lower quality valves. On loaders I've built they would stay up for days but I did use a good quality valve. Also the loader on my BX will stay up for several days as well.

 

[Bob999]

<font color="red"> Pumps should not bypass, valves should not bypass in the raise and lower situation, and cylinders should not bypass. </font>

I have a John Deere Skid steer and have the technical manual for it.

According to the tech manual for this machine a small amount of leak down is considered acceptable. The test for a problem is to time how long it takes for a raised bucket or arm to drop. Also asymetrical leak down is unacceptable.

I also have two hydraulic jacks. One appears to have no leak down. The other will slowly leak down.

I would assume that the designers of hydraulic cylinders can influence leak down with the choice of seal materials, the number of seals, parts tolerances, and probably other factors. To me the bottom line in this case is that the manufacturer of the cylinders--Power Trac--says some leak down is "normal". I think that means that the design and material choices they made result in some leak down.

 

[johara1]

my 422 seems to be ok,i can raise the mower and remove the blades ,sharpen them,put them back on,grease it and air the tire up that use to go flat.it would stay up for that,i say that is good enough.as for hyd. power it will lift a full heaping bucket of 2a modified in the big bucket that is 10 cubic ft. 2a modified weighs 3000 lbs.a cubic yd.
two things you don't do ,(1) don't go down hill with a full bucket! (2) don't run full throttle and load the bucket, or you will wear half the the stone when you close the bucket. /forums/images/graemlins/smirk.gif

 

[Sedgewood]

<font color="red"> Stand on a scale; note your weight (w); pick them up; note the combined weight (cw); subtract w from cw and divide by 16. If the result is 100, your assumption's correct. </font>

Ok, If I can keep my balance atop a stack of eight to ten bathroom scales long enough for the needles to settle I can record all the readings and add them up. That should give me (w) and (cw) to plug into your formula. /forums/images/graemlins/laugh.gif

Sedgewood

 

[Sedgewood]

<font color="red">Sedgewood: when you were researching how to restore the hoses, etc. did you come across any valve info which suggests why we get the leakdown? When you have spent time staring at the circuit diagrams, do you see any clues? Any relationship, for instance, to the syndrome where turning the steering to lock, so that a steering cylinder bypasses, it diverts available pressure from the lift cylinder?
</font>

No, that wasn't on my mind at the time - I was just trying to get back up and running. /forums/images/graemlins/tongue.gif I remember thinking when I first discovered that the cylinders won't move if the steering is at full lock that something was amiss and that Terry reassured me all was ok - that the steering is designed to have priority over lift. How that is accomplished anyway?

Sedgewood

 

[duane]

Sedgewood,

From memory, I believe the lift/tilt pump discharge is plumbed in series. First to the steering valve, then onto the lift/tilt valve. If not used by the steering valve, it goes on open center style to the lift/tilt valve.

I believe 16 cc/min port leakage is pretty common for hydraulic spool valves. You can purchase spool valves meant for holding position. Lift capacity is more a function of pressure not flow, so a little leakage should be made up from the pump. It would be a neat test to install pressure gages and see what you actually have.

Duane

 

[Charlie_Iliff]

<font color="red">a stack of eight to ten bathroom scales </font>
Nay, Nay. The scales clearly need to be in parallel, not series, so you need an infinitely rigid bridge and the scales set on a 100 percent flat level plate. The results have to be accurate to three decimal places to be acceptable. /forums/images/graemlins/cool.gif