Air in hydraulic pump at lines

[Ronray]

I suspect that my marklift 62 foot boom hydraulic pump may be sucking air when it starts making a loud noise when I engage any of the boom functions such as lift or extension or rotation. This happens on every function and the function will operate normal for anywhere between 2 to 5 Seconds before the hydraulic pump starts making a loud noise and the function stops until I activate the function again a few seconds later. So for example, the Boom Lift will only rise about a foot or two at a time before it's stops and the main pump makes a loud whining noise, as if it is out of fluid and pumping air. I see no sign of a leak or dripping between the hydraulic fluid storage tank and the pump suction line. The main hydraulic filter is on the return lines just before the storage tank. I'm wondering if perhaps there could be debris in the bottom of the tank where the suction line goes to the hydraulic pump? Or if there is some kind of an air bleed knob for the main pump? The pump sounds normal when I engage the foot pedal in the basket before engaging one of the feature valves. so therefore it seems okay with the Pilot low pressure around 200 lb. It's just when I engage one of the features and the high pressure kicks in that the pump stops after several seconds. Should the hydraulic pump clear out any air in the lines on its own if I let the machine run for a minute or two before engaging any features?

 

[funwithfuel]

You don't see any leaks, did you check the oil levels?

 

[Ronray]

View attachment 187933 It's a 40 gallon oil reserved tank and it is about half full. I checked it with the dipstick. I have been reading the service manual some more and read that there maybe some filter strainers at the suction inlet hose to the pump as well as more strainers at the inlet hose to the pilot valve spool manifold that could be clogged, but I wonder if that would cause the pump to make the loud high pitched whining noise after several seconds when a valve is turned on? I also read that the pilot valve circuit has its own separate canister filter, pictured, and wondering if it might be clogged? It has a red and green indicator, pictured, but I don't know what each color designates. It's currently showing kind of a reddish purple color, but changes to Green if I press down on the top button with my finger. Does that mean it's clogged since it's showing red? Does this filter all of the functions as well as the rotation pilot valve? I asked that because the hoses to and from that pilot valve filter enter and exit over the rotation pilot valve, pictured.

 

[Ronray]

 

[funwithfuel]

Where does your sump draw from? Is there a chance you're sucking air? Filter service never hurts, especially that one with the filter indicator

 

[Ronray]

I don't know what the word dump means? Would that be like from the larger main filter that empties into the top of the hydraulic oil 40 gallon storage tank? Also I don't know what ducking air means. Sorry I'm new to all of this. I can't believe how complicated this boom lift is compared to my old farm tractors LOL I really appreciate all of your help!

 

[funwithfuel]

Stupid autocorrect. I meant to say sump. Is your sump fully submerged in oil, or does it have the potential to draw air with it? As opposed to "ducking" air was supposed to be, sucking air. Bottom line, if you have a sight glass on your tank, your oil level should be in the middle. Filters, most definitely need service.

Before that , any of that, follow the biggest hose off the closest to bottom of the tank towards the pump. Is it damaged anywhere, is it loose at either end. If you pull tug on or flex it, will it leak oil? Is there a shut off valve at the tank that someone bumped? Is it kinked?
Now to the top of the tank, what kind of cap does it have? Does it look like an upside down oil filter? Is it a big pipe cap? Is there any kind of breather on top?

 

[Ronray]

Well, I guess pictures can probably explain it better than I can but I'll try. I'm guessing when you say sump, that must be a second compartment in the large hydraulic tank like a septic tank and that the large main hydraulic filter empties into at the top of the tank on the end. And it looks like the exit from the tank is at the other end on the bottom going towards the pump. And there is a shut off swing valve there as well. And the large 1 inch diameter hose from that valve is a straight run to the pump, and there are no bends or Kinks. But I will go ahead and shove it around just to see if I can get it to move. The area below that one inch tube was also dry . Anyway I just noticed this for the first time, that there are 4 more smaller hoses entering the same end of the tank as the large filter and 3 are located halfway up the tank and one at the bottom. There is no sight glass, but there is an oil level gauge, and the interesting thing about it is that it looks like it should measure oil level on two compartments of the tank, but there is only one arrow pointing to the right side of the tank, see picture. Also see another picture showing the cap of the tank, and there is no little pin hole on the top of the cap that would allow it to breathe.

 

[Ronray]

 

[Ronray]

so if the hydraulic storage tank had a vacuum, would that cause the hydraulic pump to stop pumping or make a loud whining noise?

 

[funwithfuel]

Yes, your pumps would be fighting negative pressure in the tank.

 

[Ronray]

So one simple test might be to just take the cap off the tank and see what happens? Thanks much!

 

[funwithfuel]

Worth a try

 

[Ronray]

Any idea of a good cheap source of parts for my 1980 marklift 62 boom lift? To my knowledge the marklift parts are available through Genie and Terex. I'm having a real difficult time with my current supplier Access Platform returning phone calls and emails and canceling online orders without explaining why.

 

[Ronray]

Well, here is some great news! I found this pictured screen filter on the sump side of the hydraulic tank and when I removed it, the pump worked just fine. But when I cleaned the screen filter and put it back on, I discovered that the pump would suck air depending on how much of that screen filter was submerged in oil. And it turns out that the tank has to be half full of oil to completely cover that sump screen filter. So my first question is this 1980 Mark lift calls for Dexron 3 transmission fluid, and I'm wondering if I could just add regular hydraulic oil to mix with that Dexron fluid that's already in the 30 gallon tank? If not, I'm wondering if I could just substitute hydraulic oil completely for the transmission fluid? Transmission fluid is a good deal more expensive than hydraulic oil.

 

[funwithfuel]

If it's a man lift, I'd stick with what oe calls for.
You dont want jerky operation where a people is concerned.

 

[Ronray]

Thanks Fun. I will follow your advice. Just out of curiosity, what is it about ATF fluid that makes it less jerky than regular hydraulic fluid?

 

[funwithfuel]

It's just a much lighter oil. It may or may not respond better to proportional valves then hydraulic oil in cold weather
Not knowing any better I once used hydraulic oil in a Hi ranger man basket truck the customer came back reporting jerky hydraulics that's why now I try to stick with what they recommend.
I believe ATF to be on the equivalent of an SAE5 or 10 whereas hydraulic oil is probably closer to an SAE20

 

[Ronray]

Thank you so much, great advice! I can't tell you how relieved I am 2 learn that this problem I was having was just from that sump screen filter not being fully submerged in oil. I'm amazed that the service manual had no comments about that. It also occurred to me that I will probably have to have even more oil in the tank in case I am driving the man lift uphill to make sure the filter stays covered up as the tank tilts upward.

 

[funwithfuel]

I would guess that tank is designed to hold all the oil of all the empt the collapsed cylinders enough so that you can extend every function on the machine to full extension With out starving the pump. I agree the manual should have been more clear about how much oil is actually required