Hydraulic Scissor Lift 7

[AC-Power]

Good Day All,

I am not a mechanical engineer, rather, I am electrical. Having said that, I am hoping there is someone in here that might have fluid mechanics experience.

I just bought a scissor lift from an auction. When I attempt to drive forwards or reverse, all I hear is the 24VDC hydraulic motor start, no movement. Too, when I attempt to raise the platform, same thing.

Is there anybody in this forum who might have a suggestion on what part I should investigate/troubleshoot in an effort to remediate this problem?

Regards to All

 

[AC-Power]

Good Day LittleInch and 3DDave,

I have the manuals already. They show everything, that is, hydraulic system and the electrical as well. It is a SkyJack SJIII 4626 scissor lift. Problem is, I don't know what to look for in hydraulics. As a Master Electrician, I do have electrical testing equipment, and knowledge. I suspect I'll have to buy a hydraulic pressure gauge to see if the pump is producing the required pressures.....but then again, I wouldn't know where to connect the gauge. Anyways, I am trying the best I can before I send it to a hydraulic shop.

 

[btrueblood]

Well, one quick thing - that big red button-activated valve in one of your photos is an emergency go-down button. It shunts all of the lift fluid back to the tank, probably when it is pushed fully "in". It might also disable all other hydraulics when pushed in, i.e. acts as a safety e-stop. You could try pulling it out, and seeing if that frees up the lifting mechanism, if not try pushing it in see if that makes any difference.

The other photos you give look like standard directional control valves (the Argo-Hytos valves), and a 2 pos. 3-way valve that probably diverts flow (interlocks) between the steering/drive motor system and the lift system.

The fluid looks clean and clear, and there seems to be enough for the lift to operate. If you don't hear the hydraulic valves clicking when you activate the various controls, and/or can confirm they get no voltage when checked with a multimeter, then there is...somewhere...a safety device that is electrically disabling the control system. It might be part of the charging system for the batteries. You will need a wiring diagram, or a qualified mechanic, or both, to diagnose.

 

[3DDave]

You first need to check for flow - does fluid go back to the tank? The schematic should show what kind of pump it is but looking at the type of valves it's most likely a fixed displacement pump, so that means if the motor is turning the pump should be pumping fluid and that fluid needs to go somewhere - if not onto the ground, then it's heading back to the tank.

If fluid isn't moving either the pump inlet is blocked or the pump shaft is broken. So start there. What you are unlikely to need is a pressure gauge. Mostly a bucket to catch hydraulic fluid. Don't disconnect anything if the lift is elevated or while the pump is operating. Get a face shield.

 

[LittleInch]

It looks like the manuals differ (a lot) by serial number - so what's the serial number?

The skylift site also gives you service manauals which have diagrams and trouble shooting check lists

ON your photo 3449 on top of the HPU there looks to be a gauge? What does it say / read when you turn it on?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AC-Power]

@ btrueblood: I checked the red valve. It's spring loaded, to return to the "IN" position. I suspect it opens when pulled (and maintain pulled muscular force), it releases the oil as you commented on. I didn't see any electrical interlocks on this NC (normally closed) valve. Thanks for the help...I really appreciate it.

@3DDave: I don't hear any oil going anywhere, nor do I see the hydro oil sightglass level change when the pump motor is running. I don't suspect any oil is going anywhere. The pump is a Haldex 123476AA. The motor is a Haldex 220 1054. Could the lack of oil flow be the SkyJack 109568 hydro oil filter on the top of the reservoir? I won't open any hydraulic hose/fitting until I feel it's needed, and yes, I do have a face shield!! Ha. Thanks #DDave for your input!

@LittleInch: Serial Number is 711931, SkyJack SJ4626 (or SJIII 4626 to be more specific), drive height = 26ft, system pressure 3000psi, lift pressure 1900psi. The gauge on the top of the HPU is an run hour gauge to act as a figurative "odometer" for the lift. Thanks LittleInch for your help too!

General Note: I checked for the presence of 24vdc power to the main solenoid valve (pressure-compensated proportional valve?).....it does get 24vdc on any command for hydraulic movement (LIFT or DRIVE).

 

[AC-Power]

One more Pic

 

[3DDave]

The filter has a bypass check valve next to it. If both were blocked the motor would stall out or fluid would go onto the ground through something broken.

It looks like the Red button is the "emergency lowering valve," V1, and it looks like a pull to activate, spring return to normal operation.

Best guess is the pump is broken. Bad news is Haldex doesn't seem to recognize that number - 123476AA Is there some other dataplate on the pump?

It could be the key has sheared, but that would require the pump to be blocked or otherwise overloaded. Possible - removing the motor from the pump will test that theory. Plus, one can turn the pump by hand (or with judicious use of pliers) to see if it turns unexpectedly freely or not at all.

 

[TugboatEng]

Sheared keys can happen due to fretting wear and don't require overloaded.

 

[LittleInch]

OK.

The manuals for anyone else benefit are attached.

The base controller seems to require you to hold in the green button ALL THE TIME whilst then asking the machine to do something. Page 16 gives you a photo.

Also make sure the emergency button on the operators platform is pulled out. If trying from the platform again the enable button / level needs to be depressed continuously whilst trying to get it to do something

Section 4 of the service manual attached in the next post gives you a comprehensive check list for the electrical system and the hydraulic system in section 4. I can only suggest you follow the list.

For sure check the filter, but if should still work.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

service manual

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AC-Power]

Thanks to #DDave, TugBoatEng and LittleInch:

This might seem stupid, and maybe it is.....but, what if I slightly open the oil line discharge from the pump and see is hydro oil squirts/sprays everywhere when the pump motor is given a command?

 

[LittleInch]

One way of finding out.

I would exhaust the trouble shooting check list myself first.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

I would not do that.

 

[3DDave]

From the manual Littleinch posted I traced down the coupler - no key, but what looks like a rubber or plastic piece to bridge between shaft adapters with double flats.

https://www.amazon.com/Skyjack-SJIII3015-HYDRAULIC-COUPLER-703183/dp/B07WCCRGH4

shows the coupler kit mentioned in the manual.

It matches the end of the pump shown here:

https://www.accessplatform.com/SKYJACK-106577-PUMP_p_4510.html

 

[AC-Power]

I removed the motor from SkyJack scissor lift, and then removed the hydraulic pump from the motor. The hydraulic pump spins freely by muscular force! Is that right?

 

[AC-Power]

Picture here

 

[AC-Power]

The spider coupling is fine.

 

[AC-Power]

BTW - The hydraulic pump is still attached to its respective hydraulic oil lines. I only removed the pump from the motors mounting bolts. Pump is still connect to it's oil lines and still in the lifts hydraulic compartment.

 

[LittleInch]

Did you follow the checklist in the service manual?

Are you holding in the enable button all the time while asking it to do anything?

Why did you buy a hydraulic lift without trying it out first??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AC-Power]

@LittleInch

Good Day and Thanks for your reply. I am responding[COLOR=in the color [COLOR=#CC0000]RED:[/color]

Did you follow the checklist in the service manual? I already accomplished the suggested remedies in the service manual, no success

Are you holding in the enable button all the time while asking it to do anything? The maintained depression of the momentary pushbutton is only for ground controls, and yes, I already tried it, no success

Why did you buy a hydraulic lift without trying it out first? I bought it from a different city, Edmonton. It's about a 3hr drive north of Calgary.....I didn't feel like doing the drive.
Next time, I might consider it. It mostly depends on the cost of the item...this lift was only $4k.