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# Hydraulic Scissor Lift7

## Hydraulic Scissor Lift

(OP)
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

### RE: Hydraulic Scissor Lift

There is fluid in the lines, right? BTW there is a fluid power forum.

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

### RE: Hydraulic Scissor Lift

(OP)
Thanks 1503-44. Well, I am going to check to ensure there is no airlock in the lines (& lines are full with hydro fluid) as the pastmost owner may of been messing with it.

### RE: Hydraulic Scissor Lift

1st thought is, indeed, a lack of enough hydraulic oil.
2nd is that the directional solenoid is not operating.
3rd is a stuck open relief valve.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Hydraulic Scissor Lift

4th, shaft/coupling is broken.

### RE: Hydraulic Scissor Lift

(OP)
Thanks So Much itsmoked and TugboatEng. I am going to look at both of those things tomorrow.

### RE: Hydraulic Scissor Lift

Check all fittings and components to see if they are operable; some you may not be able to check. I'd completely empty the system of hydraulic juice and refill it. Make sure you use the right material; the wrong hydraulic fluid can destroy seals. Make sure you purge all air from the system... it's a place to start. See if that helps.

If all else fails, I hear they make great lawn ornaments.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

### RE: Hydraulic Scissor Lift

Do not buy anything without seeing it works. I think you were either given a complete dodgy product or a product that there is need for repair, or you knew that it was requiring a repair work, that is why it was cheap. Beside all, I would ask the seller first what was wrong with it.
This kind of gadget requires a specialist to go through troubleshooting.

### RE: Hydraulic Scissor Lift

What make and model?

Some photos would be good.

Do you mean the 24V hydraulic pump?

You need hydraulic pressure before the hydraulic motor can work or the hydraulic pistons operating the lift.

Pretty simple to check if you've got hydraulic oil in the tank.... Then see if the pump is working. There should be a pressure guage somewhere.

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

### RE: Hydraulic Scissor Lift

We have a scissor lift here at work, which we inherited from the original owner who was using it during remodelling of our current shop. The stupid thing has so many "safety" features it's ridiculous, with lockouts on top of interlocks on top of keyswitches where the key is missing and replaced with a spare screwdriver...

So, once you have verified the thing has fluid and the pump generates pressure, you will need to troubleshoot the electrical system. Get a manual, and hopefully a wiring diagram for your lift model...google is your friend.

### RE: Hydraulic Scissor Lift

AC-Power (Electrical)(OP)8 May 21 21:22
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

My suggestions are purchase repair manual if possible.
second have a repair company come and do a diagnostic and a written quote.
give you and idea what is wrong with it, then decide if you can tackle it. or farm out the repair.

### RE: Hydraulic Scissor Lift

Statements above are the result of works performed solely by my AI providers.
I take no responsibility for any damages or injuries of any kind that may result.

### RE: Hydraulic Scissor Lift

(OP)
Thanks to All for the your help.

I have attached some pics. I think there a filter pictured here, a solenoid valve, oil reservoir indicator, other pics.....I don't know.

I've never attached pictures before....I hope it works.

(OP)

(OP)

(OP)

(OP)

(OP)

### RE: Hydraulic Scissor Lift

It's a Skyjack scissor lift, which probably has a data plate for the item with the maker's part number on it that could be used to track down the manuals.

https://www.skyjack.com/

### RE: Hydraulic Scissor Lift

Well all we can really say as 3D dave says is that it is a skyjack lift of some sort (photo of the name plate would help) and it seems to have enough hydraulic oil in it.

If you didn't get a manual with it then it's time to find one....

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

### RE: Hydraulic Scissor Lift

(OP)
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.

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

(OP)
@ 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).

(OP)

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

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

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

(OP)
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?

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

I would not do that.

### RE: Hydraulic Scissor Lift

(OP)
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?

(OP)

### RE: Hydraulic Scissor Lift

(OP)
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.

### RE: Hydraulic Scissor Lift

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.

### RE: Hydraulic Scissor Lift

(OP)
@LittleInch

Good Day and Thanks for your reply. I am responding[color in the color RED:

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. ### RE: Hydraulic Scissor Lift (OP) The hydraulic pump is a positive displacement pump.....should it freely spin manually with only muscular force? The input and output oil line hoses are still connected, I haven't touched them. I don't feel it building pressure and producing resistance when rotating it by hand. Is this right? ### RE: Hydraulic Scissor Lift It's probably time to find a hydraulics repair shop. I would not expect a gear pump to be easy to turn in either direct by hand, though it's never come up for me to do so, but I also don't know of a calibration I could give to measure how "easy" it should be. If the pump is damaged internally that would mean fragments could be carried into the rest of the system, potentially damaging valves. ### RE: Hydraulic Scissor Lift AC Power Lets go back to basics here. At$4K you probably aren't going to send this into a proper repair shop unless you've got another $4-5K spare?? The pump should be producing flow and if controlled correctly a lot of pressure. So the easist to try first is to disconnect the outlet hose of the pump and turn it on directing the fluid into a bucket or back into the tank. Do you have flow Y/N If you have flow then do you have pressure? Bit harder as there are no pressure guages, Things to look at on the pump - Does it have an internal pressure relief valve built into the pump? If so check it out to see if it's broken / jammed open. The next port of call is the pressure compensated proportional valve. This as shown on the hydraulic diagram ( you called it the electrical diagram) has two functions. The first item regulates the pressure downstream to be a fixed pressure at the same flow. This means your lift should go up and down at the same speed regardless of load. This one appears to have the electrical signal from the enable switch and hence only allows hydraulic oil through when the switch is depressed. The second part of it appears to maintain a fixed pressure on the output of the pump, so that when the pump is running, but there is no fluid moving into the machine, it sends the flow back into the reservoir. If this part of the valve is stuck open then all your fluid will simply go round in a short circuit. Also even if your valve is working, is the R1 system relief valve working correctly? Again a possible short circuit for your fluid. I would find out how much these two items are and replace them once you know the pump has flow. Then you can be reasonably sure that your hydraulic system has pressure available and can send flow to the pistons or the wheel motors. Then it's a matter of trying to find out what else is wrong... Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Hydraulic Scissor Lift (OP) Thanks So Much 3DDave and LittleInch for your advice. I really do take it seriously, and I apply your suggestions each day (or the next day, time permitting) that you recommend. The two of you are far smarter than I am with this. Naturally, I do good with electrical, but my experience in fluid power is quit limited. As this lift is owned by my company now, I would like to "tackle" this problem myself so as to learn how to fix this thing in the future. I own a shop with milling machines, metal lathe, metal bandsaws, 3 welders, knee mill, hydraulic press, shear, brake, water cutter, etc.....there should be no reason I can't do this.....at least that's what my wife says! :) I'll try your suggestions this afternoon (Sunday May 16). Thanks Again To All. :) ### RE: Hydraulic Scissor Lift Considering the Skyjack manual is cautioning about not letting lint into the hydraulic fluid (probably due to small clearances needed for the proportional valves) it's not the best candidate for a first timer. OTOH - it's not huge expense compared to typical hydraulics. At its heart, it's just plumbing that can make a big mess. The top concerns for hydraulics is that the actuators can kill you, either because the system is operating correctly or because it is not. And high-pressure leaks can also kill you or do grievous harm - a risk that is most often the case when there are external loads, operating pumps, or hydraulic accumulators. Typical example of bad is unscrewing a fitting from a hydraulic cylinder to see why it won't retract when there is a load on it. Or seeing a wet spot or drip on a high-pressure hose and wiping across it with a finger only to find it's a 3000 psi jet that's nearly invisible that injects fluid into the hand. Or bypassing a safety switch while reaching into equipment. OTOH, this unit in the retract position and motor off has no obvious sources of stored pressure or releasable energy - so it's just messy, hence the suggestion for the bucket. Just make sure the reservoir doesn't get empty if the pump is operating and don't leave the platform elevated when undoing any fittings. And get in the habit of never checking any drips by hand without knowing the pressure is relieved. See: https://cse.umn.edu/me/intranet/operations/safety/... https://www.hydraulicspneumatics.com/technologies/... ### RE: Hydraulic Scissor Lift (OP) My replies are in RED: Ok, I did perform the first suggestion of LittleInch's most previous comment: LittleInch = "The pump should be producing flow (It does)and if controlled correctly (It is. Pump Inlet from reservoir, pump output to pressure compensated proportional valve, motor turning correct direction, all good) a lot of pressure. So the easist to try first is to disconnect the outlet hose of the pump and turn it on directing the fluid into a bucket or back into the tank. Do you have flow Y/N" I bench tested the pump (& motor) by manually dumping hydraulic oil into the input hose (gravity assist), it sprayed well into a bucket, hard. Replaced the pump (& motor) into the lift, applied oil again manually (with a funnel, gravity feed into pump) meanwhile I GOT A HELPER TO MAINTAIN A HYDRAULIC COMMAND (in this case, turn left). So I was manually presenting oil to the inlet of the pump AND requesting a hydraulic command simultaneously, the oil sucked into the pump VERY quickly and returned to the reservoir instantly, WITH NO MOVEMENT OF THE LEFT TURN cylinder. I am wondering if I should look at replacing the system relief valve? Could it be stuck open? BTW, the left turn solenoid is receiving 24vdc upon its request for opening, and I hear it clicking. Thanks For Your Help to All of You! ### RE: Hydraulic Scissor Lift Time to find out if the fluid is not leaving the tank into the pump. Check to see that the dip-tube is still attached and not plugged. I'd first try with some tubing to attach to the upper end of the dip tube and see if siphoning into a bucket works. If it does then you should re-secure the pump inlet hose to it. If not, remove the screws holding the tank lid in place and see if the dip tube is still there and not plugged. It is certainly possible for a previous worker to have lost a rag or paper towel in the tank. (Saw an entire 350HP diesel severely damaged because a rag was used to stop a drip when a cooling hose was removed. It blocked the cooling passages in the head after the hose was reinstalled.) Also - that's supposed to be a 4 HP electric motor. The pump can make that power available anywhere the fluid can go, so remain cautious. As you noted, there was some forceful output. ### RE: Hydraulic Scissor Lift Well that's a start. So now, assuming the pump is back in it's correct location, try and work out if the flow is coming from the relief valve or not. This might be more difficult, but at least you should then know if the pressure compensating valve is working or if that is stuck open and just returning all the fluid back into the tank. I think a good investment would be a pressure guage attached to a male hydraulic connection so that you can check if any particular valve is seeing hydraulic pressure at the end of the connecting hose. Don't know what your system is intended for but suspect you're looking at a few thousand psi. You just need to follow the path of the oil and see if ther eis pressure and /or flow from each part. My current suspicions are your proportional valve is jammed open or the relief valve is jammed open, but might not be either of those things. Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Hydraulic Scissor Lift (OP) Ok, Thanks Again LittleInch. I'll go get a pressure valve today, and the necessary fittings. I'll let you know. Again, I take your suggestions very seriously....you are FAR more knowledgeable on this than myself as an electrician. Best Regards ### RE: Hydraulic Scissor Lift (OP) Ok, I finally got a pressure gauge. Checked the output at the proportional (prop) valve, nothing. Upon any command for hydraulic pressure, the prop valve routed the oil back to the tank. I checked for DC power at the prop valve, nothing! I thought I checked that before, but it appears I must have either misread the meter, or I checked the wrong solenoid in thinking it was the prop valve. I traced the valve's DC power back to a dysfunctional automotive relay (terminals 30, 85, 86, 87 and 87A). Changed the relay, all UP and running. I would not have been able to move along with this repair without the help of 3DDave and especially LittleInch. Thanks So Much for your help. If you have any need for assistance with electrical, feel free to ask me in this forum. I am mostly involved with civil electrical work, such as traffic lights, induction loops, LPR, toll controllers, classifiers, street/highway lighting, optical preemption, GPS preemption, etc. I specialize in traffic control systems, even things such as parking garage ticket dispensers, gates, pay stations, LPR, etc. Again, Thanks to both of you. ### RE: Hydraulic Scissor Lift AC-Power No problem, glad we could help and it's great you came back and updated us, You wouldn't believe the number of posts that just stop without any conclusion or response. Fault finding by remote control is not easy as you've found. You might find you can add value in this forum https://www.eng-tips.com/threadminder.cfm?pid=163 And now you've got yourself a hydraulic lift, try the fluid power forum.... Send a picture or two with it working at max height! LI Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Hydraulic Scissor Lift (OP) Ok, I will do that. Once it quits raining here in Calgary, AB, I'll take a pic or two. It started yesterday, and is supposed to keep going until Wed/Thur. Too, I will check out the "threadminder" link you've suggested in this ENG-TIPS forum. ### RE: Hydraulic Scissor Lift Ha - It's raining here as well as it has done all of May.... The other forum I linked to (Traffic engineering) doesn't look like it gets much traffic #(excuse the pun), but other forums may interest you as well as some of the civil ones get into bridges and other traffic related stuff. Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: Hydraulic Scissor Lift (OP) Ok, as promised here is the picture of the recently repaired lift raised to 26' (platform height) above grade. I repaired this in my home's driveway, so the o/h lines feeding my house are in the picture. Again, thanks for your help! I TOTALLY benefited from your help! I have another post...a math question, so I might try to close this thread (if I can) as I am understanding I cannot post (be the OP) to two (2) threads. I would need to see if there is a "math" savvy engineer in some room/thread in here. I could probably figure this out myself (after about 8-10 hours of searching), but I suspect a "math" type engineer could do it in a manner of minutes. Failing that, I will call our P Eng to figure it out for me. ### RE: Hydraulic Scissor Lift The idea is not to post the same question to multiple places. Asking different questions is fine. ### RE: Hydraulic Scissor Lift Just found this thread. Bravo AC-Power! I've had to troubleshoot lifts several times. They are often a PITA to figure out. I'm also jealous you found a lift as I spent a couple of weeks trying to hunt one down. Even used junk is typically$4~5k. I finally found a very nice new one for sale for about $2k only to discover shipping was$6k! I finally gave up.

You have a pretty cool job nitch you've made too.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Hydraulic Scissor Lift

Ac power.

Thanks for that.

You can have as many threads open as you want.

Threads close officially after 6 months when you can no longer post replies but in reality most just naturally stop and gradually fall off the first page.

The key is to only deal with one question in each thread and only post the question in one forum. Hence you need to choose your forum with care.

So figure out which branch of engineering your maths related to and post it.

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

### RE: Hydraulic Scissor Lift

(OP)
Thanks itsmoked. The problem with the lift actually was nothing hydraulic....it was just a bad ZETTER relay (automotive type, black cube, 30amp, one set of form C contacts). I bought the lift from Edmonton, approx a 3hr drive away from Calgary, but I have a 1-ton dually truck, so I got a local 3rd party crane service to lower the lift into the truck bed. The lift weighs 4700lbs, but the truck can carry 7000lbs payload. Anyways, I hope you find a lift so your business, and too, I hope your business goes well after this COVID thing is over.

### RE: Hydraulic Scissor Lift

Thanks AC! I'll keep my eyes peeled. My business actually exploded about March 2020 and I'm so busy I'm treading water. Not even sure why it got busier.. LOL

Keith Cress
kcress - http://www.flaminsystems.com

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