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Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 11:16 AM

I am the Technical Partner for O’Michael Studios, Inc; we are steel sculpture fabrication company. I have a straight forward question that I need help with. While I am a technologist, my background is civil and the problem is mechanical. Our portable mini-crane is an adapted standard garage shop engine hoist. It is mounted–dismounted on our 16’ utility trailer as needed. Lifting is by a hand operated 8-ton x 18” stroke jack piston. This gives us enough force to lift a ½-ton sculpture at full boom extension in the 0° horizontal position. At full boom extension, the crown is 90” from the lifting piston attachment / fulcrum point and 108” from the column pivot point. Attached is an annotated photo of the mini-crane in working position(s). For sculptures in excess of ½-ton we use a variety of cranes, lifting machines and transporters.

The question: we wish to upgrade our mini-crane by replacing the hand pump 8-ton piston with a 12-volt electric over hydraulic pump and actuator piston combination. The nominated pair may or may not be sufficient in lifting force to replace the 8-ton jack. Duty cycle is a single lift off the trailer, rotate to installation position and set sculpture in place or the reverse to de-install the sculpture. Will this pair be able to provide the lifting force for a ½-ton sculpture at full boom extension in the 0° horizontal position?

Basic Specs for Power Unit & Lifting Piston Pair:

· Power Unit: NorTrac 12 Volt DC Hydraulic Power Unit. At 3000 RPM it delivers 3000psi with a flow of 1.5 GPM

· Lifting Piston: Lion Hydraulics Lynx Standard Tie-Rod Cylinder. It has a 4” bore x 18” Stroke

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#1

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 11:48 AM

At the 3000 RPM and 3000 psi, the lifting force would be 3000psi/π(4"/2)^2 = 238.7lbf.

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#4
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:25 PM

Ooops. Would be 3000psi x π x 4sqin ≅ 37700lbf.

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#8
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:01 PM

Thank You!

I figured the same force, but it was based on a intuition based deducted formula. While intuition may be a good starting point it is a very bad idea when you are talking about human safety. A falling 1/2-ton sculpture can do serious damage to people near by. (FYI there is always purchasers, onlookers and workers near by at a sculpture install.)

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#2

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:12 PM

I don't see a problem....you have about a .979 gallon volume in the cylinder(guessing)...and I'm guessing you have 1.3+ gallon reservoir...What model hydraulic unit is it? You can calculate the lifting force needed by multiplying the area of the piston face pi r squared times the psi... A= ~ 12.56 square inches times 3000 psi....You could speed it up with a smaller hydraulic cylinder....like 2"

https://www.northerntool.com/shop/tools/product_200641963_200641963

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#10
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:15 PM

Speed as not the thing; safety is. A 2" bore gets me 1.25:1 affective weight to lift margin at the horizontal boom maximum load position. Industry standard for any lifting method (crane, block & tackle, come-a-long, forklift, etal) is a 2:1 margin.

FYI to all: The sculpture "wrapped" around me in my avatar is right at the 1/2-ton limit.

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#28
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 12:13 PM

....or 3" possibly....

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#31
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/17/2018 9:58 AM

You really think those controls will be adequate to the lift job?

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#38
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 1:32 AM

The 4" cylinder seems very slow moving taking almost a full minute from horizontal to erected....painfully slow...even a 3" cylinder will be slow....

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#35
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/21/2018 7:45 AM

Why is that most people use when calculating area π r2 who measures the radius of of a circular component. I always taught my students to use A = 0,7854d2 .......then you do not fall into the trap of forgetting to halve the Ø. Same with volume: v = 0,7854d2l

Much more betterer!!!

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#39
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 1:42 AM

Haha,, no wonder yer toilets flush backwards....

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#42
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 6:27 AM

Is that where I keep getting all these kittens from???

Anyhow! What's wrong with those formulae?? What IS your problem!!!!!! Hahaha

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#45
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 11:52 AM

If you have kittens coming out of the toilet in the down under land, you really need to ask yourself, who lives in the upstairs? Why do they keep putting kitties in the toilet?

This gets more bizarre as the morning progresses. Of course where you are it is still the dead of night.

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#46
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 9:43 PM

"This gets more bizarre as the morning progresses. Of course where you are it is still the dead of night."

It's nearly 1300, Tuesday 23rd, here in Adelaide where I live, or more correctly, Elizabeth, an outer Northern suburb. Really looking forward to the weekend......NOT....weather forecast is Friday 390C, Saturday 430C and Sunday 450C........can't wait for it

You really need to be careful over there.......with Donald 'Duck' as President........you may fall even further behind!!!!

".....who lives in the upstairs?"

Don't have that problem in the 'burbs, only a handful of multi story residences...... however, the last 20 - 30 years, developers are building houses that close together, that problem "may still occur,' (flushing your toilet and emptying next doors bathtub)........My house was built before that period started, my youngest daughter and her family live in the main house.....I built a spacious 2 bedroom 'granny flat,' where I live, in my 'back yard' and I could probably fit another 2 in there........well I could have, until I put an 8m x 4m x 1,8m swimming pool in......I have a car port, (almost fully enclosed), and 2 standard sized sheds.....one of which my son-in-law lined and fitted out as 2 bedrooms for the two older grand children.........and I still have a heap of room.

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#3

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:23 PM

Bear in mind that the actual manual jack is capable of 8 tons, and will have a built in bypass to prevent exceeding this. A 4 inch diameter ~= 12.5 inches and the hand pump will max out at 1,280 psi in the cylinder of the jack. If you pressurize this to 3000 psi it will exert about 37,500 pounds of force exerted by the piston shaft. If the (assumed) self protection is defeated it is almost certain to cause downstream failure of various attached mechanical components, and might even rupture the barrel of the jack itself due to the 2,35 times over pressure. I suggest you take great care in making this replacement as it could well result in a lethal failure, which could result in manslaughter charges against you/firm. So I would say not at any cost should you perform this upgrade if you defeat the safety bypass. Without the safety bypass it will operate as designed, with electric operation as the bypass will prevent breakage, and it will allow faster electrical operation within it's oroginal design paremeters

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#5
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:41 PM

With an assessment of the levers and forces exerted and assessment of the ability of the jack to allow operation at 3000 psi and all the downstream parts rated for these extra forces, this could be done with care.

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#7
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:59 PM

This would only be a problem if somebody attempted to lift far in excess of 8 tons....

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#9
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:13 PM

The usual load is 1000 pound statuary. Bear in mind the assorted mechanical advantages in those joints, to raise 16,000 pounds at full extension would almost certainly buckle something, and exceed the abilities of that cylinder

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#11
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:33 PM

The full extension load of 1000#'s is equal to 7500#'s. The crane (boom, column, turntable, base, base frame and column struts have a demonstrated ability to carry the load. All fasteners and pivot pins are Grade 8 are regularly inspected for physical damage and stress marking and are annually replaced.

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#12
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:41 PM

Yes, it will work for 1000 pound statuary. The problem that might occur if they try to lift more

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#14
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:53 PM

I am the "They" and my crew has way better sense than to make ANY lift without my expressed orders.

Basic truth about sculpture installation and the companies that do it: the max-daddy bossman is always and in-charge at installs that require cranes of any sort. Way too much human and financial risk to do otherwise. (Can you say 100-ton highway mobile crane, I can.)

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#16
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:57 PM

Yes, I see now you are aware. My comments were in the way of an excess of caution.

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#18
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 10:35 PM

Even a 5% safety factor would compute as “do not use a self built crane in a business environment and sure as hell not in a public place”

cranes are proof tested in an overloaded situation and then given a certification to the appropriate standard for your country , then recertified every 10 years (in my country).

buy a certified crane from a crane expert because you would be surprised how much funerals cost !

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#20
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 11:34 PM

The self building the crane might be just as well qualified as some other commercial self building cranes.

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#21
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 1:01 AM

Maybe so, but I'd say that operator error is usually the problem, unless it's the rigger's fault.

Also, artists do not consider lifting points.

This piece weighs just over five thousand pounds and there are no lift points. It is a challenge to move.

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#22
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 9:32 AM

They usually emplace a steel frame deep inside with thick threaded bolts with an end eye upwards at 2 centered balance points to lift with. After emplacement, the bolt is unscrewed and shorter threaded rod inserted to near the top and the hole caulked and a cosmetic match seal is made. If you ever need to move, you unseal it, remove the short bolts and add the eye bolts.

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#23
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 10:30 AM

Whoever "they" are, they must not have gotten your message.

I was involved in moving public art for 15 years, for 10 of those years I supervised the movement, and I NEVER came across a piece that had such a provision for lifting.

At one time we sponsored displays of as many as 100 pieces, from all over the United States and Canada. Polar Bear and Cubs (above) was created by Dollores Shelledy of Salt Lake City, Utah.

During those shows, the artists were in attendance to witness those placements. Again, not one of them provided attachment devices.

Also, I've never seen a bronze sculpture with an internal steel frame. They are not necessary.

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#24
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 10:49 AM

I speak of large concrete ornaments, because concrete is poor in tension, where the load needs to be born by the bulk. I worked next to a pre-stressed concrete beam company and they occasionally cast large ornamental pieces that had this sort of attachment provision

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#26
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 11:01 AM

If you assumed that the polar bear is concrete because of the color, I agree with you.

It is actually cast bronze that was painted, white. It cost $38K to purchase, just before the economy collapsed. The cost to refinish it, was too high and I was never able to raise the money during the downturn. Now I'm retired and no longer involved.

Sorry, I've gotten us off topic.

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#27
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 11:09 AM

Yes, I had assumed it was concrete as the earlier items were concrete, so I assumed.

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#33
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/17/2018 10:04 AM

OK it demonstated that it can support 1000# at full extension, but how many times before something fails? You really need to have this contraption certified by a crane inspector. Really.

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#17
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 2:07 PM

Yes that would be well in excess of the rated capacity, like I said...

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#6

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 12:51 PM

As the equipment is used in a business, that operation will have an arrangement with an insurance company for periodic inspection and testing in pursuit of continuous collapse liability indemnity insurance cover. Its condition will vary with time and will be noted on a stream of periodic inspection reports carried out in accordance with the local regulations on this type of equipment as applicable at the times of inspection. These reports are signed by the Engineer/Surveyor of that company, accepting liability on that company's behalf on the basis off the periodic inspection and testing for the purpose of issuing collapse liability insurance cover, and copies of those reports will be held at the operation's General Register. This individual, or an immediate colleague in a similar capacity, is the correct person to approach on this matter, and not the readers of an anonymous global Engineering forum.

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#32
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/17/2018 10:00 AM

Well-stated, timely advice sir. Kudos.

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#13

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:42 PM

At 3000 psi, a 2.5" bore cylinder would give 7.36 tons of piston force, and 3" bore would give 10.6 tons. If you need to limit the force, you could set the hydraulic relief valve to less than 3000 psi.

I can't see the geometry well enough to evaluate the load and lifting moments in all positions. If you accidentally try to lift a load more than 1000 lb, or if something catches or binds, any extra cylinder force could buckle the boom.

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#19
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 10:54 PM
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#15

Re: Upgrading A Hydraulic Powered Mini-Crane

01/15/2018 1:56 PM

PWSlack gave you some good advice. Liability should be your #1 concern in any home brew system such as yours.

If this crane fails and your insurance company is not aware of the degree of safely of your crane, they will NOT cover any liability issues that arise due to crane failure. Being a (VERY) small company, this could wipe out any reserves you may have and leave you without anything.

I think you have two areas of great concern.

1. Failure of the crane structure or a critical weld, allowing a collapse of the crane and the load it is lifting, causing physical injury of employees or bystanders and property of others.

2. Failure of the crane to trailer attachment hardware resulting in any or all of the above damages. (This is the first time we ever had a problem test method)

At the very least, you should perform a documented proof test with a 150-200% over load condition with the boom extended and during rotation. Proper rigging is also essential to safety.

Few foundries that I have worked with have any heavy lifting capabilities. Probably because of liability issues.

So, try it first to be sure it's safe before lifting any valuable pieces.

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#25

Re: Upgrading A Hydraulic Powered Mini-Crane

01/16/2018 10:50 AM

Insurance is the thing at issue if safety is the concern. I understand that you work with some skilled metal fabricators. That should not blind you to the litigious nature of our society. I too recommend purchasing a certified unit already trailer mounted with the necessary outriggers and safety features required for safe, certifiable, insurable, operation.

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#29

Re: Upgrading A Hydraulic Powered Mini-Crane

01/17/2018 9:44 AM

Thought rated for 3000 psi most hydraulic power packs have a pressure adjustment screw. The pressure can be adjusted so there is some control to to keep it from over stressing the boom if over loaded. Also the port at the cylinder should restrict flow if a line is broken. This would let the boom drop slowly. Giving any one time to get out of the way.

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#30

Re: Upgrading A Hydraulic Powered Mini-Crane

01/17/2018 9:56 AM

You will need some serious controls if you want smooth lifting, and gentle lowering of the sculptures. Have you considered the purchase of a used boom truck from your local electric utility? I imagine a truck capable of setting a tall wooden pole (that obviously weighs more than 1000 #, will be perfect for your jobs. Not only that, the truck will be able to pull your transport trailer.

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#34
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Re: Upgrading A Hydraulic Powered Mini-Crane

01/20/2018 4:20 PM

Not bad for 16k, plus you could plant trees when things were slow....haha

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#44
In reply to #34

Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 11:47 AM

Is that your truck, it is pretty!

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Join Date: Dec 2005
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#36

Re: Upgrading A Hydraulic Powered Mini-Crane

01/21/2018 10:46 PM

Interesting discussion. I am a bit surprised no one commented on the possible over-turning forces on the hoist arrangment while mounted on the vehicle. Do you have out-riggers on the vehicle, or rely on sufficient counterweights to avoid over-turning the hoist and or viehicle?

I've seen too many U-Tubes of cranes, tow trucks, etc. being tipped due to excessive load and insufficient counter weights to prevent an overturn.

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#43
In reply to #36

Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 8:35 AM

Trailer has outriggers and, with or without, has sufficient mass to counter balance max-lift.

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#37

Re: Upgrading A Hydraulic Powered Mini-Crane

01/21/2018 11:49 PM

I have a similar manual crane to what you have, and prefer it to most powered devices when doing installations. Last summer a client insisted on renting a million dollar "hydraulic spider crane" which runs on diesel, or 220 volt power, will fold up and get through a 36 inch door, is on tracks and came with a skilled operator, very fancy hydraulics. It was a pain to get it to slowly inch down onto pre installed mounting studs because the stops were too jerky and was nicking the threads on the way down. I finally just put a manual chain fall on the hook, got the operator to put it roughly into place, and lowered it manually the last 1/4 inch with the chain fall! Sure the power up and down will be faster and have less effort, but when you need care and precision, and you might be working with something really expensive that you don't want to bend, slow and precise win in my book. Your simple set up with solenoids will be real jerky with 1000 lbs on it. Use it the way it is or you risk getting to a job and damaging something or worse getting hurt.

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Join Date: Sep 2017
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#40

Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 3:36 AM

I feel that those companies which make the combination of DC hydraulic pump and lifting actuators are in good position here to make their offer with all the details and recommendations. Technology is is changing for the better. Please do not re-invent the wheel every time you encounter a problem but surf the internet to get the wheel you require. One advantage you will get from the new combination is that you will operate the lifting from a remote point, in safety. Go for it.

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Join Date: Jan 2011
Location: South Pacific
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#41

Re: Upgrading A Hydraulic Powered Mini-Crane

01/22/2018 4:14 AM

Some very sound advice here. Bear in mind too the legal obligations you may have. In this jurisdiction if a person materially alters a crane, such as in the way you propose, they need to start over with design verification and then commissioning testing, overload testing, to the satisfaction of an engineer surveyor.

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