Removing equalizer cables on lift

[danroy323]

I have an older Rotary SP84 2 post lift. Got it for free (inherited form dad). As it was getting rusty on the bases I sandblasted and repainted it all and installed it in my shop. Works great for my home shop just like it did back at my father's place.

I've always found that the floor plate was a hindrance though. I was thinking of rerouting the hydraulic line overhead (using hardline) and removing the cables to get rid of the floor plate. Of course I would add a flow divider to ensure equal lift from both sides. I know that the Max Jax works like this and I suspect Mowhaks too as they don't have cables.

For those that don't know a flow divider is an hydraulic component that ensures equal oil volume to 2 hydraulic circuits even if the load (and thus pressure) is unequal between the 2.

I always use the safety locks so in the event of hydraulic failure the car can't go completety down anyway.

I can't see why this wouldn't work. Am I missing something here? Getting rid of that plate would be really nice.

Dan

 

[Bob C]

I am familiar with this lift. Before you decide to re-engineer this, do you have the overhead room to just put in the proper lift? I know the EQ cables keep the load level and what you propose seems like it will work. If you choose to follow thru and modify the lift, before you try it, call Rotary and discuss it with their engineers. This is the best advice I can give you and I've installed and serviced the lifts for years.

 

[danroy323]

I am familiar with this lift. Before you decide to re-engineer this, do you have the overhead room to just put in the proper lift? I know the EQ cables keep the load level and what you propose seems like it will work. If you choose to follow thru and modify the lift, before you try it, call Rotary and discuss it with their engineers. This is the best advice I can give you and I've installed and serviced the lifts for years.

I'm about 2 inches short of 12' on ceiling height so most "clear floor" lifts with overhead cables won't fit. And I already have this lift, it's installed and works well. I'm not changing it anytime soon.

I'll check with Rotary but I'm afraid they won't approve this...

 

[wit2003]

I'll check with Rotary but I'm afraid they won't approve this...

There would be my answer to not proceed with this

 

[Bob C]

I'm about 2 inches short of 12' on ceiling height so most "clear floor" lifts with overhead cables won't fit. And I already have this lift, it's installed and works well. I'm not changing it anytime soon.

I'll check with Rotary but I'm afraid they won't approve this...

For your information you can adjust a Rotary SPOA10 to have it fit under 11'10" The adjustment is a factory inclusive extra. That lift you have is ok but uninstall it, sell it and add that cash to a new overhead SPOA10. No plate No problems.

 

[bmarshall1]

Bringing this back from the dead...

I understand the general consensus is to not do this, but I will be getting a lift for free and want to route the hydraulic lines overhead and remove the cables. Has anyone done this?

 

[firebirdparts]

Nobody still alive.

 

[ng8264723]

Not really dangerous. All he plans on doing is do away with the cables which really just eualize the lift and move the hydraulic lines. The lift is made to rest on the locks and he is keeping them

 

[matt_i]

In concept it should work. Press brakes and hydraulic shears which handle 50x the tonnage work without cables.

What I wonder though, is how you "bleed" the system to equalize the heights. This is a single acting cylinder setup fed from the bottom so it could trap air. Do the cylinders "bleed" from the rod at the top somewhere and if you bleed cylinder A, how do you account for the change in volume with Cylinder B? Bleed Cylinder B an appropriate amount of fluid is one possibility, but it has to be something that's included in the design. Same issue would be present if there happened to be a very slow leak from one cylinder where there's a loss of fluid. Same issue would be present if the pipe, hose, or tube lengths from the flow divider on out are not equal lengths. So you see the importance.

 

[firebirdparts]

The cables will hold the load if it settles down on one safety lock. Without that, you would drop the car for sure. Maybe that won't happen.

 

[ng8264723]

Firebird,
Umm no...
The cales will not hold the car. They are not designed to. They are designed for equalization only.
The cables could also be moved above. That's the way my rotary lift works

 

[AngryBeaver]

In concept it should work. Press brakes and hydraulic shears which handle 50x the tonnage work without cables.

What I wonder though, is how you "bleed" the system to equalize the heights. This is a single acting cylinder setup fed from the bottom so it could trap air. Do the cylinders "bleed" from the rod at the top somewhere and if you bleed cylinder A, how do you account for the change in volume with Cylinder B? Bleed Cylinder B an appropriate amount of fluid is one possibility, but it has to be something that's included in the design. Same issue would be present if there happened to be a very slow leak from one cylinder where there's a loss of fluid. Same issue would be present if the pipe, hose, or tube lengths from the flow divider on out are not equal lengths. So you see the importance.

I'm going to try and do my best to not sound like a ****.

hose lengths do not matter. if this was the case, every piece of farm,or construction equipment would have equal length hoses. the length doesn't matter. the pressure does. there isn't a machine in the world with two equal length hoses on parallel lift cylinders.

the cylinders have open ports on the top side of the ram. this allows air in on the top side of the ram and let gravity let the arms down with or without weight. this has nothing to do with bleeding. air is bled at the tanks. once its cycled once to twice, the air is gone.

Cylinder equalization is achieved with a flow divider and a gate valve. the flow divider distributes equal pressure to both hoses. (one 2' hose and one 14-16' hose. the gate valve allows the volume of the fluid to the long hose to be adjusted up or down to achieve the same lift speeds.


there are about 15 brands of lifts setup like this. My chippewa 10K two post uses over head HYD lines just like the OP wanted to do. No way I'd have a cable equalization setup with a floor plate to drive over or try and push cars over without engines. a leak on this system will drain the tank in short order and make one hell of a mess being under pressure. a slow drip a month isn't going to effect lift rates.

the safeties are still in place. if a hose fails, it sits on the locks, just like a cable system would. It should be sitting on locks while the car is up anyways. the cables are not for safety, just lift equalization. it is cheaper to use chinese cables than it is to put a hyd diverter in when the manufacture builds them. that is the sole reason companies build lifts this way.

 

[bmarshall1]

I'm back.... the lift is an old Ben Pearson LAS 7, it is massive. For 7,000 lbs it is way overbuilt. It appears to be much stronger that many 10k or 12k lifts I have seen; I'm not certain why it is only a 7k lift. Anyhow, the lift is in my garage but not fully set up, I need wiring and such, but, once I get some hydro fluid I can run it in place.

So - in theory (per The Angry Beaver , since the rams come up from the cylinder, there is no bleeding needed? They *should lift at the same speed/power. as long as everything seems fairly balanced, it would be OK to carefully test the lift without cables??

Here's a thought: a car's weight is not equal side to side, so, if one side is heavier would not the pressure lift the lighter side (the path of least resistance). Would I need some sort of proportioning valve?

Lastly, what is an acceptable fluid. I was told ATF is good, Ford or GM?

 

[nehog]

...
Lastly, what is an acceptable fluid. I was told ATF is good, Ford or GM?

Yes...

I used GM myself as it was slightly less expensive.

 

[matt_i]

I'm going to try and do my best to not sound like a ****.

hose lengths do not matter. if this was the case, every piece of farm,or construction equipment would have equal length hoses. the length doesn't matter. the pressure does. there isn't a machine in the world with two equal length hoses on parallel lift cylinders.

the cylinders have open ports on the top side of the ram. this allows air in on the top side of the ram and let gravity let the arms down with or without weight. this has nothing to do with bleeding. air is bled at the tanks. once its cycled once to twice, the air is gone.

Cylinder equalization is achieved with a flow divider and a gate valve. the flow divider distributes equal pressure to both hoses. (one 2' hose and one 14-16' hose. the gate valve allows the volume of the fluid to the long hose to be adjusted up or down to achieve the same lift speeds.

So just to be clear the flow divider I'm thinking of is a set of geared hydraulic motors which are attached to a common shaft. The geared motor is a metering device which enforces a specific volume of oil which passes with each rotation. This could be used for something like fuel flow but it can also be used to commonize displacement in a set of hydraulic cylinders, so that if one cylinder faces more mechanical load than the others, it won't lag behind in displacement.

A simple system with a Tee as a flow divider will extend cylinders at differing rates depending on the load they face. There is no guarantee of a specific displacement.

The example I can think of is a 2 cylinder press-brake of multi-feet size used at maximum rated capacity, if the press tooling simply extends to a pressure the bend will be unequally made due to the possibilility of material differences. If the flow divider is used then the cylinders extend to the same distance then a nice equal bend will be made in the material.

 

[Ironcrow]

Several different brands and models of lifts are mentioned. I am not familiar with these apparatus. I still think it is useful to point out the lateral synchronizing cables can be for EITHER load support OR strictly synchronization. It depends on the design of the lift. There are both types.

On my Benwil it takes at least three failures to drop a lift carriage, 1) hydraulic cylinder blows a seal, 2) safety ratchet pawl breaks or fails to engage as the lift carriage falls, and 3) lateral synchronization cable breaks (This cable system IS designed to hold the weight of the carriage and vehicle)...only then does the vehicle fall and kill everyone.

 

[Ironcrow]

The example I can think of is a 2 cylinder press-brake of multi-feet size used at maximum rated capacity, if the press tooling simply extends to a pressure the bend will be unequally made due to the possibilility of material differences. If the flow divider is used then the cylinders extend to the same distance then a nice equal bend will be made in the material.

More commonplace example: Every Kubota, tractor, skid steer, backhoe with a bucket on the front uses a flow divider on the bucket so with cylinders on both sides of the bucket raise the bucket level no matter which side of the bucket has the big rock in it.

 

[firebirdparts]

So just to be clear the flow divider I'm thinking of is a set of geared hydraulic motors which are attached to a common shaft. The geared motor is a metering device which enforces a specific volume of oil which passes with each rotation.

Of course. Volume control is the only hope. In the "usual" case of the same cylinder on both sides, the volumes can be equal. Nothing is perfect (especially gear pumps), so eventually you would have to equalize the two sides. If you used two gear pumps on one shaft, you would need to reverse it to keep it synchronized on the way down.

It can work, but if you blow a line out, here it comes (down) on one side. If the safeties work you may be okay.

Coincidentally, I sat next to Don Cray on a plane one time, just randomly. He had designed a 4 post lift that was hydraulically equalized. We talked about it the whole way. It was portable enough to be carried around in its pieces and he was promoting it for use at car shows. I don't think it was ever very successful in the market. It's not interesting but here's his patent application just for fun.

https://patents.google.com/patent/US20040020197A1

I have a floor plate lift and let me say I am not at all tempted by this plan. Not a bit.

 

[firebirdparts]

Firebird,
Umm no...
The cales will not hold the car. They are not designed to. They are designed for equalization only.
The cables could also be moved above. That's the way my rotary lift works

I don't have your rotary lift. Don't want it, either, if what you are saying is true. My lift requires 3 failures to drop a car, same as Iron crow's

 

[Ironcrow]

Oh, and another thing, the flow equalizer is more typically not a paired positive displacement pump. Too expensive. It is usually a device called a "flow divider" and is an arrangement of pressure compensated orifices or a spool valve type. It is found on hydraulic schematics as a T arrangement with two orifices, one on each output branch. Then they draw a box around the whole thing.

 

[bmarshall1]

Thanks for all the great replies. I have the lift working and apparently the cables are needed at this time... because... the pump has a single outlet that feeds the bottom of cyl A, then there's an outlet from A and a line going to cyl B. As it goes up and down I can easily affect the lift (or drop) rate simple with the weight of my arm - it's that balanced, even the drag of the safety locks will make a difference.

So, there is a second outlet on the pump outlet block (manifold?) that is plugged. I can plumb a second line into this orifice but I am thinking it is not a equalizing block but simply 2 separate holes leading from a common source and I would be nowhere ahead.

Does anyone know of a reasonably priced (<$200) equalization valve set up?

OR>>>

Lastly - I have a Maxjax pump and a spare Quickjack pump assembly, would either of these pumps do the needful? Neither uses cables and have always seemed pretty linear in their travels.

 

[bmarshall1]

Research shows I can get a hydraulic flow divider for about $100 or an adjustable one for about $150 (maybe I need a 55/45 split. This is the way Maxjax and Quickjack does it, any reason this would not work?

 

[jonwane]

I'm curious as to the outcome of your lift situation! I'm installing one and doing the same thing, deleting the overhead equalization cable.

 

[bmarshall1]

Hey Jon - I am just now getting around to installing the lift and saw your IM so thought I would reply here. For the time being I am going to install the lift as it came, cables and all. When I get the time and inclination I will re-look into the flow divider as I see no reason it should not work. I have a MAXJAX and it lifts pretty evenly, within an inch. As others have stated, the cable are more for equalization of lifting and a tertiary safety net. in your research what have you came up with? Has anyone else tried this?

 

[Aahz]

I'm not an engineer, but I have some 20+ years working with vehicle lifts (sales, service, etc.)
First of all, re-engineering something that is proven safe as designed (if used correctly) is ALWAYS a bad idea. Just like any other tool, if you don't use it the way it was intended to be used, at some point, you will hurt yourself or others.

2nd...there is a reason that most lift manufacturers don't use hydraulic flow dividers to equalize their lifts. They don't work well! Mohawk has probably been the most successful user of this design, but most customers get frustrated lifting and lowering vehicles to try and get the arms equal so that when the vehicle makes it to the ground they can remove it from the lifting pads. There have been several other companies that have attempted to use them and none have been successful in the market of 2 post lifts.

If a flow divider is used on something like a bucket on a front end loader, the bucket itself is a single continuous piece of steel that helps to equalize the movement of the 2 cylinders. When you have a 2 post car lift, without cables, there is nothing keeping the 2 cylinders equal. The vehicle sitting on the lift pads would help if the vehicle were strapped to the lift arms, but since they are only resting on the lift arms, the lighter side of the vehicle will raise faster than the heavier side. A flow divider could, in theory, help to prevent this, but you will spend an awful lot of time trying to keep the load level while raising or lowering the vehicle. (Again, back to the Mohawk design, there are many times one side of the vehicle hits the ground first and the 2nd side won't lower any more. The only way to resolve it is to raise the vehicle back up to the top, bottom out the cylinders and then lower it down while trying to keep it equal. The flow divider is very difficult to get accurate when the vehicle is actually moving).

There are different designs of flow dividers that are used on parallelogram style lifts, inground heavy duty lifts, mobile columns lifts and even some 4 post lifts. The difference in most of those cases is that you have a common structure (each runway on a 4-post, for example) that helps to keep the fore and aft level, so you only need to worry about the side to side load.

Anyways, just my 2 cents...don't do it!

 

[39CAMC]

In addition to the above, I thought the equalizer cable was also a safety in that if one cylinder failed, the other would hold the car via the cable?

I have had the "pleasure" of uninstalling and reinstalling 2 Hunter RX series scissor alignment lifts in the past two months (long story why). These are the ones with two completely separate runways. They have a sensor system to keep the runways level with each other in normal operation, but during the install, you have to put them in calibration mode which lets them run however.

I realize they probably don't have a flow divider, but after seeing how far out of sync the sides could randomly get with no load, I would never trust any lift without an equalizer system of some sort (designed in).

DaveW

 

[Profairlane]

Sounds good to me, I was thinking doing same thing. There are very good synchronizing flow divider combiners out there that will work. I am hydraulic engineer and have used them many times for industrial equipment, much heavier than automotive equipment.

 

[firebirdparts]

Sounds good to me, I was thinking doing same thing. There are very good synchronizing flow divider combiners out there that will work. I am hydraulic engineer and have used them many times for industrial equipment, much heavier than automotive equipment.

Well, there’s a big wide line of demarcation between people who understand how the lift works and people who don’t. You can do anything to redesign it if you actually are capable.

If you stay in the forum for a while, we have a steady stream of synchronization troubleshooting threads.