PDA

View Full Version : Hydraulic help again



j king
12-05-2014, 10:43 AM
Ok..back to my car scissor lift.been fighting it trying to get each cylinder to lift level.I had suggestions a while back on how to accomplish this but it seems like I don't have the skills ,room,and budget.
What I am thinking of doing is buy two Pressure Compensated Adjustable Flow Control valves .I was going to instal these at the pump area and run separate hoses to each cylinder from these.The way it is now is i have a T down by the cylinders and this isn't working.all it takes is a little imbalance in weight and things fail up and down.
I figured that if I put these on I can tweek the lifting of each if needed.Will this help the down movement also? Once they are set for a particular vehicle going up will it come down even then? Thanks once again for your help. Jim

Old Hat
12-05-2014, 10:57 AM
I see a saftety risk no matter how you apply a multiple cylinder design.
Any time one fails it will end baddly.

duckman
12-05-2014, 11:11 AM
This will entail some work, but the way I'd do it is with 2 single control valves, push both handles to lift, if one gets ahead of the other let off a little on the one that's ahead, this also builds in a little bit of safety if one cylinder lets go the other will hold.

j king
12-05-2014, 11:26 AM
I agree Phil. There is heavy safety locks that it climbs over as it raises.if it goes down it will lock the lift. Going down there is a button I hold down that lifts the locking levers and if I release it they drop. That part works good. Took a lot of trial and error but very happy with that.

Duckman, I was going to do that.if your meaning two valves like a log splitter that is. Then I found these..
http://www.surpluscenter.com/Hydraulics/Hydraulic-Valves/Flow-Control-Valves/3-8-NPT-HYD-FLOW-CONTROL-VALVE-W-RELIEF-RDRS137-08-9-064-38.axd

It seems like I could use my pendent that I made and once it starts raising even I wouldn't have to hold the levers the whole time.

Black Forest
12-05-2014, 12:02 PM
How big are the cylinders? What is the budget? Would it be enough to buy another cylinder that matches the two you have on the lift now? You could by a flow divider that would solve your problems easily and not too expensively also. Probably around $100.

Old Hat
12-05-2014, 12:24 PM
You could by a flow divider that would solve your problems easily and not too expensively also. Probably around $100.

+1 . . . .

CCWKen
12-05-2014, 12:50 PM
Pressure In = Pressure Out. Presumably, you have a cylinder that has a higher drag than the other, lifting more weight or is leaking. The two cylinders should be tied together somehow. I'm not familiar with your design but leveling should not depend on one cylinder or the other.

Black Forest
12-05-2014, 12:54 PM
A quick simulation video of what I am talking about with the third cylinder.
http://youtu.be/YmmHCnP__gE

j king
12-05-2014, 01:12 PM
Hi Blackforest.Yes you showed me that before.I don't have anywhere to put the cylinder at the lift.Its in the floor and no extra room.
If I mounted it near where the pump is I would have to have 3 hoses .one to the first cylinder then back out to the 3rd cyl then back to the other lift cylinder. I don't think I have enough room in my pipe under the floor. I guess I could try running something else in there. Hate to buy more hoses to see. They are long..
Only question I have on the 3rd cylinder is if the fluid going out of the first cylinder has the rod in it ,it looses pressure since the piston area has a rod thru it. Right?. Seems like it wouldn't have the same pressure as the first cylinder or am I thinking wrong

Black Forest
12-05-2014, 01:29 PM
Hi Blackforest.Yes you showed me that before.I don't have anywhere to put the cylinder at the lift.Its in the floor and no extra room.
If I mounted it near where the pump is I would have to have 3 hoses .one to the first cylinder then back out to the 3rd cyl then back to the other lift cylinder. I don't think I have enough room in my pipe under the floor. I guess I could try running something else in there. Hate to buy more hoses to see. They are long..
Only question I have on the 3rd cylinder is if the fluid going out of the first cylinder has the rod in it ,it looses pressure since the piston area has a rod thru it. Right?.

Wrong!

Seems like it wouldn't have the same pressure as the first cylinder or am I thinking wrong

If you want to avoid all the hoses then get a flow divider. They aren't big and you won't need any other hoses. It would be the best solution. A rotary flow divider would be my choice.

j king
12-05-2014, 01:41 PM
Looky what I found! http://www.ebay.com/itm/JOHN-S-BARNES-4F660A-FLOW-DIVIDER-HYDRAULIC-PUMP-B309851-/291316490774?pt=BI_Pumps&hash=item43d3d0e216

Looks like it should fit the bill.Question.. How can I control speed with this. A flow control after the rotary divider? I want to lift and go up and down slow. Also how does this work lowering the lift? Now I have a flow control to slow up and down. Never heard of these before but looks like it would work. Jim

j king
12-05-2014, 01:44 PM
I need about 2700 lbs pressure to raise my pickup. How does this work with cutting the flow to the rotary to slow the lift

Cuttings
12-05-2014, 02:02 PM
If I am reading this correctly you have two cylinders. If they are identical in volume a simple and fool proof way to make them operate together is.
Get your self a small two section gear pump. Run the circuit to one cylinder through each side and let the pump free wheel.
There is no way one cylinder can get ahead of the other in ether direction that way because the flow to each side will be identical.

Black Forest
12-05-2014, 02:02 PM
I need about 2700 lbs pressure to raise my pickup. How does this work with cutting the flow to the rotary to slow the lift

You just put the flow divider in place of the Tee you have now. The flow control would go before the rotary flow divider. The rotary flow divider will have no different effect on the speed than the Tee does. The rotary flow divider is just two gear pumps/motors joined together with a common shaft. The oil flows in and is pumped out through the gears. Because they share a common shaft the gears turn the same speed so pump the same amount of oil out either side. They work the same in reverse combining the flow back together. The rotary flow divider will be transparent to you as is the Tee now. Just hook it up. Don't worry be happy!

Black Forest
12-05-2014, 02:04 PM
If I am reading this correctly you have two cylinders. If they are identical in volume a simple and fool proof way to make them operate together is.
Get your self a small two section gear pump. Run the circuit to one cylinder through each side and let the pump free wheel.
There is no way one cylinder can get ahead of the other in ether direction that way because the flow to each side will be identical.

You have just described a rotary flow divider.

Black Forest
12-05-2014, 02:18 PM
Looky what I found! http://www.ebay.com/itm/JOHN-S-BARNES-4F660A-FLOW-DIVIDER-HYDRAULIC-PUMP-B309851-/291316490774?pt=BI_Pumps&hash=item43d3d0e216

Looks like it should fit the bill.Question.. How can I control speed with this. A flow control after the rotary divider? I want to lift and go up and down slow. Also how does this work lowering the lift? Now I have a flow control to slow up and down. Never heard of these before but looks like it would work. Jim

Buy that as fast as you can! If it is not broken it will solve your problem if you don't have other problems such as the seals on one cylinder. But even if you do end up with seal problems the rotary flow divider is in my opinion still a good thing to have installed.

That is a cheap price if it is OK. Buy it or I will !!!!!!

j king
12-05-2014, 02:27 PM
Buy that as fast as you can! If it is not broken it will solve your problem if you don't have other problems such as the seals on one cylinder. But even if you do end up with seal problems the rotary flow divider is in my opinion still a good thing to have installed.

That is a cheap price if it is OK. Buy it or I will !!!!!!

Got it! Thanks Blackforest!!

Black Forest
12-05-2014, 02:33 PM
Got it! Thanks Blackforest!!

Great! Can't wait for you to install it and report back on here.

superUnknown
12-05-2014, 04:51 PM
I've sequenced 8 cylinders with pressure comp FCVs. PITA to set up, but cheap and once it's done, it's done.
Rotary flow dividers are more for constant duty, higher flow, less pressure drop, but if the price is right... they'd work too.

Black Forest
12-05-2014, 05:55 PM
I've sequenced 8 cylinders with pressure comp FCVs. PITA to set up, but cheap and once it's done, it's done.
Rotary flow dividers are more for constant duty, higher flow, less pressure drop, but if the price is right... they'd work too.

No setup for the rotary flow divider. unscrew the hoses from the Tee and screw them onto the flow divider. done. No fiddling. The 1 to 5% variance in this application will have no impact unless of course a schmuii gets involved!

Seastar
12-05-2014, 06:03 PM
BF
What the devil is a schmuli?
Must be a gremlin/goblin that lives in the Black Forrest!
Bill

duckman
12-05-2014, 06:37 PM
We put a flow divider on a small shear, it would work fairly good but after a while we'd have to bottom out the shear and hold it until they balanced them selves out, then it would be good for a while. The flow divider have a little bit of slip in them, just like a gear pump will not pump exactly what it's rated for, they have built in slip
(it's called clearance).

Black Forest
12-06-2014, 07:36 AM
BF
What the devil is a schmuli?
Must be a gremlin/goblin that lives in the Black Forrest!
Bill

If you go to this video and at 5:00 the meaning of schmu_ii will be revealed!
https://www.youtube.com/watch?v=BGdhK3rMNDE&list=TLJmjcqYn66hs

Seastar
12-06-2014, 08:04 AM
Oh --- if you had said schmu in the first place I would have know what you were talking about.
Bill

Black Forest
12-06-2014, 08:10 AM
Oh --- if you had said schmu in the first place I would have know what you were talking about.
Bill

If you have more than one schmu then you have schmuii.......simple! Pronounced like Hawaii

Black Forest
12-06-2014, 08:15 AM
Gentlemen I am a little disappointed that no one commented on how incredible my simulation video was. How educating and beneficial it was to clear the fog. What a great guy I am to have gone to the effort to make the video and setup the simulation in my hydraulic simulation software. What a saint I am to have done all this for you all.

Geeez......you guys are a tough crowd!:cool:

vpt
12-06-2014, 08:19 AM
My vehicle hoist uses two steel cables between the two sides to keep them level. Hydraulic rams to lift and take the weight and the cable to take the difference of the load between the two sides and keeps them level with each other.

j king
12-06-2014, 08:29 AM
Hey Black Forest. That was a great animation! Didn't know you made it.thought you copied it. Thanks again. I can't wait to get this thing finished up..been an on going project that is much needed..getting to old to crawl around on my back.

Ps...great guy.. Lol. Seriously..thanks

ulav8r
12-06-2014, 09:37 PM
BF,

Due to limited data capacity, I do not look at videos unless I have time to go to the library. Therefore I have nothing to say about your animation.

andywander
12-06-2014, 09:59 PM
If you only have a single cylinder, and it fails, it would end badly as well, no?

Old Hat
12-06-2014, 10:26 PM
A str8 down "stattic" drop or fall is bad enuff.
A drop that is offset, or glanced off in an additional direction,
can gather up additional casualties as it goes.
Also, one may escape a str8 drop, if he can get out from under it quick enuff.
Something coming down unevenly complicates the chances of escape.

j king
12-06-2014, 11:21 PM
If you only have a single cylinder, and it fails, it would end badly as well, no?

You have a point. Lol!

J. Randall
12-07-2014, 12:56 AM
I am wondering why you didn't build in the cable and pulley system like Andy mentioned. They can be rigged with the pulleys at the bottom of the lift or overhead, depending on the design of the lift. Using them the lift can gravity down and never get out of sync.
James

oldtiffie
12-07-2014, 01:50 AM
Why not have your cylinders arranged such that each is part of a identical separate sets of pump, control valve and cylinder?

The separate controls can be "ganged" if needs be and/or operated separately.

Black Forest
12-07-2014, 04:48 AM
Why not have your cylinders arranged such that each is part of a identical separate sets of pump, control valve and cylinder?

The separate controls can be "ganged" if needs be and/or operated separately.

The rotary flow divider is essentially two pumps ganged together. But with the RFD you only need one directional control valve.

vpt
12-07-2014, 09:31 AM
I have it!

Install a sway bar between the two sides.

:)

Black_Moons
12-07-2014, 11:10 AM
My vehicle hoist uses two steel cables between the two sides to keep them level. Hydraulic rams to lift and take the weight and the cable to take the difference of the load between the two sides and keeps them level with each other.

I have taken a look at the pro hoists and yes this is how they do it, cables. Flow dividers won't work properly IMO because they have slip, maybe 5% or whatever it is difference in height is not a big deal.. but at 8' that is 5", kinda large if you don't have a way to compensate.

Run two cables to one cylinder (one via pullies) and you are guaranteed an even lift.

3rd cylinder I guess works, but the cylinder has to match your existing cylinders since its being used to 'fix' the ratio between the side with the piston and side without.

As for ending badly if the hydraulics failed with 1, 2 or 3 cylinders, I am pretty sure he has stated he has safety locks/latches (Ratchets?), because you can NEVER trust hydraulics not to fail, no matter how many extra cylinders you add to the system.. :P

j king
12-07-2014, 01:37 PM
Here's my locking system. A little vid of it. http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/th_1417977024_zpsedc3dcd5.mp4 (http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/1417977024_zpsedc3dcd5.mp4)

Black Forest
12-07-2014, 01:44 PM
If I recall J. King has two sissor lifts embedded in his concrete floor. The range of travel for the cylinders is quite short. The rotary flow divider will work just fine. Everytime he lets the car/truck down it will synchronize the cylinders. In the last year I have used three rotary flow dividers on different projects and they have functioned perfectly in my application. It isn't like he is moving a mill table and needs absolute accuracy.

j king
12-07-2014, 01:44 PM
VPT
It has a bar between the two. I was positive that it would keep it even. Wrong ! it really torques that bar if it goes up crooked. Welded together on each side and have a heavy coupling with 3/4 dual key in the center. It hasn't broke but....I am amazed it hasn't.

j king
12-07-2014, 01:51 PM
Here is what I am doing.hard to have cables.http://img.photobucket.com/albums/v24/ikimjing/1383108156_zpsb4c96575.png (http://smg.photobucket.com/user/ikimjing/media/1383108156_zpsb4c96575.png.html)

Black Forest
12-07-2014, 01:53 PM
That is what I thought you had. Don't worry the RFD is going to work.

j king
12-07-2014, 01:55 PM
No worries..can't wait. : )

goodscrap
12-07-2014, 02:29 PM
Looks really nice

Does the ratchet pawl have some sort of stop to prevent it over-riding the rack, I'm thinking sudden hydraulic failure when you're lowering and have it retracted, the lift gains momentum because of the vehicle weight, you release the button and the ratchet locks but there is so much momentum it can ride it over the ratchet ( snapping chain/destroying solenoid) because it pushes the pawl under and lifts the leg over, then releases the lot onto the floor. With a longer leg on the pawl that hits the base first, or a stop it would prevent this.

Hopefully you've got this covered.

Brian

j king
12-07-2014, 02:36 PM
Have pins in a slot on each leg to keep it from lifting.i had a hell of a time getting the lift mechanism to lift high enough .as it rose the leg changes orientation to base and required more lift to be able to get over lock teeth.. Been a lot of trial and error. If I get it level up and down it will be good.

j king
12-07-2014, 02:50 PM
Here it is in testing..it picked the truck up nice and even..after I cut the floor out and set it in the floor it has been fighting me.I thought it was air but after numerous bleedings I kinda gave up for a while.I believe Black Forrest's cure will fix this.

http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/1417981399_zps88458e89.jpg (http://smg.photobucket.com/user/ikimjing/media/Mobile%20Uploads/1417981399_zps88458e89.jpg.html)

goodscrap
12-07-2014, 03:34 PM
Excellent, looks a top notch piece of kit, seems you've put a lot of thought into it, and it looks very well built, just the levelling issue to sort.

Brian

vpt
12-07-2014, 05:09 PM
Just need to bore a single hole from one side to the other under the cement for the cables.

J. Randall
12-07-2014, 08:03 PM
Here is what I am doing.hard to have cables.http://img.photobucket.com/albums/v24/ikimjing/1383108156_zpsb4c96575.png (http://smg.photobucket.com/user/ikimjing/media/1383108156_zpsb4c96575.png.html)

I see what you mean, little late now to try and work cables into the mix. Nice looking lift, I worked off a factory one similar to that design yrs. ago. Mostly front end work and alignment, worked pretty good for that.
James

j king
12-07-2014, 08:22 PM
The pic isn't mine. Mine is very similar except I have a trench across the front end to allow the tie bar that is supposed to keep the 2 together. Lol.. I wanted nonintrusive style lift for a low ceiling. This is going to be great once the bug is worked out. Getting too old for creepers and floor jacks.i wanted the center open so you have a clear access from front to back down the center.
I can sit on my wheeled stool and work under my car. The truck is too tall to sit upright but it is still nice.

Black_Moons
12-09-2014, 12:40 AM
Here is what I am doing.hard to have cables.

Doable.

What you do, is have rods travel down from your platforms into a pit, you put the lifting pulley at the bottom of the rod, then a fixed pulley near the top of the rod going to your cylinder. I assume you already have something like that or how is the platform supported? Can we see it extended?

Pulling on the cable will raise the rod. Or if its a scissor lift mechanism you just have to have the pulley between two of the scissors. (multiple pulleys will reduce side loading the scissors with the pull force, but then you are talking a winch needed (or multiple pulleys on the hydraulic cylinder) due to the extra cable pull needed.

Basically, you have this:
http://cdn4.explainthatstuff.com/pulley3.jpg
mounted underneath your platform, with a long rod (or two) going from the center moving part to the top of it to support your platform above it.
Replace the censored guy with hydraulic cylinder.

Black Forest
12-09-2014, 11:36 AM
Black Moons I have no idea or get no picture in my head of what you are explaining!

epanzella
12-11-2014, 01:33 PM
For 2 cylinders use one pump to a tee and then 2 controls. Relying on purely on identical flow to a pair of cylinders under load means you have no way to sync them when they get out of time. One gland seal doing a better job than the other or air in the system getting routed more to one cylinder or the other could throw them off. This will happen to a some extent with 2 way cylinders and be more pronounced with one way (power up/gravity return) cylinders. Two controls are simple, cheap, and you're always in control of the relationship between the two cylinders.
My $.02

Black Forest
12-11-2014, 02:25 PM
For 2 cylinders use one pump to a tee and then 2 controls. Relying on purely on identical flow to a pair of cylinders under load means you have no way to sync them when they get out of time. One gland seal doing a better job than the other or air in the system getting routed more to one cylinder or the other could throw them off. This will happen to a some extent with 2 way cylinders and be more pronounced with one way (power up/gravity return) cylinders. Two controls are simple, cheap, and you're always in control of the relationship between the two cylinders.
My $.02

There are easy ways to sync them.

j king
12-11-2014, 04:40 PM
Got the rotary divider today. Will be trying it tonite!

vpt
12-11-2014, 05:53 PM
How about this idea, just thinking out loud here and it may have already been mentioned.

Use one double acting cylinder on one side but only "power" the lift side of the cylinder. The "output" side of that cylinder would then "power" the other cylinder.

That way the one cylinder has to move in order to move the other up or down and they would remain in sync so long as there are no leaks.

Black Forest
12-12-2014, 03:23 AM
How about this idea, just thinking out loud here and it may have already been mentioned.

Use one double acting cylinder on one side but only "power" the lift side of the cylinder. The "output" side of that cylinder would then "power" the other cylinder.

That way the one cylinder has to move in order to move the other up or down and they would remain in sync so long as there are no leaks.

Andy that wouldn't work because of the different volumes of the extend and retract. It would work if the two cylinders were double ended meaning the rod stuck out each end of the cylinder.

j king
12-12-2014, 06:04 AM
Delay on the launch pad Black Forrest. Divider has different fittings so need to go shopping .stay tuned. : )

j king
12-12-2014, 03:49 PM
It's alive! Thanks Black Forest.I wish I knew about these things from the start!Man,that would have saved me a lot of messing around. Here is a little video.http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/th_1418416968_zps4aacbf9b.mp4 (http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/1418416968_zps4aacbf9b.mp4)

And it comes down even too like you said. Thanks again! Jim

Black Forest
12-12-2014, 04:07 PM
It's alive! Thanks Black Forest.I wish I knew about these things from the start!Man,that would have saved me a lot of messing around. Here is a little video.http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/th_1418416968_zps4aacbf9b.mp4 (http://img.photobucket.com/albums/v24/ikimjing/Mobile%20Uploads/1418416968_zps4aacbf9b.mp4)

And it comes down even too like you said. Thanks again! Jim

Glad it worked for you! Did you build the lift yourself?

j king
12-12-2014, 04:42 PM
Yes .i believe it's overbuilt.lol.. Wanted one where the center is completely open to the back of the car..

Can't have a high lift either.Didnt want post up in the way also so this should be great.

Black Forest
12-13-2014, 07:16 AM
Feels good doesn't it when something you have struggled with finally works. Just don't let yourself get caught in the "shaper trance" thing and stand there and make your car go up and down repeatedly just because you can!

j king
12-13-2014, 07:32 AM
You been peeking in garage window Black Forest? Lol. Thanks again