Does anybody understand Hydraulics?

[imagineero]

I've got a tip truck that just isn't tipping now I've increased the bin size. Even the original bin size was pretty marginal when full. I understand the basics - pressure x ram diameter = tonnage or whatever, so If I need to get more lift I need more pressure (difficult!) a bigger diameter ram, or a second ram.

I've looked around, and bigger rams are $$$$. The ram I have is already reasonably large. The second throught was getting a longer travel ram, and moving it further away from the hinge point, so it needs less effort to lift. That's still a possibility, but the new ram could only be about 2' further back due to the gearbox.

So we come to adding a second ram. I've seen plenty of dual ram tippers, but they are all 'side by side' rams, 2 x identicle rams next to each other. What I'm wondering is, can I have 2 rams of different stroke length in line with each other? That is, leave the existing ram, and fit a second, longer travel ram further away from the hinge? So long as they both reach the end of their travel at the same point (so as not to rip each other apart), will that work? Will the pressure be distributed equally automatically so they both share the load? Somebody throw me a line here!

Shaun

 

[blades]

Getting 2 different size rams to extend at the same speed would be pia. You would need to add a proportioning valve in the system Plus your thoughts on location of second ram to match extension of first another pia. 2 rams sxs or 1 larger capability unit would be your better bet. Pressure is another area as to increase it likely would require a different pump. Depending on the age of the equipment you could have other issues affecting the operation such as leaking seals in the ram or pump or a problem internally in your control valve. You could only increase pressure to the lowest component rating in your system.

 

[imagineero]

I hadn't even thought about the speed of extension, knew there had to be some reason I'd never seen it!

If I was any good at math I could pop a gauge on my system and see my pressure, then calculate the ram size I'd need for my load at any given ram location which would help me size it. Unfortunately I think I'm going to have to take a stab in the dark and see how it goes! I can get a ram with a longer extension, and slightly larger on the first stage, which then makes it slightly larger at each stage on down. The little bit larger ram, plus locating it further from the hinge should hopefully be enough.

My last truck had a really long travel 2 stage ram located between the cab and the bin. It wasn't a large diameter ram by any means, maybe 1/3 the diameter of my new truck.... but the travel was enormous, maybe 4x as long as the current one. The old truck easily tipped 8 metric tonnes without even slowing down. The new one struggles to tip 2.5 metric tonnes and it needs to tip at least 4.

Shaun

 

[dave_dj1]

I think you have the basics for the math from what you have stated above. That being said, It is possible that the cylinder is leaking by internally or the pump may be worn. How old is the unit and what type of pump, pto or electric over hydraulic?
We hardly ever see telescopic cylinders here unless they are on big dump trucks. Most small stuff like yours would have a scissor type lift.
If you go to tractorbynet.com and go to the hydraulic sections there are some very good guys there that are quite knowledgeable with hydraulics.
good luck,
dave

 

[imagineero]

The truck's about 15 years old, it's an isuzu NPR 400. The pump is PTO, and came factory fitted. The bin and ram were fabricated by a reputable company, and it was original owned by the city. It's low mileage and has seen not much use. There are no visible leaks anywhere (unlike my old truck that left a puddle wherever it was parked!) The componentry is all high quality, it just wasn't specified to lift the kind of weight that is being put in it now. It was originally a recycling truck, now it's being used as a chip truck.

Does anyone know the rough math for working out how much tonnage is needed to lift a given weight at a distance from the hinge? My max load capacity on this truck is 4 metric tonnes (around 8,800lbs), and the current ram is set back from the hinge by, say, 5' (i haven't measured). How can I work out how much tonnage I'll need to lift at that point?

I don't know the pressure, but I can fit a gauge pretty easy. If I've got some rough idea on what I need to lift, then I'll have a pretty good bet at getting the right sze ram, positioned in the right place. I'm looking around $700 for a ram, plus extra for mounting blocks, hoses, bearings etc. I can't return the ram if it's used.

Shaun

 

[jasult]

I would look at the simple things first. If this is PTO style then look at the valve that you use to lower the body. Make sure it is moving all the way closed when you try to raise the body. A simple rag or coffee cup can be blocking the travel in cab and body will not raise right. Also check both ends of that valve to see if worn pins or linkage. Also load the back of body heavier then front and try it

 

[Fifelaker]

Surplus center has some good calculators and I will second the TBN site some good people over there. I would put a guage in and see what your pressure is before any thing. JJ will want the number before he hands out much advice. Kinda the same as pulling a muffler on a saw.

 

[cmsmoke]

The cylinder on the truck should be able to push up through the floor...given enough load and hydraulic pressure. That particular truck body isn't overbuilt in that area and doesn't show any signs of distortion. I've been around dump trucks a long time and underbody hoists will start to show some distortion in that area when loaded heavy. I would start with a pressure gauge and test the system pressure. It could be as simple as adjusting the pressure regulator. It may be hitting its limit early and holding back. There could also be something bypassing the pressure, like a hydraulic accessory line...I see a valve on the side of the frame. Could this have been a municiple truck and be equipped with central hydraulics? Like I said get a pressure gauge and check it out. I would however warn you to watch how much weight you try to lift without reinforcing the lift points. You didn't mention how much weight you have on it now...Taking an educated guess, I would say it should lift 3-4 tons easily. That hydraulic cylinder will move the largest section first, then move on up the line. The thought is the load will be the heaviest at the start, as the load is lifted, the center of gravity moves back and requires less force, so the cylinder pistons change size and get smaller as it extends. It will pick up speed as it travels, as well. I won't say what the body can tolerate. Be careful and don't disconnect lines with the body raised, even if you use the safety supports. Do it from underneath. Many people get crushed from working in between the dump body and frame. Did I say be careful?

 

[imagineero]

I would look at the simple things first. If this is PTO style then look at the valve that you use to lower the body. Make sure it is moving all the way closed when you try to raise the body. A simple rag or coffee cup can be blocking the travel in cab and body will not raise right. Also check both ends of that valve to see if worn pins or linkage. Also load the back of body heavier then front and try it

it is PTO, with a linkage to activate the pump from the cab. The valve itself is located in the middle of the chassis and is activated electronically by a switch in the cab. It's a 3 position switch with up/down/stay put. I'd need to have another look at how the hoses are routed, but if I'm guessing right, then there out to be no leakage anywhere on the return side when the 'up' valve is activated. The simplest way can thnk to test this would be to pull the return hose off the tank, and let it drain until there isn't a drop coming out. Then start engine, activate pto, and engage lift. If there's any leaks in the system, it ought to start dripping at the return, right?

Shaun

 

[imagineero]

The cylinder on the truck should be able to push up through the floor...given enough load and hydraulic pressure. That particular truck body isn't overbuilt in that area and doesn't show any signs of distortion. I've been around dump trucks a long time and underbody hoists will start to show some distortion in that area when loaded heavy. I would start with a pressure gauge and test the system pressure. It could be as simple as adjusting the pressure regulator. It may be hitting its limit early and holding back. There could also be something bypassing the pressure, like a hydraulic accessory line...I see a valve on the side of the frame. Could this have been a municiple truck and be equipped with central hydraulics? Like I said get a pressure gauge and check it out. I would however warn you to watch how much weight you try to lift without reinforcing the lift points. You didn't mention how much weight you have on it now...Taking an educated guess, I would say it should lift 3-4 tons easily. That hydraulic cylinder will move the largest section first, then move on up the line. The thought is the load will be the heaviest at the start, as the load is lifted, the center of gravity moves back and requires less force, so the cylinder pistons change size and get smaller as it extends. It will pick up speed as it travels, as well. I won't say what the body can tolerate. Be careful and don't disconnect lines with the body raised, even if you use the safety supports. Do it from underneath. Many people get crushed from working in between the dump body and frame. Did I say be careful?

The system pressure is the biggest variable, and I'm guessing it's not that high. I need to pickup a 3000psi gauage and tee it into the system near the ram. It orginally had a selector valve after the pump, that could be switched between the tipping ram, or a bin lifter. I removed all the bn lifter hydraulics, and the selector, and plumbed the output straight to the lifting ram. The circuit is very simple - tank-pump-ram-return. The valve you can see is just being used as a stopper. There is a T in the return line at the bottom of the tank, the second return was for the bin lifter hydraulics but I didn't have a cap to cap it off, so I used the valve because it bolted on. It will be blanked off.

I'm hearing you on the safety, in terms of pressurised hydraulic lines, working under loads, and the potential for punch through at the ram tie in point. I did my trade as a younger bloke as a boiler maker. I spent a few days choppng this bin shorter in length, adding all the toolboxes from my old truck, then raising the height by about 3' and adding cross bars and a tarp roof. I've taken it out for a trial this week and want to get it right before sending it off to get painted. The ram was a weak point before the height extension. I've had it on the weighbridge before and after mods. The weight is about the same because it originally had a steel roof (now tarp). Even fully loaded with chip, the truck is still within its legal carry. The ram attachment pont may need some renforcing.

Shaun

 

[imagineero]

Surplus center has some good calculators and I will second the TBN site some good people over there. I would put a guage in and see what your pressure is before any thing. JJ will want the number before he hands out much advice. Kinda the same as pulling a muffler on a saw.

I sure do appreciate that information, but I'm living in australia. I bring a lot of stuff in from the states, but I'm sure that the shipping on a ram would exceed the ram price 2 or 3 times over. I don't like to trouble people if I'm not going to be a customer. This is one of those times I'm just going to have to buy local.

Shaun

 

[sb47]

The cylinder on the truck should be able to push up through the floor...given enough load and hydraulic pressure. That particular truck body isn't overbuilt in that area and doesn't show any signs of distortion. I've been around dump trucks a long time and underbody hoists will start to show some distortion in that area when loaded heavy. I would start with a pressure gauge and test the system pressure. It could be as simple as adjusting the pressure regulator. It may be hitting its limit early and holding back. There could also be something bypassing the pressure, like a hydraulic accessory line...I see a valve on the side of the frame. Could this have been a municiple truck and be equipped with central hydraulics? Like I said get a pressure gauge and check it out. I would however warn you to watch how much weight you try to lift without reinforcing the lift points. You didn't mention how much weight you have on it now...Taking an educated guess, I would say it should lift 3-4 tons easily. That hydraulic cylinder will move the largest section first, then move on up the line. The thought is the load will be the heaviest at the start, as the load is lifted, the center of gravity moves back and requires less force, so the cylinder pistons change size and get smaller as it extends. It will pick up speed as it travels, as well. I won't say what the body can tolerate. Be careful and don't disconnect lines with the body raised, even if you use the safety supports. Do it from underneath. Many people get crushed from working in between the dump body and frame. Did I say be careful?

I agree. Check everything first, its an old system, may just need new seals and or some adjustment. A pressure test should be done first. Duh! Did you change the filter?

 

[cmsmoke]

it is PTO, with a linkage to activate the pump from the cab. The valve itself is located in the middle of the chassis and is activated electronically by a switch in the cab. It's a 3 position switch with up/down/stay put. I'd need to have another look at how the hoses are routed, but if I'm guessing right, then there out to be no leakage anywhere on the return side when the 'up' valve is activated. The simplest way can thnk to test this would be to pull the return hose off the tank, and let it drain until there isn't a drop coming out. Then start engine, activate pto, and engage lift. If there's any leaks in the system, it ought to start dripping at the return, right?

Shaun

Yes, you are correct.

 

[kevin j]

you don't need any sort of flow divider as the box structure itself ties the cylinders together. With the lines teed together, the flow balances to the two cylinders as needed in proportion to the size of the cylinder and distance each one moves. Maybe 5 gpm to one cylinder and 8 to the other for instance. just making up numbers. The pressure will be the same in both cylinders, and determined by the weight of the load. The speed will be much slower based on size of each cylinder and the distance each moves, compared to all oil going to one cylinder.


Yes, pressure gauge is first step.

The math is fairly simple once you understand the concepts: the leverage or 'moment' in one direction from the cylinders, about the rear pivot point, must be higher than the moment in the other direction from the load. The load moment is the weight of load and box times the distance, measured horizontally, from the pivot point to the center of mass of the load. (or mass of load times distance plus mass of body times distance if they are odd shapes. Half way if probably close enough). Typically this is half the length of the bed if it is a uniform rectangular bed and loaded equally. With a chipper truck, maybe your load is biased towards the front of the bed making the length longer and the load moment higher. That is the highest with full load and box down. As it lifts, and tilts backwards, the horizontal distance gets shorter and shorter so the moment is less and the load is easier to lift.

The opposing force necessary to lift that load moment is the sum of cylinders forces times the distances, perpendicular distance between the centerline of the cylinder to the pivot. Not the horizontal distance, but the perpendicular length of the imaginary 'lever' the cylinder line of force acts on. If the cylinder is tilted, the perpendicular distance may be quite a bit smaller than the horizontal distance. Cylinder 1 force times distance plus cylinder 2 force times its distance, added together, is total cylinder moment lifting.

Cylinder force is pressure times area (first stage area if a telescopic cylinder)
Area in extension is the full bore (the inside diameter of tube) as: Area of a circle is Pi * R *R
but since cylinders are defined in Bore diameter, not radius, and Radius is Bore diameter /2, It is easier to remember Pi * B * B / 4 or (3.14... * B * B / 4

Psi times square inches is pounds force. Metric bars x cm or mm squared takes some conversion to force.

Working one way determines the max load the rig lifts at xx pressure. Working backwards determines the pressure needed to lift xx load.

The structure is a whole different issue. Is it strong enough?

 

[sun64]

Can that pump be adjusted for a higher pressure or is it fixed ?
As stated before, it could be your pump is worn or internally bypassing.
Yes, get the guage on it.
The other option is to take it to a reputable hydraulics company and just pay them to have a look at it and give a documented sheet on what is wrong.
You could then get on the net for that part if they are too dear.

Sometimes stuffing around, second guessing and buying the parts you think dont always work plus the time you put into it and then someone says, hey this is your problem, we see these wear out all the time at that age.
Just because the truck has low kilometers dont mean it wont be worn. Heat, sunlight and old age kills seals and rubber goods.
Also what type of hydraulic oil has been added over its life.
Sometimes the wrong oil can do damage to seals and parts.
All the best with it shaun
Wayne

 

[turnkey4099]

you don't need any sort of flow divider as the box structure itself ties the cylinders together. With the lines teed together, the flow balances to the two cylinders as needed in proportion to the size of the cylinder and distance each one moves. Maybe 5 gpm to one cylinder and 8 to the other for instance. just making up numbers. The pressure will be the same in both cylinders, and determined by the weight of the load. The speed will be much slower based on size of each cylinder and the distance each moves, compared to all oil going to one cylinder.

Thanks, that was my understanding. Basically self regulating just like hooking two (or more) engines to one drive shaft. The only thing I wonder about is the stroke length - what happens when one is at max extension and the other is getting full pressure trying to extend further?

Harry K

 

[sun64]

Thanks, that was my understanding. Basically self regulating just like hooking two (or more) engines to one drive shaft. The only thing I wonder about is the stroke length - what happens when one is at max extension and the other is getting full pressure trying to extend further?

Harry K

When one is at full stroke, then the hyd pressure will go to the other clyinder that is still trying to extend
The one fully extended cannot go any further so flow will be diverted to the extending ram.
As long as the pressure relief is set then no harm will come to the cylinders when fully extended

 

[dave_dj1]

When one is at full stroke, then the hyd pressure will go to the other clyinder that is still trying to extend
The one fully extended cannot go any further so flow will be diverted to the extending ram.
As long as the pressure relief is set then no harm will come to the cylinders when fully extended

BUT, if the one cylinder is already at max stroke then something is going to tear apart if the other one is still trying to push!

 

[woodman6666]

First check pressure. Dont put 2 cylinders unless they are the exact same and hinged from the exact same points. To me it looks that your cylinder is awfully far back, under the load per say. if you dont need that steep of angle you could move it forward a few inches which would give you much more push in the begining of the the lift cycle which is where I am sure you are having trouble.

 

[Mhusby]

Hydraulics

I've got a tip truck that just isn't tipping now I've increased the bin size. Even the original bin size was pretty marginal when full. I understand the basics - pressure x ram diameter = tonnage or whatever, so If I need to get more lift I need more pressure (difficult!) a bigger diameter ram, or a second ram.

I've looked around, and bigger rams are $$$$. The ram I have is already reasonably large. The second throught was getting a longer travel ram, and moving it further away from the hinge point, so it needs less effort to lift. That's still a possibility, but the new ram could only be about 2' further back due to the gearbox.

So we come to adding a second ram. I've seen plenty of dual ram tippers, but they are all 'side by side' rams, 2 x identicle rams next to each other. What I'm wondering is, can I have 2 rams of different stroke length in line with each other? That is, leave the existing ram, and fit a second, longer travel ram further away from the hinge? So long as they both reach the end of their travel at the same point (so as not to rip each other apart), will that work? Will the pressure be distributed equally automatically so they both share the load? Somebody throw me a line here!

Shaun

You need to check you system pressure before you proceed. The psi rating on your cylinder, and pump should be at least 2500psi. If you are not developing that you need to find out why. I used be be a factory hydraulic rep. I will assist you if you would like.
Marty