Does anybody understand Hydraulics?

[Mhusby]

speed vs. power

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

Remember speed is flow (gallons per minute) and pressure is power.

 

[turnkey4099]

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!

Only if the construction is shoddy. A cylinder can only push so much pressure even if it is still trying to extend.

Harry K

 

[turnkey4099]

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.

As long as both (or all) cylinders in the circuit are fed by the same source they don't hae to be identical or even in the same position. The pressure will self modulate to allow all cylinders to work either sequentially or at the same time, whichever the load calls for.

Harry K

 

[dave_dj1]

Be careful what info you offer to someone who doesn't understand the concept. I'm no expert by any means but I don't want to see anyone get hurt. Like I already said, you get one cyl. to the end of it's stroke and another cyl is still trying to go you are going to rip stuff apart. At least up until the point the relief valve opens.

 

[sun64]

Be careful what info you offer to someone who doesn't understand the concept. I'm no expert by any means but I don't want to see anyone get hurt. Like I already said, you get one cyl. to the end of it's stroke and another cyl is still trying to go you are going to rip stuff apart. At least up until the point the relief valve opens.

No, not really tear them appart. I have seen one hydraulic cylinder that stroked out and blew the shaft out. It was a tensioner shaft on our oil rig.
As has been said before, if the cylinder is of decent quality, it wont blow it up. The cylinder has stroked out so the fluid will now go to the other ram.
If both your cylinders are the same length and spacing on an inverted truck tray then their stroking out wont be a problem.
If you have used 2 different length cylinders there could be a problem if you have not worked out their positions fully extended.
In saying that though, generally if the system if working fine the excess pressure will be bled off through the relief valve arrangement if one stroked before the other.

 

[imagineero]

Well guys,
I got my gauge and a hand full of fittings/elbows to get it on the truck. As an aside, we get shafted on stuff like this in aus just like everything else. A single 90 degree elbow in BSP costs around AU$40! Cost all up for 2 gauges (one for my chipper too), one flow control valve and less than 10 elbows/fittings was $750!

So I popped the gauge on, and the pressure doesn't look too bad. First stage hits about 600 or something, second stage 900 or so, and 3rd stage is where it starts to not want to tip. At idle it just sits at the 3rd stage and pressure hits around 1500. Give the engine some revs and it maxes out at 2200psi, and will tip at that pressure if half or slightly more than half full. If you get to 3/4 full then it wont tip, you have to resort to reversng at speed and slammng on the brakes to try to get some mulch out.

So I guess I'm looking at a new ram? found one that extends nearly 3' longer, so I could mount it further from the hinge. It's also about an inch larger in diameter at each stage. Is it acceptable to mount the ram off centre in the bin, to avoid the tailshaft when closed? We're talkng about 8-10" off centre here.

Shaun

 

[turnkey4099]

Well guys,
I got my gauge and a hand full of fittings/elbows to get it on the truck. As an aside, we get shafted on stuff like this in aus just like everything else. A single 90 degree elbow in BSP costs around AU$40! Cost all up for 2 gauges (one for my chipper too), one flow control valve and less than 10 elbows/fittings was $750!

So I popped the gauge on, and the pressure doesn't look too bad. First stage hits about 600 or something, second stage 900 or so, and 3rd stage is where it starts to not want to tip. At idle it just sits at the 3rd stage and pressure hits around 1500. Give the engine some revs and it maxes out at 2200psi, and will tip at that pressure if half or slightly more than half full. If you get to 3/4 full then it wont tip, you have to resort to reversng at speed and slammng on the brakes to try to get some mulch out.

So I guess I'm looking at a new ram? found one that extends nearly 3' longer, so I could mount it further from the hinge. It's also about an inch larger in diameter at each stage. Is it acceptable to mount the ram off centre in the bin, to avoid the tailshaft when closed? We're talkng about 8-10" off centre here.

Shaun

I'm farfrom an expert but that sounds more like a pump vice cylinder problem.

Harry K

 

[imagineero]

I'm farfrom an expert but that sounds more like a pump vice cylinder problem.

Harry K

What's a pump vice cylinder?

 

[blades]

pump verses cylinder, Think he had finger failure

 

[imagineero]

pump verses cylinder, Think he had finger failure

What's a pump vs cylinder problem?

 

[blades]

Pump seals internal leaking not providing constant pressure
Cylinder same thing internal seals leaking allowing pressure/ hyd fluid to slip past ram assembly.
Last is valve where the relief valve section is weak or not closing completely or worn o-rings in valve assembly allowing leakage between ports.
Your pump has a rpm rating for max output something like: x liters/min@x psi @x RPM
Example: single stage pump 11gal/min@2700 psi @ 3000 rpm

 

[kevin j]

what do you mean by first second third stages?
The first stage of the cylinder is the largest area, of all sectons together. Also the highest load. If the load is not lifting and stalled, you should see maximum relief pressure (1500-2000) if the system is solid and going across relief.
If you see 600, either that is what it takes to move the load (but then it should be moving) or that is what it takes to move all the pump flow across leaks, either in cylinder, in valve, or in worn pump.

Now you said it gets 1500 psi on third stage, do you mean with cylinder fully etended and stalled at end? that would then mean the relief valve is 1500, low but ok for low tech equipment.
But in that case 600 psi at the start means probably a bad spot in the cylinder tube bypassing the seals.

Is this a single acting cylinder? Most telescopics for small dumps are. There will only be one hose at the bottom. Power extend, gravity retract. If there are two hose it 'might' be double acting (power extend and power restract) but it could also be single acting with a second hose just as a vent line to the other side.

If it is single acting, without the second hose keeping the other side full or oil and keeping air out, the top side is exposed to air in and out. The bottom ends of these cylinders, just above and around the piston resting position, gets condensation and rust and can damage the tube ID or the piston seals. The pump flow can leak past, but it would leak like a sieve to the ground.
Some single actings are actually rams: the sealing is done at the rod seal and there are no piston seals at all. The rod diameter is the area that hydraulic area pushes on.

Explain what conditions you are getting what pressure gauge readings. I assume the gauge is between control valve and the cylinder, not on the pump side?

 

[turnkey4099]

Pump seals internal leaking not providing constant pressure
Cylinder same thing internal seals leaking allowing pressure/ hyd fluid to slip past ram assembly.
Last is valve where the relief valve section is weak or not closing completely or worn o-rings in valve assembly allowing leakage between ports.
Your pump has a rpm rating for max output something like: x liters/min@x psi @x RPM
Example: single stage pump 11gal/min@2700 psi @ 3000 rpm

And if it is a positive displacement pump, the delivered pressure (not volume) should remain constant. Thus him being able to get more pressure at max rpm seems to indicate the problem is in his pump.

Harry K

 

[kevin j]

it is a positive displacement pump, the delivered pressure (not volume) should remain constant. Thus him being able to get more pressure at max rpm seems to indicate the problem is in his pump.




Other way around: positive, fixed displacement pump output is constant flow/gpm. The pressure is defined by the resistance is it pushing against (lifting a load, or going across relief, or leaking by worn parts somewhere). The flwo will vary by engine rpm but 'ideally' would be constant.

Variable pump is usually a constant pressure source, against a closed center valve, so the pump pressure remains roughly constant. Typically used on motion control or servo or many cylinders in parallel.
The piston pump pressure will drop off if the circuit changes to flow limited, say a large circuit with lots of loads all at once. Then the pump hits its moximum volume stops, is flow limited, and the pressure drops off to whatevr the loads are.

Lots of possible issues, have to wait for more info and more definitive pressure readings.


gpm is speed, and psi times area is force.

 

[b fish]

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

Sir, the formula for area on your ram is: pi (3.14) times radius squared.

 

[b fish]

Sir, the formula for area on your ram is: pi (3.14) times radius squared.

Multiply that number with your psi hydraulic pressure. Then you will have the force your ram is able to push. This is only part of the equation though. Look up the mfg. design parameters for your bed. You could have a failing pump or relief valve causing your trouble.

 

[olympyk_999]

Multiply that number with your psi hydraulic pressure. Then you will have the force your ram is able to push. This is only part of the equation though. Look up the mfg. design parameters for your bed. You could have a failing pump or relief valve causing your trouble.

looks like you're almost 3 years late with that info...he likely scraped the idea because you were not here to help

 

[b fish]

looks like you're almost 3 years late with that info...he likely scraped the idea because you were not here to help

You are correct!

 

[muddstopper]

3 years old!!! dang I was wanting to add my two cents worth to this discussion. Might anyways, let me think about it.

 

[ChoppyChoppy]

It's good info though. I have a similar issue with the 18ft bed on my International. It uses 2 3 stage cylinders.