pistons

[mtb345]

can anyone explain why lieberh puts thier boom piston upside down on the exavator:beatsme

 

[Dozerboy]

To protect the finish on the ram?:beatsme

 

[wrenchbender]

Maybe

Maybe it's easier to plumb the hydraulics this way due to the design of the machine. And how do we know what is right side up anyway :beatsme

 

[Ross]

Maybe it's easier to plumb the hydraulics this way due to the design of the machine. And how do we know what is right side up anyway :beatsme

Yeah i agree.

I think O&K put theres upside down because of the Main Valve block location and float valve pipework.

Maybe the same case in question.

Ross

 

[Truckie]

To protect the finish on the ram?:beatsme

That’s what I was always told, also Fuchs dose the same thing.

 

[Wulf]

The way I see it, more lifting power is provided on the piston side of the cylinder than the rod side however cylinder speed will be slower given that a fixed volume of oil flow is available... it depends whether you need power or speed which way the cylinders are mounted

 

[alco]

The way I see it, more lifting power is provided on the piston side of the cylinder than the rod side however cylinder speed will be slower given that a fixed volume of oil flow is available... it depends whether you need power or speed which way the cylinders are mounted

Since the oil being supplied to the cylinder side always expands the cylinder and the rod side always retracts it, wouldn't that be a bit of a moot point? It should make no difference speed or power wise as to which way the cylinder is mounted.

I have always seen them mounted reversed to eliminate the dust buildup around the rod seal.

Brian

 

[Wulf]

Since the oil being supplied to the cylinder side always expands the cylinder and the rod side always retracts it, wouldn't that be a bit of a moot point? It should make no difference speed or power wise as to which way the cylinder is mounted.

I have always seen them mounted reversed to eliminate the dust buildup around the rod seal.

Brian

Brian... yes you are right because the cylinder has to be fed from the base end not the rod end, I guess I didn't think it through fully:Banghead

the hydraulic theory is correct though... piston end provides more power etc

 

[esobofh]

the hydraulic theory is correct though... piston end provides more power etc

That's a physical impossibility. Equal and opposite reactions and all that... They are pushing against each other, one side can't possibly provide "more power" - only more oil pressure/flow will provide more power.

 

[Cmark]

That's a physical impossibility. Equal and opposite reactions and all that... They are pushing against each other, one side can't possibly provide "more power" - only more oil pressure/flow will provide more power.

No Wulf is right. The head side has more surface area for a given pressure to act on. The rod side of the piston has the surface area of the head side, MINUS the area taken up by the rod so less area for the oil to act on.

For a given flow, a cylinder will be quicker to retract than to extend because the rod side has less volume due to the rod taking up some of the volume. Hope this makes sense.

 

[cps]

No Wulf is right. The head side has more surface area for a given pressure to act on. The rod side of the piston has the surface area of the head side, MINUS the area taken up by the rod so less area for the oil to act on.

For a given flow, a cylinder will be quicker to retract than to extend because the rod side has less volume due to the rod taking up some of the volume. Hope this makes sense.

:iagree

 

[Dozerboy]

X3 look at every machine made and the way the rams set up.

 

[gasfield315c]

now that i think about it, the stick out function always seems quicker, but has less power, as well as when you roll the bucket out, quicker but not as strong as when you roll it in, it all makes sense now

 

[Chris5500]

The reason the boom cylinders are mounted upside down on the larger excavators and shovels is mainly due to easier maintenance for example measuring cylinder drift (creeping) and it's easier to reseal the flange bushing (Komatsu's only) since you can won't need an EWP.

Secondly, you get extended chrome and seal life due to debris being unable to build up on the scraper ring.

Hose positioning is more ergonomical and as a result less friction is generated and thus less heat.

You also get slighlty more power due to the barrel being approximately 2.5 times lighter than the rod (and when worked out the mechanical advantage is alot more than 2.5 times what it would be the "right" way up)

Also, just to clarify, by applying oil pressure to the piston side of the cylinder you will have power as the surface area is larger than that of the rod side (force multiplication).

Likewise, the rod side of the cylinder has less power due to the surface area being smaller but will have greater actuation speed as a result.

 

[esobofh]

No Wulf is right. The head side has more surface area for a given pressure to act on. The rod side of the piston has the surface area of the head side, MINUS the area taken up by the rod so less area for the oil to act on.

For a given flow, a cylinder will be quicker to retract than to extend because the rod side has less volume due to the rod taking up some of the volume. Hope this makes sense.

'fraid not. We may be arguing semantics though. There is no difference between either end of the rod in terms of power. The fact is the cylinder and piston are acting against each other in the same fashion, regardless of orientation. Failure to understand this is a failure to understand basic physics.

That said, there are differences in expansion & retraction - that's a whole 'nother ball of wax. Here the discussion becomes somewhat more complicated, but not really. There is more power in expansion (but less speed)due to the higher volume of fluid and the surface it's acting on (the piston, minus the rod to act on - vs the piston + the rod to act on). Retraction is faster, but less powerful.

Two very different discussions here.

 

[alco]

Two very different discussions here.

First thing you need to do is learn the correct terminology. There is really only one discussion here, but you are clouding the issue by using the incorrect terminology and in due course, introducing a different discussion.

No one is arguing that the power exerted by the cylinder is different at either end of the rod, or that orientation will change the power exerted. They are simply saying that power is different depending on which end of the cylinder assembly is being acted upon by the oil at a given time.

Do you even know how a hydraulic cylinder works? You have previously stated that both sides push against each other and that only more pressure or flow can create more power, when in fact, this is not the case. A basic understanding of physics on your part would help you to understand that when oil with an equal pressure and flow is introduced into two separate vessels (in this case the two sides of a hydraulic cylinder assembly) at separate times, the amount of force developed by the oil on the given cylinder will in fact be larger on the barrel side of the cylinder than the rod side due to the larger surface area for the oil to act against. Basically, the same pressure applied over a larger surface area equals more force applied by the cylinder.

There is never oil trying to apply force against itself by pressurizing both ends of the cylinder assembly at the same time unless the is a mechanical malfunction in the control valving. So the equal and opposite reactions you mention are a moot point.

 

[esobofh]

First thing you need to do is learn the correct terminology. There is really only one discussion here, but you are clouding the issue by using the incorrect terminology and in due course, introducing a different discussion.

On the contrary, the original question/discussion was regarding the orientation of the boom lift cylinders on a Leibherr.

Subsequent comments made to the affect of "piston end provides more power" introduced a second point of discussion related to the relative power at either end of the cylinder.

No one is arguing that the power exerted by the cylinder is different at either end of the rod, or that orientation will change the power exerted.

I'll direct you to the comments and posts above, that's exactly what they are saying "piston end provides more power". As I mentioned, we're likely arguing semantics here. What was probably intended by this comment was that there is more power in expansion (expansion being; oil filling the chamber formed by the cap-end and the piston), rather than contraction (contraction being; oil filling the chamber formed by the head/rod end/seal/gland and the piston).

They are simply saying that power is different depending on which end of the cylinder assembly is being acted upon by the oil at a given time.

Again, semantics. If that's what was said, there would be no argument here, as that is a correct statement. It's not what was said though.

Do you even know how a hydraulic cylinder works?

Indeed, we're not talking rocket science here - basic physics.

You have previously stated that both sides push against each other and that only more pressure or flow can create more power, when in fact, this is not the case.

This statement was taken from when the discussion was about orientation.

The two sides I was referring to were the barrel-end and the piston/rod end of the cylinder assembly. Not the seperate chambers as "sides". the reference was the the single act of filling one chamber where the pressure in that chamber works equally against either end of that same chamber. In this case the only thing that will change the amount of power available is to increase the oil pressure. Between the two chambers, there is an obvious diference in power. Between the two ends, there is not. The two ends act equally and oppositely. This is as simple and basics as physics gets.

A basic understanding of physics on your part would help you to understand that when oil with an equal pressure and flow is introduced into two separate vessels (in this case the two sides of a hydraulic cylinder assembly) at separate times, the amount of force developed by the oil on the given cylinder will in fact be larger on the barrel side of the cylinder than the rod side due to the larger surface area for the oil to act against. Basically, the same pressure applied over a larger surface area equals more force applied by the cylinder.

That was never under question. I think I clearly stated the possibility we were just arguing semantics. The reason I went so deeply into such a simple topic with an emphasis on clarity, was because there *can* actually be a difference in power where it relates to cyclinder orientation, but the root of that discussion is seated in the fact that there are differences between the seperate operations of expansion and contraction. If you want to have *that* conversation moving this to a disucssion on the placement of trunnions, lever points, and physical design aspects of the actual equipment, i'm happy to go there.

There is never oil trying to apply force against itself by pressurizing both ends of the cylinder assembly at the same time unless the is a mechanical malfunction in the control valving. So the equal and opposite reactions you mention are a moot point.

Again, not moot if we're talking about the single action of filling/emptying one chamber and the orientation of said cylinder front to back.

 

[alco]

It seems you would only like to argue, so you can argue away instead of listening to what people are trying to tell you to help you understand. It has become clear that you are confused about what is being said, and continue to argue the same point even though you are incorrect and trying to jumble up the whole situation by making it far more complicated than it needs to be. You say you are going into this in such detail for clarity, but the detail you are attempting to add is merely clouding the issue.

Have fun, but I won't argue any more. I know how this stuff works, and if you want to think you know better than someone who has been doing this for 20 years despite admitting to having little knowledge or experience, then have at it. You said the first step is to learn, but clearly, you have no intention of doing that.

 

[OneWelder]

Esobofh
Explain the basic physics - please use basic English and finish your thought so that the rest of us understand-
I have a several basic hyd. books that say what the the other members have said- pressure times area- makes the rod provide less lbs of power
So it would seem that we do not understand what you are saying or you do not understand us or do not think us to be on your level

 

[esobofh]

Esobofh
Explain the basic physics - please use basic English and finish your thought so that the rest of us understand-
I have a several basic hyd. books that say what the the other members have said- pressure times area- makes the rod provide less lbs of power
So it would seem that we do not understand what you are saying or you do not understand us or do not think us to be on your level

I'm honestly baffled as to how this conversation has gone where it has. The simple point I was trying to make is that the orientation of the cylinder makes no difference in terms of what power can be had from it. That's it!

By orientation I mean physical placement of the cylinder - in the Leibherr excavator it is "upside-down" when compared to your standard Deere, Cat, etc. Someone had suggested that this might be because it is "stronger" in that arrangement. This is not the case.

That point was then driven off a cliff by people talking about the fact that a hydraulic cylinder has more power when expanding vs. contracting.

This is absolutely true, for the physical reasons everyone (including myself) has posted here (larger volume, more surface area.. etc). But this fact has absolutely no bearing or meaning in terms of the discussion on cylinder orientation. Everyone who has ever used a simple floor jack knows that a bigger one will lift more than a smaller one.