Proper use of skidsteer throttle?

[digger242j]

I've operated a number of different skid steers, but I must admit, I've never read the owner's manual for any of them. There are a lot of experienced people here, both operators and those who are more involved in the technical aspects. I'd like a clarification...

There are a couple of guys on the job who say that you should run a skid steer with the engine wide open--that to do otherwise is bad for the machine. One mentioned that is was supposedly hard on the hydraulic pumps to be run at less than full throttle. I can't see that being true.

Certainly, the engines are desigend, and governed, to run at some maximun RPM setting. If you're running a long distance, or digging into hard material, go ahead and run it at full throttle. It's desigened to do it, and in the case of working the machine hard, it's better than lugging the engine down and stalling it out. However, if you're handling loose material, like sand or gravel, and putting a quarter of a bucket here, and another quarter of a bucket five feet away, or doing fine work like handling material on pallets with forks, my personal opinion is that it's unnecessarily abusive to the machine to have the engine screaming away at max RPMs. All that expensive stuff inside there has a finite life span, and the more times it goes around, the closer it is to its final revolution. Throttle back to some setting that still allows you sufficient power and speed, but that's easier on the equipment.

Yes, you can run it wide open, but there's ne reason you must run it wide open.

This came up agian today. One operator was moving pallets of concrete block. The other guy commented that he should be faster, "and he's going to hurt the machine too".

I'm open minded enough to know that I don't know it all. I could be wrong about this too. Anybody got an opinion? And can you cite from an owner's manual, or share the opinion of a professional equipment engineer or mechanic?

 

[Steve Frazier]

Most newer machines are equipped with a foot throttle as well as a hand throttle. My Cat does, and I run as I would a truck, using only the amount of throttle necessary to get the job done. I use the hand throttle only when running a hydraulic attachment, and the use the rpm that gets the job done.

 

[Jeff D.]

Anybody got an opinion? And can you cite from an owner's manual, or share the opinion of a professional equipment engineer or mechanic?

I've been told the same thing(from other operators only), That they're designed to be run at 100% all the time. I personally don't agree with that though.

I think they can be run at 100% continuously, without undue damage, but that doesn't mean they "need" to be run at 100%. I haven't any concrete info though, pro or con to my own opinion.

When I start mine up, I'll idle it for about a minute, then throttle up to about 1/4 and start moving the machine around( with no work involved) as it warms up I'll slowly increase the %, but normally stop at about 3/4 throttle. If I need the extra I'll put it upto 100%. If it's really cold mine will have a groan in the hydraulics at low rpms that's annoying, so I'll let it warm up longer, or bump it up to about 1/2 throttle earlier to avoid it.

Engines don't need to be run at 100% to avoid damage, nor do hydraulic pumps. Cylinders and hydraulic motors have a constantly varying flow anyways, so they're not affected.

I'm not sure about hydrostatic drive pumps, but guess they're similar.

I can see it if the hydraulic fluid temps were getting too high at lower rpm's, increasing the rpm's may help by increasing flow through the cooler. I've never had my fluid temp light come on while running at less than 100% yet, so..........:beatsme

 

[digger242j]

I purposely didn't mention the Cat foot pedal, just because I think it's consistant with my opinion, and didn't want to prejuduce anyone else's reply.
(But I figured I could bring it up as a rebuttal point if I needed to.)

And, Jeff, it seems like you're thinking the same way I am. As far as fluid temps, I hadn't considered the flow through the cooler, but if you're not working it as hard to begin with, does it really get any hotter?

 

[Jeff D.]

but if you're not working it as hard to begin with, does it really get any hotter?

It wouldn't think so if you're not working it hard.

I was thinking if someone were working it hard, at lower RPM's. I think fluid temps might be higher then, but am not sure.

I know on my trucks, the oil temps are higher at lower rpm's/max power than at high rpm's/max power because of the flow issue. Exhaust temps also.

I was just extrapolating that out to include hydraulic fluid too........possibly wrongly.

It's hard too tell with only the "Dummy lights" in my skid steer. Someone with actual temp gauges might be able to let us know.

 

[Bob Horrell]

I have found that most skidsteers run real well (and more efficiently) at somewhere between 2/3 and 3/4 throttle. Somewhere in that range is where max torque resides and this is what really gets the work done. Running at higher throttle only wastes fuel and really doesn't produce more work. There are a few exceptions. When working on a steep hillside carrying full buckets of dirt to the top, I found full throttle worked better. I probably only use full throttle less than 5% of the time. Since I have foot controls, there can't be a foot throttle. I have used pilot controls with foot throttles and loved them. Cat is the best in that regard (pilot controls with foot throttle).

 

[tylermckee]

I run them a little below full throttle simply because it beats me up a little less, if im running around on smooth ground for a distance i'll crank it up though.

 

[Blademan]

Personally , I run them wide open . I want 100% power , 100% of the time . It makes getting the feel of it much easier then trying to , say , dig into a pile till it starts to bog and then trying to give it more throttle . I find by that time it's too late , especially if it's a hand throttle only . Also , to me , if you take ' working the throttle ' out of the equation , it gives you more time to concentrate on whatever you're doing . You just go .

I almost even do this on my grader ( cat 14H ) . I set the electronic cruise at around 1400-1500 RPMs , so even when I slow down or stop to reverse , I have excellent hydraulic response . Makes doing everything that much faster and easier , especially when I'm lifting the blade , turning the circle , side-shifting and cranking the steering all at the same time .

 

[Squizzy246B]

This came up agian today. One operator was moving pallets of concrete block. The other guy commented that he should be faster, "and he's going to hurt the machine too".

Well thats a big load of Bollocks... but it WAS true.

The modern multi stage (or combination) hydraulic pumps fitted to compact machine will produce little more force, if any, at full power than at idle. They will move faster, they will provide more tractive effort but they will not produce anymore hydraulic pressure at higher Rpm.

Increasing the pump speed will increase the volume but not the hydraulic power.

Manufacturer's don't fit foot throttles for the novelty. Use a foot throttle and improve your work with greater control and also use less fuel. I use both depending on the task. The progressive nature of well setup pilot controls also compliments a foot throttle.

I havent seen a wheel loader run constant full throttle so I don't see why a modern skid should. Its just a habit from old piston/constant displacement pumps. The 3044 mitsupillar engine in my skid is used extensively in a lot of different machinery and mostly its variable speed. Constant high speed is sometimes necassary on an auxilliary circuit that has constant displacement gear pump or the like.

We all have operating habits...for whatever reasons...but the reasons behind them should be based on solid engineering facts.

Having just read about a zillion differnt placards and stickers...well maybe about eight....on my new mini-ex...I'm sure a constant speed setup engine in a piece of machinery would have plenty of documentation and instruction to say that the engine will be damaged if you don't run it flat out "despite the fact we put a foot throttle in"

 

[Ford LT-9000]

On most equipment with a hand operated throttle I usually crank it all the way up and turn it back a little. There is no need to run maxed out unless your digging into something hard. Skid steers should have a decellerator like a dozer seeing as most new skids don't use yankem sticks.

If skid steers had a transmission with gears like a loader or rubber tired backhoe they could make it so you can have variable throttle positions while travelling.

 

[will_gurt]

Mr. Digger Sir,

I can remember having this conversation today with you. The person in question was told that to run at less than full throttle would damage the pumps by the delivering dealer. Remember the old 1840 that was replaced by this 60XT. The 1840 had over 4000 hours on it with no real damage to the pumps. it was consistantly ran at way less than1/2 throttle.

Now would an air cooled skidder have to run at an elevated RPM, just to keep enough air flowing.

 

[digger242j]

...but it WAS true.

...so I don't see why a modern skid should. Its just a habit from old piston/constant displacement pumps.

So, could you elaborate on why it was true? (I was on their New Holland 555 today, and it's got to be what, 15 years old? Do you remember, Will? Its predecessor, of the same type, did have to have the pumps changed at one point.)

 

[Squizzy246B]

So, could you elaborate on why it was true?

Ok..you asked for it...but so I don't confuzzle you anymore and to explain properly to others; I need to quantify and explain a couple of things when just explaining the operation of constant displacement versus variable displacement.

1. radial piston pumps can be constant or variable displacement depending on the design. Most commonly they are variable delivery which means they can vary the direction of delivery whilst still spinning in the same direction by changing the position of the swash plate. By doing this they can also vary the volume. A fixed head (no swash plate) will be constant displacement.

2. We need to set aside a couple of things to compare a constant to a variable; firstly most modern skids will have load sensing valves in some circuits..usually the drive system at least. This is often coupled to the ECM thus the governor can receive electric inputs to continue to manage the engine under load. This "helps" but is no help to the topic here its just you need to know other factors are at play...so forget that for the time being:yup You can also forget relief and bypass valves for the minute...

3. All these systems have physical limits no matter what design they have an ability to operate within design parameters. Sometimes...us ugly operators will apply loads to the system which exceed the physical constraints...its just a fact of life and it will be reached no matter what the design.

4. Take a gear type constant delivery pump and apply a load to the output...such as a hydraulic cylinder. Basic physics tell us that to get anymore work out of that circuit the only way we can do it is to make those gears turn faster..its as simple as that. Additionally, when a load is applied to the circuit that load is applied to the gears and tends to make the pump slow down and then the governor trys to up the fuel to maintain the desired engine speed. Essentially to get the most work out of it you have to run it as fast as possible within the design capabilities.

5. With a variable displacement pump when a load is applied to the circuit the swash plate in the pump will shift to increase the flow, loading the engine and requiring more power, which the governor accounts for. The flow will increase until the limits of the pump, governor, fuel pump etc are reached.

The reality is that its not so chalk and cheese as my simplistic explanations above and designers add more and more complexities to the system each day to take care of various deficiencies that the simple systems above have.

Bottom line is a modern skid running at about 50 to 60% is gunna do all its gunna do in terms of straight up hydraulic power (lift) Increasing the engine speed will; a) make it go faster b) will provide more power to auxilliary circuits which are on gear type pumps or c) where the demand on one pump is to mutiple circuits whose demand exceeds the output of the pump at a given speed regardless of the pump type. c) above is why we now see many machines with 2, 3 or even 4 pumps.

The quality of engine management we have today is really exceptional and I can't see that running your skid at less than flat out will harm it...quite the opposite really IMHO...but then again engineering school was 25 years ago:wink2

I hope this helps but I must say that I am generalising. I hope somebody who currently hands on in skid engineering can contribute to this thread.

 

[will_gurt]

Mr. Digger Sir,

The current NH555 is a 1994 model. Has around 3500 hours and had regular oil/filter changes.

The antique old NH555 was around a 1989 model with a Perkins in it. Them blasted pumps!!!! were removed and rebuilt twice in 4000 hours.The first was at +/- 2400 hours. the second was around 3900 hours along withthe drive motors. I attribute this to a very total lack of proper maintenance. I can't remember if any oil changes let alone filters ever back then. The super thinking "it is running so no to any maintenance " mentallity then applied.

Crazy how a few pleas and several thousand dollars out of the bosses pocket made the change HUH?

Now the boss(not the super) is anal about the oil/filter use. He insists that they are done evey 150 to 200 hours. This resulted in the 1840 having over 4000 hours without any major oil related break down.

 

[Jeff D.]

Squizzy, I not disputing any of what you said, but wouldn't that make the statement "Not" true?

The other guy commented that he should be faster, "and he's going to hurt the machine too".

I take the statement to say, he's running too slow, and he's hurting the machine in the process of running slow, but it seems you're saying (and I agree)he's not hurting the machine by running slower.:beatsme but you say the statement is true.

Also, I'm not up on modern hydraulic pumps, but from your discription it sounds like the modern variable displacement pump operates similarly to a hydrostatic pump, but without the reverse in fluid flow ability, and the flow volume control being controlled by a govonor instead of by the driver.

Is that correct? It's just so I understand them better/at all.

 

[Tigerotor77W]

I hope none of you were hoping I could provide a technical answer to this question... because at the moment, I can't.

I know from a fuel consumption and noise standpoint, there's obviously an advantage to foot-throttle machines. But that's not what you're looking for, so until I learn about this stuff, sorry, I know nothing. :crying

 

[Squizzy246B]

Squizzy, I not disputing any of what you said, but wouldn't that make the statement "Not" true?

There is a lot of factors at play and I've been with hydraulics (as an engineer) all my working life, but I've only been around skids for like 5-6 years...but here's why: firstly with a constant displacement pump you will definetly need full power to get the full performance (not that that has anything to do with damaging the machine) and secondly;

take the older Bobcats with the Kubota engine. Kubota biggest production line was generators...constant speed engines. If the engine's capability was capable of say 1800 Rpm at 100% then as a genset it would be governed to say 1500 RPM (about 70-80% of what it was capable as in other applications) and whatever speed the frequency of the power output required. Those engines could do like a guzzillion hours flat out. The governor, fuel pump and injectors where set up for full load at that speed. You took the thing up to flat out and put it on load and away it went.

So..all I'm saying is that if the manufacturer didn't fit a foot throttle and told you run the machine flat out (on the governor) thats where it would be happiest and probably provide the longest service life. If the manufacturer fitted a foot throttle and the machine has variable displacement pumps then it certainly isn't going to harm it to run the machine at various different speeds.

Hydrostatic pumps more refers to the control of a pump and system than as to the pump itself. Technically a hydraulic pilot system on a variable displacement pump is a hydrostatic system....a mechanical input to a "variable delivery" (see above) is most commonly called hydrostatic..and would be the steering system on modern trucks.

The thing that I have ommitted is the different control inputs and systems of todays machines. Just ask Steve to pop the cab on his 248 and have a look under the seat.

 

[Squizzy246B]

I just read through my B series manuals and couldn't find anything that states any specific speed that the machine should be run at. It says to operate the foot or hand throttle for smooth operation....I'll have to work on the smooth bit

 

[Cat420]

Here's a great page showing how both gear and variable displacement pumps work. The have video and everything. http://science.howstuffworks.com/backhoe-loader8.htm

 

[Squizzy246B]

Jeff, I also think that sometimes the term Hydrostatic is used to describe the hydraulic motor not the pump. The drive system on a skid is "hydrostatic"...self explanatory really.