Snowblower lift/lower speed

[Don_Sullivan]

Baptized my new BX1500, BX2750A 50"front blower on 18" - 20" from the Sat,Sun storm here. Use turf tires, Kubota weight box with 200 lbs bagged sand and 4WD. It behaved like a champ in nearly all respects on asphalt, grass and gravel surfaces. Total seat time about 12 hours over 3 days. The float feature works perfectly on asphalt, well on grass and poorly or not at all on gravel.

The reason for this post is that when float doesn't work as well as you need, you are continually making very fine corrections on the blower height. Not easy to do with the hydraulic pressures designed for lifting full loader buckets. The blower goes from full down to full up in a small fraction of a second so fine tuning the height requires microsecond applications of juice. My geriatric hands are a bit lethargic.

Does anyone have a suggestion (other than developing the required skill) for coping with this situation? Replacing the 2"D cylinder with a smaller one comes to mind, or somehow throttling the flow rate for this cylinder.

Don

 

[sandyc]

I have a 2200 with a front mount blower and have no problem with the speed, either up or down. My float is effective and as long as the shoes keep the blower out of the gravel I have no problem. At 2900 RPM it takes a few seconds to raise and or lower the blower. Maybe the older it gets the slower it gets......sort of like people.
Do you have a four way valve? It would be the valve that controls the fel?
I wouldn't think a smaller cylinder would work....I think a larger one would damp the pressure so it wasn't too fast.

 

[Pks]

Don,

The speed of cylinder travel is affected mostly by pump delivery rate (gallons per minute), not by the pressure. If the cylinder diameter were made smaller, it would travel faster.

Think of a 5 gallon bucket; if you fill it at a rate of 5 gallons per minute, then it takes 1 minute to fill that volume. If you filled the same bucket with you standing at the top of the house and the bucket on the ground, this increases the pressure of the water column filling the bucket. But it still takes 1 minute to fill the same volume.

Now make that bucket smaller and pour in the water at the same 5 gallon rate, and the bucket fills faster and with the same pressure.

So that's why a smaller cylinder (all other things being equal) would move the blower up and down faster.

If what I've just stated makes sense then here's a wrinkle that's sure to mess it all up. If the cylinder were made significantly smaller, such that the cylinder required about 95% of the total system pressure to lift the blower, the lift speed would begin to slow down. At the moment I can't be sure of how to design for this condition, but it does work. I don't recommend trying to do it this way.

There are really two ways to slow the lift, use a bigger cylinder (it takes more time to fill) or put in a flow control device. The flow control is the easiest. It can be as simple as a washer-like device inserted into the fittings right where the input and output lines attach to the cylinder.

The safest way to control the speed of a cylinder or any actuator for that matter is to put the metering device on the oil output side of the load. This means the device is controlling how fast the oil leaves the cylinder. That way, the oil in the cylinder must push past the device. This prevents runaway load conditions.

I hope my explanations haven't confused the issues too badly.

 

[JASTN70D]

Nice explanation I am really starting to get hydraulics a little better from all the great posts. /forums/images/graemlins/smile.gif I cant say I fully understand the even smaller cylinder slowing down /forums/images/graemlins/tongue.gif. But its a start of an understanding of the big picture. Thanks PeterKS!

 

[Pks]

Jsdk55,

The smaller cylinder will slow down when it starts to get slightly overloaded.

For example: if a loader bucket is REALL full (like with gravel or wet clay), it will be slow to rise because the system is at (or nearly at) its peak hydraulic pressure. The relief valve begins to leak a little, the piston in the cylinder leaks a little, so does the controlling spool valve and the pump becomes less efficient . With these little internal leaks, the gallons delivered to the cylinder goes down a little so the raising of the bucket becomes slower. The same can be seen at the 3 pt.

 

[JackIL]

Don,

Since you have both paved surfaces and gravel to contend with, you probably will need to set the skid shoes for what you have the most of. For gravel, usually this means setting the shoes so that the cutting edge is at least an inch above flat on the ground. Leaving that little bit of snow mixed with the top of the gravel won't hurt anything. Then if you leave the shoes in that position when you do the paved portion, there will also be some left--probably not what you want.

The more common approach would be to set the shoes so that the edge skims the pavement and then just raise the blower about an inch or so on the gravel. When doing this, you need to try to develop a "light" touch so that a very slight nudge of the control lever "feathers" the blower slightly up or down. Don't try to "barely skim" the gravel or otherwise you will end up fighting to achieve the proper height. Again, for car, truck, tractor, or human traffic on gravel, a little bit of snow mixed on top won't hurt anything.

Another suggestion is to slow the engine speed way down before you start to move the hydraulics to set the blower position an inch or so off the ground for gravel. Once it is about right, then open the throttle fully an proceed forward.

Hope this helps.

JackIL

 

[JASTN70D]

Makes sense Now I could see why you would not recommend that. It is a overload situation that probably wouldn't be good in the long run.? Thanks again /forums/images/graemlins/smile.gif

 

[jrlichina]

You could put a flow restrictor each of the up/down lines. This would slow it down without affecting the lifting power. They are pretty cheap, about $6.00 bucks each. You can get them from any good hydraulics supplier.

 

[Don_Sullivan]

Thanks all for the info -this forum is really great! sandyc is right that dropping the RPM a bunch slows down the SB lift/lower. The problem is that for pushing out the snow you really need full engine RPM. On gravel unless you are doing everything right you don't make a smooth path for the wheels. So you really need to tweak the height on the run without dropping and raising the RPM.

Pks' explanation re pump delivery rate being the controlling factor makes perfect sense. Learned something else new today.

Pks and jrlichina's flow restrictor scheme sounds like the best way to go, particularly since I don't envision ever wanting anything close to the lift/lower speed I now get at full RPM.

My normal practice on previous machines has been to set the shoes first with 1/8" shims and do the asphalt. That works great with float. Then I move the shoes down for 3/4" with some scrap wood shims and do the grass. If the ground is reasonably frozen this also helps to prevent scalping. For gravel I've found the shoes to be only marginally useful.

Thanks much,
Don