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Introductory Hydraulics Questions

Started by Rougespear, March 28, 2014, 11:23:01 AM

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Rougespear

Hello all,

I've been browsing through the forum for a little while, but I figured I would join.  I'm building my own bandsaw mill, and I'm now considering the hydraulics I would like to eventually have.  Initially, I would like to power: head travel, head height adjustment, and clamping dogs; and eventually a chain turner, backstops, and toe-boards.  I've done a decent amount of research on hydraulics, but I still have many questions, so I was hoping folks out there "in the know" might be able to lend me a hand?

I would like to build a portable hydraulic powerpack, that I will connect to the mill with quick-connects to the valves (permanently mounted to the mill).  I have an industrial quality TEFC 2hp 220v electric motor that I would prefer to use as the hydraulic power source for two reasons: (1) I already have it, and (2) the amp draw is low enough that I can run it on a decent length of extension cord from a 15amp 220v outlet.  So that being said, now I'm trying to size a pump for this motor.  My mill is just a hobby mill, so hyd speed is not of utmost concern, but I am shooting for realistic cyclic speeds.  I was reading threads and it seems between 2 and 3 GPM at 2000 psi is a good place to be for the mill's functions.  This is where I begin to get lost though...  I figure that 2000 psi would be around the pressure I need, so I use the following formula to deduce HP required: GPM x PSI / 1714 = (gas) HP.  I divide that again by 2 to get the electric-equivalent HP (because I was told on average 1hp electric = 2-2.5 hp gas).  So to me, driving 3gpm at 2000 psi is within the realm of possibility of a 2hp electric motor, correct or no?  Does this all sound right so far?  Does 2-3 GPM sound like an alright flow-rate for a bandsaw mill?

So when I begin to search out hyd pumps, there are a myriad of them.  I've found many that are around my desired flow-rate but much higher psi, or vice versa.  So is it possible to take a hyd pump and reduce the output pressure of the pump to reduce the power needed to drive the pump?  Or does the pressure stay constant and I have to reduce the RPM of the pump to reduce flow (so if I turn a pump at a slower speed: is the pressure or GPM reduced)?  I'm assuming there is a formula out there something like: "GPM = PSI x RPM" but I have yet to find it...

I would be most appreciative of anyone's help!  Thanks! 
Custom built Cook's-style hydraulic bandmill.

StimW

A hydraulic "Circuit" must have a relief valve in it. You set the operating pressure by adjusting the relief pressure. Also the reservoir has to be big enough to let the oil cool between cycles, an oil cooler helps. 
The best bang for the buck is a two stage pump. They will shift automatically when the pressure builds but when pressure is light they move more volume making things move faster.
Surplus Center has good prices on hydraulic supplies.
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Magicman

I can not help you but Welcome to the Forestry Forum, Rougespear.   8)
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bandmiller2

Welcome Rougespear, the big problem with hydraulics on a band mill is you need two systems or long hoses to follow the carriage.  You drive the hyd. pump that is on the carriage with a belt from the engine, that powers your head up and down and gives you power feed with a cable or chain system. You can use your motor to drive a hyd. pump on the bed for turner, lift, and clamping. You don't need 2000 psi pressure under 1500 psi will handle anything you want to do. Two or three gpm pumps should be fine as your not in a huge hurry. Read through past posts theirs weeks of reading about mill building. Frank C.
A man armed with common sense is packing a big piece

pineywoods

There's a few confusion factors, 3 gpm gear pump, the simplest and cheapest type will serve your purpose nicely. For all practical purposes, you do not need to be concerned about pressure ratings. That spec is a MAXIMUM rating, not necessarily working pressure. RPM is relevant. A 3gpm pump turning 3600 rpm will only deliver 1 1/2 gpm at 1800. Using an external electric motor is the best way to go unless you need to operate the mill as a portable. If your motor is 3600 rpm, couple that to a 3gpm gear type pump, should be just about optimum. Gear pumps are rotation sensitive, needs to match your motor. A control valve bank will have a pressure relief valve, there is none in the pump. Be sure to specify open center control valves. I have added hydraulics to 3 different manual mills, be glad to elp any way I can. You might update the info in your profile so we have some idea where you are located and what facilities you have available.
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Rougespear

Thanks for the replies all, and thanks for the warm welcome.  I've been out of town for a few days, so my apologies for not replying sooner (I wanted to get all my ducks in a row before coming back with more questions).

I am building a heavily-modified Linn-style mill up here in Canada; I will post some photos soon as I can.  As for the hydraulic system, I would prefer to stay away from a 2-stage pump because I'll be running motors and I don't want the speed randomly changing while I'm operating those motors.  So I'm limited to a single stage pump (also easier on the math end of things).  The powerpack will be stationary (re: not mounted to the mill head), so I will run hoses to the head for the up/down motor... everything else will be attached to the log deck I figure. 

So the general consensus here is that ~3 GPM at-or-below 2000 psi will be sufficient for my needs yes? 

Pineywoods: thanks for your offer to help, so I will pick your brains a little further if I can.  Why should I not be concerned with pressure in the system... is it because I will rarely ever reach the max operating pressure using typical functions?  If I do find I reach that limit, then I could just use a larger bore cylinder (which would reduce pressure needed for the same task, but also reduce cycle time) yes?  I have attached a drawing of my proposed setup that I was hoping you could review.  I want to make a powerpack with two quick disconnects which could be hooked to various valve banks on different hydraulic applications (re: not the mill).  I've included a relief valve in the system to dump the pressure when the power pack is not connected to any valves... is this the correct way to do it?  I have shown my two pump choices: which do you think would best utilize the power of the 2hp electric motor without exceeding its maximum amp draw (I'm thinking the 2.73 GPM pump might be best)?  Can you offer any other suggestions for the design of this hydraulic circuit?

Custom built Cook's-style hydraulic bandmill.

hackberry jake

I designed my system to handle 3000 psi... that was a waste of money. I have a 2hp electric motor and a 2gpm pump on my system with an adjustable relief valve. I usually leave my relief valve set between 500-600 psi and it will roll some Massive logs at that pressure. A lot depends on which cylinders you choose. If you choose 3' diameter cylinders than you will probably want a 5gpm pump and you can get away with less pressure (but you have more losses due to transporting more fluids. If you choose 1' diameter cylinders than you would be better off with a 1.5gpm pump. hope this helps.
https://www.facebook.com/TripleTreeWoodworks

EZ Boardwalk Jr. With 20hp Honda, 25' of track, and homemade setworks. 32x18 sawshed. 24x40 insulated shop. 30hp kubota with fel. 1978 Massey ferguson 230.

bandmiller2

The only function you need higher pressure for would be the log loader arms. All other functions limited pressure is desirable so nothing gets bent and cants not defaced. If you are going to mill stationary you just need a dead log deck to feed logs to the mill saving a lot of hydraulics and expence. Would be nice to have a Pineywoods  or A two plain clamp to turn and clamp logs/cants. Frank C.
A man armed with common sense is packing a big piece

Rougespear

Bandmiller2: I was kinda of wondering the same thing you just mentioned regarding pressure when I was watching a video of Cook's AC-36... "how do the long clamps not split the cant"?  I won't be using/building any sort of log loaders because my father-in-law has a large articulate rubber-tire CAT loader with log grapple.  So basically what you guys are saying is I would be better off with lower pressure (less than 1000 psi) and higher flow?  I will be using 2" bore cylinders because they appear the most cost effective at Princess Auto (where I'll be sourcing most of my hyd parts).

I'm hoping pineywoods will come back with some more thoughts too...

Cheers, Brent
Custom built Cook's-style hydraulic bandmill.

Ga Mtn Man

If you don't have enough pressure your chain turner won't be able to handle big logs.  Of course, your mill will have to be built stout enough to handle the load.  Wood-Mizer set the pressure on the LT40 at 2000 psi.
"If the women don't find you handsome they should at least find you handy." - Red Green


2012 LT40HDG29 with "Superized" hydraulics,  2 LogRite cant hooks, home-built log arch.

pineywoods

Rougespear, I said you needn't be concerned about pressure, based on my experience building 3 of the pineywoods hydraulic turner/clamp systems. That 3 gpm gear pump will stall the 2 hp drive motor long before you bust anything.
It appears to me you are assuming a fully pressurized system, where with the pump running and no control valves actuated, your pressure gauge would show 2000 psi. For us doityourself types  there's a better way. Use open center control valves and you will see 25-30 psi under those conditions. Open center valves have an open passage to allow oil to flow freely through the valve bank, through the filter, and back to the tank with very little pressure involved. When the valve is actuated, this passage is blocked and the passage leading to the hydraulic cylinder is opened. Closed center valves have that passage permanently blocked. Pressure will then be directly proportional to the load on the cylinder. Much less stress and wear on everything. Go to the sawmill and milling forum and search "manual to hydraulic". Lots of pics and autocad drawings. If you can't find it, holler and I'll post a link.
Chain log turners are not my favorite, they are expensive, work well, but no good for anything else. I opted for a claw type turner, with a little tweaking, it makes a combination turner and a very nice 2 plane clamp.
External power pack is a good idea if you are fixed location. I seriously considered using a log splitter for a power pack. One enterprising sawyer in Oklahoma built a homemade system and used a hydraulic outlet on his farm tractor as a power source. Said it worked well, but climbing up on the tractor to turn a log got to be a pain..
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

WoodenHead

Here are a few formulas that might help.  It looks like you already are using one of them (#2 below).

1. GPM (supplied by the pump) = Pump displacement (in Cubic inches per rev)  x RPM / 231

2. HP required to drive pump = GPM x PSI x 0.90 / 1714

3. GPM (required) = Cylinder volume (Gals) x 60 / Cylinder extend time (seconds)

4.  Cylinder volume = Area of piston (sq inches) x cylinder stroke (inches) / 231

5.  Cylinder force = PSI x Area of piston (sq inches)

So, you have to worry about pressure (PSI) when you want the cylinder to lift/push/pull a certain amount force/weight.  You worry about GPM when you want a certain sized cylinder to travel through its stroke within a certain amount of time.  You worry about both PSI and GPM when comes to sizing the pump and the motor to drive it. 

I use a 4 GPM 3000PSI gas powered single stage pump.  It is more than I need.

Rougespear

Right, this all sounds good everyone.  Thanks all for the help!

Woodenhead: any word on whether the HP formula you posted is applicable to gas or electric hp?  I've read that it is for electric hp, but when I apply the formula to an off-the-shelf gas powerpack it works out right for them too.  I always thought electric hp was about twice that of gas...
Custom built Cook's-style hydraulic bandmill.

WoodenHead

Quote from: Rougespear on April 05, 2014, 09:01:29 PM
Woodenhead: any word on whether the HP formula you posted is applicable to gas or electric hp?  I've read that it is for electric hp, but when I apply the formula to an off-the-shelf gas powerpack it works out right for them too.  I always thought electric hp was about twice that of gas...

The formula is for an electric driven pump.  My gas powered unit has a 13 HP motor on it.  The formula indicates that I would need about a 6.5 HP electric motor to drive it.  So the 2 to 1 rule seems to prove correct.

My unit is much more than I need, but a local surplus store had a sale - $450 for gas engine, pump, 5 gal reservoir and pressure relief valve.  The intent was to use it in case I needed to go mobile.  Right now I'm using it for my new stationary setup.  I also have a 3HP electric unit with a 3.5GPM pump.  I have the pressure relief set to 1500 PSI for that setup.  When I get the opportunity, I will move it over to my new mill location for stationary operation.

Rougespear

Finally getting around to purchasing some hydraulic components.  My pump will be ~2gpm (but I want to design for a 3-3.5gpm pump in the future if needed).  I understand to size the hyd reservoir 3x the pump capacity for best system design.  I see 5 gal and 10 gal reservoirs ($30 difference).  My hyd will control: head up/down + fwd/back; log dogs; backstops; and a log turner.  Should I go with a 5gal or 10gal reservoir?
Custom built Cook's-style hydraulic bandmill.

Nomad

Quote from: Rougespear on February 09, 2015, 11:53:58 AM
Finally getting around to purchasing some hydraulic components.  My pump will be ~2gpm (but I want to design for a 3-3.5gpm pump in the future if needed).  I understand to size the hyd reservoir 3x the pump capacity for best system design.  I see 5 gal and 10 gal reservoirs ($30 difference).  My hyd will control: head up/down + fwd/back; log dogs; backstops; and a log turner.  Should I go with a 5gal or 10gal reservoir?
Go with the 10.  If you're using it for head controls as well as bed controls, it won't be too much.
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Ljohnsaw

I just read though this old thread.  Since you could do all of your functions except raise and lower the head with hydraulics easily, why don't you consider something else for raising/lowering the head.  The reason I say this is the hoses to run to the head would be somewhat expensive and prone to wear.

Three ideas:

1) Use a geared hand crank system.  If you have the parts or get them cheaply, you would have the most reliable setup (IMO)

2) Do it with electric - since you are powering your unit with electricity already, a power cord would work pretty easy.

3) Don't have it figured out exactly, but what if you had some sort of hydraulic powered shaft running the length of you bed that you could use to raise and lower the head. 
   - A rotating shaft would be the easiest to make on the bed, but not sure how you could harness that motion.  I splined shaft would tend to clog up with junk.  Maybe have your wheel/gear on the base of your head-works "grab" the shaft when needed?
   - A shaft that moves forward and back.  Have a system like woodworking pipe clamps - you stop the head movement on the track, engage this clamp, move the shaft forward or back (hydraulic) and this mechanism would move your head up or down (after releasing the head lock).  There would need to be a big mechanical advantage on the lever - move the shaft a little to push the head up a lot.


4) Just thought of another system - should work.  I'm assuming that you are moving your head-works down and back on the track with a chain feed attached to the base - chain on each side so it travels straight?  If so, then just run another chain, around some idlers, up to the head and back down again.  This chain would be locked on the head but free-wheeling down the track when cutting.  You would run this motor raise and lower the head when needed.  You would need a cam-lock setup to hold the head in place when not adjusting. 

To complicate it further, you could have one motor running both chains.  Have a splined shaft that locks them together when cutting or pulls back for only the height adjustment.  That would work real slick!  For a fixed length of track, this wold be a real good setup.  Probably a little trouble when extending track.  You would only need about 1/2 the length of your track of chain, the rest could be cable to save on weight and cost.

Just call me Rube (Goldberg) :D
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

bandmiller2

John, raising and lowering the head can be done easily with hydraulics. My home built bandmill uses a hyd. cylinder and wire cables and worked well for the last 12 or so years. There will be nay sayers that will say the head will drop, it will if you use an old leaky cylinder, a new tight one no problem. My mill is a four post with the cylinder mounted vertically. The 3/8" wire cable is reeved to give 2" head  travel for 1" of cylinder travel. It is easy to feather the valve and adjust head height. An advantage is you can have as heavy an engine or motor as you like. Hydraulic cylinders and wire cables are good enough for aerial ladders and their plenty good for mill heads. Frank C.
A man armed with common sense is packing a big piece

hackberry jake

If you live in an area that gets cold winters, spring for the higher $ thinner hydraulic fluid. I just used the cheapo "tractor hydraulic fluid" in mine and it turns to honey in the winter time. It makes it hard for my electric motor to start. It may have a weak capacitor as well though. I have also heard people recommend automatic transmission fluid for thinner hyd fluid.
https://www.facebook.com/TripleTreeWoodworks

EZ Boardwalk Jr. With 20hp Honda, 25' of track, and homemade setworks. 32x18 sawshed. 24x40 insulated shop. 30hp kubota with fel. 1978 Massey ferguson 230.

5quarter

No specific advice to offer...but I just wanted to mention that the more robust you build a system, the less it will have to work relative to its capacity, and the longer the components will last. It looks like you're putting together a good plan.  8) 8)
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Ljohnsaw

Quote from: bandmiller2 on February 09, 2015, 08:40:32 PM
John, raising and lowering the head can be done easily with hydraulics.
<<snip>>
Frank C.

No doubt.  But, I was proposing an alternative to avoid either having to have a second pump on the head or long hoses.

I still think my double chain idea has some merit.  I'm still pondering the idea - it gives control of head height as well as track movement from one position with one motor.  It could be powered either by hydraulic motor or a high torque (i.e. treadmill), low speed motor.

Then again, I nether have nor used a sawmill... :-\
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

Rougespear

Thanks for the thoughts folks... I'll grab the 10 gal. 

Also: head up/down is 12v electric gear drive as built right now to avoid that very problem of dangling hoses.  I will run it and see how I like it - I think it may be too slow though (it travels 6" in 10 seconds, and I can't gear it any more than it already is).  I had envisioned a hyd debarker on the head eventually, so I may have to run a feed circuit out to the head either way... then it'd just be a matter of another 12v solenoid valve on wireless control.
Custom built Cook's-style hydraulic bandmill.

bushhog920

http://www.ebay.com/itm/Using-Industrial-Hydraulics-Rexroth-Frankenfield-/161218003419?pt=LH_DefaultDomain_2&hash=item25895781db

I have read this book it is a must read if you are building your own hyd. system. very easy to read lots of examples, explains all the pros and cons of different pumps and systems. I'm telling you get the book well worth the read.

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