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Kenzen

Hydraulic Capacity Calculations

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Kenzen

I'm doing some math to calculate how much reserve reservoir capacity my DA917H (aka AC917H, Simp 7117H) has to support hydraulic cylinders on a custom front end loader.

The 7117 manual quotes a 3 quart hydraulic capacity. It's not clear if this is total system capacity, or the reservoir capacity.

The sundstrand 15 manual quotes it's "important" to have a reservoir capacity of 5/8 the charge pump capacity flow rate, and a minimum of 1/2 this flowrate.

So the math becomes: recommended reservoir capacity (gal) = charge pump capacity in gpm (assume 3600 rpm) x 5/8).

The Sundstrand 15 manual quotes 3 different charge pump capacities: .19, .30 and .33 in^3 per rev. Which one applies?

Second, doing the math for the highest and lowest charge pump displacements, assuming 3600RPM, and converting with 231 in^3/gal:

@ .33 in^3/rev, the charge pump gpm is 5.14 gpm, making the recommended reservoir capacity 3.21 gal, which is "way more" then the 3 qt stated hydraulic capacity of the 917/7117.

@ .19 in^3/rev, the charge pump gpm is 2.96 gal/min, making the recommended reservoir capacity 1.85 gal, which is "still way more" then the stated 3 qt capacity.

Was the reservoir capacity grossly undersized per Sundstrand recommendations? Am I suffering from a gross conceptual error?

I'm just trying to figure out how much reserve there is to support additional hydraulic cylinders.

Thanks,

Ken

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Kent

Without doing any math, my answer is essentially none... The current system isn't sized for it, either in reservoir or cooling capacity, nor does it run at high enough flow and pressure for the much larger loader cylinders needed.

I would plan on adding a separate pump (and reservoir) for the loader. You can pick up one big enough for about $100 at places like this: https://www.surpluscenter.com/sort.asp?catname=hydraulic&keyword=HPSR

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Kenzen

I'm actually sizing it for something a little more than a johnny bucket. I'm really just adding a second cylinder for the dump circuit (controlled by a 12vdc 8 port control transfer valve) , and using the existing cylinder (my DA917H is retrofitted with a hydraulic lift) for the lift circuit. I'm really just looking to run an additional small 1" bore, maybe 12" stroke cylinder. If it has a small diameter shaft (1/2" or 5/8"), the additional capacity needed would be just to cover the displacement of the shaft (e.g. 2.36 in^3 for a 12" stroke and 1/2" shaft).

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MysTiK

Fascinating.

I tend to think 'gross conceptual error'. Methinks there is simple capacity. And then there is flow rate, in which the capacity is 'flowed'.

Adding all the loader cylinders, etc. is large increase in 'simple capacity' - the simple amount of fluid IN the system.

You need to maintain pressure - and that is done by flowing ADEQUATE fluid through the parts in play.

There are valving changes that are often required when people have a simple hydro tractor, and want to add hydraulic lift, or power steering, or both. the Sundstrand will do those; but only with the valving changes on the pump itself.

so, I daresay, that the 3 different figures you displayed, are about those valving changes.

But beyond that you should be calculating flow adequate to maintain the system - which is about maintaining pressure - not the capacity of the system. You could add a fluid tank, and still the same. The flow has to keep up.

this is very interesting. I could be totally 'out to lunch' - never mind 'gross conceptual error'. But I have wanted a loader forever; and I read these crazy threads on hydro, etc. I think it's great that there is a possibility that the simple Sundtrand 15 could maybe pull this off.

So, my 2 cents, if that. Don't quit until you prove it one way or another - but the theory is good, and someone with more experience than me might be able to help further. I just have a high conceptual math aptitude - doing actual calculations makes me stress.

But it's necessary to be clear on what is truly being calculated; and not what one thinks is being calculated.

So, yes - that is conceptual. and I think you are on the right track, regardless it will or it won't maintain the system. But it seems about maintaining pressure by using rapid flow, cos that fluid is moving and is under pressure. So the amount MOVED must be REPLACED immediately. Pressure calculations are really crazy; I don't think you need that yet; pressure will increase as flow increases due to resistance - that which makes movement. The flow must go through simultaneously.

I'm losing it here. :D

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MysTiK

Yours was the only post when I was typing mine. If JB, and a small cylinder, and you are willing to maybe sacrifice hyd lift, etc.; I think this is very doable.

just get the math calculations on track.

EDIT = also verify if those 3 different specs you mentioned are about the valving changes on the pump.

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MysTiK

There was a recent thread where someone had hyd lift and was adding pow steer. The key was in the actual hose routing and a T JUNCTION. I see this as similar to that; rather than a larger loader project.

Not sure - will see if i can locate that thread. for reference.

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Kenzen

Good point on the valving being the factor for the different charge pump rates. I did the valving when I retrofitted the hydraulic lift kit, and there's a big charge pump pressure range to be "in spec" (75-150#???) and that would affect that flow rate.

So my concern is not so much flow, because flow = speed (for a constant pressure). It can't dump any slower then my current prototype with an electric 8" linear actuator. My concern is that the reservoir level will not handle the surge or demand for fluid from the cylinder movement, and starve the charge pump of "net positive suction head" required to function (and then possibly eat itself). The worst case surge/demand is both the lift and dump cylinders go from retracted to extended (e.g. the lift is up in the air and dumping, and then the bucket comes down and levels), or vice versa. The reservoir has to accommodate that change in level, and still meet the charge pump (surge/suction) demands.

Related to this is I'm considering using a auto power steering pump that utilizes a remote reservoir. I don't need the pressure of a "real" hydraulic pump - in the neighborhood of 1000# is fine. The remote reservoir allows me to use any size I need, and also makes the pump compact enough to mount just about anywhere. (And the cheap side of me likes the idea of a $15 pull at the salvage yard.) :)

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MysTiK

Well, 1000# is out - I read the SStrand will crack over 800#.But I do see this as similar to a pow steer setup where there are constant inputs for steering, left, right, nothing, etc. and the simp pow steer simply gets T'd into the existing system that has hydro + hud lift.See thread below - and, from that thread, this quote from RayS - this thread lacked clarity it the end; but no matter. I'm showing the setup for pow steer from MANUAL. = from PAGE 2 OF THIS THREAD:http://www.simpletractors.com/club2/topic.asp?TOPIC_ID=123136&whichpage=2&SearchTerms=power,steering

quote:Originally posted by RayS

John, that is correct.Dennis, the manual below in the link is a step by step walk through of of installing a power steering unit on these tractors. It also has the parts and part numbers of what is needed. You get Simplicity parts from a Simplicity dealers or they show up on ebay and Craigslist at times. Hydraulic shops can get the fittings and hoses but if you don`t know the sizes of fittings or lengths of hoses the best bet is through Simplicity.http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=jgEBGP_dqH5tG7EPl7mRgtLvBCd6


id="quote">
id="quote">

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Kenzen

Without priority valving, simultaneous driving and lifting/dumping would prove "interesting", like moving in molasses.

The 1000# was in reference to the auto pwr steering pump, not the sundstrand. However, I actually had my sundstrand running with a #1000 gauge pinned high on charge pressure while I was setting the charge pressure (with the shims). The check valves were leaking past the buttons - it's a tough little unit... :)

Now I'll dig into the power steering link above...

Thanks all!

Ken

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Kenzen

I actually contributed to that power steering discussion, in reference to this same effort that started this thread. I was considering power steering on my DA917H, but then I came across the "poor man's power steering" mod with the bearings on the axle - that will be good enough.

My reference to the power steering pump in this thread was to use it for hydraulic power for my loader project, if the sundstrand will be inadequate (or if I want to put the loader on my 3314v). As I understand these power steering pumps, they are internally relieved for overpressure, and the flowrate is readily adjustable with pulley sizing (considering the constant engine speed of the tractor). Using a pump depending on an internal reservoir, I can put any size/shape tank wherever it's most practical (as long as it's a bit higher then the pump itself).

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Kenzen

The older JD318 has a sundstrand 15 (actually sauer-danfoss - same thing), and 2-spool hydraulics with dual hydraulic ports on the front end for attachments. It also has hydraulic power steering. However, the 318 has a 1.2 gal hydraulic reservoir, compared to the 3/4 gal of the 917h. So from a flow/capacity perspective, the sundstrand 15 should be "fine", it's just the reservoir size still in question.

Hmmm, can the reservoir capacity be increased? I don't believe it can be too high relative to the unit casing since the unit casing would become the reservoir. The level of the hydraulic fluid in the casing has to stay consistent.

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Kent

Again, rather than risking cavitation in the Sundstand and ruining the swashplate, or frying it from overheating -- personally I'd look for a totally external solution such as a power-steering pump that has its own reservoir, whether attached or remote. Robbing enough flow from the Sundstrand to run a small, short cylinder that lifts or raises your mower deck is one thing... robbing enough flow to continually raise and dump a loader bucket (regardless of how big a bucket, how high you lift it, or how far you tilt it to dump) is something totally different IMO.

Raising and lowering an implement, whether a tiller, mower deck or snowblower is not something that you're doing nearly as frequently -- that cylinder would stay stationary most all the time... I've found that the totally separate hydrolift for the old FDTs would heat up snowblowing or tilling, because you're lifting and lowering the implement on each pass. Usually, when mowing, the deck is only lifted for transport.

Operating a loader requires almost constant operation of the lift or dump cylinders -- the only time they're stationary is during transport of the material, and then you have to maintain lift fighting potential bleed-down and gravity...

It would be an interesting engineering exercise, but I'm not sure I'd want my tranny to be the guinea pig...

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Kenzen

Great points Kent - I hadn't thought of the "duty cycle" of lifting things like tillers and decks, vs that of a loader. But I have to consider the heat load of running my tractor at full throttle for the 1.5 hrs it takes to mow my lawn, especially in summer heat. Is there a "heat-trade" for relatively stationary operations with a loader (i.e. short burst moving of the tractor), traded with the resultant heat loading of operating the loader itself? I dunno... But you are convincing me to build a more elaborate loader, which isn't a bad thing... :)

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rokon2813
quote:Originally posted by Kenzen

Good point on the valving being the factor for the different charge pump rates. I did the valving when I retrofitted the hydraulic lift kit, and there's a big charge pump pressure range to be "in spec" (75-150#???) and that would affect that flow rate.So my concern is not so much flow, because flow = speed (for a constant pressure). It can't dump any slower then my current prototype with an electric 8" linear actuator. My concern is that the reservoir level will not handle the surge or demand for fluid from the cylinder movement, and starve the charge pumpid="red"> of "net positive suction head" required to function (and then possibly eat itself). The worst case surge/demand is both the lift and dump cylinders go from retracted to extended (e.g. the lift is up in the air and dumping, and then the bucket comes down and levels), or vice versa. The reservoir has to accommodate that change in level, and still meet the charge pump (surge/suction) demands.Related to this is I'm considering using a auto power steering pump that utilizes a remote reservoir. I don't need the pressure of a "real" hydraulic pump - in the neighborhood of 1000# is fine. The remote reservoir allows me to use any size I need, and also makes the pump compact enough to mount just about anywhere. (And the cheap side of me likes the idea of a $15 pull at the salvage yard.) :)


id="quote">
id="quote">If your using double acting cylinders, ie; powered in both directions the surge at the tank will be minimal because the fluid that comes out of one end goes back into the other end of the cylinder, it does not displace any more than the piston rod itself. So even a 1" rod a foot long is only going to displace a few ounces.The problem comes with the reservoir not holding enough to allow sufficient cooling.You really can't compare the heat created by lifting (compressing the oil) with traveling at WOT mowing. Just traveling is relatively easy on the oil, since it does not require a lot of compression and the oil is constantly flowing. Unless you only mow up steep hills, or pull a heavy trailer while your mowing ;)Lifting and lowering, the oil is compressed and uncompressed, but does not actually flow constantly.My explanation might not be the best, but I hope you get the idea.

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Kent

I know virtually nothing of the specs or internal workings of a Sundstrand. But, for example, my Power Trac uses an 8GPM, 2500 PSI circuit to:

(a) steer the tractor with two hydraulic rams and a steering valve similar to the ones that Simplicity used - flow goes to steering valve first, which diverts it to the rams as needed

(b) control the two lift cylinders next, and

© then control the bucket curl/tilt/dump

(d) finally, there's an Auxilliary (power beyond) circuit that controls the Quick Attach ram or a grapple, etc.

Basically I can operate any two of those controls just fine if I'm at full throttle. The third one will slow, and the fourth one won't move at all...

And that's with an 8GPM dedicated circuit, totally separate from the hydrostat pump or the dedicated 8GPM, 2500 PSI PTO circuit. When trying to drive all three pumps, performing work, then the limitation becomes the 25HP Kohler Command... Overall, it balances pretty nicely - seldom are you using the power-robbing PTO circuit, driving the wheels, and trying to operate the lift arm controls much at the same time. Steering is still strong when using the PTO and driving, but the lift arms/bucket tilt will slow down a bit...

And OBTW, I have a 10 gallon reservoir and a 12" thermostatically controlled fan blowing through an oil cooler that's about 14" x 20" or so... Hydraulics generate a lot of heat. Perhaps as much as 5Hp of my 25Hp Kohler is getting converted to nothing but heat...

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HubbardRA

Other than for cooling and reserve capacity, a large reservoir tank also is used to allow the bubbles formed by use of the system to dissipate. If the tank is too small the pump will suck in fluid with bubbles in it and this will cause cavitation and will ruin the pump. This is why most reservoir tanks are larger in the horizontal directions than the vertical direction. The larger the surface of the fluid is, the quicker the bubbles will rise to the top and dispense the air. This is one item that most novices or first time hydraulic designers will tend to overlook.

Also, power steering pumps make great hydraulic lift pumps. I have a friend who has two homemade tractors with full hydraulics, he even has trailers with hydraulic dump setups on them that connect to the tractor through quick disconnects. He uses only power steering pumps to drive the hydraulics on his tractors. Most of the older ones are around 2 gal/min at around 1500psi. This should be totally adequate for most garden tractor uses.

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Kenzen

Excellent feedback! And I like the size/design of that loader Bob! Most of the loaders I see on garden/lawn tractors seem too big and over-engineered for what the tractor should be handling - yours seems to be a more appropriate scale.

Ronkon2813 - "exactly" on the fluid displacement calculation/consideration. And note that on a power steering system (with rack-and-pinion steering), there's a piston rod on both sides of the piston, so there's no change in displacement as the car rack is moved. This concerns me when considering a power steering pump with an integrated reservoir - it's designed to this lack of displacement.

I'm going to seriously look into the power steering pump solution, mostly because it seems to internally solve a lot of the external plumbing challenges a "normal" pump doesn't address (e.g. pressure relief).

Thanks all!

Ken

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BLT

I think with power steering, hydraulic lift and end loader, you'll need three return lines or manifold into one. I don't think Sunstrand has capacity to handle loader and steering. The unit I helped with had a 10 GPM cartridge in the pump and even at idle had decent lifting. I havw a 1691021 power steering kit that I am going install on one of my tractors when it gets warmer out.

I just looked at a Sunstar end loader and it has its own pump.

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Kent
quote:Originally posted by Kenzen

Ronkon2813 - "exactly" on the fluid displacement calculation/consideration. And note that on a power steering system (with rack-and-pinion steering), there's a piston rod on both sides of the piston, so there's no change in displacement as the car rack is moved. This concerns me when considering a power steering pump with an integrated reservoir - it's designed to this lack of displacement.


id="quote">
id="quote">

Well, technically the only change in displacement on a double-acting cylinder is only the volume of the connecting rod that goes to the piston, when fully retracted. The volume of the extend side is slightly larger than the volume of the retract side because that connecting rod occupies part of the space. Consequently, a cylinder always has more power to lift than retract...

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HubbardRA

Kenzen,

The subject was brought up about using a power steering pump with a built in reservoir. Most American power steering pumps, at least on Fords and Chevys have a removable reservoir. I have replaced some that did not come with a reservoir and you had to use the one from the previous pump.

Anyway, if the reservoir is removed, there is an intake port to the pump inside the reservoir. Sometimes it it threaded, sometimes not. You can just tap that port and install a hydraulic suction line directly to the pump and then the reservoir can be located elsewhere. This allows for a larger reservoir for use with the larger cylinders.

Of course return lines must go back to this tank, not to the pump. Since air rises to the top of a fluid, and the only portion of the fluid that is in contact with air is the top, any foam caused by fluid flow will dissipate only on the top of the fluid volume. The return fluid should dump into the top of the tank for foam dissipation, while the fluid going to the pump should come off the bottom. As air leaves the fluid it becomes heavier and sinks to the bottom while the fluid with air in it floats to the top.

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D-17_Dave

One simple way to increase the tank size on a power steering pump is to place a large diam. rubber hose over the filler spout instead of a cap. run the hose up as high as desired and add a tank to the hose as large as needed. the need then becomes proper venting so the large flow can move the oil in or out of the reservoir so as to not starve the pump.

Most general hydraulics systems have 3 times the pumps flow rate in reservoir capacity.

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