03/14/14
OK class, pay attention, no sleeping.
Most of my writing is to other readers then the OP, who what to go deeper.
If you can hang in here, bring the teacher an apple or a beer.
I was able to open the service manual/schematic file last night at home, but can’t during day.
First, kudos to Ryan company for a good actual schematic with tech info. Most consumer product ‘schematics’ are a couple boxes with hoses connecting them. This was great.
ENGINE: ‘rated 18 hp’ is at 3600 rpm, but high idle setting is 3150 I think. So right off the bat, they are doing marketing BS, and you have about 15 or 16 hp, assuming the same torque. That is still not shabby.
One question was no aerator drive shown, but you answered that with chain drive.
Single drive motor to differential, 16.4 in3/rev. Need sprocket ratios and wheel diameter and machine weight to calculate max speed and maximum drawbar pull, but not really part of this discussion so ignore.
ISO 68 oil, typical for hot use. Good choice for the OEM. You might want ISO 46 if you use it in cooler weather. Try the 68 and see.
CHARGE PUMP is 0.33 cubic inches per revolution. 0 .33 x 3150 rpm (direct drive?) = 1040 cubic inches per minute. Dividing by 231 in3/gallon = 4.5 gallons per minute at 100% efficiency. Say 4 gpm at 90% efficiency out of the cylinder/charge circuit at full rpm.
HYDROSTATIC PUMP is 0.91 in3/rev (or CIR) at maximum stroke. X 3150 divided by 231 = 12.4 gpm, so just under 12 gpm at maximum swash plate and reasonable efficiency and full engine rpm.
PRESSURE is determined by the load resistance, not by the pump. A positive displacement pump (centrifugal water pumps are totally different theory) moves a certain volume of liquid against a motor or cylinder resistance. Flow rate, determined by the pump, creates motion and speed of the cylinder or motor. The REQUIRED pressure to move that load is put into the fluid by the engine pushing on it at the pump end. So your 6 mph speed on flat concrete might be 1000 psi of pressure, but rise to 2000 or more going up a hill, then back down when the load decreased.
The MAXIMUM pressure the system will produce is limited by the lowest of several factors:
1. Torque of the engine to turn the pump shaft and not stall the engine. In this case, at maximum pump output 15 hp and 12 gpm, the engine would probably do about 1400 psi max before stalling. However, if the pump was at a smaller displacement, lower flow output, the pressure can be higher. At half pump stroke, the engine should drive to 2800 psi or so, and so on as the pump stroke decreases. Its fairly easy to stall out a small skidsteer at maximum speed when you come to a grade with \full pump sttroke, but when the pump is almost at neutral and pushing into a pile it will reach high pressures without putting much load on the engine.
2. A relief valve (see below) LIMITS, not creates, the maximum pressure. It is like a fuse or circuit breaker except that it opens to pass flow out of the circuit, instead of tripping to interrupt the supply of electricity into the circuit. Flow starts relieving out at the ‘cracking pressure’ setting. Pressure in the circuit rises as the flow across the RV increases. (side trail- If all flow is going across RV, a typical log splitter control valve will rise 200-400 psi.)
3. Controls on the pump, if pressure compensated. This one does not have any pressure controls, and no pressure limiter or relief valve on the drive loop. I assume it is direct stroking with manual lever onto the shaft on the side of pump. Then it would have an increasing pushback against the manual operators lever as the pressure and volume increased. That force would either tell the operator subconsciously to back off, or it may push back hard enough that the operator cannot physically hold the pump on stroke at that pressure.
4. Spin the wheels or move the load. May stall out on dry concrete, but spin out in mud.
5. Mechanical limits. Blow up a hose, motor or pump housing. Not a good thing.
-Most L&G equipment is limited by the pushback against the linkage. Basically, the operator is the pressure compensator.
SMALL RELIEF VALVE marked 90-150 psi determines maximum charge pressure needed to make up leakage in the pump or motor, and the rest can go onward to the open center condition of the cylinder lift valve at top of page, then back to tank. When the cylinder is lifted, the small RV holds the charge pressure from dropping below 90-150 even if the cylinder could move freely at very low pressure.
RELIEF VALVE 700-1000 is the limiting pressure to the lift cylinder. If the valve is shifted, the path to tank is blocked, but if the cylinder cannot move and take any flow, the oil flows out this RV to tank. The pressure at the cylinder will then be (700- to 1000, whatever the setting is) minus (90 to 150 setting drop across the small RV). Note: the charge pressure would go to about 1000 psi during the cylinder max pressure, so the travel pump has to be designed for that, but that is easy enough.
RELIEF VALVE AT CYLINDER VALVE 2000 psi. I am not clear on that one. Pressure cannot reach 2000 because flow would go out the 700-1000 RV first. So the cylinder pressure WILL NOT be 2000 psi. I suspect it functions if the cylinder kicks back up, say driving over a high mound where the aerator pushes back upward more than normal. The oil can’t go back through the RV90-150 backwards, so it is trapped and would compress to high pressure. The RV 2000 I think relieves that excesspressure to tank. I have done that sort of thing many times to resist a high backwards load when it does not need to push down so hard normally.
CYLINDER You are getting the terms sorted out, but were confusing at first.
These are ‘cylinders’. They can be single or double acting. A ‘ram’ is always a single acting cylinder but does it not have a piston with seals around it. Rod is the same length all the way along, and is only sealed around the rod itself at the outer end, like a porta power ram.
The shiny chrome thing is the rod. Its diameter is ‘rod diameter’, that is not the size of the cylinder.
The ‘bore’ is the inside diameter of the tube, which is also the outside diameter of the piston that fits inside the tube. Piston is on the end of the rod. Pressure on the full area of the piston on the ‘closed end’ pushes out with pressure against the full area and the rod extends. When pressure is on the rod side, pulling back in, the only effective area is the space between the ID of the tube and the OD of the rod. The area of the rod steel is not being acted upon by pressure. So retract force will be less than extend force, but speed will be greater.
The distance the rod moves pushing and pulling is ‘stroke’.
The cylinder itself can have any size of tube od, only the ID matters for force. The length of cylinder can be anything, stroke can be much shorter than the overall length, so the actual stroke is the real number that matters for calculations.
So, you said the rod was about an inch, so if I guess one cylinder with a 2 inch bore, 1 inch rod, and 3 inch stroke, the 4 gpm charge circuit diverted to the lift should move the 3 inches in less than a second at full engine rpm. Couple seconds at half engine speed. You said a couple seconds to lift, was that at full rpm or half speed? This seems to match up ok.
Now, looking at options:
1. Use the lift circuit to move a 4 bore x 20 stroke x 2 rod typical shorter splitter cylinder. (24 inch stroke just takes 24/20 ratio longer to move the longer stroke)
a. 4 gpm is very slow. 16-18 seconds out. similar to retract.
b. 700-1000 psi of the RV setting is only 5 or 6 tons of force.
Don’t think you would be too happy with either of those results, especially with 16 hp engine running full rpm.
2. Use the HST circuit, (through the 6 port selector someone posted above to change from travel to cylinder function) on the same 4x20x2 cylinder.
a. 12 gpm would be better, about 5 or 6 seconds extending a bit less in retract.
b. When extending, less oil comes back from the rod side than is going out to the closed side. Depending on the rod size, and the sized of the two charging check valves shown into the A & B sides of the hydrostatic loop, the 4 gpm charge flow ‘might’ keep up with this and hold charge ok. I’d have to know more about circuit and rod size. If it doesn’t keep up, and you lose charge pressure, pump life would be shortened. If charge drops seriously with each cycle, pump life could be minutes or hours, not days or years.
c. If the charge does keep up in the extend direction, then it has to absorb that difference in flow in retract direction. Since the charge oil goes in through the two charging check valves shown in the loop, there is no way out of the loop other than leakage. The oil being compressed on the closed side out would lock up the motion of the cylinder, or cause a situation known as ‘intensification’ that creates a much higher pressure in parts of the circuit than you started with in other parts of the circuit. Not good.
There are ways to tell the circuit whether the closed side is supposed to be pushing, and don’t let anything out, or if is supposed to be retracting and to let out the oil so it doesn’t lock, but that is way more complicated than you want to hear about.
d. Even with all this, the engine hp would stall out with 12 gpm at 1400-1500 psi, so your force would be about 8 tons.
Don’t think you want this option either.
3. Add a two stage pump to the other end of engine and build the splitter on this frame package.
You could use the full gpm for speed, unload for high pressure and force, and use all of the engine hp available. Might be able to use the existing tank, but would take larger lines, hoses, ports, etc.
Some other things you might consider:
4. Buy a regular splitter and tow it around with this power unit.
Easiest, probably cheapest, but it would bother me to run a 5 or 8 hp splitter knowing the 16 hp was sitting there unused. I don’t want more force, I want more SPEED.
5. Build a dump box on this thing using the 1000 psi 4 gpm circuit and a much larger cylinder. Then you could tow the splitter with this, go get rounds, split wood and put it back in the dump box, and pull the splitter home.
6. Take the 16 hp engine out and build your splitter as usual with that engine, and scrap the rest
Personally, assuming with limited funds, I would buy a good used splitter, start with option 4 and get some work done. Then, as a fun project, build the dump box option 5.
If more money was available, I would do option 6, but buying larger pump, hoses, control valves, beam, etc all cost more than the normal 11 gpm range of components.
Being realistic, not kidding anybody, I would really do option 4, work on dump box 5, and collect parts slowly and cheaply towards option 6, Then, if no other big motor comes along when I have accumulated all the parts, I’d do option 6. If I found another motor cheap to run the splitter, or to put into this thing with smaller motor, it would be nice to keep option 5 as a small wood hauler and splitter towing machine
.
It would be fun project any way but options 1 or 2. I think they are doomed.
Curiosity, at the end of the manual, WHY does it call out listings for two cycle oil, and 10 and 25 lb kegs of lapping compound? Must have gotten in there from some of their other machines. Maybe concrete grinding or polishing or coring or something.
Out, kcj
