PSI of splitter's return line

[leon]

log splitter-ugh!!!

Actually a 60HP PTO diesel. But it loafs at the job. I run it at 1500RPM and it sounds like its running at fast idle. The pump never loads the motor at all even when I'm on the relief valve. 21GPM and 2200PSI.

Ok before this goes any further;

The pump and valve body are heat sinks as they will shed off as much heat as is physically possible simply due to the job they are doing.


You are most likely running the pump revolutions per minute too low, where is the relief valve in the system?



If the relief valve is fully open it will not place a load on the pump; it will create additional heat load as it is passing through the relief valve.


175-180 degree "OIL" is fine-if it is "HYDRAULIC OIL"

Do not lose sight of the fact that there is a "minimum amount of oil" entering your cylinder and leaving it. so that oil always stays there.

The hotter your "hydraulic oil" the more efficient the hydraulic system-no matter if its a front end loader/log splitter etc.

Buy a bigger tank with an oil baffle in it-this slows down the oil and reduces the amount of air possibly entering the pump and valves.



opcorn: :spam:

As I mentioned on a previous posting the addition of a race track configuration of check valves and hoses which will allow oil to exit the cylinder ports and retun back to tank will heat the oil much quicker and maintain temeperature with out temperature spikes and the splitter will be more efficient.

 

[wkpoor]

Hold on Leon! I think you got a little off track no thanks to me. I'm not having any temperature problems at all. I was only posting in response that I have a fairly good sized pump working under some pretty demanding conditions and it is still running cool. And that when my system hits the relief setting I'm pumping 21gallons through it at 2200PSI which is probably 10-20 times that of a normal setup (2 stage pump ). Therefore the possibility for heat is great but with a large reservoir I have no problems at all. It stays nice and cool. I can regulate the temperature with the amount of oil I run. I'm now at 15gals and the cylinder is warm to the touch say maybe 100-125 degrees.

 

[leon]

log splitter

Hold on Leon! I think you got a little off track no thanks to me. I'm not having any temperature problems at all. I was only posting in response that I have a fairly good sized pump working under some pretty demanding conditions and it is still running cool. And that when my system hits the relief setting I'm pumping 21gallons through it at 2200PSI which is probably 10-20 times that of a normal setup (2 stage pump ). Therefore the possibility for heat is great but with a large reservoir I have no problems at all. It stays nice and cool. I can regulate the temperature with the amount of oil I run. I'm now at 15gals and the cylinder is warm to the touch say maybe 100-125 degrees.

Sorry if I misunderstood you.

 

[cityevader]

125 F tank is not bad (if that is tank temp also. Check that first.)

If the issues was tank size only, not dissipating enough heat, the entire system would heat up evenly. The control valve and relief valve may be hotter, and the pump slightly hotter, but only maybe 10-20F above the tank average temperature.

Any local hot spot indicates fluid bypassing under pressure and causing heat.

If pump is significantly hotter, it may be losing efficiency and leaking internally, or the unloading valve may be acting up.
Run it at high engine speed, no splitting a while and see if the pump cools down a lot. Meaning, under almost no pressure, there is very little leakage/heat in the pump.

Without a flow meter is it hard to measure a two stage pump, but basically you have to compare the unloaded speed with the speed when on load, but before it shifts into low speed. The difference is leakage. More than about 15% leakage (85% efficiency) indicates worn pump.


K

I've got minimal knowledge of hydraulics, so bear with me. I can visualize cavitation as perhaps lack of flow in the suction side? But bypassing? If the pump has a single hose in and a single hose out, how can it bypass? I've no idea what/where an unloading or relief valve is/does. I can visualize a pressure relief dumping fluid elswhere, but there are only single push/pull hoses with no additional "dump" hose.... holy mackerel, I'm a 13-yr master Ford tech and can barely keep from describing something as a doo-hicky!!

I've only run 2 gallons of gas through this thing, so wear seems less likely. I'll try to get a sold chunk of wood and a decent stop watch and check it out, then call Harbor Fright.

I wish I didn't go through all my wood so far, nothing to put a suitable load to measure times of travel, only some easily split straight grain oak...hmmmm, maybe i'll put a spongy section of redwood in sideways and see if it'll stain first or kickdown into second.

 

[wkpoor]

I've got minimal knowledge of hydraulics, so bear with me. I can visualize cavitation as perhaps lack of flow in the suction side? But bypassing? If the pump has a single hose in and a single hose out, how can it bypass?

If the pump were 100% efficient then all the fluid coming in would be going out. Of course that is not real world. Imagine a set of gears slipping against the fluid so say 95% of the fluid is going out instead of 100%. That slipping is the bypass internal in the pump that accounts for the loss on the output side.

I've no idea what/where an unloading or relief valve is/does. I can visualize a pressure relief dumping fluid elswhere, but there are only single push/pull hoses with no additional "dump" hose..

Most of the time it is intregal to the control valve. Somewhere in the control valve casting there is a port with a valve and preset spring pressure to allow fluid in excess of the preset to return out the return hose. This can easily be seen on a pressure gauge.

 

[cityevader]

So I'm assuming these pumps are similar to car oil pumps, with two gears meshing, and where they squeeze together the pressurized fluid shoots out a port in the side? So "bypassing" would be in the tiny space between the side of the gear and the pump case then? I still don't understand how that can create additional heat within the pump.

Can I back-track? Bottom line question...how hot is too hot, and where should that measurement be taken? Fluid within the reservoir? External housings of pump or cylinder? In cars, a temp sender is located before the fluid goes out to be cooled...but that means nothing at all here.

 

[cityevader]

If the pump were 100% efficient then all the fluid coming in would be going out. Of course that is not real world. Imagine a set of gears slipping against the fluid so say 95% of the fluid is going out instead of 100%. That slipping is the bypass internal in the pump that accounts for the loss on the output side.
QUOTE]

ohhhhh, thought about it some more. OK...So if the fluid, for lack of better words backs up as the gears close, squirt backwards instead of forward, so that the compressed/heated fluid is recirculating in the pump instead of shooting out cool fluid flowing in?

Even with a "normal" running machine, I imagine the temp increase after being compressed so much would be more than 20*F? Does anyone have a "normal" splitter who could take a couple temp readings in various locations?

 

[Jkebxjunke]

I just found a quick and dirty explanation at these sites :

http://science.howstuffworks.com/hydraulic2.htm

http://science.howstuffworks.com/hydraulic3.htm

 

[kevin j]

pump: yes, like a car oil pump, two external gears side by side.
I sent you a pm for an email address, I can send you a file on how they work.

Assume 10 gpm comes in the oil pump/hydr pump. perfect world, 10 gpm goes out. Energy is added from the engine to compress 10 gpm of oil to say 2500 psi under a load.

Real world, the gears have side clearance, and tip clearance. So 10 gpm, maybe only 90% goes out, or 9 gpm outlet. The other 1 gpm leaks around the sides and tips back to the suction side. If you measured flow in the suction hose it would actually only be 9 gpm, because the 1 gpm going around back to the inlet. So inlet hose is 9 gpm, pump moves 10 gpm, 1 goes round and round, and 9 goes out the pressure hose.

Then engine still compressed that full 10 gpm to 2500 psi. 9 gpm goes to the cylinder and does mechanical work splitting wood (exlcuding some pressre loses in valves and fittings, which turns to heat). The 1 gpm leaking around the gears goes from 2500 psi to 0 psi, but does not do any work.

Key here: any time high pressure fluid goes to low pressure WITHOUT taking energy out in work, the energy is converted to HEAT. Just the physics of the world we live in. That heat is created by pressure drops in lines, in leakages, in cylinder seals and across a relief valve dumping over pressure to tank.

1 gpm of leakage is no big deal. But if you were leaking say 4 gpm, you have 4x as much heat being created.

That's why I think the tank size is not the focus, nor the solution, here.
I think something is generting too much heat.

Yes, 175 F is not excessive for petroleum, but it is borderline for oil and viscosity. I design for about 125-140 F maximum tank temperature. Above that, oil life is shortened, and the viscosity can become too thin. 140 tank temperature may mean 200F case temperature in industrial equipment.

More importantly, a simple circuit like this should NOT be generating enough heat to drive even a small tank to 175 F. Especially if it was working more normally earlier in its life.

 

[cityevader]

Again, tank temp is not 175*, only the pump. The ram and valve were at 125*f, and i didn't measure the tank, but felt a little cooler that 125*.

That is where my confusion lies, without having measured stroke time loaded/unloaded, I certainly cannot rule out pump issues, but if the tank stays at 125* after say, a couple hours, would it be alright then, regardless of pump temp?

Will try to round up some rounds for further checking.

 

[wkpoor]

Real world, the gears have side clearance, and tip clearance. So 10 gpm, maybe only 90% goes out, or 9 gpm outlet. The other 1 gpm leaks around the sides and tips back to the suction side. If you measured flow in the suction hose it would actually only be 9 gpm, because the 1 gpm going around back to the inlet. So inlet hose is 9 gpm, pump moves 10 gpm, 1 goes round and round, and 9 goes out the pressure hose.

Actually I would tend to think a pump's rating factors in any slippage or clearance issues. So a 10GPM should be that or more in good working order.
Don't forget there more pump designs others than gear type. Vane type and piston are 2 others. Then there are pressure compensating pumps to add to the mess.

 

[kevin j]

a pump's rating factors in any slippage or clearance issues. So a 10GPM should be that or more in good working order.
***nope, the theoretical displacement is given in cubic inches per revolution, or cc per revolution, at 100%. Then, with rpm, and given that 231 cubic inches is one gallon, the 'rating' of 11 gpm or whatever is determined. Of course, that is at (usually) 3600 rpm, but not always given. Thus the sizing by in3/rev.
Then, the mfr charts output gpm vs. pressure and rpm and oil viscosity and other variable, but usually for gear pumps, 85 to 90+ % efficiency is normal.
So when Northern or whoever advertises a 11 or 22 or 28 gpm pump, under actual testing it will be maybe 9.5 or 19 or 25 gpm to the cylinder.
It's only when excessive leakage occurs that the flow drops off and heat is generated.
If your tank is 125 F, and pump is 175 F, I think a pump problem. But first, take out the unloading valve and check valve in the pump and make sure they are not acting up due to bits of dirt or junk.


Don't forget there more pump designs others than gear type. Vane type and piston are 2 others. Then there are pressure compensating pumps to add to the mess.
****Good point. Internal, external gear, gerotor, etc. Almost always though, cheap consumer stuff will have two shafted spur gear pumps. Cheap to make, durable, subject to abuse, etc.
Cheap vane pumps are a bit pressure limited. Getting high pressure and low leakage with vanes takes precision parts and materials which cost money. Vanes also need better antiwear hydraulic oil. They are smooth and quiet though. Also not so good at high rpm.
Piston pumps most efficient, many advantages, most industrial pumsp will be piston type. but a 10 to 20 gpm piston (fixed displacement) will push $1000. A variable one more than that.
pressure compensated is great for adding other valves in parallel. Just plug and play. But needs a closed center valve, and under the load cycle of a log splitter are actually not as energy efficient as a simple fixed gear pump.

sent you a file


k

 

[wkpoor]

The prince pump I'm using to power my splitter is probably a vane type. They advertise it as wear compensating which to me means its basically an air motor that runs in oil. It makes alot of volume at a slow RPM. And yes pressure is limited to 2200PSI per prince. Still I couldn't be happier with its ability to do the job. They aren't cheep though!