Oil tank for splitter

[kevin j]

Both!

Purpose of having the tank higher is to increase the head pressure on the inlet. Same reasons why suction should be large, straight, without a filter, and strainer oversized if one is used. When pressure drops too low at the pump inlet the fluid can cavitate in small local bubbles. Cavitation is a bit of fluid basically 'boiling' by turning to vapor at low temperature and low pressure. When the bubble gets compressed through the pump, the vapor bubble collapses and the shock wave causes an impact on the metal surfaces of the pump parts. Very much like detonation in an engine. If you tap on a metal surface with a molecule sized hammer long enough, eventually a piece of metal fatigues and flakes off. Enough molecules come off and eventually the pump has pit marks. An engine piston gets the sandpaper looking marks from detonation. A pump part will show the same microscopic pits due to cavitation. Usually it doesn't matter in noticeable performance. By the time the pump fails and is removed from service, the other damages are so great the cav marks are not noticeable.

Cavitation is not the same as sucking air, but the higher suction can also draw air into bad joints. Doesn't seem like much, but a few inches of mercury vacuum is about what most pumps can tolerate and a couple feet of tank height helps a lot.

More important for mobile equipment because it runs outside in colder weather, and typically is gas engine drive at higher rpm. There is much less time for the tooth to fill as the pump turns, so has to have more head pressure to push the oil in. The obvious solution there is reduce speed until the oil is warmer and flows easier. Note: cavitation is NOT noticeable in flow output. It occurs long before the flow is reduced. If the oil is really thick enough for things to work slow, that is obvious. Cavitation doesn't hurt at cold start if it only happens for seconds or minutes at slow startup.

Industrial stuff is typically on top of tank for convenience in layout, less floor space, easier to work on, less mess when changing pumps. Also usually runs 1800 rpm electric motor speed, and more constant temperatures inside a building. Some use the L shaped mount where the pump/motor is beside the tank, but takes more floor space, which is expensive space in most factories.

It is good practice, but NOT required by any means. How many mobile and industrial pumps are mounted above tank level? Most of them...

It does make the 'priming' issue more important though. A positive displacement pump will prime. It is not like a centrifugal water pump that simply runs forever spinning in air if the housing is not primed. So actually 'priming' is not the main issue, it is lack of lubrication during startup. In most cases the oil left in there from manufacturing or testing is enough to lube it for a few seconds. Maybe this machine had oil suction leaks and lost its 'prime' over many years of storage and started dry. Maybe it is just coincidence and the pump just failed.

I really stress putting oil in the pump inlet and outlet for that lubrication on startup, and filling the case of piston pumps or hydrostatic pumps/motors. They won't fail immediately, just shortens the life a lot and somewhere down the road the mechanic wonders why pumps are failing in a year instead of 5 years. Of course, a year of mobile equipment life may be 25 years of logsplitter life so many of these concepts don't matter that much in real life in this board.

Anyway, sounds like pump is toast, can be changed in half hour for less than $200 and life is good. Way better than changing some 700 pound, $25,000 hydrostatic pump, Course that is not 'personal money'....

k

 

[wireedm]

Enjoyed reading your thread Kevin. I just love getting into the physics of how things operate.

I do have a question: There is an earlier thread that mentions hydraulic oil getting hot because of the flow in the small and large lines (to sum it up). I always had the understanding that the heat buildup was from the pump trying to compress the oil under high loads, thereby "squeezing" the molecules, causing the heat. Sort of like an air compressor creates gobs of heat by compressing the air. The same concept of how a heat pump works. I do realize that a gas easily compresses (even to the point of becoming a liquid), and that technically a liquid doesn't compress (although I would argue the point). But, one can squeeze the molecules into moving faster, which in turn is heat.

One simple reason I would argue that a liquid can be compressed, although small, is that the heating and cooling of a liquid will EASILY change it's volume. Is my reasoning correct?

Seeing that you are a mechanical engineer with an emphasis in hydraulics, shed some light on this please.

 

[triptester]

Compression in itself does not cause heat. Friction during compression causes heat.It is the velocity while under pressure that is the cause Example , a rope held tightly in your hand will not cause heat but if that tightly held rope slides in your hand you will end up with rope burns.
Fluids or even air under pressure at high velocity through hoses or any restriction will cause heat.

 

[wireedm]

Compression in itself does not cause heat. Friction during compression causes heat.It is the velocity while under pressure that is the cause Example , a rope held tightly in your hand will not cause heat but if that tightly held rope slides in your hand you will end up with rope burns.
Fluids or even air under pressure at high velocity through hoses or any restriction will cause heat.

Is 13 gpm considered "high velocity"?

 

[cmetalbend]

Home built tank from scrap steel for my splitter. If you have the time and can weld. No torch or good grinders? Take your scrap to a fab shop and have it sheared to your specs.

Nice job, interesting color choice.

 

[kevin j]

trip answered it good analogy.

Pressure itself is not heat. Energy isn't created or destroyed, just converted back and forth in forms. Compressing a gas or liquid is not necessarily heat. (Although a compressor gets hot, that energy in theory comes back when air is expanded and it gets cold. Way more complicated topic.) The engine/pump puts energy into the fluid via compression. That energy comes back out in a motor or cylinder. As long as it does actual work, (force and motion tearing wood or moving a load), it does not go to heat.

No process is 100% efficient. Energy in the oil goes to heat if that mechanical energy is converted to friction (steel on steel rubbing in the pump or cylinder, or brakes, or rubbing the gears and shafts inside the pump) of if the pressure is dropped through, basically, ‘fluid friction’ of pushing it through a tube or orifice. A gear pump idling at 200 psi is converting that 200 psi into heat as it does no work. One stalled across relief at 2500 psi is converting ALL that 2500 psi of energy into heat. That can be the entire 5 or 10 or 16 hp of engine power going to heat. Wrote about that earlier as a main cause of system overheating.

Think I posted some charts earlier. Rather than figure all the fittings and pressure drops (few engineers do that on day to day basis), the rules of thumb are about maximum of 10 to 15 feet per second velocity on fairly short pressure lines, 2 to 4 feet per second on suction lines. Very loose, but at least a guide.

A system pushing 13 gpm through a huge two inch hose at 10 psi pressure drop would have very little heat produced. Pushing 13 gpm through a 1/4 inch hose extreme at 2000 psi drop is converting (13 x 2000 /1714 ) = 15 hp of heat, or 11 killowatts of heat. It is not the actual pressure but the ‘pressure drop’ that goes to heat. Granted, at high pressures, more leakage in pump gears, through valve spools, etc and there is more heat there. That is also pressure drop across leakages that is not doing work.

13 gpm in half inch (-8) hoses is 20 feet per second, workable but high. Since the outlet of the cylinder in retract may be at 15-18 gpm when 13 gpm goes into the rod side, I would use -10 or -12 hoses, not -8. 13 gpm in -12 hose is under 10 ft/second for example.

How much is too much? Only depends on fuel and heat and what you are willing to pay. The circuit still works fine, just requires more engine hp to push it around and convert that energy to heat. Typically, small gear pump logsplitter at high idle in neutral is maybe 100 psi to move oil in a circle? 200, 300 psi not unusual, but 25 and 50 is way better.

Don’t want to make it overly complicated. Use the biggest lines you can, sweeping turns and minimal fittings, and large ports.

Topic for another day, but that is also why flow controls, priority dividers, and tapping one circuit out of another can bite you for heat. The controlled side may do work, but the other side is a heat generator from the throttling in the divider.

kcj

 

[triptester]

wireedm,

When you consider that most splitter pumps are rated at 3600 rpm's and it is only moving a fraction of an ounce per revolution, yes it is high velocity, and the velocity increases anytime the fluid passes through a restriction. Restrictions can be the relief valve or openings in fittings that have a diameter smaller then the hose.

 

[eric_271]

Nice job, interesting color choice.

Thank's. As for the color I decided on JD green and called the local paint store to mix it for me. When I got home with it and opened it I thought no way so I went back and got a small can of dye to change it and boy did I, lol. I think I will call what I ended up with ''nitrogen rich green'', real rich for sure. I should of stoped while I was ahead if I ever was.