Cylinder Pressure

[Millman]

I have a home built splitter that we bought a couple of years ago and fixed it up so it runs pretty good. We had to replace the engine, pump, hoses, tank, add a filter assembly and finally replace the control valve. The question I have is about my Cylinder. It is 6" in diameter and has a 5" rod. When I put a gage on it to measure the output, it take about 400 PSI to start and push the rod forward. On the back stroke, it shoots up to 1200 psi or so. I am guessing from the diameter of the rod, there is less surface area for the hydro. to push against the seals. Normally I see a 2 to 1 ratio of rod size to diameter. Here is a picture of the cylinder. We are currently rebuilding the thing again. Any thoughts as to why????

Millman
MS310
346XP soon I hope!
:spam:

 

[leon]

cylinder

I have a home built splitter that we bought a couple of years ago and fixed it up so it runs pretty good. We had to replace the engine, pump, hoses, tank, add a filter assembly and finally replace the control valve. The question I have is about my Cylinder. It is 6" in diameter and has a 5" rod. When I put a gauge on it to measure the output, it take about 400 PSI to start and push the rod forward. On the back stroke, it shoots up to 1200 psi or so. I am guessing from the diameter of the rod, there is less surface area for the hydro. to push against the seals. Normally I see a 2 to 1 ratio of rod size to diameter. Here is a picture of the cylinder. We are currently rebuilding the thing again. Any thoughts as to why????

Millman
MS310
346XP soon I hope!
:spam:

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If you have not taken it apart yet- take it to a hydraulic rebuild shop and ask them to test it on their test bench to see if it is blowing oil past the seals.

You may have a bad seal in the valve spool which will cause presssure loss problems as the oil will go back to tank rather than the work port of the cylinder.



My not knowing if you have a piston with a two seal piston or a compression piston packing gland or a piston with a metal piston ring is another matter.
You may have a cut o-ring in the piston area between the inner bore of the piston and the cylinder stem.That in its self will lose a lot of oil pressure in a hurry.

The larger the piston rod the faster the retract speed as the volume of oil on the rod side of the cylinder occupies more area and take up more cylinder space and reduces the amount of oil in that side of the cylinder.

You may be dealing with a cylinder bore that is worn beyond an acceptable tolerance and the oil is simply passing by the piston packing seals with little effort.

leon:notrolls2:

 

[mga]

I have a home built splitter that we bought a couple of years ago and fixed it up so it runs pretty good. We had to replace the engine, pump, hoses, tank, add a filter assembly and finally replace the control valve. The question I have is about my Cylinder. It is 6" in diameter and has a 5" rod. When I put a gage on it to measure the output, it take about 400 PSI to start and push the rod forward. On the back stroke, it shoots up to 1200 psi or so. I am guessing from the diameter of the rod, there is less surface area for the hydro. to push against the seals. Normally I see a 2 to 1 ratio of rod size to diameter. Here is a picture of the cylinder. We are currently rebuilding the thing again. Any thoughts as to why????

Millman
MS310
346XP soon I hope!
:spam:

really????

 

[Moss Man]

With a cylinder that big, you must be popular with the ladies! :deadhorse:

 

[Zodiac45]

With a clylinder that big, you must be popular with the ladies! :deadhorse:

LOL! Yep that's a massive cylinder for splitting firewood! Bit of overkill honestly. What the pump and motor set up?

 

[Millman]

But if i have a bad seal and oil was blowing by, wouln't the pressure be less and the rod retract slower?

I have a 9HP Robin engine with a 16 GPM pump. If you look at the picture, by the way the return port is made with the long tube welded to the cylinder, it looks like it might have been a single acting that someone made into a double.

Millman

 

[mga]

But if i have a bad seal and oil was blowing by, wouln't the pressure be less and the rod retract slower?

I have a 9HP Robin engine with a 16 GPM pump. If you look at the picture, by the way the return port is made with the long tube welded to the cylinder, it looks like it might have been a single acting that someone made into a double.

Millman

i has a cylinder like that once. that welded tube had a valve in it. i believe it acted much like a two stage pump, where the fluid would fill rapidly, then, when pressurized, would fill slow....at least that's what i thought. it had a spring and ball type valve in it. i guess it acted like some by-pass or something. but, it did work great.

i threw it out because someone bent the rod on me. but, it's servicable via the inside...if i remember right. maybe it's stuck and that's why you're getting different readings?

 

[boostnut]

I feel sorry for that old chair.

Is there any reason you run such a large cylinder? I've never split huge chunks of elm but thats about the only reason I could justify using such a large cylinder. Replace it with a 4" to 5" cylinder and watch your cycle times skyrocket.

 

[leon]

cylinder

But if i have a bad seal and oil was blowing by, wouln't the pressure be less and the rod retract slower?

I have a 9HP Robin engine with a 16 GPM pump. If you look at the picture, by the way the return port is made with the long tube welded to the cylinder, it looks like it might have been a single acting that someone made into a double.

Millman

If it had a pilot operated check valve it would be a large square block welded to the cylinder tube.

Single acting cylinders have one oil port only and an air vent on the rod side unless it is a telescoping cylinder.

leon

 

[kevin j]

the pipe is just to relocate the hose connection away from the battle zone. Appears to be no valve block on the rod end.

The pressure to move seems excessive for that size bore. Is there internal rust or damage?
Rather than spend any money, I'd ebay it and buy a 4 to 5 inch one for the splitter. Seems awfully big, and you have to design the structure to withstand the forces, thus the entire size/weight/cost escalates.
Backingoff pressure of course would work, but then you are still stuck with big flows or low speeds.

 

[Millman]

Thanks guys. As far as I know there is no internal damage, of course I haven't had it apart. I might take it up to a repair shop in Rochester and have them check it out. As far as e-baying, my partner in crime is a 78 year old fellow who still cuts, bucks and splits his own wood and of course he likes the cycle time nice and slow. Cycle time really isn't bad, I only have to extend the cylinder about 1/3 to 1/2 before the wood splits.

The Cylinder came witht the splitter we bought 3 years ago. we are now doing some major overhauling and will post some pictures. when we are done.

Greg

 

[Crofter]

It does look like it might have been born as a truck hoist cylinder. 6' makes it a bit slow but not excessivley with a 16 gpm pump; with a 5" shaft, return will be snappy. I agree that the starting pressures seem a bit high but the forward and retract pressures are in the right relation considering relative area. It depends on how tight and long of a packing was used on the piston what the pressure will be to break it loose. If the splitter is already built to fit it, it might be worth a peak inside to make sure it is not all rusted up or scored.

 

[AKKAMAAN]

When I put a gage on it to measure the output, it take about 400 PSI to start and push the rod forward. On the back stroke, it shoots up to 1200 psi or so. QUOTE]

1200psi is a lot of pressure for idling the cylinder...you have 8.5 sqinch on the rod side, which is a pulling force around 10200lbs, 5 tons.
400psi on the capped side, 28.1 sqinch is a pushing force around 11400lbs, 5.5tons.
No leeking seal in the cylinder can craete that pressure. Even rust shouldn't take that force to overcome.

I assume you attached the gauge between pump and valve!!

If you measured between pump and valve, you can't really say for sure that your cylinder is defect, because the high pressure can be caused by restrictions in the valve, or hoses.

I would attach the gauge between the valve and cylinder on the rod side to cylinder (as close to cylinder as possible) on retract....check pressure both in and out cycle

Do the same thing with gauge on the capped side....in and out

Also try to make the in and out cycle on the lowest possible rpm and check the pressures, if cylinder moves with lower pressure it is probobly the valve that restricts the flow...
To check piston seal, make retract cycle, de-attach one cylinder hose on capped side, Plug port on valve!!!!run continous retract cycle and se if fluid is coming out of de-attached hose....be ready with the bucket....