How large a reservoir do you really need?

[ovrszd]

I have a 42 Ton Splitter with a 28gpm pump operating a 6"x30" splitter ram and two 2"x12" rams for log lift/wedge lift with 20 gallon of oil in the reservoir.

This fall I split for 90 minutes with two people so the splitter was moving a cylinder almost constantly in 80 degree heat. The oil temp when I stopped was 170 degrees in the tank.

To stay under JJs recommended 200 degrees I was pushing the limit. I'm sure the oil temp within the pump and cylinders was greater than the tank temp of 170.

My tank capacity is 28 gallon. I could probably add another 5 gallon of oil and drop that operating temperature a little.

 

[J_J]

If you wanted to cool the fluid more, then a radiator and fan assembly could be used, as long as the engine could produce fan voltage. 170 degrees temp is fine. A temp sensor on the radiator hose could activate the fan.

 

[IceStationZebra]

I agree with FordTractor. I have worked for 4 different off-road OEM as an engineer on new products and none of them had a reservoir 3-5x the system flow. Only a few were over 75%! Now I will say getting down to 25% is starting to cut it close depending on the reservoir shape and the angles of operation.

I can also say from personal experience that the normal rectangular reservoir does a poor job of letting particles and air settle out. We were having problems with a prototype machine, so we cut a window into the side of the reservoir. We started the machine and watched all the air bubbles come in from the return line. Several minutes of running at idle didn't help. We shut off the engine and watched the bubbles SLOWLY rise to the surface - it took ~15 minutes to get rid of ~90% of the bubbles. System design is the best way to beat aeration. And I like to put magnets in my reservoirs for cheap insurance.

As for cooling, the reservoir makes a very poor heat exchanger. You have limited surface area vs. volume. Adding more volume only adds a little more mass to heat up, which will only slightly delays your time to temp. And adding surface area to the reservoir is only slightly better, especially when you consider that most reservoirs are covered on several sides. If you need cooling adding a small cooler is the way to go - or try to increase your system efficiencies.

JJ's recommendation of 200ｰF max temp is about right (for equipment you care about ). With regular hydraulic oil every 10ｰF over ~160-170ｰF (depending on the base stock and additives) you double the oxidation rate which halves the life till change out. Regular NBR seals and low end hydraulic hoses are good to ~215ｰF. The problem with hydraulic systems is that over-temp just decreases the life expectancy, so it ends up being a ticking bomb.

ISZ

 

[Rocwin]

We design and repair mobile hydraulic work equipment, it is rare to see a properly sized hydraulic system but they are around. Generally you see 1-2x the flow rate, the equipment that uses tanks less than 1x flow have very serious problems in the long term. It seems those systems have have major issues with pumps and drives, along with cylinders needing overhaul serious containmination.

 

[AKKAMAAN]

We also have to remember that constant flow displacement systems (fixed pump) turn around fluid constantly, while in a constant pressure system, the variable pump only deliver flow on demand to actuator.....so a 10gpm fixed pump will definately need larger tank than a 10gpm variable pump.....
Most mid size and full size mobile equipment has variable pumps today....