Hydraulic Tank Design

Wild Bill the 2nd · Jun 8, 2015

I am working on a firewood processor and am looking to build a hydraulic tank. I had some questions, in particular about baffle design.

Note: The processor will have a 17 GPM saw pump, 6.5 GPM pump for misc cylinders, and a 28/7 GPM 2 stage pump for the splitter. That is up to 51.5 GPM.

Here is my current design. Work has some 16" OD dished lids that are scrap due to the metallurgical properties not being correct. At 16" Dia. you get 1.15 gal per inch of length. I have roughly decided on a 50 gallon tank which comes to about 57.5" in length. (I am not including the amount of fluid in the dished ends in my calculation, it is extra capacity) I was thinking we'd fill it with 40 to 45 gallons. I have a 2" suction port and a 1.25" return port, two 3/4" drains, and two 1/4" fittings for a temp sensor and a dipstick.

This pic shows the dished end removed. My plan for the baffle was to have it run top to bottom the full length of the rolled tank. Return comes in on one side of the baffle and the suction is on the other. The fluid will be forced to travel to the dished ends to get back around to the suction side.

I think the tank will have a lot of surface area for the volume of fluid. I'm not sure if that will allow us to get away without a hydraulic fluid cooler due to the shear GPM the pumps will be putting out.

Opinions on anything? Baffle? Port sizes/qty? Tank volume? Think it will work? Am I missing anything?

kiotiken · Jun 9, 2015

I'm no expert at all but from the crash course I've been subjected to over the past couple months, I'd say you're going to need a cooler with that much flow. 1 gallon per GPM flow on low pressure but 3 gallons per GPM flow on high pressure.

Baffles are also usually only half to 2/3 high on bottom port tanks. That's what all the diagrams I saw showed while researching building my tank. In the end, I got a used one for less than the materials would cost to build one. I ended up with an aluminium 75 gallon tank for roughly 2/3 the cost of the materials to build a 35 gallon steel tank. Now if you're getting some if your materials for free, it might be different. I simply stopped by a heavy truck repair shop and walked around the yard with them, they didn't even know about all the tanks they had.

oldnslo · Jun 9, 2015

You must ensure that enough oil gets around or past the baffle to prevent one side from over flowing while the other is empty. Possibly add a large hole at each end a couple inches off the bottom for some sediment settling. Yes on having returns on one side and suction on opposite side of the baffle.

Tanks reject very little heat with out adding cooling fins and air movement.

CJONE · Jun 10, 2015

And be sure the returns are BELOW the oil level, either entry below or with drop tubes. CJ

Farmerford · Jun 12, 2015

Are you sure it is 1.16 gal/inch? I get 0.87.

Baffles separate the tank into two parts: one where the return enters that is always disturbed due to the return; the other where the fluid is somewhat less disturbed for a short time to allow contaminants to settle out and air to release from the fluid. It seems like that would work best if the path between the two parts of the tank were along the floor of the tank, which is accomplished if the baffle is say an inch or so above the bottom. That way the least disturbed fluid in the return part, which is presumably at the bottom, will be traveling to the suction part along a long slot that does not create more agitation.

Wild Bill the 2nd · Jun 12, 2015

My mistake. It is 1.15 inches per gallon. You are correct .87 Gal per inch. Dimensions are still correct though.

My thoughts on the baffle was to place the intake and return on opposite sides and make the oil go around the plate at the ends. I was hoping to increase flow across more of the tank surface in an attempt to increase cooling. But I realize that might be a lost cause. I like the idea of adding fins though. That is a possibility. Then add a small electric fan at one end.

If I leave the baffle open at the bottom I would definitely need to move the supply and return to opposite ends of the tank. I'm fearful that would leave too much of a direct route between ports though. Maybe not.

oldnslo · Jun 12, 2015

Leaving a gap at the bottom of the baffle would allow contaminates to travel easily from the return to the inlets. That is usually not a desireable feature in a reservoir.

the old grind · Jun 12, 2015

Can you plumb a small auto radiator (w/fan) into the 1 1/4" return line for cooling? (Use a 7.5psi pressure cap & route the overflow line to tank.) tog

Wild Bill the 2nd · Jun 13, 2015

We can do whatever we want. Though I wouldn't run an automotive radiator in line with the return If I do that I will run a purpose built hydraulic cooler that is built to withstand the greater potential pressures of a hydraulic system.

If I do run an automotive radiator it would have a separate supply and return port welded into the hydraulic tank with a small pump of its own for flow so that it has virtually no pressure on it. In order for that to work I would need to see if the charging system on our two little tractor engines would support an electric pump for the fluid and a fan for the radiator. I kind of have my doubts.

The in line radiator thing has been discussed in some detail here. I just wouldn't trust a standard radiator to flow 50 GPM with surges from cylinders, motors, etc.

Wild Bill the 2nd · Jun 13, 2015

Forgot to mention, I don't know that 3/8" ID tubing would handle the flow required if you had a 7.5 PSI cap. Not that I'd know for sure but I would imagine that regular unrestricted flow on the return line would top 7.5 PSI.