SMD Hydraulic system design

Dan MD · Feb 26, 2012

I am in the process of replumbing my entire hydraulic system. I am using the gutted belly reservoir with an IH live pump. Originally I was going to return the oil into the side 1/2" NPT hole that used to be a pressure port. Searching this sight, it sounds like the best results are when the return line enters the bottom of the reservoir. I am mostly going to be using the hydraulics for the 3 point hitch I installed with 2 way cylinders. I currently have 2 questions.

1. I have a 1" NPT hole on the side of the bottom of the tank for the suction line. Is it ok to "T" my return into this same suction line?

2. My tractor had the pressure side of the pump necked down to 1/2" right at the pump outlet instead of using 3/4" line. The valve I got is a 15 gpm valve with 1/2" in and out ports. Am I hurting anything using a 1/2" pressure line. I assume it may add some heat. I don't want to get a different valve.

Thanks,
Dan

Dan MD · Feb 26, 2012

Actually while laying things out, I see I would really like to plumb my return into the original fill hole. If I do this and move the fill hole over to one of the old 1/2" pressure ports, would I have fluid puking problems? I would put like a 6" nipple up from the 1/2" "fill" hole.

Thanks,
Dan

Janicholson · Feb 26, 2012

I would not. In my opinion, the open center system heat will not have the casting of the reservoir to dissipate is the intake is connected to the return. If the port you describe on the side is used for suction only the return could be plumbed into the bottom. Retapping that hole for 1" would be pretty easy.
The fluid would then enter and leave the res at different locations with little construction effort. Jim

Janicholson · Feb 26, 2012

If the pump is gutted, and the pressure port is open to the reservoir, I see no issue. If at any time you use one way cylinders, the system must be vented. With two way cylinders, the system can be closed after filling. Do not open it if it has gotten dramatically hot, but that is common sense. The displacement difference between the two ends of the cylinders due to the rod displacement will not be dramatic. Jim

Bud DeLong · Feb 26, 2012

My question is where are you putting a modern spin on hyd filter? Bud.

rustcollector · Feb 26, 2012

Never seen a hydraulic system that did not have a vent to accommodate heat expansion and cylinder displacement volumes. A double acting cylinder with a smaller rod than piston will require a vent since one end of the cylinder will have a different volume than the other with a rod. Do not put the return directly into the intake as this will cause the oil to heat much faster.

State of Jefferson · Feb 26, 2012

I re-plumbed my SMTA a couple years ago. I ran 3/4 lines from the pump through the valves then through a spin-on filter housing, and back to the res. I used the 3/4" only for the purpose of creating less friction, and hoping to dissipate more heat. Weather or not it helps any significant amount, I cannot say.
One concern I would have about using the gutted belly pump as the only res, is weather the pump will be able to suction-feed itself. My understanding is the live pumps need gravity feed, but I may be wrong on that point...
Another thing you will need to consider, is pressure relief, the valve you have is likely designed for a modern system, commonly in the 2000psi range, your live pump only puts out about half of that, and if you don't have low enough pressure relief, something is gonna give. It will either be the cam timing gear, or your pump. Don't ask me how I learned this little nugget of info... But it is not a lesson you wanna learn the hard way. You can get add-on pressure relief valves from Northern, or Surplus center, among others.

Good luck

Ben

Janicholson · Feb 26, 2012

C through 200 series, and many with two way design. the expansion space in some trans/hydraulic systems is 50% of the volume. Jim

Heat Houser · Feb 26, 2012

One of the items to keep in mind when plumbing any return is to have the oil enter below the oil level. If the oil is dumped back in above the oil level, it will aireate the oil as the stream will pull air into the pool of oil.

Air bubbles in oil is a bad thing when it hits the pressure side of the pump gears. The bubbles implode, pulling metal from the brass pieces inside the pump.

D Slater · Feb 26, 2012

On some M&W systems using the liftall housing as a reservoir and a double acting valve or valves. Return line was placed in the hole that the liftall control shaft went through. Hole was tapped with 3/4 inch pipe threads. seemed to work okay.

Dan MD · Feb 26, 2012

True or not, I was told the return in any of the top holes would be fine for cylinder work but that running a motor would cause air entrapment problems. It may not be the best solution, but didn't the Christmas tree valves return the oil through the fill hole? I feel that the return in the bottom would be optimal, but I can make it look so much cleaner by plumbing the return into the top side.

I've been kicking this around in my head and that is why I am asking.

Thanks,
Dan

Dan MD · Feb 26, 2012

My tractor came with the belley pump reservoir feeding the pump. I was told lots of people did it this way without problems.

I special ordered a valve with a 500-1500psi relief.

Dan MD · Feb 26, 2012

That is part of my plan.

Dan MD · Feb 26, 2012

My 1" suction line is only an inch away from the drain plug.

State of Jefferson · Feb 26, 2012

Sounds like you're on top of things! At least more than I was...

Ben

M Diesel · Feb 27, 2012

(quoted from post at 18:04:05 02/26/12) True or not, I was told the return in any of the top holes would be fine for cylinder work but that running a motor would cause air entrapment problems. It may not be the best solution, but didn't the Christmas tree valves return the oil through the fill hole? I feel that the return in the bottom would be optimal, but I can make it look so much cleaner by plumbing the return into the top side.

I've been kicking this around in my head and that is why I am asking.

Thanks,
Dan

Yes it did. Mine is that way, but it is prone to foaming and continuous flow would probably do it in at some point. I have seen where several people have used the return at the bottom technique and it seems okay as well. I now have a separate 3 spool valve with a filter right after that on the way back to the tank.
For crawlers IH actually just recirculated the oil directly back to the pump. They use a check valve arrangement to keep the lines filled from the reservoir. (Crawlers need to work on steep inclines) Gets just a little warm but these pumps aren't fast enough to worry about heat. If the crawler doesn't heat up with a 82 GPM pump, a 12 GPM SMD is good to go.
If you do run a T down below, have the return line go straight through towards the pump.

SMD Hydraulic system design

Dan MD

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Janicholson

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Dan MD

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