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Old 08-17-2004, 06:21 AM
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Default Sizing a hydraulic fluid reservoir

Hi,

As some of you may already know my latest project is fabricating a truck mounted hydraulic crane. I have a few questions for anyone who would be kind enough to help.

1) I will be using a 4" x 30" double acting tie rod hydraulic cylinder. On my present power pack unit the hydraulic fluid reservoir holds approx 3/4 gallon of fluid. Someone who answered one of my other posts stated that I may need a larger holding tank depending on what size of cylinder I decided upon. Well, they were right, but I have no idea how large of a tank to make or buy. Can someone give me a ball park figure how much fluid I would need the capacity for if the ram was fully extended?

2) I got this double acting cylinder because the price was right, but will be using it as single acting only. Any idea how to modify it for a single acting function only, or will it only work as a single acting cylinder because the power pack only supplies forced fluid in one direction?

3) Are the anchor blocks that fasten the hydraulic cylinders ends to devices made of anything other than mild steel? I would really like to make my own if possible rather than spend $30.00 each plus shipping...........thanks
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Old 08-17-2004, 08:05 AM
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Pat,

As a for instance, I am running a 4 inch bore cylinder with a 17 inch throw on my little log splitter and for me it was quicker to go with the oil reservoir from Northern like this:
http://www.northerntool.com/webapp/w...roductId=13100

Looks like it's gone up about ten bucks since I ordered it but something similar in the 5 - 8 gallon range should do you just fine. A couple of things to consider before you haul off & build you own is that you usually have to have 3 openings on the tank: filler tube, inlet and outlet and that you should also have a strainer & filter arrangement (see representative items on the same page). All things considered, I decided it was more efficient for me to spend the 80 bucks and have the whole package arrive on my porch it 3 or 4 days since I would probably have spent at least that much trying to build my own & probably spend at least 2 weeks fabricating & scrounging for parts locally.

As to the clevis mounts, we used 1" steel plate & that has worked well for several years.
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Old 08-17-2004, 09:47 AM
david_r david_r is offline
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piR^2 and 1 gallon = 231 ci should get you close. We can ignore the lines, valves and pump since they will always have the same volume of oil in them

I get 377 ci for the ram, fully extended.

Then , for a double acting cylinder, you need to subtract the amount of fluid you'd have on the rod side with the cylinder full closed. You get that by taking the bore size, figuring the capacity of it (360 ci) then subtracting the rod size volume. Let's say it's a 3 inch rod. That gives 212 ci. So 360 ci - 211 ci = 148 ci

So, in this example, mimimum reservoir capacity is 377 ci - 148 ci = 229 ci = darn near a gallon of fluid.

As to converting a da to an sa, just buy a colt ... oops, wrong message board. Look at a forklift. If it uses gravity to drop the forks, you should see a low pressure line hooked to the top of the mast cylinder. This lines leads directly to the tank.

I think I'd add an additional return port to the tank for the return from the retraction side of the cylinder.

I'm curious as to how you're controlling drop on your system. Does the power pack hold pressure when not engerized? If not, it seems you'd be at the mercy of gravity.

good luck
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Old 08-17-2004, 05:45 PM
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don't forget to add room for expansion of fluid as it gets hot .
i come up with 377 ci ...same as david did ...and that comes to be alittle over 1 1/2 gals.(1.63)....i would go with something in the 2 gals size tank cuz the fluid will expand when the truck is sitting in the sun and it gets warm.
if you are going to run it and have fluid on both sides of the piston(double acting) you can go with a smaller tank. my 2 nickels worth
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Old 08-17-2004, 08:17 PM
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Pat, this sounds a whole lot more complex than it is, so don't get excited.
You can use the top half of the cylinder for the reservoir, and along with the pump reservoir, it should be sufficient.

As to heat concerns, you probably won't encounter them, unless you plan to be lifting and lowering all day.

Install a T in the port at the piston end of the cylinder, and run a hose from one side of the T back to the reservoir, same location you ran the lowering valve to. This doesn't need to be pressure hose. Remove the breather cap from the reservoir, and install the breather in the other side of the T on the piston.

You need to fill the top of the piston with oil while it is collapsed, and partly fill the reservoir, leaving about an inch of air space.

As the pump begins to fill the back end of the piston, the oil from the rod end will be pushed into the reservoir and keep the pump full.

Generally, this hydraulic circuit provides sufficient capacity to fully operate the piston. If not, you may need to increase reservoir capacity.
You may get some oil blowout thru the breather if it has too much opening, you'll know that real quick if you get a bath.

As far as the mounts are concerned, make your own, mild steel is fine.
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Old 08-18-2004, 08:40 PM
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I dug out my AaronCad 4.0, and made this highly technicle drawing.
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Old 08-19-2004, 05:24 AM
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Smile

Thanks for the info and illustrations guy's,

Sorry I didn't get back sooner. I have a 1989 Chevy Astro Van that has a fuel delivery problem. I need to get it running so I can help some friends move this weekend, so I have put everything else on hold for now. As usual, what would appear to be a simple fix is turning into a nightmare. I need to replace the in-tank fuel pump, and try to get the rusted and crusted on fuel filter removed and replaced without damaging the fuel line connectors. I can't believe they would place a fuel filter under the vehicle open to all the nasty elements (salt, dirt,etc).

Anyways, I appreciate all the excellent suggestions and the highly technical AaronCad 4.0 drawing provided by "Franz-O-Graphics". LOL Thanks again.
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Old 08-19-2004, 05:34 AM
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Quote:
Originally Posted by Pat
Thanks for the info and illustrations guy's,

Anyways, I appreciate all the excellent suggestions and the highly technical AaronCad 4.0 drawing provided by "Franz-O-Graphics". LOL Thanks again.
Just think where we would be today without such technology.
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Old 08-19-2004, 09:46 AM
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Quote:
Originally Posted by cutter
Just think where we would be today without such technology.
Back to the days of soapstone on the shop floor, or welding bench, but how in hell would we ever ship such drawings.
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