Corey Rasmussen, Author at Mentored Engineer

In this video, Corey explains what to look for in a hydraulic reservoir and pump. https://www.youtube.com/watch?v=PjmpRLuaTFQ Video Transcript Hello. Welcome to the Mentored Engineer. In this video, we are going to be looking at the four components that every hydraulic system must have. In this one, we're going to talk about the reservoir and the pump. In our next video, we're going to talk about relief valves and filters.Alright, so let's talk about reservoirs. Reservoir is a large container of oil. The general rule of thumb is whatever your flow rate is, you need three times that in hydraulic oil storage. So, if I have a 10 gallon per minute flow rate, I need 30 gallons a minute in oil storage. Alright, so that's a lot.And that doesn't hold up very well in my world. So, for example, I have that log splitter. It's got an 11 gallon a minute pump when it's doing free flow. It's only got a two gallon tank. So, it doesn't hold up.There's no heat buildup, which is one of the main reasons that reservoirs are so large is they want to make sure that you have a way to dissipate that heat. Alright, so with the log splitter, mostly I'm just pushing a cylinder in and out, that's where most of my flow is going, I want to make that quick, but I'm not building up any heat and pressure. In fact, when I am building up heat and pressure, it's when I'm actually contacting the piece and then pushing through the knife, and that's the only time I can get a bigger or get more heat generated by the system but even then I'm still doing work so it's not just heatalright so at that point my flow rate goes from I can't remember I think it's 11 gallons a minute down to like one and a half or two so then I'm at a one to one ratio which I'm at least on the right side of the equation I at least have a ratio where the flow rate is equal to the tank size okay so At that point, there's other things to consider. As I mentioned, heat generation is one of them.But if I have a lot of heat generation, adding a lot more oil doesn't seem like a good idea to me. A better thing would be to add a heat exchanger if I have that problem. It's a lot simpler, cheaper, I can control my temperature of my fluid a lot better than trying to just add more oil and hope that's a big enough heat sink that it'll work. The other thing is if I have large cylinders, especially ram cylinders. That could be a problem. For example, I just designed some very long cylinders to be powered, and when they're fully extended, the differential in oil in the cylinders is 45 gallons.Alright, so if I only have a 30 gallon tank, I'm going to run out of oil about halfway through that. I'm not going to be able to fully extend those without bleeding the pump dry. I'm going to need a much bigger tank for that. In that case, if I have a 10 gallon flow rate, but I need 45 gallons of oil, I probably should be looking at about an 80 gallon tank for this application, if not bigger. That kind of covers the size of a reservoir.The physical size and shape would be the next thing. I like a tall tank, and I like it for the reason of my passes and mobile equipment. So, as I tilt and I move this thing, a tall tank will still have a lot of heat or a lot of oil in its vertical direction. If I have a very wide tank or a very long tank, as I tilt, I might not have any oil in one end or the other depending on where I put my suction. If I'm traveling downhill and my suction line is up at the top, I might not get any oil in that.Plus, if it's not a very tall tank I may actually be spilling oil out of the top. So, I don't want to do that. So, I like a very tall tank with a very narrow base. I would say I would start off with a cube and then add height as I needed to get to where I want it to be. So, looking at what actually makes up a reservoir, we're looking for several things.The first of all would be some way to drain the tank. If you buy a pre-made tank, they're going to have this. I like putting a vol valve on it so that I can drain it by adding a hose to it and I can shut the thing on and off. I don't have to get covered in oil doing it. So, on your suction line, you’re going to want to have it sized for no more than 5 foot per second of fluid motion in that.Anything more than this you can start to cavitate your pump. So, you want to keep that line size big and that oil flowing very slowly. Alright, one of the things you're going to want on there is a suction strainer. Now this just filters out the big stuff. If you imagine making pasta, you wouldn't want to drain it with cheesecloth.You'd want to drain it with something a little bit bigger in holes. You keep your pasta in the bowl and the water goes out. Same thing with this. We want to keep major chunks of stuff out. We don't want to filter the oil at this point.And a benefit here is if you get a magnetic one, all the parts that are steel will be magnetized. And if you have a steel tank, even better, the whole tank will be magnetized. And what happens is any iron particles in there will stick to the side of the tank. And they won't get sucked through the system and wreak havoc on everything else in your system. So that's one benefit of a steel tank as opposed to a plastic or aluminum or whatever other material you might use.Alright, so... You also want to be able to clean your tank out. So, when you drain it, you want to get in there and you want to wipe it out with some towels and stuff like that. But you've got to be able to get your arm in there, preferably both arms. I've actually seen tanks so big that you can walk in them. So, what happens here is there's usually a gasket with several bolts and you can remove those and go in there and clean it out and then replace that.Make sure it's good. I personally like to have the clean out accessed from the top. That way you don't have to worry about the gasket seal as much as you do on the side. All right, so one of the last things here is the breather assembly. And a breather assembly is where you're going to fill your tank and where you cap it off to keep stuff from coming out.It's kind of like your gas cap on your car. There's one major difference. A gas can on a car is now pressurized. So, as you're taking fuel out, you're replacing it with pressurized air coming back. With a hydraulic tank, that level is going to change a bunch.So, as you're extending and retracting cylinders, it's going to go down and up. What you don't want to have happen is have a locked system where you have to overcome that air pressure. So, a breather is like a gas cap, but it's got an air filter in it so that it allows air to come in and out, and it filters it at the same time. so, what you want to remember there is to you know keep that clean; clean the area around it before you open it to add more oil so the area I worked in we had a lot of chainsaws working around so you had sawdustand you know shavings all around and you never wanted to open up that breather filter with all that around so we'd make sure that it was very clean around that and then we'd open it up and add oil or check the levels whatever we're going to do at that point okay so moving on to pumps there's basically three different types of pumps you have gear pumps you have vane pumps and you have piston pumps now gear pump is a positive displacement pump so every time I rotate the shaft I’m getting oil out And that's very simple.It's the simplest pump you can buy. Vane pumps come in both fixed displacement and variable displacement. So, they behave like a gear pump, or they can behave like a piston pump, which is a variable displacement pump. all right and we could spend a lot of time talking about those and I won't in this episode all right well that's all we have time for today thank you for watching this episode.

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