So valves are used in nearly every hydraulic circuit, either to direct flow, or to control pressure, or to control flow. Now in this class, we're going to talk about lots of different types of valves, because there are hundreds of different styles of valves, we won't be able to cover all of them. But hopefully, we'll give them, give you the tools so that you can understand how they function and analyze how they work. So, to get us started here and starting to look at applications of valves, let's take a trip to the lab and we'll look at a common application of a directional control valve to control hydraulic cylinder. I'm standing here in front of one of our training benches and I've hooked up a sim, simple hydraulic circuit. We'll talk about the hydraulic circuit, we'll then run it and see how it behaves. So, the circuit that I have, I've got a pump that's below the bench here and built into the pump is a relief valve. The outlet from the pump then comes to this supply port. The supply port is then connected by a flexible hose to a directional control valve. The A-port of the directional control valve goes to the rod side of my hydraulic cylinder. The cap side of the hydraulic cylinder goes to the B port, and then the tank port of the directional control valve goes back here to my return, which then goes through a filter and back to the reservoir of the hydraulic power supply. So, now I'm going to run this and we'll look at how the cylinder moves as I actuate the directional control valve. [SOUND] So, now you can hear the pump running. And I'm going to cycle the valve. And you can see how it's extending and retracting. You will not that there's a slight difference in the velocity that it extends versus retracts, and this is due to the difference in the cap in the rod side areas. [NOISE] Now let's say that I want to control the speed of this actuator. Well, one way I could do it, is I could feather this directional control valve, have it partially open. Another way is I could add an additional valve. So, what I'm going to do is I'm going to take a needle valve here and I'm going to add it between the A port and the, the cap, the, the rod side of my cylinder. So let me disconnect this port right here. We'll plug in our needle valve. And then we'll grab an additional hose. Connect that to the A port. Connect that to my needle valve, and now I should be able to use this to do speed control. So, we'll run it again, and I'll demonstrate how this is throttling the flow going to the rod side of the cylinder. [SOUND]. So, we'll start it up, and you'll note that as I move the, the lever. The cylinder's really not moving, and that's because I've got this valve fully closed. And now you can see, as I start to open it, I'm throttling the flow and I'm able to control the speed. I could open this more and have it move faster. And you might be able to hear the fluid throttling through this valve. And so, what it's doing is it's creating a pressure drop. And this pressure drop is reducing the flow rate and therefore controlling the speed of this actuator. All right, now that we're back from the lab let's talk a little bit about how the circuit worked that you just looked at. So, I have an hydraulic schematic here of the exact same circuit. And we had talked about the components in the lab but sometimes it's a little bit difficult to see how they actually layout. So, let's talk about what happened here. So, first of all, I've got this what we call a directional control valve right here. And I've got all my labels right here. And the directional control valve is simply what were grabbing onto and shifting the positions to drive the hydraulic cylinder to one direction or the other. And so, as we move it to the top position, this is how we would retract the cylinder and vice versa as we move it to the other position. Now, when we then started to control the, the velocity of the hydraulic cylinder, that's when we started using this throttling or needle valve right here. And, the purpose of this was then to restrict the flow. And, so what was happening is, we were building up pressure upstream of this valve. So, ha, from the outlet of the pump, through the directional control valve to the inlet of this pressure re, relief valve. And so what happen is we exceeded the pressure, the pressure relief valve, we cracked the spring open, and then had our additional flow go across that pressure relief valve. Therefore slowing down the hydraulic cylinder. So, I've got three primary valves in this circuit for such a simple circuit, a relief valve, a directional control valve and a needle valve. Now we're going to talk about these valves in, in various detail throughout the course. The one I want to talk a little bit more about is the directional control valve here. So, how does a directional control valve work? Well, basically, one style is a spool style and so this would be a manually operated valve where I have a lever here that's able to move this spool back and forth and on the slide you see two different positions of this, of a, a similar type of valve. And this is what we refer to as a four way valve. Meaning there are four different ports that we are connected to. Four different paths that the, the flow can move through. And so in the, the top position I'm connecting my pressure to the A port. And the tank to the B port. And then that would cause the cylinder to move in one direction. And then, as I shift the valve to another position, I would then shift and, and connect the pressure to the B port and the tank to the A port. And so, just by moving the spool back and forth we can control the direction of the flow and hence a directional control valve. Now, we classified directional control valves in in a variety of different ways. The first is by the number of flow paths, the number of ways that I mentioned just a moment ago. There's a large number of one way valves, meaning just one flow path through the valve. But very often we're, we're seeing, you know, two, three, four port valves. The second is the number of positions of the valve. So this refers to, how many different shiftable positions do I have. So this valve right here, I have a center position, and then I have a position that is to your left, and a position that's to your right. So this would be a three position valve. Then we talk about actuation methods. This would be a manually actuated valve with a lever. There's lots of different, manual actuations. We also have solenoid actuated valves. We often have a spring return such as this valve has a spring right here that's returning the valve. We can have hydraulic pilots, pneumatic pilots, lots of different ways to drive valves. And then the last main one is the center condition. And this refers to what happens when I do not have the valve shifted, when it's just in its center condition. Am I going to be either having a closed port which is what's sketched right here where all four ports are blocked. Do I have a tandem operation where the pressure would be connected to the tank, or do I have an open configuration where the A, the B, the pressure in the tank are all connected. So those would be the, the center conditions. Now, I've got three example valves down here, lemme quickly explain how we take these schematics and then take that to, to describe the valve. So, this first valve that I have shown here, this would be referred to by, first of all, it's number of flow paths. So in this case we have three different flow paths, so I would refer to this as a three way valve. I have two shiftable positions so this is a three way, two position valve and then I next look for the actuation method and what's giving it away in this case is this guy right over here. And you'll notice that I have an arrow there which is then completely shaded in. That refers to a hydraulic pilot, so this would be a hydraulic pilot operated. If that arrow was open, then it would refer to a pneumatic pilot. Now this next valve, I have four different ways, which is similar to the valve that I have sitting on the desk here. So this would be a four way valve, and this one has three positions. Pardon me. And then, our actuation method is a lever in that case. So this diagram right over here refers to a lever actuation, and then the very last case on the bottom I actually have five ways in this valve. I have three positions, and then the symbol that I've got on the, the right side here. This is a solenoid actuated valve, very similar to this valve that I have sitting here. This one happens to have two solenoids that shifts it back and forth, often if we have one solenoid we usually have a, usually have a spring return to the center position. So, a variety of different types of control valves, and, you know, this is kind of scratching the surface of talking about types of valves, so where we're going to be moving from here is talking about how to model valves and how to understand complex flow paths through a variety of types of valves.
