3D Model Description

Introduction

Pneumatic pinch valves are suitable for start, stop, and throttling applications (typically 10-90% throttling range). Pneumatic pinch valves have a very simple design with few moving parts; they are also cheap to manufacture.

The pneumatic pinch valve is very well suited for operating in slurry systems or those with a large amount of suspended bodies within the flowing medium. It is also very well suited to pneumatic systems and the conveying of solids.

The response time of the valve (time from fully open to fully closed, or vice versa), is usually very low.

Unlike many other types of common valve, the pinch valve completely separates the flowing medium from its operating parts; this is of great advantage when the flowing medium is corrosive.

The pinch valve consists of a body and sleeve. The material of the sleeve is chosen to be flexible and durable; typical construction materials include natural and synthetic rubbers. The body of the valve is usually manufactured from metal or a plastic polymer based material. Most pinch valves allow for replacement of the sleeve within the body without requiring the whole valve to be replaced.

The design of the pinch valve allows almost unimpeded flow through the valve which creates a very low pressure differential across the valve. Usually, the pinch valve is actuated pneumatically or mechanically, although electrical and hydraulic actuation is also possible. Non-mechanical actuation methods have the benefits that the valve can be actuated quickly and remotely.

3D Model Components

This 3D model contains all common parts of a pinch valve, these include:

  • Sleeve
  • Housing
Video Lessons

https://www.youtube.com/watch?v=DVd0TW7HffU   https://www.youtube.com/watch?v=naXxsXJzLvg

3D Model Details
Fully Interactive 3D Model

Yes

Animation Working Function

Yes

Explode/Assembly Animation

No

Annotated

No

Cross Section

No

Quiz

No

Virtual Reality (VR)

Yes

Learning Interface

No

Podcast

No

Video

Yes

Augmented Reality (AR)

No

Written Content

No

Video Transcript
- [Instructor] Let's have a look now at a valve, and its construction, and some of the main components. As you can see in front of us, we've got a valve. This is actually a globe valve. We'll just give it a little spin. What we're gonna do is work through the exterior of the valve first, and I'll explain to you the main components of the valve. Then we'll take a cross section of the valve, and I'll show you some of the internal components. Let's start at top. At the top of the valve, we have what's called a actuator. Now, an actuator, it may be pneumatic or hydraulic, or it may be manually operated, or perhaps even electrically operated, such as with a motor. The actuator is essentially opening or closing the valve, or moving it to a position between opening or closing, which is known as throttling. As we can see here, this is a hand-operated valve. This is the hand wheel. We zoom in, we can see some labeling. On the right, we have close, and on the left, we have open. This means that, if we turn the valve to the right, we will put it into the closed position, and stop the medium flowing through the valve. This may be a liquid, or a fluid, or perhaps a gas. Or we can turn it to the left, which is to open the valve, and again, we will then have a medium that flows through the valve. The setup for valves is always the same. It's always righty tighty, lefty Lucy. Try and remember that. Otherwise, you're gonna put the valve into the wrong position. Let's zoom out. We can see the actuator. It's being turned to the left. The valve is now open, and the stem, which is this spindle or long screw shape, has now come out the top. This is known as a rising valve because we can see that the stem has risen out of the valve. If we go back the other way, the valve is now being closed, it's being turned to the right, the hand wheel, and the stem has gone back into the valve. This is a rising type valve. Zoom out. Can see that the stem comes down, and can see it here, continuing down into the main valve body. At this point here, we actually enter the sealing arrangement, or part of the sealing arrangement, for the valve, so there's always gonna be some sort of a sealing arrangement to stop the fluid or the gas passing between the valve and the stem, and leaking outwards. That is this sealing arrangement that we're looking at now. We're gonna take a cross section of that later. Let's just zoom out a bit more. Can see another area of interest here. This is referred to as the bonnet. The bonnet is held on by these array of nuts going around the entire top of the valve. The bonnet is designed so that we can open the valve and access the internals. The internal components are actually referred to as trim, so we're gonna access the trim. Almost all valves will have some form of bonnet because it is essential to be able to get in there and maintain the valve. However, there are exceptions to this. Some valves are not maintained in this manner, especially some of the smaller valves that have a lower monetary value. In other words, it doesn't make sense to repair them or maintain them. It's a lot easier and quicker just to replace them. Let's go down a bit further. You can see we've got a connection on the end. This connection, with all the holes, these holes are actually for passing bolts through. Then we'll use a bolt and nut arrangement to tighten the flange, that is, if we look from the side here, this whole section, that's referred to as a flange, and each end has a flange. We can see another flange here. The flange enables us to connect to the piping and support the valve between the piping. Typically, we're gonna use nuts and bolts, although it is possible, also, to weld the flanges to the pipe work. Obviously, once you've welded the valve to the pipe work, it's a lot more difficult to remove than if you've used a nut and bolt arrangement. You'll generally only use this welding type arrangement when the medium flowing through the valve is particularly hazardous. Now, each of the flanges also has a sealing arrangement. This allows us to seal the valve to the pipe work. If we can see here, this sealing arrangement is the black highlighted area we're looking at now. It has a ridged profile. This helps it to seal, and typically, we use a paper gasket or maybe a nitro rubber gasket, and that will help us to seal the valve to the pipe work when we clamp the nuts and bolts together. The main reason for the gasket is simply that, if we try to clamp two metal surfaces together, there would be some sort of leakage. This is because, when you press two metal surfaces together, they're both quite hard, so when you press them together, they don't seal very well. There's always some sort of a gap between them unless you use a very soft metal. What we'll do, we use some sort of rubber or paper gasket, and we'll squeeze that between the two metal surfaces, and this will then form our seal. We can see the inlet and discharge holes. Not sure which is which. I have to have a look around the valve. Can see here on the side that there is actually a flow indicator. That is this arrow here. The flow is coming from the left and going to the right. That means, on the left hand side, we have the suction, or the inlet, and on the right hand side, we have the discharge, or the outlet. Between the two flanges is actually the body of the valve, that is, the entire area between the two flanges. Sometimes, people will also include the flanges as part of the body. The body houses internals of the valve, referred to as trim. Let's now take a cross section so we can look at the internal components. Okay, there we are. Now we can see some of the internal components, and as you can see, we've also added some labels. Let's do the same again, let's start at the top. You can see a hand wheel, as it's labeled there, or handle wheel, as it's been labeled. We've got a yoke sleeve. That allows us to lower and raise the stem. That is effectively a anchor point, and without it, we would just be spinning the valve right or left, and we would not have any vertical movement, so the yoke sleeve allows us to draw the stem up or lower it down. That is essentially its main function. If we look off to the right now, we can see a label for the stem. We can see something else, which refers to as a gland bush. The gland bush is used to press down onto what we refer to as a gland packing. The gland bush will press down onto the packing, and that will give us a seal. Now, gland packing has come a long way in the past 100 years. Traditionally, they would've used something like horse hair, and they would've wound it together, and then they would've inserted that in the area we're looking at now, where this gland packing is. That's the black three stripes area we're seeing. This sort of wound horse hair would've been stuffed in there, and we would've used the gland bush to press down onto this horse hair, and squeeze it between the valve bonnet and the valve stem. That, essentially, then forms a seal, and prevents any liquid, or gas, or whatever the flow medium is, from leaking out of the valve. Obviously, we've come a long way since using horse hair. We now often use plastics or Teflon, and it is a lot more durable than horse hair. I should also mention that the horse hair would usually have been soaked in some sort of fat or oil to make it a little bit more durable, and to allow the stem to turn more easily. The way that this sealing arrangement actually works is, if we go up to the top here, we can see, on the left hand side of the screen now, we have a nut and stud arrangement. A stud is essentially a bolt, but without a head. We can see that the stud has gone though the entire piece here, and it has two nuts on the end. Zoom in. There is one nut, and there is the other nut. We're not using a nut and bolt arrangement. We're using what's called a stud, and stud and nut arrangement. We're gonna clamp these two nuts down, and we're gonna do the same on the other side. Just switch back so you can see it. When we tighten these down, we're essentially going to push this metal plate, the top metal plate, down, and that is then gonna push the gland bushing down, this section I'm wiggling about here. As the gland bushing gets pushed down, it's gonna compress the packing, and as it compresses the packing, it is going to seal the space between the stem and the valve bonnet, and that is how we get our seal. Important to realize that we don't want to over-tighten the top nuts and studs because, if we do over-tighten those nuts at the top, and we push the gland bush too far down onto the packing, what we're actually gonna do is squeeze the packing tight onto the stem, and also the valve bonnet. This is gonna create a lot of friction when we try and open or close the valve. In fact, it can be incredibly difficult to open or close the valve when someone has over-tightened the packing. Let's go down now. We're going past the bonnet. We can see that the bonnet has been, again, sealed onto the body. There's another seal, that is this black piece here. We've sealed the body, the lower piece, to the bonnet, the upper piece, and we've sealed the stem to the bonnet, and that's gonna be the pressure boundary area, so we're gonna be staying inside this space where I'm going around with my mouse now. That's very important. We want to ensure that we have as few seals as possible, and where we do have seals, we want to ensure that they are adequate and sufficient to prevent leakage. As we can see now, we've gone down, down, down. This is the stem coming down, and we're gonna finally reach what we refer to as a disc. A disc is also sometimes referred to as the lid. This is the lid or the disc, and the disc is going to sit onto a seat. Let me just push play so that we can get some distance between our seat and disc. We can see there that the disc has moved up. The valve is now in the open position. Let's have a look at the seat. The seat is this area, just zoom in, here. Where I am with my mouse now, this is the seat, and including the side piece. We want the disc to come down and land on the seat, and form, ideally, a perfect seal. Then we will prevent any flow through the valve. That is when the valve is in the closed position. When we want it in the open position, the lid will rise, or will move away from the main seating area, and then we will allow the medium to flow through the valve. It is very important that the disc and seat contact surface areas are clean. We want them to be as clean as possible because any debris or foreign bodies that get stuck between the disc and the seat are essentially gonna stop it from sealing correctly. Then we're gonna have a valve that allows the medium to pass through when it shouldn't. Imagine, for a moment, that we had, just for example, a big piece of metal that got stuck across the valve seat here, and as the disc came down, it tried to crush the metal, but unfortunately, it wouldn't be able to do that, and what we'd actually have is a gap between the seat and the disc. Just zoom up. Imagine a gap here, and the fluid, or liquid, or gas, or whatever's moving through the valve is gonna pass through here. Then we've got a leaking valve, or what we refer to as passing, a passing valve. That is not good. We don't want that. The idea of the valve is that it can open or close. We can start or stop fluids flowing, and we can't do that if the disc and the seat are not perfectly sealing together. We actually refer to this as seating. The valve should seat perfectly, and if it's not seating perfectly, then we are not gonna have a seal. Valves are almost always named after the type of disc they use. The type of valve we're looking at now is a globe valve. However, if you look at a plug valve, a butterfly valve, a ball valve, a gate valve, they're all named after the type of disc that they are using. The valves may appear differently, but essentially, they're built always for the same function, which is to start and stop a flow, control a flow, control the pressure, relieve pressure, they're all gonna be working to obtain some of all of those objectives. When you're looking at a valve, ask yourself, what is it doing? Then, how is it doing it? Then apply the knowledge that you've got from this video, and you'll be able to figure out the rest.