The system begins by actuating valve A. This changes the state of valve B and causes cylinder A to instroke, raising the door. When fully instroked, or negative, the piston trips valve C and this sends a signal to valve D. When fully outstroked, the piston trips valve E and the cylinder instrokes. When negative, valve F is actuated and causes cylinder A to outstroke and stay in the positive position.
The system stops and waits for a signal from valve A. We can summarise the sequence of this circuit as follows. Study this sequential circuit. Redraw the circuit to take this into account.
A pneumatic system is used to transfer packages between conveyor belts as shown. The pneumatic circuit is also shown.
Build and test this circuit. Name valves 1, 2 and 4. Describe how the circuit operates. If the packages were too light to actuate valve 1, describe another way to detect the packages. Describe how you would do this.
Forces in a single-acting cylinder When a single-acting cylinder outstrokes, it produces a force. We can use this force to carry out tasks. When we are designing pneumatic circuits, we must use a cylinder that is capable of completing its task. For example, if a single-acting cylinder is used to push parcels off a conveyor belt, then it must produce a big enough force to be able to do this.
If the force is not big enough, then the parcels will not move, and if the force is too big, the parcels may be damaged. The size of the force produced by the cylinder as it outstrokes depends on two things the air pressure supplied to the cylinder and the surface area of the piston. This means that if we want a bigger force we can either use a larger piston or increase the air pressure.
However, it is not a good idea to increase the air pressure because this can damage components. The instroke of a single-acting cylinder is controlled by a spring. The spring returns the piston to its original position. We do not normally use the instroke of a singleacting cylinder to carry out tasks. We can measure the pressure in a pneumatic system using a pressure gauge. A gauge will always be connected to the compressor, but other gauges may be connected throughout large systems. This helps to detect leaks, as the pressure in the system would begin to fall if air was escaping from the pipes.
This conversion is easy, as you simply divide the value in bars by Therefore, the value would be 0. The chart below provides a quick reference. Area The surface area of the piston is the area that the air pushes against to outstroke the piston.
This area is circular. Force The force produced when a single-acting cylinder outstrokes is calculated using the formula:. In some situations, we would know the size of the force needed to do a job properly. In this case, we would want to calculate the pressure needed or the size of the piston.
To do this we need to rearrange our formula. The diameter of the piston is 25 mm. Calculate the force produced as the piston outstrokes. Step 1 Write down any information that you have from the question. In this case, calculate the force. Assignment 15 1. Write down the formula that we use to calculate the force in a single-acting cylinder as it outstrokes.
A pneumatic stamping machine is used to stamp the company logo onto metal casings. It is discovered that the stamp does not imprint the logo properly.
Suggest ways of increasing the size of the force produced by the cylinder. What controls the instroke of a single-acting cylinder? A single-acting cylinder is used to press two sheets of acrylic together when they are gluing. The process requires a force of N. The only piston available has a diameter of 20 mm and it is supplied with air at a pressure of 0. Will this arrangement enable this process to be carried out properly? What force will be produced by a 20 mm diameter cylinder as it goes positive using a pressure of 0.
Calculate the outstroke force produced by a 40 mm diameter cylinder when it operates with a supply pressure of 3 bars. Write down the formula that we would use to calculate the pressure of a system if we already knew the force required and the size of the cylinder available. A stamping machine exerts a force of N with a piston diameter of 34 mm.
Calculate the air pressure required for this operation. A machine that places tops on bottles uses a single-acting cylinder. What air pressure needs to be supplied to the cylinder with a diameter of 56 mm?
A force of N is needed to push a packing case off a conveyor belt. The singleacting cylinder used has a diameter of 60 mm. What air pressure should be supplied to the system? A pneumatic system is used to test the quality of drawer guides in kitchen cabinets. A force of 16 N is needed to open the drawer. The single-acting cylinder available has a piston diameter of 10 mm. What air pressure should be supplied?
Write down the formula we would use to find the area of a piston if we already knew the size of the force it needed to produce and the air pressure being supplied. A single-acting cylinder is used to lift parcels on to a conveyor.
This requires a force of N with the system operating at a pressure of 6 bars. Calculate the area of the piston required. A door requires a force of N to slide it open. A single-acting cylinder supplied with a pressure of 5 bars controls the operation. Calculate the diameter of the piston required to produce this force. A furnace door weighs N and is lifted by a single-acting cylinder as it outstrokes.
Compressed air is supplied at a pressure of 4 bars. Calculate the diameter of the piston required to raise the door. Forces in a double-acting cylinder We already know that a double-acting cylinder can be much more useful to us in pneumatics because both the outstroke and instroke are controlled by compressed air. This allows us to make use of both the outstroke and the instroke force. What we learn, however, is that the outstroke force is greater than the instroke force.
Why is this the case? During the outstroke, the compressed air pushes against the surface area of the piston in the same way as in the single-acting cylinder. However, during the instroke the surface area is reduced because of the piston rod.
This means that the compressed air does not have as big an area to push against and so it does not produce as big a force. We can find this surface area, or effective area as it is known, by calculating the area of the piston rod and subtracting it from the surface area of the piston. Worked example A double-acting cylinder has a piston with a diameter of 25 mm.
The piston rod is 5 mm in diameter. Calculate the force produced by the cylinder as it outstrokes and instrokes. In this case, calculate the outstroke force. We already know the piston area from step 2. Step 6 Calculate the instroke force. Assignment 16 1. Explain why the forces produced by a double-acting cylinder on the outstroke and instroke are different. A double-acting cylinder found in a Technological Studies room has a piston diameter of 20 mm and is supplied with air at a pressure of 0.
What force is produced as the piston outstrokes? The piston rod has a diameter of 6 mm. What force is produced on the instroke? A double-acting cylinder is used to raise and lower a barrier in a car park. The air pressure is 0. The piston rod is 12 mm in diameter. What forces are produced when the piston outstrokes and instrokes? A double-acting cylinder is used to set up skittles in a bowling complex. An instroking force of 0. The effective area of the piston is mm2. Explain your answer.
Components on a conveyor system travel along and drop onto a table attached to the end of a double-acting cylinder. As the cylinder instrokes, the components are raised up and then pushed by another cylinder on to the next conveyor. The piston diameter is 20 mm and air is supplied at a pressure of 0. The effective area is mm2. Draw the symbols for the following components.
The diagrams below have a basic fault. Identify this fault and then redraw the diagram properly. Why do we restrict the exhaust air from a cylinder rather than the air entering the cylinder? Name the components used to create a time delay. Draw a diagram to show how they are connected together. Describe the difference between a T-piece and a shuttle valve. You may use sketches to help.
A circuit allows a door to be opened by pressing either valve A or valve B. What type of control is this? Explain why the force produced by the instroke of a double-acting cylinder is less than the outstroke. Safety barriers on a fairground ride are held in place by pneumatic cylinders. Which type of cylinder would you recommend? Describe the reasons for your choice.
A double-acting cylinder is used to open and close a window in a greenhouse. The window weighs 20 N and the piston diameter of the cylinder is 10 mm. What air pressure should be supplied to this system? Show all your working. A force of N is needed to tip over a container full of rubbish. Compressed air is supplied to the pneumatic system at a pressure of 0.
What cylinder diameter is needed to complete this task? We take our exhaust restrictors one step further with our range of silenced exhaust restrictors. A flow control combined with a silencer takes two different functions and incorporates them into one handy product. Exhaust flow restrictors and silenced exhaust restrictors are usually installed on valve exhausts or quick exhaust valves. Not only does API Pneumatic UK manufacture a top range of pneumatic flow regulators, we also offer next day delivery to top it off!
Get your flow under control immediately with next day delivery on all of our pneumatic flow regulator products. For more information on any of our flow restrictors, controls or regulators, contact API today. We can advise you on the best form of flow control for your requirements. Restrictor There are two types of flow control valve available to us. The first type is called a restrictor or sometimes a throttle valve. This valve works by reducing the amount of space that the air can flow through.
We can adjust the airflow by turning the small screw on top of the valve. The symbol for a restrictor is shown right. This restrictor slows down the flow of air in both directions. This means that using only one extra component can slow both the outstroke and instroke of a cylinder. In the circuit shown below, the restrictor is used to slow down the speed of the single-acting cylinder.
We can adjust this speed by turning the small screw on the top of the restrictor. The problem with this type of restrictor is that it always slows down the speed of the piston in both directions. In many cases, we would only want either the outstroke or the instroke to be slowed down. Also, if we study the piston movement very carefully, we sometimes find that it is quite jerky - not smooth as we would want it to be. Unidirectional Restrictor To solve these problems we can use a component called a unidirectional restrictor.
As its name suggests, it only slows down the air in one direction. The symbol is shown right. When air flows into port 1 of the restrictor, some of the air takes the bypass route. A small ball is blown against a valve and blocks this path. The air is then forced to go through the restriction and this slows down the airflow. When air flows into port 2 of the restrictor, again some of the air takes the bypass route.
This time, the ball is blown away from the valve and the air passes through unrestricted. In pneumatics, unidirectional restrictors are much more useful to us. However, we must always be careful to insert them in the circuit the correct way round. Study the circuit right and take note of the position of the unidirectional restrictor. Is it where you expected?
The restrictor is placed so that it slows down the exhaust air coming from the cylinder. Air trapped on the other side of the piston escapes through the restrictor slowly.
This makes the piston outstroke slowly. This means that the output from one valve becomes the input to another. Study the diagram left and the truth table below. Sometimes we need to control a pneumatic circuit from more than one position. This can be done using OR control circuits. These circuits are quite simple but they need another component called a shuttle valve.
A shuttle valve is used to change the direction of air in a circuit. It has a small ball inside that gets blown from side to side. A picture is shown below. When air is supplied from valve A, the ball gets blown across and the air is directed towards the cylinder. When air is supplied from valve B, the ball is blown to the other side and again the air flows into the cylinder. If air comes from both directions, air still manages to reach the cylinder, as this is the only path it can take.
The symbol for a shuttle valve is shown right. This means that either valve will outstroke the cylinder. Sometimes in a circuit we want a pause or delay before something else happens. To create a delay we need to use two components — a unidirectional restrictor and a reservoir.
A reservoir is simply an empty container, just like an empty bottle. The bigger the reservoir, the longer it takes to fill up with air. To make the delay longer we use a unidirectional restrictor in front of the reservoir. This slows down the air so that the reservoir takes even longer to fill. The length of time it takes to fill creates the delay.
We can change the length of a delay by changing the size of the reservoir or adjusting the restrictor. Sometimes with pneumatics we find that the actuators on valves can get in the way of the circuit. Also, some actuators need a big force to make them work and this is not always possible.
There are different ways to overcome these problems and one of the most common is to use an air bleed. An air bleed is simply an open pipe that allows the air in the circuit to escape. Air bleed circuits rely on a component called a diaphragm valve. This valve is capable of detecting small changes in air pressure. The symbol is shown below. The diaphragm is a piece of rubber stretched inside the valve. When air flows into the top of the valve, the rubber expands much in the same way as when a balloon is blown up.
When the diaphragm expands, it presses down inside the valve and changes its state. The signal to the diaphragm comes from an air bleed. When the air bleed is blocked, air is diverted back towards the diaphragm. Notice that the airflow to the air bleed passes through a restrictor. This slows down the air before it is allowed to escape. Many pneumatic systems and machines are designed to perform a range of tasks in a certain order or sequence. This usually involves the use of two or more cylinders working together to complete the task.
For example, a company has automated its production line that involves metal blocks being placed in a furnace for heat treatment.
0コメント