Symbols PDF

What’s this for? This document is intended to help you understand and remember pneumatic, electro- pneumatic and hydraulic symbols that are used as part of this module. This document lists the components used during the module, some of the symbols will have to simply be remembered whereas others m...

What’s this for? This document is intended to help you understand and remember pneumatic, electro- pneumatic and hydraulic symbols that are used as part of this module. This document lists the components used during the module, some of the symbols will have to simply be remembered whereas others must be understood so they can be applied. First, we will look at pure pneumatic symbols, next electro-pneumatic symbols, electric symbols and finally some hydraulic symbols. Pure pneumatic symbols Air service unit The air service unit has (from left to right) a filter in it with manual drain, a pressure relief or pressure reducing valve and a pressure gauge. It stops unwanted particles from entering the system. Air service unit simplified This air servicing unit is the same as the one above it, but it is now smaller and takes up less space on the drawing. Two pressure/AND valve The two pressure/AND valve needs two input signals at the same time to get an output signal on port two. Shuttle/OR valve The shuttle/OR valve will produce an output signal on port two when there is a signal on the left port one or the right port one. If both left and right ports are active, then we will get an output on two as well. One way restrictor valve When compressed air is applied on port one, it will be able to bypass the restriction, and the compressed air will travel from one to two unhindered. Conversely, if compressed air is applied to port two, then the flow of compressed air is forced to go through the restriction, therefore slowing down cylinder extension or retraction. Compressed air supply This symbol represents a compressor. The pressure and flow can be adjusted in FluiSim. Single acting cylinder This actuator generates linear movement (extend/retract). Compressed air is needed to make it extend and the onboard spring makes the cylinder retract as soon as the pressure is removed on the back of the cylinder. Double acting cylinder This actuator has two ports, one can be used to make the cylinder extend (port on left) and pressure on the other port will make the cylinder retract. In this case the double acting cylinder is equipped with two limit switches, a0 and a1. When these switches are activated -through full extension or retraction- a new event can be triggered in the system. Quick exhaust valve This valve enables a cylinder to retract or extend faster than normal. Normally the exhaust air from a cylinder will have to travel through the body of a valve and the channels for that are very small and therefore restrictive in the amount of air they can exhaust. When exhaust air travels from port two, it can only exhaust through port three as port one is blocked off by the shuttle. Variable pressure reducing valve or pressure relief valve This valve will open and let air escape when the pre-set pressure is too high. This way the system is protected from over-pressure. Time delay valve This component consists of a group of valves and elements. Compressed air will flow from port one to port two after a time delay. The timer is triggered when an air signal arrives on port 12. When port 12 in connected to compressed air, the oval shaped chamber will start filling up with air. The rate of filling will depend on the setting on the flow restrictor. If the flow restrictor is 100% open, then the timing will be short. If the flow restrictor is set for 10% open, then the timing will be long. Once the oval chamber is full, the three two valve will switch to open and compressed air can travel from port one to port two. The next section consists of valves that can be configured in ways of actuating them. These components should be understood rather than remembered. Three two valve, no actuation This valve has three connections and two positions. From this symbol it can not be determined how the valve is actuated or operated. When the block on the right is active, compressed air on port one will be blocked off and the exhaust port, three, will be connected to port two. This is the rest position of the valve. When the valve is actuated, the block on the left will engage and port one will be connected to port two. The exhaust port, three, will be blocked off. The same approach applies to, for example, a five two valve as shown below. Ways to actuate/operate a valve Valves can be actuated mechanically, pneumatically or electrically. We will start with mechanical ways of actuating valves. The symbols below are sections of complete valves and are used to illustrate how a valve is actuated. Valves can be actuated through a mix of mechanical, pneumatic or electrical signals. However, most of the time one would use only one medium, being compressed air, electricity or by mechanical means. Roller lever actuation The actuation happens when a cylinder is fully retracted or extended. It can be labelled a0 or a1 for example. This form of actuation can be used on different valves such as tree two valves or five two valves. Idle return roller actuation Actuating a valve with the idle return roller, will result in a valve being operated on either the retract or extend stroke. Not on both, like the roller lever valve would do. This type of actuation is not used on full extension or retraction, instead they are used on partial extension or retraction. Pneumatic actuation The valve will be operated when a pneumatic signal is presented on port 12. Spring actuation (spring return) actuation In this case a spring will operate the valve. The spring signal will dominate when there is no active actuation on the left-hand side of the valve. It is often used to bring the valve back to its original position (rest position). Pushbutton actuation The valve is operated by a pushbutton. A spring brings the valve back to its original position (spring return). Selector switch (detent switch) When a valve is actuated by a selector switch, it will keep actuating the valve without having to manually hold it there. The valve is ON and stays ON until it is turned OFF. Foot pedal actuated In this case a valve is operated by a foot pedal. This concludes mechanical actuation. Electro-pneumatic symbols Next some electro-pneumatic symbols. These are components that have electrical connections and pneumatic connections. Even though they are one component, in diagrams they are split up in an electrical and a pneumatic part. Solenoid actuated This is not a mechanical way of actuating a valve. Instead, we use electricity (24V DC) to actuate a valve. The symbol on the left is the pneumatic part of the component. The symbol on the right is the electrical part. In the real world they are one component. The valve will become active when 24V is applied to the solenoid. This concludes valve actuation. Pressure sensor This component consists of a pneumatic part and an electrical part. The pneumatic part is shown by the symbol above. The pneumatic port is connected to the pneumatic system so it can sense the pressure. Once the variable pre-set pressure is achieved, an electrical switch will be operated. The electrical part that belongs to the pressure switch is shown to the right of the sensor. Electric symbols We will start with three different types of relays first the normal relay, then a time-on delay relay and we will end with a time-off delay relay. After that we will discuss some switches, pushbuttons and electrical limit switches. Normal relay This is the symbol that represents the coil of the relay. The symbol beside it is its contact (to the right). Delay-on timer When this relay coil is activated by electricity, the contact associated with the coil will switch after the time delay. The symbol beside it is its contact (to the right). Delay-off timer When this relay coil is activated by electricity, the contact associated with the coil will switch. When the relay coil is de-energised, the contact associated with the relay will stay on until the delay time has elapsed. The symbol beside it is its contact (to the right). Pushbutton normally open This symbol represents a normally open pushbutton. When the button is pushed, an electrical connection is made between the contacts three and four. When the button is released, the contacts will break. Pushbutton normally closed This symbol represents a normally closed pushbutton. When the button is pushed contact between one and two is broken. When the button is released, contact between one and two is restored. Selector switch/detent switch This symbol represents a selector switch. When it is switched on, it will stay on until it is turned off. The symbol on the left is of the normally open type whereas the other symbol is of the normally closed type. Electrical limit switch This symbol represents a limit switch. In our case these switches are operated when a cylinder is fully extended or fully retracted. The last section of this document covers some hydraulic components such as a supply unit and some valves. Hydraulic symbols Pump unit The pump unit consists of a motor (M) which drives a pump. The pressure generated by the pump is supplied to the system through port P. Other components in this unit are the pressure relief valve and a pressure gauge. The letter T represents the return flow of hydraulic fluid to the tank. Four three hand-lever valve centre shutoff This hydraulic component is actuated by a lever. In the middle position, all ports are blocked off. In that position the cylinder will stop extending or retracting. Four three hand-lever valve with bypass position This hydraulic component is actuated by a lever. In the middle position, port P is connected to port T. this means that hydraulic fluid can flow from the pressure side to the tank without pressure building up in the system. Four three hand-lever valve with floating position This hydraulic component is actuated by a lever. In the middle position, hydraulic fluid can flow from port A to B and some can return to the tank. This valve can be used for dynamic breaking.