Iso 14617 P Amp;id Symbols
Jonathon Burnside
It is also important to take as a reference standards that ensure an update of their content based on the evolution of technology, this ensures that our reference p&id standard always provide a solution to the different representation problems that will arise over the years.
Whatever the choice of a reference standard is a decision that will condition the plant documentation for a long period of time, this implies that the change of standard or reference will be complex or practically impossible.
As a general rule, the standards mentioned in this article are used as reference documentation in the process of creating process plant standards. Each plant/organization adapts the content of these standards to its own internal standard by selecting the most significant material that best suits its purposes, thus generating its own internal rules.
The revisions on the P&ID diagram allow to reflect the changes of the process and it is essential that they follow some rules whenever a revision is necessary. A P&ID diagram with incoherent formats leads to confusion and misunderstandings on the part of process technicians.
ANSI/ISA-5.1-2009 Instrumentation Symbols and Identification latest version has significant changes over the previous version ISA-5.1-1984 (R1992). This release includes new and evolving Instrument Technology, Control Systems and Computer Networks.
The latest version of American standard ANSI/ISA-5.1, Instrumentation Symbols and Identification, is approved by Standards and Practices Board of International Society of Automation (ISA) in 2009. This standard describes the instrumentation symbols and their identification systems. This drawing standard introduces a consistent mechanism that comprises identification schemes and graphic symbols in order to describe and identify instruments and process items and their functions. The ISA standard is widely applied in commercial process software, which is used for measuring, monitoring and controlling actual process production (ISA, 2009).
The purpose of this standard is to establish documentation for that class of instrumentation consisting of computers, programmable controllers, minicomputers and microprocessor-based systems that have shared control, shared display or other interface features. Symbols are provided for interfacing field instrumentation, control room instrumentation and other hardware to the above. Terminology is defined in the broadest generic form to describe the various categories of these devices.
It is not the intent of this standard to mandate the use of each type symbol for each occurrence of a generic device within the overall control system. Such usage could result in undue complexity in the case of a Piping and Instrument Drawing (P&ID). If, for example, a computer component is an integral part of a distributed control system, the use of the computer symbol would normally be an undesirable redundancy. If, however, a separate general purpose computer is interfaced with the system, the inclusion of the computer symbol may provide the degree of clarity needed for control system understanding.
This document defines graphical symbols for the basic representation of process instrumentation and controls including conventional measurement and control equipment. This standard applied to the preparation of design documentation for process control engineering incorporates existing measurement, operation, and control instrumentation (DIN, 1993).
The P&ID standard published by the International Organization for Standardization (ISO) technical committees belongs to the standard series ISO 14617, graphical symbols for diagrams. The purpose of ISO 14617 is to develop a library of the harmonized graphical symbols for diagrams used in technical applications.
The main purpose of this standard is define a set of basic symbols for process computer, interface and shared display/control functions. It is divided in four different parts.
Having a universally understood pneumatic symbology means that the operation and functionality of particular components and machinery can be effectively described to anyone, anywhere, as long as a consistent system is used for the icons. This makes it much easier for manufacturers and operators of machinery to identify individual parts and recognise their function. It also facilitates the diagnosis and repair of faults. With today's technologies, this can even be carried out remotely, just by sending a snapshot of the component in question to a service engineer.
ISO 1219-1:2012, which is a sub-division of the ISO 14617 series, lays down the basic elements required to produce such universally recognised symbols. This standard established the rules for creating symbols specifically related to fluid power systems, i.e. hydraulic and pneumatic systems. Symbols used in pneumatic air supply and distribution are designed to illustrate the function of valves and other necessary devices in the system.
Pneumatic symbols were principally created to identify components on circuit design diagrams, but they can also be used on the components themselves. On a valve, for example, there will be a manufacturer's label carrying pressure and power information, as well as a small diagram of how many ports and outlets it has and how they work. The fixed dimension ratios of the diagrams may be slightly variable, as they were originally intended solely for use in data processing.
Pneumatic cylinders are designed on several different operating principles, which are split broadly into piston rod or rodless actuation. Double-acting cylinders drive the rod back and forth, allowing a push-pull load motion, while single-acting cylinders use a return spring with only the outstroke moving the load.
In a single-acting cylinder, compressed air is used to push the piston out, and a spring to return it (instroke). In a single-action rod type, compressed air entering through a port at one end of the cylinder extends the piston rod (outstroke), the output connection moves the load, the air is exhausted when the valve is turned off. The rod's extension speed depends on the rapidity of the exhaust. Single-acting cylinders can have the spring mounted at either the front or rear depending on the application.
Double-acting cylinders use compressed air for extending and retracting the piston rod, by reversing the air flow direction. They can produce greater forces, and are used more commonly than single-acting cylinders. They can be used for both pushing and pulling.
In this type of cylinder, the piston rod does not end its stroke at an end cap, but extends the stroke through both ends of the cylinder. This allows for the forces and speeds of the stroke to be equal on either side.
Tandem cylinders are a system whereby two or more pistons are connected via a common piston rod. This system is useful where only a small bore is possible or the supply pressure is low, and can generate a relatively high level of force.
These are cylinders that impart force by means of a mechanical slide or magnetic coupling, which is typically attached to a table or other component that travels along the cylinder body. The stroke does not extend beyond the body of the cylinder, but the cylinder length can be greater, and force is the same in both directions.
A cable cylinder still has an opening at one end, or both ends, but the piston rod is replaced by a flexible cable. A belt cylinder is open at only one end, with the belt passing round a motorised screw or toothed gear that keeps it turning. Cylinders using flexible cable or belts must be kept in tension.
Pneumatic rotary cylinders are available in two main types: vane or swivel, and rack and pinion. In the latter type, a rack gear is attached to the cylinder piston. When actuated, their linear movement causes the pinion gear and output drive shaft to rotate. Vane cylinders operate in the same way as windmills: a lightweight (usually aluminium) vane is mounted inside the cylindrical chamber on a central shaft, and the air pressure makes it turn. Both types can be either single-acting or double-acting.
In a single-acting rotary cylinder, air pressure is applied to only one side of the centrally mounted vane, which forces it to rotate until the drive shaft has completed one stroke. In a double-acting rotary cylinder, once the drive shaft has completed one stroke, air pressure is then applied to the opposite side of the vane, forcing it to return in the opposite direction.
Rotary indexing tables are used in machining and a wide variety of other applications. Objects are mounted on a flat disc that rotates, using pneumatic power to start and stop the table at precisely measured angular intervals.
As well as the cylinder body and piston rod, the pneumatic cylinder is constructed with metal end caps. The piston decelerates as it reaches the end of its stroke so as to reduce the impact of a metal piston on a metal end cap. Pneumatic cylinder cushioning is added to the assembly to reduce this impact further, cutting down on vibration or bouncing. Cushioning also reduces impact noise, which could, if excessive, constitute a health and safety hazard.
Cushions can be applied to the cylinder in a variety of configurations, including fixed mechanical options such as shock absorbers or bumpers. There is also a magnetic type, an option with adjustable cushioning at one or both ends, and a relatively new type of cushioning which is self-adjusting.