TO: All fluid power engineers and designers. FROM: The Fluid Power Safety Institute™. SUBJECT: Fluid power system schematics. What's the problem? - We are appealing to engineers, designers, and any other people who's job is to generate fluid power schematics, to do everything in their power to curb the proliferation of inaccurate and incomplete schematics that is plaguing the fluid power industry. What is a fluid power schematic? - A schematic is a representation of a fluid power system or circuit using various symbols that show connections, flow paths and functions of fluid power components. Hydraulic symbols were introduced in 1967. The idea of symbols was to broach language barriers and promote a universal understanding of fluid power systems. According to the ANSI (American National Standards Institute) Y32.10, "a "complete" graphic symbol comprises all the parts of the component it represents. It is not always used because it is complex to draw, and can occupy a lot of space on a drawing. It can also be difficult to comprehend especially when knowledge of symbols and actual component operation is limited." Therefore, simplified symbols are commonly used. They save space on a drawing, and avoid confusion when reading the drawing. Symbols show connections, flow paths, and functions of components represented. They can indicate conditions occurring during transition from one flow path arrangement to another. However, symbols do not indicate construction, nor do they indicate values such as pressure, flow rate, and other component settings. In a nutshell, there is a symbol for every fluid power component. Therefore, a schematic MUST BE a perfect image of the circuit it represents. If we fix the problem who will benefit? - Every entity in the fluid power industry will benefit from well-conceived fluid power schematics. Here are just a few examples: 1. Engineers, designers, and their respective companies will immediately benefit by improved productivity. Engineers will reduce the time they spend with e-mail and on the telephone giving specifications, and answering questions about information that should have been on the schematic. 2. Assembly line personnel will not have to continually bother engineers and supervisors for specifications, information and clarification. In addition, they will not have to "guess" which way to connect transmission lines to a component. 3. Field service personnel will not have to drive for miles to find a telephone with which to call the factory for help with specifications and troubleshooting. 4. Clients will not have to tie up their valuable time sourcing information that should be on a well-conceived schematic. 5. Maintenance personnel will not have to tie up their time calling for information that they need to be able to set valves, make adjustments, and simply work safely. 6. Instructors will be able to use a well-conceived schematic to explain how the system works to students, assembly line personnel and others. 7. Purchasing agents will be able to share the schematics with vendors, and not have to arrange time-wasting meetings with colleagues to discuss information that should be on a schematic. 8. Technical writers and illustrators will compose more meaningful and accurate technical information and specfications. Tell me more! - We must never overlook the fact that a schematic is, for all intents and purposes, the seed out of which a hydraulic system grows. If the hydraulic system is not exceptionally conceived, there will in all probability, be problems. Inaccurate and ill-conceived schematics create a veritable breeding ground for accidents and misinformation. Here a just a few examples: 1. If the proper pressure settings, flow rates, prime-mover speeds, step-up and step-down ratios are not reflected on a schematic, maintenance people will be left to guess. Alternatively, they will have to spend time finding the bits and pieces of information within the covers of a service manual. Hopefully the serial number of the service manual matches the serial number of the machine. Of course this also applies to the schematic. 2. The vast majority of industrial hydraulic systems have "stacked" valve assemblies. These "stacks" or "towers" incorporate all the valving for an actuator. The "stack" usually consists of a sub-plate, one or more circuit modules, and a directional control valve. The directional control valve is ALWAYS on the top of the "stack." The circuit modules CANNOT be alternated. If they are, it could cause a malfunction that could lead to an unexpected failure. The failure could cause severe injury, death, or substantial property damage. Thus, the circuit modules must remain in the same order in which they were designed It is commonplace to find schematics that show the directional control valve as the first valve off the sub-plate, with the circuit modules stacked above. Thus, the schematic fails to represent the correct "stacking" order and leaves an unsuspecting person vulnerable to any number of problems. The most important thing that an engineer or designer MUST realize is that, through no fault of their own, the majority of people who work on and around hydraulics have absolutely no formal training. The very least they deserve is a schematic, a blueprint, that shows how oil transmission lines are connected to their respective components. While this might hint at being contradictory, we are referring, in this instance, to the reference number on, for example, cartridge valves. This problem, in and of itself, raises the bar for accurate and meaningful schematics that have the appropriate specifications and necessary settings. What immediate action must I take? - Engineers and designers, must strive to include as much data as necessary on the schematic/s they generate. The information must be correct in every respect because maintenance personnel use it to set valves, make adjustments, execute proactive maintenance, connect transmission lines to components, follow flow paths to identify components, etc. The schematic must reflect the machine serial number and show reference from individual valves to the service manual. One other point - some schematics have "too much" information. For example closed-loop (hydrostatic) transmission drawings invariably show the control circuits inside pumps and motors. This makes a fluid power schematic appear extremely intimidating. There is no need to show this part of the circuit, because it usually has absolutely no bearing on how the overall system operates. There really is no need to see how the fluid flows through the channels within the pump or motor, because there is absolutely nothing one can do should there be a problem. Conclusion - On behalf of all the maintenance, assembly line, training, and other personnel, we at the FPSI™ urge engineers and designers to pause for a moment and consider the severity of the problem Maintenance professionals and assembly-line personnel have got to be able to rely on the schematics you produce. They have very little time to find specifications; they spend hours in the field, and away from home. Much of what they do is guesswork or trial and error. They get soaked with oil daily. Yet they do their best to keep your creations running - they desperately need your help! Note: If you need help understanding symbols, our director, Rory McLaren wrote a manual about how to read symbols. We also have a "quick-reference pocket-book for symbols. Just let us know how we can help you!