Should directional valve stacks be drawn on the top or the bottom in the schematic?
We get this question quite often from our users of HydroSym software. Some feed back we get is that it’s easier to draw the actuators on the top part of the schematic and therefore are easier to connect when the stacks are on the bottom, and some tell us they prefer to mount the valves on TOP of the manifold so it’s a better schematic representation of the actual parts. We were curious to bring this discussion to hydraulic engineers worldwide and see if there was a clear preference for one way or the other.
What ensued is a very interesting discussion on LinkedIn. At first it seemed that the “top” was the more preferred option, however as more and more of you commented it became apparent that the meaning was evenly divided. Many of you also agreed that it depended on the purpose and the intended user of the schematic.
We have highlighted some of the discussion below:
I like hydraulic diagrams that represents the real position of hydraulics components between each other but i prefer the classic diagrams with valves on bottom and actuators on top. When dealing with a hydraulic diagram, almost every hydraulic engineer is expecting to find the components from bottom to top in this order: tank-pump-manifold-valves-actuators. This is how designers worked for many years so is kind of hard to change this professional habit.
I particularly prefer to insert the weighted valves at the bottom of the block, precisely to facilitate the actuators’ intelligence at the top. But there are also elaborations of circuits in other ways, not so standardized. By holding the block at the bottom and adding the valves that are connected at P and T below the directional valve and valves connected at A and B above the directional valve and thus already connecting to the actuators. Also having an understanding of the hydraulic circuit.
Schematics with better representation of actual parts also provide better communication between Hydraulic specialists & the mechanics or technicians on site. As quite often there is quite a lot of distance between them, or they are in an isolated area & it is difficult to get a hydraulic specialist there right away. Quite often I myself am called by my clients Marine engineer who is in the Caribbean at the time, myself in Spain, & I am walking through with them over the SAT Phone possible causes to there problem, where to look etc… So a schematic with good representation of actual parts & there position in the system will help a lot with Over the Phone diagnoses.
It depends upon the purpose of the schematic and how it will be used. If it is to be used for installation of the system, then of course it should be drawn as closely as possible to the actual configuration of the machine. But when we draw schematics, we draw them specifically for the troubleshooter, eliminating extraneous information, simplifying the system to make it much easier for the troubleshooter to trace the hydraulic flow while integrating the electrical operation. This usually means that the power supply is drawn at the bottom of the page, then the directional valves, any flow controls, pressure controls, piloted check valves, etc, and finally the actuators at the top. While this may not reflect the actual location of the components, it makes the schematic much more user friendly as a troubleshooting tool.
ANSI and ISO developed symbols and left the drawing of hydraulic schematics to the discretion of engineers and draftsmen and women. In my humble opinion, the fluid power industry should have moved swiftly to develop a standard for the layout of hydraulic schematics. However, it seems layout wasn’t that important. Accordingly, most hydraulic schematics are terrible. I agree with the folks that opine that schematic should be drawn to suit the respective user. It seems most schematics are drawn by engineers for engineers. Consequently, most are not only useless for the purpose of machine assembly and troubleshooting but they a hazardous to workers. Many years ago I took the liberty of writing a manual, which is appropriately titled “How to Layout and Draw Hydraulic Schematics.” The primary objective of the project was safety. Of course, the fluid power industry once again dropped the ball with respect to safety. This time it was the irresponsible cartridge valve manufacturers. It continues to amaze me that cartridge valve manufacturers could not get together and develop a “standard” for port reference.
We build HydroSym to support you whichever way you prefer to draw your schematic, but we are curious if top or bottom is a clear preference. If you’d like to see the whole discussion and add your thoughts please go to the original post on LinkedIn below: