For those not in the know, most concrete plants use pneumatic systems (compressed air) to operate the various functions of the concrete plant like opening and closing the cement silo valve and the gates on the aggregate bins. These devices use a solenoid valve to turn the air on and off. These valves can be configured many ways but concrete plants commonly use the simple open or closed valves meaning they are all open or all closed; or they use inching meaning they can be opened all or partial. Some concrete plant operators, especially those with manual control systems, will have a difficult time controlling precision weighing of materials when the simple on/off valves are used which is discussed further in a separate post.
The decision whether to use inching solenoids or the simple open/closed solenoids are determined by most concrete plant manufacturers engineering departments or sometimes the purchaser of the plant themselves. Most times, these people make the decision for simple financial reasons. When looking at the details, specifications and designs of almost any concrete batch plant you can find multiple occurrence of “it wouldn’t have been very expensive to do this differently to get a better result.” The problem is what is better for one customer may not be better for another. Also when a concrete plant manufacturer adds ever single add on for just a small increase in price the price of the concrete plant ends getting very expensive. While there is not a lot of downside to using inching solenoids across a plant, they are not needed on many functions when an automatic control system is used and therefore not worth the additional cost.
The other factor is that concrete plants with automatic control systems don’t necessary need inching solenoid valves on every gate and valve. Unlike manual control systems, an automatic control system can control multiple plant functions in hundredths of a second. The concrete plant automatic control systems will also calculate the amount of material that goes through the gate enabling the control to open and close gates precisely in fractions of a second making the inching solenoid valves on some gates unnecessary. While a human can manually jog a gate with a manual control panel, it is not accurate and simple can’t be as fast as an automatic control making the inching solenoid valves more important.
If you are thinking about purchasing a concrete plant without an automatic control system, you may want to ask about the types of solenoids used on your gates and how their speed and accuracy are controlled.