The most basic 800 Series Control Valve is the on/off configuration. As a hydraulically operated sleeve-type valve, the Nelson on/off valve can be easily and inexpensively automated where traditional butterfly or gate valves cannot. They are designed to open and close smoothly, so they are less susceptible to being accidentally opened/closed too quickly and causing water hammer like commonly occurs with traditional manual valves. And where traditional butterfly and gate valves are known to seize up over time, Nelson valves are operated with a simple manual selector that is easy to operate and will never seize.
The valve is controlled with a 3-way manual selector (open/close/auto) that is used to fully open or fully close the valve. When the selector is pointed to the “AUTO” position then the electric solenoid is used to automatically open or close the valve. Pointing the manual selector handle to “OPEN” or “CLOSE” will override the “AUTO” control. The manual selector can be used to hold the valve partly open by allowing the valve to go open opening the valve part way and then pointing the selector handle midway between “OPEN” and “CLOSE”.
In the standard configuration, the 3-way electric solenoid must be energized to open the valve and de-energized to close the valve. Thus, all Nelson control valves come standard "normally closed", which means they require pressure to open. When configured with a solenoid, the valves can be specified "normally open", which makes the valve open when the solenoid is de-energized.
Care must be taken to ensure the right solenoid is specified to ensure compatibility with the controller and valve size. Consult the solenoid resource document for full specifications.