ASCO 2-Way Valve Operation
Two-way solenoid valves have one inlet and one outlet, and are used to permit and shut off fluid flow
Two Types of Operations
Normally Closed (NC) – Fluid is shut off when the coil is de-energized, flows through the valve when the coil is energized.
Normally Open (NO) – Fluid flows through the valve when the coil is de-energized, shuts off when the coil is energized.
Two Types of Construction
Direct Acting – When the solenoid is energized, the core directly opens the orifice of a Normally Closed valve or closes the orifice on a Normally Open valve. The valve will operate at pressures from 0 psi to its rated maximum. The force needed to open the valve is proportional to the orifice size and fluid pressure. As orifice size increases, so dose the required force. To open a larger orifice without increasing solenoid size, internal pilots are used.
Internally Piloted – These valves use line pressure to assist operation. When the coil is de-energized (on a Normally Closed valve), the pilot orifice is closed and line pressure is applied to the top of the piston or diaphragm through the bleed orifice, closing the valve. When the coil is energized, the core opens the pilot orifice, relieving pressure from the diaphragm or piston. Line pressure, alone, opens the valve by lifting the diaphragm or piston off the main orifice.
ASCO Engineering Guide (PDF)