Solenoid Valves For Vacuum or Low pressure applications such as header tank pressures or closed loop systems with little or no differential pressure across the valve we use "Zero Rated" solenoid valves. These will work with zero or little pressure differential. There are two main types of Zero Rated solenoid valves "Direct" and "Assisted".
An "Assisted" Solenoid Valve has an attachment from the armature that mechanically lifts the diaphragm/piston off its seat thus causing the valve to open even if there is no or little pressure from the media. Good for Zero to Medium Pressures with good flow capabilities.
A "Direct" Solenoid Valve uses the armature directly over the valve seat as the mechanical means to Directly open and close the valve regardless of the media pressure. Good for High Pressures with Lower flow capabilities.
Solenoid Valves for high pressure or vent to atmosphere applications can use a "Servo Assisted" or "Pilot Operated" Solenoid Valve sometimes called a "Diaphragm" valve.
A "Servo Assisted" or "Pilot Operated" Solenoid Valve uses the pressure difference across the solenoid valve (Differential Pressure across inlet and outlet valve ports) to do the mechanical work of lifting the diaphragm/piston to open the valve. This is achieved by controlling the pressure above the diaphragm/ piston via a pilot system which can release this pressure through to the outlet port of the valve down stream allowing the inlet pressure to overcome the now reduced pressure above the piston/ diaphragm and allowing it to lift and open the valve allowing flow and vice versa.
Most valves of this design require between 0.1 and 2 bar pressure difference to operate correctly normally about 10% of the working pressure. Choice of valve size is of paramount importance in achieving this as too much or too little could adversely affect the operating function.
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