STATIC PURGE DESIGN
In order to reduce substantially the purge gas flow consumption, the system is based on a static purge system, i.e by successive dilution, instead of a dynamic, i.e. continuous flow, purge concept. This typically results in only 5% of the purge flow consumption compare to a standard purge valve. Here how it works.
Reference to the functional block diagram, shown in figure 2, when SV1 is turned ON, it allows the actuation gas, typically the carrier gas, to flow and pressurise the volume between the two internal pistons, moving them apart so actuating the valve. At the same time, the gas flows through CV1 and flows into R1. The purge flow through R1 builds-up a pressure into the volume to be purged and eventually depressurises when it CV2 opens. This results in a pulse or oscillating purge pressure into the internal volume. This repetitive cycle is going on until the SV1 is turn off and the internal volume is still slightly pressurised with inert gas, keeping air outside. The first time the valve is used, it takes a few cycles before completely eliminating the air inside the internal volume. See the curve at figure 3. The purge gas flows around the plunger through their grooves and sweep away the volume under the diaphragm. This prevent any permeation through the diaphragm from ambient.