About single valve controllers
Single valve controllers are based upon a single proportional valve, a pressure sensor, a PID controller, and a flow restrictor. The PID controller actuates a proportional valve to fill (or drain) a volume. With the proportional valve placed upstream and a flow-restrictor is placed downstream actuating the valve results in a pressure build up. The proportional valve is sized in such a way that it overwhelms the capacity of the flow restrictor resulting in an increasing pressure when opening.
Single valve compared with dual valve controllers
The advantage of a single valve against a bleed is that the valve is always “in control”. This results in the best possible stability. However, because single valves are constantly opened, reference gas consumption of single valve controllers is higher compared to the use of dual valve controllers. PCS developed flow restrictor that matches the proportional valve with a minimum flow consumption. As a rule of thump approximately, 80 mln/min N2 is consumed when running at 100 bar gauge.
To achieve good response time with minimal consumption, the dead volume should be as small as possible. PCS developed ultra-low dead volume single and multi-channel manifolds that meet extreme pressure stability, reasonable response time and flow consumption requirements. For more information, you can read more in the ERC-series.
When a fast response is more important than ultra-high stability, dual valve controllers are in favor. Dual valve controllers have the advantage that they can increase and decrease the pressure equally fast by opening the upstream or downstream valve. Most dual valve pressure controllers have certain dead-band in with both valves are closed. The bandwidth is typically o,1% of the full scale, but can sometimes be reduced to a value close to zero.