Single-Stage Regulator

Hi sadibo, Yes this is true.

Consider this for instance a single stage regulator where the diaphragms forced against the high pressure valve by a spring which is usually adjustable to enable different pressures to be delivered. When the higher pressure in a cylinder starts to fall the spring has less pressure to work against so it opens the valve up slightly which gives a slight increase in pressure , this effect is very noticeable when the cylinder pressure aproaches the outlet pressure. It is possible to compensate for this to some degree by running a rod through a seal from the high pressure side of the valve to atmospheric pressure this acts as a counterbalance and removes a large part of the pressure effect on the valve seat.

Where as with a two stage system the secondry valve works against a much lower pressure [ie it does not need to work over such a large pressure range and the components can be designed for a more accurate pressure control] and this pressure to the second stage is kept relativly constant by the first stage over most of the cylinders pressure range.

This is not a huge problem in systems with a large gas resovoir as the inlet pressures do not vary much but on smaller cylinder supplies it is noticible but not detrimenatal unless the outlet pressure is critical and is being delivered at very low pressures., in this case the regulators should be designed to suit the delivery volume and pressure requirements.