Intermediate Pressure

[DA Aquamaster]

Another question here. Would there be an effect on the IP pressure (and by how much) when air is drawn from the second stage? Thanks.

Drop in IP is entirely normal and it is the drop in IP that provides the force needed to lift the seat off the orifice in the first stage.

How much drop occurs depends on the flow capacity of the first stage and on how much air is being drawn through the second stage. A normal inhalation produces relatively little drop, while a full depression of the purge button will normally produce a larger drop.

What is more important is that the IP locks up tightly after the inhalation stops and no IP creep occurs.

 

[Tim Wong]

Drop in IP is entirely normal and it is the drop in IP that provides the force needed to lift the seat off the orifice in the first stage.

How much drop occurs depends on the flow capacity of the first stage and on how much air is being drawn through the second stage. A normal inhalation produces relatively little drop, while a full depression of the purge button will normally produce a larger drop.

What is more important is that the IP locks up tightly after the inhalation stops and no IP creep occurs.

Thanks for the reply. Would it be safe to say that a balanced first stage would have a lesser IP pressure drop than an unbalanced one during heavy air demand situation ?

 

[DA Aquamaster]

Yes, but not directly.

Balancing a first stage insures the IP will remain constant as tank pressure changes during the dive. IP will otherwise decrease with a piston first stage as tank pressure falls and increase with a diaphragm first stage as tank pressure falls. The change in IP in an unbalanced reg can affect flow rate slightly, but the major difference in performance comes from the larger orifice that can be used in a balanced regulator.

With an unbalanced first stage, the downstream force on the seat caused by the effects of tank pressure cause the change in IP as tank pressure falls. Consequently, the larger the orifice, the larger the change in IP through the range of tank pressure. This puts a significant limit on orifice size and tends to limit the flow rate performance of unbalanced regulators.

So directly, the balancing the first stage seat against this downstream force has only a small impact on flow rate. But indirectly it allows the designer to use a much larger orifice and this allows much larger flow rates which reduce IP drop significantly.

 

[scubatoys]

But the interesting thing about poseidons... If you take say an odin, and check the IP - holding around the 145 range, hit the purge hard and it will jump up to 175, while most other regs will drop down to about 125.

 

[DA Aquamaster]

Poseiden's don't count. They are just plain different and pretty much defy description in terms used to describe other reg designs.

 

[scubatoys]

Poseiden's don't count. They are just plain different and pretty much defy description in terms used to describe other reg designs.

True