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Hydrogen mass flow

The hydrogen gas inside the generator is usually at a pressure of approximately 4 barg, which means that air cannot leak “into” the generator casing where the hydrogen is. In effect, this is the primary method of preventing air from getting into the casing and contaminating the hydrogen.
However, oil, which will have entrained air in it, is used as the sealing medium, the air released from the “seal oil” that flows into the hydrogen area can reduce the hydrogen purity if not removed.
So, there is a system to remove the air which is liberated from the seal oil that flows into the hydrogen side of the generator seal. That system is typically called a “scavenging” system. A small amount of gas is allowed to be vented from the seal oil enlargement tank. The pressure inside the generator would decrease if nothing else were done so by flowing a small amount of pure hydrogen into the generator casing, the pressure is maintained.
The scavenging flow rates must also be set and monitored to prevent excessive hydrogen consumption (to replace the hydrogen lost with the air that’s being vented to atmosphere).

The ST75V is ideally suited to measuring the very low flow rates required to maintain hydrogen pressure whilst at the same time has a very wide flow range. It is therefore capable to measuring the higher flow rates used when the alternator is being filled from empty after being off line.

Key Features

Ideal alternative to Rotameters

Direct mass flow measurement

No moving parts


Calibrated using Hydrogen gas

Pipe sizes from 1/4″ to 6″

Flow rates from  0.15 Nm3/hr

Wide flow range with 100 : 1 turndown

ATEX Exd ll C rated

All welded 316 st/st