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Valve Unloaders - Hydrogen Recip Machine

Valve Unloaders - Hydrogen Recip Machine

Valve Unloaders - Hydrogen Recip Machine

Hello All,
I have recently run into some issues with using instrument air versus nitrogen for actuating the valve unloaders on a hydrogen service recip machine. In our existing plant we have recip machines that are using instrument air for capacity control of the existing hydrogen compressor. However, a new vendor on new equipment for the same service (hydrogen) is recommending the use of nitrogen rather than instrument air citing safety concerns (possible leakages of instrument air into the hydrogen) causing safety concerns.

What are youre experiences with recip machines in hydrogen service. Is there a document stating that instrument air is restricted in use for actuation in hydrogen service or otherwise a document stating that we can use instrument air for hydrogen service....

I am a bit confused thought would like to resolve this since its a critical safety issue.


RE: Valve Unloaders - Hydrogen Recip Machine

The majority of our hydrogen make-up compressors use instrument air to actuate the valve unloaders. We do not consider this to be a hazard for a number of reasons.

First, there is a physical separation between the actuator and the valve cover. There is a seal within the actuator and another seal where the stem passes into the valve cover. The support housing between the actuator and the valve cover is not sealed and is incapable of holding pressure. There is no situation I can imagine where air could make it past these barriers to get into the process.

Second, our instrument air pressure is lower than the lowest suction pressure we would ever have to one of these compressors. It would be impossible for 110 psi air to enter into a compressor with 240 psi suction pressure.

Third, we would be more concerned about the inherent hazard associated with nitrogen. Many years ago, we experienced a fatality from nitrogen asphyxiation. We use great caution when placing nitrogen into any area where it could accumulate.

I am not aware of any standard or document that prohibits the use of instrument air to actuate valve unloaders on hydrogen compressors. I did not have time to review API standards and recommended practices for relevant references. I might recommend that you do so.

Johnny Pellin

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