Any special requirements for a CNG pressure gauge?

[jblue]

Besides the obvious need for the gauge to be rated for the pressure, is there anything else?

Or is a gauge is a gauge is a gauge?

[larrycng]

Re: Any special requirements for a CNG pressure gauge?

It is my personal preference is to use a liquid (silcone) filled gauge, this is not a requirement. NFPA 52 requires a gauge with a restrictor orfice and must read 1.2 times system pressure.

Larrycng

[jblue]

Re: Any special requirements for a CNG pressure gauge?

NFPA 52 requires a gauge with a restrictor orfice and must read 1.2 times system pressure.

What is the operational purpose of the restrictor orifice?

Can you point me to any mfg's or suppliers?

[soutthpaw]

Re: Any special requirements for a CNG pressure gauge?

any hydraulic or welding supply like airgas usually keeps gauges in stock. 4000-5000 psi would be good.. I just need a female connector for the fill port and can make one for myself... I have several gauges floating around the garage

[Franz]

Re: Any special requirements for a CNG pressure gauge?

The orifice is there to reduce the flow if the gauge is broken off. Top shelf gauge suppliers include WIKA and Ashcroft, with others as good as. Just remember the 1.2X safety factor, minimum.

Any adapter you might make should hold at least 4X the max pressure in the system. I recently saw a 1/4"NPT galvanized elbow on a CNG system. This had a 125 psig working pressure but it actually held 3600 psig.

Franz

[jblue]

Re: Any special requirements for a CNG pressure gauge?

The orifice is there to reduce the flow if the gauge is broken off.

Roger.

Is there a spec on the size of the orifice?

[larrycng]

Re: Any special requirements for a CNG pressure gauge?

I guess the only thing remains is the 0.055" (or #54 drill) orfice size requirement (NFPA 52 - 5.6.2). Without the restriction, if the the tube in the gauge ruptured the flow would be equiviliant to a line breaking. That is why the pressure gauges are not allowed in the passenger compartment; tube rupture, gas flow and gauge len material flying all over the place, it ain't pretty

Larrycng