CNG Station operation and repairs – keep that final stage loaded!

Posted by cngcenter on May 16, 2013 in Tips

If added to the order for CNG fast fill-slow fill, CNGCenter provides a priority valve on the discharge of the compressor skid.This priority valve is really a back-pressure regulator, designed to maintain a minimum discharge pressure from the compressor package. The purpose of this is to assure that the final stage of the compressor is loaded.

It is important to keep this final stage loaded in order to prevent oil carryover. Most of the Valves recommends 2500 psi as the minimum pressure to be maintained on the CNG packages and, of course, higher pressures are quite acceptable.

Compressors tested without a back-pressure regulator show as much as 8 times the amount of oil carry over as those that include the valve. In addition, loading the unit also allows the compressor to operate under a more consistent load, reducing problems that maybe associated with large swings in the rod loading.

Priority valves should never be adjusted at the compressor outlet with the compressor running. The Joule – Thompson effect from taking a large pressure drop across the valve causes a severe cooling effect that can cause the valve stem to momentarily “grab” its seating O-rings. Should this happen, the O-rings will move with the stem and tear. A damaged O-ring is easy to find. Gas vents will vent up the valve stem and exit out the top of the valve.

Remember; adjust the regulator with the compressor off.