Company: CNG S. Oakford
Case #: 8


Customer has large integral angle compressor units with infinite step capacity control devices over compressor valves to effect the desired load and capacity control of the units. The system was basically a one of a kind system and the OEM no longer made replacement parts available. Maintenance of the valve plate depressors required specialized skills which also are not generally available.

Customer's Need:

A suitable replacement system that would provide the required capacity control and one that would be simpler in design and easier to service as well as being more thermodynamically efficient.

ACI's Solution:

Replace infinite step capacity control system with appropriately sized fixed volume capacity control devices. These would include front head and valve pocket fixed volume unloaders. Existing front heads were checked to determine the interior volumes. These volumes were available for use in the capacity control systems. Utilization of the existing heads reduced the customers cost of the revamp. The multiple, valve-cap pockets, each provided with strategically sized volumes created an unloading schedule that minimized the step size associated with the opening and closing of the individual pockets. The deviation from an infinitely variable flow rate by the fixed volume pockets is more than offset by an increase in compression efficiency.  The infinite step system is associated with very substantial back flow losses when the suction valves are held open to reduce capacity.


Performance of the units has demonstrated that the desired capacity/load control has been accomplished along with the improved efficiency.

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