MKS 248A, Manual

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Chapter Three: Operation General Information
13
Chapter Three: Operation
General Information
The 248 valve (<10,000 sccm) may be operated with 150 psig maximum inlet pressure, however,
the nominal flow rating is established at 1 atmosphere differential across the valve, increasing the
inlet pressure up to the maximum allowed. This extends the maximum flow control range from
approximately 3X (10K sccm range) to 250X (10 sccm range). Decreasing the outlet pressure
increases the flow range until the choked flow condition is reached. Further lowering of outlet
pressure for a fixed inlet pressure will not increase flow because a sonic restriction exists.
For 20,000 and 50,000 sccm 248 valves the maximum operating pressure drop is 15 psig to
atmosphere.