the present invention is a valve defining at least a first modulated or variable flow path and a second , unmodulated or bypass flow path . while the inventive valve is described below in reference to a nitrogen generating system ( ngs ) for an aircraft , it should be understood that a valve in accordance with the present invention is suitable for any application in which it is desirable to implement a valve with at least two flow paths that share a common inlet portion . fig1 shows nitrogen generating system ( ngs ) 10 , which includes inlet air valve 12 , heat exchanger 14 , motor 16 , first compressor 18 , and second compressor 20 . valve 12 is mounted to the inlet header of heat exchanger 14 , and includes valve body 30 , baffle 32 , modulating valve disk 34 , actuator 36 , and shaft 38 . valve 12 provides dual flow paths for ram air into heat exchanger 14 . bypass path b is shown to the right of baffle or separator 32 , while variable path v ( shown to the left of separator 32 ) has a variable opening controlled by modulating valve disk 34 . the position of disk 34 , and therefore the flow through variable path v , is controlled by actuator 36 , which rotates shaft 38 , on which disk 34 is mounted . as shown in fig1 , heat exchanger 14 includes intercooler 40 and main heat exchanger 42 . intercooler 40 is divided into two sections : intercooler section 40 a , which is dedicated to cooling motor 16 ; and intercooler section 40 b , which cools air from first compressor 18 . separator 32 is a vertical wall that extends into heat exchanger 14 to separate incoming ram air to intercooler 40 . separator 32 defines a constant flow opening for ram air to flow through section 40 a of intercooler 40 . the opposite side of separator 32 provides for ram air flow to enter intercooler section 40 b through the variable opening of valve 12 controlled by disk 34 . the variable flow of ram air also is delivered to main heat exchanger 42 , and is used to cool air from second compressor 20 . heat exchanger 14 includes compressor air inlets 44 and 46 , air outlet 48 , air outlet 50 , heat exchanger outlet 52 , ram air outlet 54 ( shown in fig2 ), and mount 56 . motor 16 drives first compressor 18 and second compressor 20 . motor 16 includes air inlet 60 for receiving cooling air from outlet 48 of heat exchanger 14 . first compressor 18 includes inlet 62 and outlet 64 . air from outlet 64 of first compressor 18 is delivered to inlet 44 of heat exchanger 14 . second compressor 20 includes inlet 66 and outlet 68 . as shown in fig1 , second compressor inlet 66 receives air from outlet 50 of heat exchanger 14 . air from second compressor outlet 68 is delivered to inlet 46 of heat exchanger 14 . in operation , air is drawn through inlet 62 into first compressor 18 . air flows out of outlet 64 of compressor 18 to inlet 44 of heat exchanger 14 . the first compressor air flows through intercooler section 40 a to outlet 48 , where it is delivered to air inlet 60 of motor 16 . the air passing through intercooler section 40 a is cooled by ram air which has flowed through the open bypass section of valve 12 . a portion of the air delivered from first compressor 18 to inlet 44 flows through intercooler section 40 b to outlet 50 , and then is supplied to inlet 66 of second compressor 20 . the air flowing through intercooler 40 b from first compressor 18 is cooled by a variable flow of ram air that is modulated by disc 34 . output air from second compressor 20 is delivered through outlet 68 to inlet 46 . the second compressor air flows through main heat exchanger 42 to heat exchanger outlet 52 . fig2 shows valve 12 and heat exchanger 14 separate from the other components of ngs 10 . valve 12 provides two separate passageways for ram air : unmodulated or bypass passage b and modulated or variable passage v . bypass passage b allows a portion of ram air received at the inlet end of valve 12 to pass directly to intercooler 40 a . variable flow passage v controls the flow of air to intercooler 40 b and main heat exchanger 42 . the amount of air flowing through passage v is controlled by the position of disc 34 . actuator 36 rotates shaft 38 to position disc 34 in passage v . disc 34 , in combination with actuator 36 and shaft 38 , operates as a butterfly valve assembly , which rotates around centerline cl of shaft 38 . in fig2 , disc 34 is shown in a closed position , thereby blocking airflow through passage v . in fig3 , disc 34 is shown in an open position , so that a portion of the ram air delivered to valve 12 can pass through passage v to intercooler section 40 b and main heat exchanger 42 . valve 12 provides multiple flow paths that share a single inlet . bypass passage b provides a constant airflow , while variable passage v provides a variable airflow , depending upon the position of valve disc 34 . although both passage b and v are shown as having a d - shaped opening , other shapes can also be used . for example , fig4 shows an embodiment in which separator 32 is curved and bypass passage b is crescent shaped . similarly , although the butterfly - type valve is shown in variable passage v , other types of flow modulating valves may be positioned within passage v . examples include a ball valve , a gate valve , a spool valve , and a flapper valve . although inlet valve 12 is described as being used to introduce ram air into ngs 10 , it should be understood that an inlet valve in accordance with the principles of the present invention may be used in conjunction with other fluids , such as liquids , as well as other assemblies . furthermore , the inlet valve may be formed of any suitable material , such as , but not limited to , metals , polyvinyl chloride , and other plastic materials . the terminology used herein is for the purpose of description , not limitation . specific structural and functional details disclosed herein are not to be interpreted as limiting , but merely as bases for teaching one skilled in the art to variously employ the present invention . although the present invention has been described with reference to preferred embodiments , workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention .