A positive fluid displacement apparatus, comprising: a) an orbiting scroll member including an end plate (61, 61') having a front plate and a rear plate arranged back to back, and two scroll elements (62, 62') are affixed to and extend from opposite sides of the front and rear plates, respectively; said orbiting scroll member comprises a front orbiting scroll member that includes said front plate and said attached scroll element, and a rear orbiting scroll member that includes said rear plate and said attached scroll element; and three, equally-spaced peripheral extensions (160a, 160'a, 160b, 160'b, 160c, 160'c) for each of said front and rear plates; b) first and second oppositely disposed, fixed scroll members (50, 70), each fixed scroll member including an end plate (51, 71) having a scroll element (52, 72) affixed to an internal facing surface of the respective plate, each scroll element (52, 72) of the fixed scroll members engageable respectively with one scroll element (62, 62') of said orbiting scroll member, wherein when said orbiting scroll member orbits with respect to said fixed scroll members, flanks of said engaged scroll elements (52, 62, 62', 72) of the orbiting and fixed scroll members (50, 70) along with said front and rear plates (61, 61') of said orbiting scroll member and the internal facing surfaces of said end plates (51, 71) of said fixed scroll members define moving pockets of variable volume and zones of high and low fluid pressures; c) a housing (20, 21) supporting said first and second fixed scroll members (50, 70); d) a rotatable shaft within said housing arranged to drive said orbiting scroll member in orbiting motion with respect to said fixed scroll members; e) three equally spaced crank handles (162a, 162b, 162c), each rotatably supported by said housing; f) radially compliant linking means connecting said shaft to said orbiting scroll member and connecting said crank handles to said peripheral extensions of said orbiting scroll member to maintain a predetermined angular relationship between said orbiting and fixed scroll members and to allow said orbiting scroll member to slide radially to effect tangential sealing between said involute wraps of said orbiting and fixed scroll members which make moving line contact as said orbiting scroll member is driven; g) a synchronizer (170, 173a-c, 174) synchronizing said crank handles such that in a plane perpendicular to said rotatable shaft, lines drawn through centers of said crank handles and perpendicular to the direction of orbiting motion of said orbiting scroll member remain parallel; and h) a plenum chamber formed between said front and rear plates of said front and rear orbiting scroll members, wherein a pressurized fluid introduced into said plenum chamber urges the front and rear orbiting scroll members towards the fixed scroll members. a) an orbiting scroll member including an end plate (61, 61') having a front plate and a rear plate arranged back to back, and two scroll elements (62, 62') are affixed to and extend from opposite sides of the front and rear plates, respectively; said orbiting scroll member comprises a front orbiting scroll member that includes said front plate and said attached scroll element, and a rear orbiting scroll member that includes said rear plate and said attached scroll element; and three, equally-spaced peripheral extensions (160a, 160'a, 160b, 160'b, 160c, 160'c) for each of said front and rear plates; b) first and second oppositely disposed, fixed scroll members (50, 70), each fixed scroll member including an end plate (51, 71) having a scroll element (52, 72) affixed to an internal facing surface of the respective plate, each scroll element (52, 72) of the fixed scroll members engageable respectively with one scroll element (62, 62') of said orbiting scroll member, wherein when said orbiting scroll member orbits with respect to said fixed scroll members, flanks of said engaged scroll elements (52, 62, 62', 72) of the orbiting and fixed scroll members (50, 70) along with said front and rear plates (61, 61') of said orbiting scroll member and the internal facing surfaces of said end plates (51, 71) of said fixed scroll members define moving pockets of variable volume and zones of high and low fluid pressures; c) a housing (20, 21) supporting said first and second fixed scroll members (50, 70); d) a rotatable shaft within said housing arranged to drive said orbiting scroll member in orbiting motion with respect to said fixed scroll members; e) three equally spaced crank handles (162a, 162b, 162c), each rotatably supported by said housing; f) radially compliant linking means connecting said shaft to said orbiting scroll member and connecting said crank handles to said peripheral extensions of said orbiting scroll member to maintain a predetermined angular relationship between said orbiting and fixed scroll members and to allow said orbiting scroll member to slide radially to effect tangential sealing between said involute wraps of said orbiting and fixed scroll members which make moving line contact as said orbiting scroll member is driven; g) a synchronizer (170, 173a-c, 174) synchronizing said crank handles such that in a plane perpendicular to said rotatable shaft, lines drawn through centers of said crank handles and perpendicular to the direction of orbiting motion of said orbiting scroll member remain parallel; and h) a plenum chamber formed between said front and rear plates of said front and rear orbiting scroll members, wherein a pressurized fluid introduced into said plenum chamber urges the front and rear orbiting scroll members towards the fixed scroll members.