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A flow regulator particularly for sub-sea chemical injection at low continuous rates includes a piston moveable in response to differential pressure and controlling via a lever connection an inlet valve. The differential pressure is balanced by a dual rate spring assembly which is positionally adjus

A flow regulator particularly for sub-sea chemical injection at low continuous rates includes a piston moveable in response to differential pressure and controlling via a lever connection an inlet valve. The differential pressure is balanced by a dual rate spring assembly which is positionally adjustable by means of a screw-threaded adjusting rod.

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1. A liquid flow regulator including:first and second chambers and a flow passage connecting said chambers; a piston responsive to differential pressure between said chambers to move in a valve-closing direction in response to excess pressure in the first chamber over pressure in the second chamber;

1. A liquid flow regulator including:first and second chambers and a flow passage connecting said chambers; a piston responsive to differential pressure between said chambers to move in a valve-closing direction in response to excess pressure in the first chamber over pressure in the second chamber; a bias member urging said piston to move in said value-closing direction; a varying rate resilient load opposing movement of said piston in said valve-closing direction; a positionally adjustable datum member for said resilient load; a motor coupled to move said positionally adjustable datum member; an inlet passage coupled to said first chamber; a regulating valve which is controlled by the piston and is disposed in said inlet passage upstream of the first chamber; and a lever connection between said piston and said regulating valve. 2. A flow regulator as in claim 1 wherein said resilient load provides an initial low spring rate and a subsequent higher spring rate.3. A flow regulator includingfirst and second chambers and a flow passage connecting said chambers; a piston responsive to differential pressure between said chambers to move in a valve-closing direction in response to excess pressure in the first chamber over pressure in the second chamber; a bias member urging said piston to move in said valve-closing direction; a varying rate resilient load opposing movement of said piston in said valve-closing direction; a positionally adjustable datum member for said resilient load; a motor coupled to move said positionally adjustable datum member; an inlet passage coupled to said first chamber; and a regulating valve which is controlled by the piston and is disposed in said inlet passage upstream of the first chamber; wherein said resilient load comprises a low rate spring in series with a high rate spring. 4. A flow regulator as in claim 1 wherein said positionally adjustable datum comprises a screw-threaded member.5. A flow regulator as in claim 4 and comprising a stepper motor for the rotation of the screw-threaded member.6. A flow regulator as in claim 1 wherein said flow passage includes a flow constrictor.7. A liquid-flow regulator comprising:(a) a body defining a first chamber and a second chamber, an inlet passage for the first chamber and an outlet passage for the second chamber; (b) a regulating valve disposed in the inlet passage; (c) a piston disposed between the first and second chambers so as to be moveable in response to differential pressure between the chambers; (d) an orifice connecting the first and second chambers; (e) a connection between the piston and the valve whereby movement of the piston in response to an increase in the differential pressure tends to close the valve; (f) a multiple-rate resilient load structure which balances the differential pressure on said piston, the rate increasing as said piston moves in a valve-closing direction; (g) a bias member disposed to urge said piston to move in said valve-closing direction; and a lever coupled between the piston and the valve, whereby closure movement of the valve is in an opposite direction to said movement of the piston. 8. A regulator as in claim 7 wherein the lever is disposed to extend transversely of the piston and is pivoted between ends which engage the piston and an operating member for the valve respectively.9. A liquid-flow regulator as in claim 7 comprising:(a) a body defining a first chamber and a second chamber, an inlet passage for the first chamber and an outlet passage for the second chamber; (b) a regulating valve disposed in the inlet passage; (c) a piston disposed between the first and second chambers so as to be moveable in response to differential pressure between the chambers; (d) an orifice connecting the first and second chambers; (e) a connection between the piston and the valve whereby movement of the piston in response to an increase in the differential pressure tends to close the valve; (f) a multiple-rate resilient load structure which balances the differential pressure on said piston, the rate increasing as said piston moves in a valve-closing direction; and (g) a bias member disposed to urge said piston to move in said valve-closing direction; wherein the multiple-rate resilient load structure comprises an adjustable datum member and between said datum member and the piston a compressive assembly comprising a relatively high-rate spring in series with a relatively low rate spring. 10. A regulator as in claim 9 wherein said adjustable datum member is a screw-threaded rod.11. A regulator as in claim 10 and including a stepper motor for controlled rotation of the screw-threaded rod.12. A regulator as in claim 9 wherein the compressive assembly comprises a first guide and a second guide between which the high rate spring is disposed, and a third guide slidable within the second guide, the low rate spring being disposed between the second and third guides.13. A regulator including:first and second chambers and a flow passage connecting said chambers; a piston responsive to excess pressure in the first chamber over pressure in the second chamber to move in a valve-closing direction; a resilient load opposing movement of said piston in said valve-closing direction; an inlet passage coupled to said first chamber; a regulating valve which is controlled by the piston and is disposed in said inlet passage upstream of the first chamber; a lever coupled between the piston and the valve, whereby closure movement of the valve is in an opposite direction to said movement of the piston; and a bias spring coupled to said piston to urge said piston in the direction for closing said valve. 14. A regulator as in claim 13 wherein said lever is disposed to extend transversely of the piston and is pivoted between ends which engage the piston and an operating member for the valve respectively.15. A regulator s in claim 13 wherein said resilient load comprises a low rate spring in series with a high rate spring.16. A regulator as in claim 14 and further comprising an adjustable bias for said resilient load.17. A liquid-flow regulator comprising:(a) a body defining a first chamber and a second chamber, an inlet passage for the first chamber and an outlet passage for the second chamber; (b) a regulating valve disposed in the inlet passage; (c) a piston disposed between the first and second chambers so as to be moveable in response to differential pressure between the chambers; (d) an orifice connecting the first and second chambers; (e) a connection between the piston and the valve whereby movement of said piston in response to an increase in the differential pressure tends to close the valve; and (f) a positionally adjustable datum member; (g) a compressive assembly, comprising a relatively high-rate spring in series with a relatively low rate spring, disposed between said datum member and said piston; and (h) a motor coupled to move said positionally adjustable datum member. 18. A regulator as in claim 17 and including a lever coupled between the piston and the valve, whereby closure movement of the valve is in an opposite direction to said movement of the piston.19. A regulator as in claim 18 wherein the lever is disposed to extend transversely of the piston and is pivoted between ends which engage the piston and an operating member for the valve respectively.20. A regulator as in claim 17 wherein said adjustable datum member is a screw-threaded rod.21. A regulator as in claim 20 wherein said motor is a stepper motor coupled for controlled rotation of the screw-threaded rod.22. A regulator as in claim 17 wherein the compressive assembly comprises a first guide and a second guide between which the high rate spring is disposed, and a third guide slidable within the second guide, the low rate spring being disposed between the second and third guides.23. A regulator as in claim 17 further comprising a bias spring urging said piston in a direction for closing the valve.