Case No. 68295(2)
CLAIMS
1. A multiple stage pump assembly comprising at least two pumps arranged in series,
wherein at least the second and each subsequent pump comprises a pump inlet, a pump
outlet, at least two threaded rotors and a pressure controlled valve, the pressure controlled
5 valve being capable of controlling re-circulation of fluid from the pump outlet to the pump
inlet.
2. The assembly of claim 1, in which the pressure controlled valve is adapted to control
the rate of fluid flow there-through in proportion to the gas to liquid ratio of a fluid being
pumped by the pump in use.
10 3. The assembly of claim 1 or claim 2, in which the pressure controlled valve is a
control valve.
4. The assembly of any one of the preceding claims, further comprising a conduit
connecting the pump outlet to the pump inlet and through which re-circulated fluid can
flow in use.
15 5. The assembly of claim 4, in which the pressure controlled valve is located wholly or
partly within the conduit or adjacent one or other end of the conduit.
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6. The assembly of claim 4 or clam 5, f~~rthceorm prising a recess in the pump outlet to
preferentially allow, in use, liquid rather than gas to flow from an enclosure in which the
threaded rotors are located to the conduit.
20 7. The assembly of any one of the preceding claims, in which the pressure controlled
valve is one which responds to the absolute pressure difference between the pump outlet
and the pump inlet such that the valve permits fluid to flow there-through when the
absolute pressure difference between the pump outlet and the pump inlet reaches a
threshold level.
25 8. The assembly of any one of claims 1 to 6, in which the pressure controlled valve is
one which responds to the ratio between the pressure at the pump outlet and the pressure at
the pump inlet, such that the valve permits fluid to flow there-through when the ratio
between the pressure at the pump outlet and the pressure at the pump inlet reaches a
threshold.
30 9. The assembly of claim 8, in which the valve comprises a piston having an inlet face
and an outlet face, the surface area of the inlet face being greater than the surface area of
the outlet face and the ratio between the area of the inlet face to the area of the outlet face
Case No. 68295c2)
prescribing the threshold ratio between the pressureat the pump outlet &d the pressure at
the pump inlet.
10. The assembly of any one of claims 1 to 6, in which the pressure controlled valve is
one which responds to the ratio between the pressure difference between the outlet and the
inlet of the pump (dPSt,,,) and the pressure difference between first and second pressures
(dpassembly) which, in use, are communicated to the valve, such that the valve permits fluid
to flow there-through when the ratio between dPstage and dPassembrleya ches a threshold.
11. ' The assembly of claim 10, in which the valve comprises a piston having end faces
and two chambers, one chamber being adapted for fluid communication with an intake of a
multiple stage pump assembly which is at the second pressure and the other chamber being
adapted for fluid communication with a discharge of said multiple stage pump assembly
which is at the first pressure, such that, in use, the pressures in the chambers which
correspond to the intake and discharge pressures of the multiple stage pump assembly
*
oppose the inlet and outlet pressures of the pump respectively, wherein the ratio of the
surface area of the end faces to the cross-sectional area of the chambers prescribes the
threshold ratio at which the valve will permit fluid flow.
12. The assembly of any one of the preceding claims, wherein each pump has the same
swept volume.
13. The assZmbly of any one of claims 1 to 11, wherein there is a reduction in the swept
volume of each pump from the first pump to the last pump in the series.
14. A method of pumping a fluid from a first location to a second location comprising ,
providing a multiple stage pump assembly having two or more pumps in series wherein the
second and each subsequent pump is adapted to re-circulate fluid from its outlet to its inlet,
positioning an intake end of the multiple stage pump assembly at or near the first location,
activating the multiple stage pump assembly to pump the fluid from the f ~ slot c ation to the
second location, and re-circulating fluid from the outlet to the inlet of said second and each
subsequent pump.
Dated this 08/01/2014
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]