Leistritz introduces a new screw pump for API applications
Leistritz Pumpen has launched a new series of pumps designed to comply with API 676 3rd Edition. API 676 – Positive Displacement Pumps – Rotary, 3rd Edition, Nov. 2009, is a standard put forth by the American Petroleum Institute. 'It covers the minimum requirements for rotary positive displacement pumps for use in the oil & gas, petrochemical, and chemical industries,' explains Heinz-Dieter Roß, MD at Leistritz Pumpen. 'It provides a purchase specification to facilitate the manufacture and purchase of rotary positive displacement pumps.'
Function of triple screw pumps
Triple screw pumps are self-priming rotating positive displacement pumps suited to handle various oil types and other liquids with a minimum lubricating quality. The design simplicity makes these screw pumps intrinsically reliable and efficient. Only three moving parts – a driving spindle and two idler spindles – rotate inside a casing with close tolerances, so forming sealed chambers and provoking the axial displacement of the fluid. The idler spindles rotate without contact with the driving spindle because of the fluid itself. The accurate hydraulic balance and the special profile of the screw thread guarantee a continuous flow with minimum pulsations and turbulence, resulting in extremely low noise levels even at high rotational speed.
Up until now triple screw pumps, which exist on the market have been adapted in such a way that they complied with this standard as much as possible. Roß explains: 'Oftentimes these pumps are based on a standard execution and therefore do not represent an optimum in features and cost. Leistritz decided to make a fresh start on the digital drawing board to find the optimum solution and have been able to come up with a new concept.'
The new L3MA pump has no separate steel casing with an internal liner for the screw spindles to run in. A new spindle material makes it possible to have the spindles run directly in a steel casing and avoids an expensive construction with a coating in a separate liner.
Only three static seals, executed as O-ring seals instead of flat gaskets, are used. This eliminates the risk of leakage due to insufficient compressed flat gaskets. A single balanced acting mechanical seal has been chosen as shaft seal which proved itself in thousands of applications. A cartridge seal can be provided as an option. Suction and discharge flanges are according to ANSI B 16.5 class 300 lbs. The L3MA pump series is available in 12 different frame sizes with defined rotor pitch angles.
The maximum operating conditions of the pump are defined with a maximum flow rate of 276 m3/h, a differential pressure of 20 BarG and maximum speed of 3600 rpm.
A minimum viscosity of the pumping fluid should be around 10 cSt to secure the required lubrication.