Driver-limited pumps

A turbine-driven pump is said to be driver-limited when the governor speed-control valve is wide open. This speed-control valve, is usually called the Woodward governor. It is not that easy to see if the governor is really wide open. A few simple methods to make this determination are... 

If we cannot open the discharge control valve of a centrifugal pump 100 percent before the FLA point is reached, then we say that the pump is driver-limited. This is a frustrating problem for plant operators, and clearly reflects poor design practice in undersizing the motor driver horsepower. 

Driver-limited A pump that is limited by the horsepower of its turbine or... 

FIG. 29-59 Head-horsepower-capacity characteristics of a power-recovery turbine operating as the sole driver of a lean pump. If the total capacity of lean and semilean pumps exceeds the values indicated by available head limit, bypass must be used. Net recovery-pump head at 8.71 mVmin (2300 gal/min) is figured as follows ... 

Most pumps are considered constant speed, but the true speed changes with variations in suction pressure and back-pressure caused by restrictions in the discharge piping. The narrowband should have lower and upper limits sufficient to compensate for these speed variations. Generally, the limits should be set at speeds equal to the full-load and no-load ratings of the driver. 

All positive-displacement pumps have one or more rotating shafts that provide power transmission from the primary driver. Narrowband windows should be established to monitor the actual shaft speeds, which are in most cases essentially constant. Upper and lower limits set at 10 per cent of the actual shaft speed is usually sufficient. 

Pumps (centrifugal, reciprocating) Fluid density, capacity, dynamic head, type, driver, operating condition limits, material of construction... 

Sound. The maximum sound pressure level produced by tiie pump and driver shaU comply with the limit specified by tiie customer. Test, if specified, shaU be conducted in accordance witii tiie standards of HI 9.1/9.5, para. 9.4. Driver noise data must be determined separately. 

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