0 50 100 150


FIGURE 4 Compressibility factor (Flowserve Corporation) (bar X 14.5 = lb/in2)

Based on discharge capacity,

where ps = suction density pd = discharge density S = slip

Torque The average torque required by a power pump is independent of the pump speed, assuming the suction and discharge pressures are held constant. This means that the pump is a "constant torque" device and, unlike a centrifugal pump, will have a flat speed-torque curve. The torque required at the input shaft is as follows:

In SI units M = p X 9.549/n where M = pump torque, lb-ft (N • m) n = speed, rpm p = power, bhp (kW)

Break-away torque, or start-up torque, is the torque required to initiate the motion of the pump to enable it to accelerate to a constant speed. If the pump is started against an open bypass to pump suction, the torque requirement is 25% of the running torque. If the pump is started against full discharge pressure, the torque requirement is 125% of the running torque. When selecting a drive system, the break-away torque of the pump must be considered. Special "high torque" motors are often required if the pump is to be started under the load.

TABLE 5 The pulses per revolution and pulse amplitude for various pump types

Pump Type

No. of Cylinders

Pulses per Rev.

Pulse Amplitude

Duplex, double-acting

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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