Capacity

FIGURE 10 The centrifugal pump characteristics changes depending on speed and head at inlet.

(Figure 9). The method services for condensate, and design precautions prevent rapid cavitation damage.

valve-throttling control The chief elements of centrifugal pump performance are shown in Figure 10. At any given flow rate (capacity), a centrifugal pump produces a discharge head consisting of the static head on the pump inlet and the dynamic head imparted by the pump. At higher flow rates, speed usually declines slightly, lowering the characteristic curve as shown. In addition, the higher flow rates produce more frictional head loss in the inlet piping so the pump senses an inlet head slightly less than the static head developed by the weight of the liquid column and the effect of compressed gas or upstream pumps.

The pump can deliver any flow rate along the curve. What determines the actual flow rate at any instant is the characteristic curve of the downstream piping (system curve), as shown in Figure11. Under zero-flow conditions, there is a gravity head of liquid and perhaps a pressure in a container, such as a boiler drum. When liquid flows, piping friction head is added. Piping friction causes the system curve to turn upward, roughly paraboli-cally. If a downstream control valve, previously wide open, is throttled, a new and more rapidly rising system curve is established. The intersection of a pump curve and system curve plotted on a single chart (Figure 12) indicates conditions at the pump discharge. The combined plot also shows that the flow rate or discharge head will be modified by a change in other parameters besides throttle valve setting. For example, an increase in pump speed

valve

iri-r with valv -> T throttle hi/ „ / / /

; open ^-piping friction

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

Get My Free Ebook


Post a comment