Boilers, pumps & valves
surface pumps 101 1. Surface pump categorieS
atlas copco surface pumps are divided into the following ranges:
centrifugal dry prime (pas) centrifugal wet prime (var)
Wellpoint (Wel) centrifugal wet prime plus vacuum assistant (Wel eco) piston positive displacement (Wel pst) modular vacuum and submersible system (Wel taNK)
all categories are self-priming, although the
wet prime models initially require manual filling of their pump cavity with liquid. Dry prime (pas) pumps have a suction
system, which rapidly draws liquid in, so there is no need for initial manual priming. it means you can start pumping from the moment you turn the switch. compared to the wet prime (var) range, these pumps offer faster flow rates, higher lift capabilities and greater energy efficiency. they are suited to pumping larger volumes of liquid and handling bigger solid particles. although dry prime is superior in those
respects, wet prime has advantages too. var wet prime pumps are more portable and are
therefore ideal for areas where access is difficult, and terrain is rough. With their relatively simple construction and fewer components, they are lower in price, easier to maintain, and offer a long and reliable service life even in tough conditions. once filled, they are self-priming, provided that the liquid level remains above their impeller. Both pas and var pumps are specially
designed to handle dirty water with a high solid content. By contrast, applications for wellpoint pumps (Wel) involve comparatively clear sources such as groundwater. they are fitted with filters to remove sand and other small solids. in wellpoint dewatering, narrow shafts are
injected into the ground to create small wells, which are then connected to a pump. this method is typically used to reduce the groundwater level when it is close to the surface, or to remove water completely from a structure. the compact, robust Wel pumps use vacuum assistance and are technologically adapted to handling a high percentage of air. Wel eco centrifugal pumps are best for larger areas of application, while Wel pst piston positive displacement pumps give an energy- efficient and low-maintenance option for smaller jobs. finally, Wel taNK offers the benefits of all of these technologies - for situations where liquid is present intermittently - as they will cope with dry running and high proportions of air in the flow.
2. Dewatering
flooding due to unusually high rainfall and overflowing of rivers, reservoirs or other water bodies is a common problem today in many areas. on construction, quarrying and mining, sites there is the additional issue of groundwater, which appears as excavation lowers the land surface. this is also a problem during tunnelling operations. When alleviation of a heavy flood requires
rapid removal of water, a powerful pas dry prime pump is the obvious choice. this is particularly true when the water has a high solid content. for small or medium-sized floods, especially in less accessible places, a var wet prime pump may be the easier option. these pumps are also suitable for reducing
groundwater and accumulated rainwater on construction sites, so that workers can operate more safely. However, a more specialised solution for lowering groundwater level before excavation for footings is wellpoint dewatering using Wel pumps. Wellpoint pumps will efficiently extract a flow
of water and air from the ground material to achieve and maintain the necessary reduction in its level. Depending on the size of area involved, you can choose between Wel pst piston positive displacement models, for lighter duties, and higher-flow Wel eco centrifugal pumps for large sites. constant ingress of groundwater when
excavating tunnels can be similarly controlled using the wellpoint approach and Wel pumps.
62 octoBer 2021 | factorY&HaNDliNGsolutioNs
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