XCS Screw Centrifugal Pump

The XCS screw centrifugal pump offers unique technological advantages that are well suited to municipal sludge pumping applications.

Services like Return Activated Sludge (RAS), Waste Activated Sludge (WAS), and Digested Sludge Recirculation often involve short pipe runs with relatively little static head, resulting in low overall total dynamic head (TDH). Required flows can be especially high when tanks are being recirculated or mixed. This high flow/low head hydraulic requirement is difficult to obtain with conventional centrifugal “non-clog” pumps but matches the performance characteristics of the screw centrifugal impeller very closely.

Solids such as rags, hair, and/or clusters of stringy material are often encountered in RAS, WAS, and digested sludge applications. This material hangs up on the leading edges of conventional “non-clog” impellers causing unbalance and eventual clogging. In order to pass such solids, screw centrifugal impellers feature a single spiral vane which creates one large, smooth passage without abrupt redirection of the fluid. Specially designed cutting grooves further ensure that any material caught in the close clearance between impeller and cone is sheared off and re-introduced into the flow.

On some sludge services, variations in solids concentrations can be experienced (as ranges between 2-7% are common). In these circumstances, consideration must be given to changes in available NPSH, TDH, and power consumption which can result in problems such as cavitation, loss of flow, and motor overload respectively. The positive displacement action of the impeller’s “screw” section acts as an inducer which provides very low required NPSH. Screw centrifugal pumps also exhibit steep head-capacity curves that are typically non-overloading at a given speed making their performance relatively insensitive to changes in TDH. These design characteristics make screw centrifugal pumps extremely accommodating under varying sludge conditions.

Resistance to abrasive wear is often a concern with pumps for sludge handling services. To resist abrasion, all wet end components including; impeller, casing, and suction cone can be manufactured in wear resistant materials such as high chrome iron with a minimum hardness of 450 BHN. It is particularly important to maintain the pump’s close running clearances in order to ensure optimum performance. To assist in maintaining optimal clearances, the XCS impeller clearances can be externally adjusted on screw centrifugal pumps without the need to disconnect piping or remove the pump.

Our XCS screw centrifugal pump is designed for high flow, low head service typical of transfer applications. This pump has the ability of passing long fibrous and stringy material without clogging, it is also the pump of choice for handling shear sensitive material like flocculants and delicate crystals.