Hidrostal Submersible Pumps

The Hidrostal submersible is a wet well pump. It goes into the sump, the liquid closes over it, and the medium the pump is moving is also the medium taking heat out of the motor. Hidrostal states it plainly: the robust motor is cooled by the liquid in which it is submerged during continuous operation. Get that one fact right and most of the selection follows from it.

The duty it is built for is general effluent and process fluid carrying large amounts of solids and fibrous material. Hidrostal also names viscous liquids and media that need gentle handling, which is the screw centrifugal impeller doing what it was invented to do. Municipal wastewater, stormwater, industrial process water and sludge transfer all sit inside that description.

Where it is the wrong pump

If the sump draws down below the motor in normal operation, or the station is designed to run dry-pit, this is not the range. Hidrostal allows short-term dry running for cleaning and maintenance work only, and only within the maximum operating times it specifies. Anything else wants the immersible range, which carries its own closed cooling circuit and does not depend on the liquid level at all.

The other honest limit is the head. 100 m is the top of the range, and the pumps that reach it are not the pumps that reach 2500 l/s. Send the duty point, not the ends of the range.

What we see go wrong on wastewater stations is rarely the pump. It is rag arriving faster than anything downstream can handle, grit getting past a screening stage that is not doing its job, and a sump geometry nobody checked. A better pump does not fix any of those. Tell us what the water carries and how the sump fills, and we will say which of the three you are actually dealing with before we quote anything.

A Hidrostal submersible pump is a compact integrated unit, with the motor mounted directly above the wet end, so there are no exposed rotating shafts or couplings in the sump. Liquid enters through the suction, is picked up by the screw centrifugal impeller and driven out through the volute to a side discharge. Hidrostal's hydraulics brochure attributes the low required suction pressure to the suction area upstream of the impeller and to the design of the blade's inlet edge, and describes the head curves as continuous and steep. A steep curve is what you want on a variable-speed drainage duty, because flow holds up as the discharge level rises.

Cooling

Hidrostal builds its submersible motors for wet installation, permanently and completely immersed in service. Heat generated by electrical and mechanical losses transfers directly to the surrounding medium through the stator housing. The finned back cover acts as a heat exchanger. Hidrostal's own claim for this arrangement is that the efficient cooling reduces the thermal load on the motor and minimises surface temperature. If the sump has to be emptied for cleaning or maintenance, Hidrostal permits short-term operation in dry condition provided the maximum operating times are observed.

Sealing and monitoring

Tandem mechanical seals separate the pumped medium from the motor, and Hidrostal manufactures the seals itself. The motor is a high efficiency dry motor with class F insulation and built-in thermal sensors. An upper bearing temperature probe is optional, and Hidrostal lists a range of further monitoring and safety options. The cable entry gland is a high strength, leak-proof design with a separate cable cap, so a new cable can be fitted without disturbing the motor cover or the bearing.

Wear parts

The wet end carries a replaceable liner with optional external adjustment, set by external regulating nuts. An adjustable entry cone is available for abrasive process fluid. Hidrostal offers cast iron, ductile iron, Hi-Chrome, stainless steel and Duplex, and for extremely corrosive and abrasive media its own special alloys. An inspection port lets you look at the wet end without stripping the pump.

Hazardous areas

Hidrostal supplies explosion-proof versions of its submersible motors as an option. Those motors are certified for use in Ex zones 1 and 2, type of protection flameproof enclosure, temperature classes T3 or T4, to the requirements of ATEX and FM. Electric motors are prohibited in Zone 0; for those duties Hidrostal offers hydraulically driven pumps instead. Certification applies to a specific build, so send us the zone classification for the station and we will get the certificate for the exact pump and motor from Hidrostal before anything is ordered. Hidrostal does not offer explosion-proof versions of its flywheel motors, so if you were planning a flywheel to hold up the run-down time in a hazardous area, that combination is not available.