HODD instead of AODD — filter press feed in a steelworks

In the tinning line of a German steel producer, a pump feeds tin sludge to the membrane filter press. The plant runs around the clock in shift operation, with pressings carried out as required. With a pH value between 3 and 8 and traces of HCl and zinc, the medium is chemically demanding.

This duty was previously handled by an air-operated double diaphragm pump. The core problem was recurring diaphragm failure. Every failure meant an unplanned shutdown, and because it could not be predicted, a complete spare pump sat permanently in stock — capital tied up without producing anything.

Two drawbacks of the air drive came on top: a long filling time for the press and high compressed air consumption. Air operation is one of the most expensive ways to drive a pump — not only because the compressed air has to be generated at considerable cost and a substantial share of the energy is lost between compressor and consumer, but also because the pumps consume large quantities of it.

A Model TP in size TP32 has been in operation since, supplemented by flow control. The diaphragm is guided hydraulically rather than driven by a cushion of air — it therefore works under defined conditions instead of against the pressure fluctuations of a compressed air network. The movement stays smooth and controlled at all times, which translates directly into diaphragm service life.

The specification matches the environment: polypropylene housing, polyethylene diaphragms, FPM seals and stainless steel fasteners. The metallic components are of high grade throughout and the frame is powder-coated — no side issue in the corrosive atmosphere of a steelworks.

During integration, the tight space and accessibility were the real constraints. HODD supported commissioning on site, including training.

The start was deliberately conservative: the pump initially ran up to 8 bar, matching the previous air-operated pump. Only afterwards was the pressure raised to optimise the pressing cycle — something the air drive did not allow.

No diaphragm failures have occurred since commissioning, and the plant has run without an unplanned shutdown. That also removes the spare pump from the store. No wear parts have needed replacing so far.

According to the operator, cycle time has shortened and the filter cake comes out drier at consistent quality. The drive now draws its energy directly from the mains rather than through the compressed air network, and diaphragm service life exceeds that of the previous solution.

For context: no measured before-and-after figures exist for cycle time, residual moisture or energy consumption — the operating point changes with every pressing. These statements reflect the operator's assessment. The changeover took place in 2026; statements on service life refer to the period since commissioning.