Pelton turbine System Erlach: Distributor

System Erlach, distributor: one pipe in the centre, equal paths to all nozzles

For every Pelton turbine with several nozzles: the distributor lies between the penstock and the nozzles. It splits the water and is good when every nozzle gets the same amount of water and the water arrives steadily. Every disturbance that arises on the way ends up in the jet. An unsteady jet hits the buckets less well, and that costs efficiency.

The more nozzles a machine has, the more depends on the distributor. Horizontal Pelton turbine covers the number of nozzles.

System Erlach has up to six nozzles. For this it offers, alongside the conventional ring distributor, a design of its own: the axial inlet with a distributor pipe in the centre.

Pelton turbine and System Erlach: two distributors, around the outside or through the centre

Pelton turbine, conventional ring distributor: each nozzle sees a different inflow

In the common design the pipe runs around the runner like a spiral, and one nozzle after the other branches off. The first nozzle receives the water differently from the last. The 2012 paper gives, for a machine with six nozzles, the known value from experience that the nozzles deviate by plus or minus 0.3 to 0.6 per cent, depending on which one runs on its own. The test in Lucerne showed at full load a spread of 1.3 to 1.6 per cent below the best value between the best and the worst nozzle. In that case the last nozzle had the best inflow. With a different distributor this can be different. In his loss balance Josef Erlach allows about 1.5 per cent for the distributor.

Source: J. M. Erlach, New Pelton Concept, Viennahydro 2012, Full Paper, section 2.4 and Fig. 6 (deviation read from the figure); Josef Erlach, 11 October 2026 (loss balance).

System Erlach, axial inlet: identical pipes for all nozzles

The Pelton turbine System Erlach offers a second design. The water arrives in the axis of the machine. A distributor pipe in the centre passes it on to identical pipes that lead to the nozzles. The model for these pipes was the inflow of the last nozzle in the ring distributor, that is the best one.

Every nozzle therefore gets almost the same inflow, whichever nozzles are running. If a nozzle is closed, the flow to the others changes only insignificantly according to the patent specification. This applies to the state afterwards. The closing itself must happen slowly enough that no water hammer arises in the penstock.

In the model test the difference between the six nozzles thereby dropped to about 0.4 per cent below the best value at full load (2012 paper, Fig. 5, read by Josef Erlach).

Source: Viennahydro 2012, Full Paper, section 2.4 and Fig. 5; patent EP 2 035 689 B1, inventors Josef Erlach and Thomas Staubli.

System Erlach, inlet manufacture: off-the-shelf components, fewer weld seams

• The whole inlet from the shut-off valve to the nozzles can be made from standard pipework components.
• Compared with a conventional distributor for six nozzles the weight falls by about 20 per cent and the length of the weld seams by up to 50 per cent.
• The design is easy to adapt to other runners. In a refurbishment the distributor pipe stays and only the pipes to the nozzles change.

Source: Viennahydro 2012, Full Paper, section 3.2; EP 2 035 689 B1, paragraphs 0007 and 0010.

System Erlach, choice of distributor: the housing with guide rings works with both designs

The axial inlet is not a must. The housing with the guide rings, the core of System Erlach, also works with a conventional ring distributor.

Source: Viennahydro 2012, Full Paper, section 3.2, Fig. 10 and 11.

System Erlach, testing the inlet: model test or flow calculation

Whether a distributor divides the water fairly is shown by the model test or by the flow calculation. In 2023 TU Wien published such a calculation for distributors with axial inlet. It is listed under Pelton turbine research. How the design performs with little water is described under Pelton turbine efficiency.