I have to design waste water lift station with the following criteria: 135 meter total head, flow 300 m^3/hr per pump. Each pump line should be one stage.
What should be my design focus, beside the pump unit itself?

Hi Dror, can you advise why you need to design with just 1 stage for each pump, this will help me to understand your problem in more detail/.

Thanks,

Paul.

Paul.
Why two? More problems, complex control, instrumantation, civil work and more.

Dror: first what type of pumping station do you will design, vertical pump or horizontal pump?
wet installation or dry installation?
You shall follow recomendations for the dimensions of inlet chambers and inlet piping.
You must care for priming requirements, NPSH and formation of vortices in the inflow.
You must asses the filtration requirements.
Also pump maintenance and filters cleaning.

KSB Pump Type KWPK 150-500 at 1450 RPM can achieve a Head of 90 Meters at 300 M³/Hr. However, if you have 60 Hertz Power Supply then you can achieve 135 Meters Head with this Pump.

You have not specified complete system parameters. Main consideration as also limitation here will be solid content and whether it is abrasive. If abrasive solids are present, single stage pump may not be possible. If abrasive solids are absent, you may still have significant solids present and a semi-open impeller pump may be the best option.
If your power supply is 50 Hz, you will need to consider only 3000 RPM option for single stage. If your power supply is 60 Hz, you may have an option of 1500 RPM drive but the pump will operate at low efficiency.
I would therefore recommend going to two pole motor drive regardless of power supply frequency being 50 Hz or 60 Hz. You have a choice of large number of pump suppliers from all who make chemical process pumps. Goulds/ITT, Durco/Flowserve, Buffalo, Lawrence/United are some of the options. There are not many significant European manufacturers with semi-open impeller pumps that I can suggest.

Please fill in the blanks of one pump data sheet inclduing all you know about the system such as the operating data , NPSHA , fluid properties ( solid content, SG,...).Your preference of the pump type and configuration( submerged pumps, vertical suspended pumps, OH2 type,...)

In case of solid content , the best case can be a big circular volute aith the vertical suspended design to overcome the solids.

I don't think you will be able to design an efficient pump with a single impeller for such a high head.