Lusip – Swaziland

Project overview


  • Purpose: control flow into holding dams and close off when full.
  • Performance requirements: non electro-mechanical operation; Automatic regulation of flow, Close off when dam is full, Operate in dirty water
  • Type: FDS automatic regulating valves
  • № off: 60
  • Size: 200 NB and 300 NB
  • Operating Pressures: max 450 kPa (45 m); min 15 kPa (1,5 m)
  • Maximum flow: 140 l/sec (200 NB); 300 l/sec (300 NB)
  • Manual override: yes
  • Material: mild steel, Galvanised

 Location: Lower Usuthu River, Siphofaneni, Swaziland

 Client: Swaziland Water and Agricultural Development Enterprise (SWADE)

 Consultant: Coyne Bellier

Fabricator: Iron Engineering (Pty) Ltd, Swaziland

Contractor: Stefanutti & Bressan, Swaziland

Scope of services: Design of civil works and valves, Fabrication, Installation, Commissioning

Completion: Work in progress



The client SWADE is developing in the order of 8000 ha for sugar cane under irrigation in the lower Usuthu River region of Swaziland.  The area is divided into a number of smaller farms of approximately 100 ha each.

Each farm has a holding dam which is fed from a high level canal via delivery pipes.  The flow into each dam must be regulated to not exceed the maximum design flow and the valve must close off when the dam is full.  The regulating device must be non electrically operated and must be totally automatic with little to no maintenance required.

A trial FDS automatic DV was installed to demonstrate its operation.  The client and consultant were satisfied with is performance and placed an order for the full scheme of 60 valves.


The diaphragm valves (DVs) discharge into a chamber where the energy is effectively dissipated due to the radial discharge of the water.  The float valve which controls the water level in the chamber, is situated adjacent to the valve chamber.  The water discharges over a weir plate into the dam which is set at the required design flow.  When the dam reaches F.S.L., the DV closes down.  As the water level in the dam drops, the DV automatically opens to discharge into the dam.

The DV is designed to handle dirty raw water with sediment and debris.  The design includes a special sediment removal device for this purpose.

These DVs are simple to manufacture and operate and were preferred to other types of regulating valves for both cost and performance benefits.