Untreated water transfer between the Prims and
Steinbach valley reservoirs

The water supply association in the district of Birkenfeld has the task of ensuring the extraction, treatment and distribution of water for its members, the local authority associations of Baumholder, Birkenfeld, Herrstein and Idar-Oberstein, to provide approx. 77,000 inhabitants with a total annual volume of 4.8 million cubic metres of water. In order to be able to continue to guarantee a reliable supply into the future, a renovation of the dam at the Steinbach valley reservoir – important for raw water extraction – is necessary. This was the reason for the construction of an untreated water transfer pipeline using ductile iron pipes between the Steinbach valley reservoir (Rhineland-Palatinate) and the Prims valley reservoir (Saarland). During the renovation work on the Steinbach valley reservoir dam, the task of delivering water for the Steinbach valley reservoir waterworks is being taken over by the Prims valley reservoir.

In the first 20 km long section of the transfer pipeline, the raw water from the Prims valley reservoir is pumped into a DN 500 pipeline from Saarland to the highest geodetic point at the Hattgenstein water tower. From there onwards it flows along a 12 km long double gravity-fed pipeline (DN 400) to the Steinbach valley reservoir waterworks. The hydraulic energy released in this process is used to produce electricity in a “Pump as Turbine” unit, or PAT for short, in the Steinbach waterworks.

The course of the 32 km connection pipeline between the Prims valley and Steinbach valley reservoirs, showing the territory of the water supply association in the district of Birkenfeld (Source: http://www.wzv-birkenfeld.de/aktuell2.htm)

In addition to the pumping stations at the Prims reservoir and at the Steinbach reservoir, a variety of valves have been installed in low-point, pressure-break and valve chambers. Erhard valves from Heidenheim were able both to cover the broad spectrum of valves required and to supply the relevant technical calculations. In the context of the project, Roco wave type butterfly valves, plunger valves, check valves, air valves and ball valves with the corresponding adaptors and spacers as well as pipe-break safety devices with break-and-lift units in DN 500 to PN 40 were delivered. By way of example, a few of the valves used are described below:

High-quality ERHARD ROCO wave butterfly valves ensure the reliable and clean transport of water. With their optimised gate geometry, the valve is characterised by a low pressure loss coefficient (ζ value), which helps reduce pumping costs. The slider-crank mechanism (SCM) developed and produced by ERHARD and used here is the ideal solution for the secure opening and closing of the valve. The movement kinematics of the SCM are perfectly tuned to the torque progression of the valve; the slowed-down speed of closing minimises the risk of water hammers.

ROCO wave butterfly valve with slider-crank mechanism (SCM)

Ball valve positions (1) open position with free passage; (2) half-open; (3) closed

The smooth-running SCM mechanism is also used with the ERHARD ball valves installed. In the open position, ball valves are characterised by a free passage and hence a very low pressure loss coefficient (ζ value). With the high speeds of flow, as well as pressures of up to 40 bars, to be expected in the untreated water pipeline, the choice of this type of valve means a reduction of energy costs for transporting the water.

The ERHARD plunger valves used for controlling the volume of water have been designed for the specific use in each case, e.g. with special slotted cylinders. The advantages are:

• Optimised flow controls allow cost-effective operation.
• The main seal is located in the hydraulically non-critical pressure zone and is anchored in a stainless steel chamber.
  This offers both optimum sealing and minimum wear.
• The four wide guide bars in aluminium-bronze mean that the weight force of the plunger is evenly distributed.
  This reduces wear and increases working life.
• Even when the valve is open to just 4% the volume of water can be precisely controlled, which corresponds to a control range of 96%.

Close-up of the special slotted cylinder