Valves in Action -
Pressure Reducing Valve DM 555 and XLC 410
Pressure Reducing Unit for a Drinking Water Supplier

TASK // Highly volatile consumption Quantities

During regular operation, water suppliers must furnish between 2 and 20 m³/h of drinking water. The demand rises to up to 96 m³/h if extinguishing water is required.

pressure reducer DM 555 - Universal Valve for Small and Medium Flow Rates

TASK // Highly volatile consumption Quantities

During regular operation, water suppliers must furnish between 2 and 20 m³/h of drinking water. The demand rises to up to 96 m³/h if extinguishing water is required.

The valve used in this system would have to feature a regulation ratio of 48 (regulation ratio, also called quantitative ratio: Qmax/Qmin = 96/2 = 48). This would be physically impossible with a self-acting control valve. From the technical point of view, a max. regulation ratio of 10:1 could be achieved.
In our example, the reduction ratio is up to 8 (p2max/p1min = 8 bar/1 bar). This would result in cavitation at the valve cone and seat.

SOLUTION // Pressure Reducing Unit with Main Valve and Bypass Valve

The Main Valve:

In this case the main valve is a pilot-operated pressure reducing valve (type Mankenberg RP 115, also known as CSA XLC 410) in DN 80 with anti-cavitation equipment. The adjustment range is between 0.7 bar and 7 bar. The valve has been set to ≤ 1.0 bar.

Additionally it has been provided with pressure gauges on the upstream and downstream side. This industrial valve is suitable for quantities from approx. 10 m³/h to 96 m³/h. At 96 m³/h the valve reaches its performance limit.

The Bypass Valve:

The bypass valve is a pressure reducing valve (type Mankenberg DM 555) in DN 50. The Kvs value is 4.2 m³/h. An adjustment range of 0.8 bar to 2,5 bar has been selected. This pressure reducing valve is suitable for quantities between 1.5 m³/h and approx. 10 m³/h. The valve has been set to ≥ 1.5 bar.

Function of the Valves

During standard operation (remember: 2 - 20 m³/h), the bypass valve (Mankenberg type DM 555) is the first valve to work for quantities up to approx. 10 m³/h because its set pressure (p2 ≥ 1.5 bar) is higher than the main valve pressure (p2 ≤ 1.0 bar). Initially the main valve remains closed. For consumption quantities of > 10 m³/h the performance of the bypass valve does not suffice. The downstream pressure will drop to such an extent that the main valve response pressure is reached. From this point the main valve opens and works up to the maximum quantity of 96 m³/h. Once the drinking water demand falls below 10 m³/h, the main valve closes and the bypass valve works alone again.

Extra hints from our experienced engineers

Choose set pressures with a minimum difference of ≥ 0.5 bar for this pressure reducing unit with bypass valve. Otherwise the valves would have a negative influence on each other.

The flow directions must also be aligned with the mounting positions, as important operating elements such as the needle valves (throttle block) point towards the wall and may be difficult or impossible to operate! Therefore, please always indicate the flow direction in your plant when you place the order for a valve. In this way, operating elements can be attached mirror-invertedly to the industrial valves, if necessary.

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