Applications of Cla-val control valves with BLACKOUT mode

The use of control valves offers a wide range of possibilities and sometimes very high demands are placed on the multifunctionality of these control valves. Although there are sophisticated solutions available that lead to a suitable solution, local conditions do not always play to the operators’ strengths and so it is necessary to provide a backup power supply, which is essential for such designed control valves.

In general, the advantage of diaphragm control valves is their enormous multifunctionality, so it is good to think also about emergency conditions, i.e. how the device should “suitably” behave during a prolonged central power failure. And in the case of larger pressure zones, this concern is certainly compounded by the number of customers and businesses that are heavily dependent on a continuous supply of potable water within normative parameters. One such location that has long faced this problem in the past is the city of České Budějovice. Here, the operator has for a long time used diaphragm control valves at key nodes into the city, but unfortunately without taking into account the longer term power failure known as BLACKOUT. When this condition occurred, the existing control valve was unable to change the settings correctly, and this caused the operator some uncomfortable operating conditions, which he wanted to fundamentally solve and improve.

Within the framework of the already confirmed real concern about the Blackout, six strategic reduction/regulation shafts have been identified as the most important transfer points for the transport of drinking water to the city of České Budějovice. In each shaft, the existing control valve was assessed and replaced with a CLA-VAL valve of the same dimension, but with Blackout mode equipment and a higher hydraulic flow coefficient. All this was done with maximum acceptance of the existing control style by GDF. The newly designed control valves were equipped with three solenoid valves (the original control valves had only two solenoid valves each) and the principle is that the control circuit, which is only used for control during the Blackout activation, is completely isolated from the GDF control.

This solution concept has two advantages:

• The first one is from the point of view of service and also of the operator – here it is possible to perform any service operations without affecting the classic PLC automatic control, this control circuit is in addition to the third electromagnetic valve (which is permanently blocked under voltage in the closed position) also equipped with separate ball valves with colour differentiation against the classic PLC automatic control.
• The second advantage is the “simplicity and reliability” of this control, which can indeed be used for a long enough period of time to allow the operator to focus and release energy at the more “critical” points in a given pressure zone.

The solution chosen was the proven for many years single-stage pressure reduction, which, thanks to its sensitivity and control accuracy, is fully sufficient to supply the pressure zone for the entire duration of the active Blackout mode. In principle, at the moment of power failure and thus the start of the Blackout mode, the control according to the PLC of the GDF automat will be deactivated and the third solenoid valve will be automatically unblocked and thus the control will be switched to single-stage pressure reduction with appropriate pressure control sensitivity. This method of control is then completely independent of electrical energy!

Example of the first installation of two control valves on the Jubilejní and Nemanická shafts

This is a pilot project, the two reduction shafts are located relatively close to each other and are used to supply the inner part of the city. The pressure layout of the manholes is such that the outlet pressures from these pressure reducing manholes are directed against each other, so the valves are set so that they do not overpressure each other and supply the zone evenly. Since the two shafts are each at a different elevation, a different type of spring was used for each control valve. The whole plant was then successfully commissioned and after a reliable 6 months of operation, the installation of other even more important control nodes was proceeded with.

The largest control valve at the Litvínovická shaft

The input pressure is approx. 7.0 bar and the output pressure is programmed according to the PLC from 4.5 -5.2 bar. Diagram of the shaft visualization:

As this is the largest pressure reducing valve in this city, commissioning was carried out with the assistance of the company’s technicians. HUTIRA in the night hours. The hiring of this pressure reducing valve went smoothly without any interference with the GDF system. The pressure reducing valve is in the full flow version DN 300 and the maximum flow through the pressure reducing/control valve CLA-VAL is approx. 100 l/s according to the consumption.

Installation of another valve at the Švábův Hrádek shaft

Here the situation of pressures / withdrawals is somewhat different than at the Litvínovice shaft, because the required output pressure is only between 0.02-0.07 MPa, Švábův hrádek is the highest hill on the left bank of the Vltava. Precisely because the required outlet pressure is close to 0.5 atm, it is important that its value is as stable as possible; in the case of such a small outlet pressure, this is ensured by a softer type of spring and a slower reaction of the main valve. In order to achieve the closest possible response with the previous control valve, a different type of solenoid valve has been chosen which offers a smaller orifice diameter and therefore a more gradual discharge/filling of the main valve chamber. The historically fitted HAWIDO valve serves as a reserve to this CLA-VAL control valve.

Schematic of the shaft visualization:

The full-flow type of diaphragm control valve was used again, now DN 200. The installation in the Švábův Hrádek building highlighted the importance of fitting a high quality automatic vent valve on the outlet side of the pressure reducing/control valve. The HAWIDO valve is not considered and this single stage pressure reducing valve only acts as a backup in case of regular service on the CLA-VAL control valve.

Since we live in an era that is, to put it mildly, dependent on electrical energy sources, it is a good idea to take this fact into account and always plan ahead for the worst possible scenarios that can practically occur. Once we have described the worst that could happen if …. then we can start to create countermeasures that will provide us with states that will be acceptable even with the possible observance of certain “special” conditions, e.g. grid manipulations, etc. The BLACKOUT situations and states have recently taken on quite significant contours and it is necessary to be prepared for this time. Thanks to the application of diaphragm pressure reducing valves in České Budějovice, acceptable operating conditions have been achieved, as well as an overall higher safety of the operated water supply network. It is important to select and then apply a solution that is as reliable as possible and that will last for decades. This was also our aim in this project, and although the whole installation of the control nodes is still relatively young, we expect it to be of great benefit to the operation and provide operators with a quiet night-time regime.