Exploring a number of valve applications—and solutions—during unique situations or emergencies at water treatment facilities.
By Roger Lah – Technical Sales Engineer – Cla-Val
Conventional motorized valves typically serve a single control function with minimal capacity for electronic versatility or hydraulic backup capabilities. In contrast, hybrid valves, which combine electronic and hydraulic control mechanisms, can streamline system design by reducing the total valve count. They also simultaneously provide crucial redundancy during power outages and protect against expensive pipeline ruptures.
Hybrid Multi-Function Electronic and Hydraulic Metering Valves
There is an arduous, lengthy process that water treatment plant operators need to quickly perform when a power failure occurs. To prevent water from overflowing onto the plant floor, they must manually close several motorized valves for influent and effluent flow rates.
Backwashing a filter occurs when a filter starts to clog with entrapped sediment. As a result, water is pumped back up through the filter to expand the filter bed and then its run to waste. The flow rates are ramped up and then backed down during the varied backwash cycle before the filter is brought back online. So, the flow rate is important for correct cleaning.
A programmable logic controller (PLC) usually controls the valves, which control flow into a filtration backwash process, and utilize Venturi flowmeters. These flow meters operate on the principle of differential pressure, utilizing the Venturi effect where a fluid’s velocity increases as it passes through a constricted section of the pipe. This results in a pressure drop and the difference is measured and used to accurately calculate the flow rate.
Butterfly valves are susceptible to cavitation problems. Therefore, a hydraulic pressure reducing valve is normally installed upstream to reduce the pressure and prevent cavitation. This traditional arrangement requires significant piping space for two valves and a Venturi flowmeter. Further, power failure to the motor-operated valve can cause significant problems.
Another approach is to replace the hydraulic pressure reducing valve with a hybrid multi-function electronic and hydraulic metering valve.
This valve is capable of measuring and controlling flow based on valve position as well as from differential pressure sensors installed on the valve. It also incorporates anti-cavitation trim to prevent cavitation due to the high pressure drop in the filtration process.
The electronic metering function utilizes dual solenoids. They simply change the upstream closing solenoid from “normally closed” to “normally open,” which results in hydraulic valve closure when a power failure occurs. This allows plant operators to manage other important duties during a loss of power.
The single metering valve replaces the previous lengthy piping arrangement, saving significant space. As the replacement valve discharges directly into the filtration process, a hydraulic pressure limiting function can be added to provide a “hydraulic guarantee” against over-pressurizing the system.
Combining Hydraulic PRV with Electronic Timed Closure
In another treatment plant application utilizing prefabricated treatment equipment, a hydraulic pressure reducing valve was used to limit the pressure in the process. A relief valve provided protection for a 10-mile pipeline feeding into the plant with a fast-closing butterfly valve to shut down the process during a power failure.
However, this sometimes resulted in a surge. The engineer’s surge analysis determined the pressure reducing valve was required to close in 12 minutes when this occurs, and a standard closing needle valve is incapable of controlling these long closing times.
The simple solution was to modify the pilot control system to perform a switch between the normal pressure reducing function and electronic controlled closing of metering flow to zero flow, in a programmable period. In addition, a third solenoid was installed to switch between the normal hydraulic control to electronic control in the event of a system shutdown.
Operators can easily see the status of the closing sequence on the valve controller screen. They are also able to adjust closing times if the required closing time requires amendment.
This valve, therefore, accomplishes two particularly essential functions. A hydraulic pressure reducing function during normal operation, and an electronic “time of closure” function to prevent surging in the long upstream pipeline.
Electronic Flow Control Valve with Hydraulic Protection of Downstream Piping
In a recent new treatment project startup, an electronic flow control was barely able to crack open. A check of the downstream pressure gauge revealed the pressure had already reached the setting of the pressure limiting pilot control. It was realized that the water district had forgotten that an isolation valve had been closed some distance downstream.
In effect, the hydraulic control system prevented a pipe break from occurring. The electronic control system is capable of multiple functions such as flow control and pressure reducing. In this instance, the hydraulic pilot was used as “backup insurance” where the pilot control adjustment was set to not interfere with normal electronic multi-function control.
The normal operation consists of electronic flow control and electronic pressure reducing control and seamlessly transfers between functions with specialized software. In the event of power failure, or solenoid malfunction, the hydraulic pilot will take over and limit downstream pressure, preventing pipe breakage.
Up to four modulating electronic functions are possible, including flow, pressure sustaining, pressure reducing, and level control. Reservoir level control, for example, can include flow control and pressure sustaining control. Conversions of existing altitude control valves often include the hydraulic altitude control pilot for backup control to prevent the overflowing of a tank. There is often a long pipeline upstream of these valves, which is susceptible to surging during valve closure. A hydraulic “surge relief override” pilot control will prevent surges in the event of faster-than-normal valve closure.
Numerous Hybrid Electronic and Hydraulic Combinations
There are several other hydraulic and electronic functions that can be combined into one valve and reduce the number of valves in an installation, protect aging and sensitive pipes, or prevent overflow of tanks and reservoirs.
A particularly popular combination is an electronic flow control with a hydraulic pilot control to limit downstream pressure. This example of hybrid electronic and hydraulic control allows normal electronic flow control unless downstream pressure exceeds the limit of the hydraulic pilot setpoint.
Working with a valve manufacturer can help provide the best option for unique situations. They can assist with solutions to effectively protect a treatment plant and—most importantly—safeguard continued operation of the water distribution network in the event of a power failure.
About the Expert
Roger Lah is the Technical Sales Engineer at Cla-Val and has more than 20 years of experience at Cla-Val. Roger has a deep technical understanding of valves in waterworks applications.