In fluid systems, pump control valves play a crucial role in safeguarding equipment from the damaging effects of a pressure surge, also known as water hammer. These valves adjust their opening and closing times to mitigate the impact of rapid changes in fluid velocity, preventing potential damage to equipment and ensuring the efficient operation of the system. In this article, we will delve into the technical aspects of how pump control valves work to protect equipment in various fluid-handling applications.
Understanding Surge and Water Hammer
Surge, or water hammer, is a phenomenon that occurs when there is a rapid change in fluid velocity within a pipeline. This can be caused by sudden pump starts or stops, valve closures, or other changes in the fluid flow. The resulting pressure waves can cause significant stress on pipeline components, potentially leading to equipment damage, leaks, or system failure.
Pump Control Valves and Critical Periods
Pump control valves are specifically designed to minimize the risk of surge damage by carefully controlling their opening and closing times. The valve's operation is based on the concept of "critical periods," which is the time it takes for a surge wave to travel down a pipeline after a rapid change in fluid velocity and return to the point where the change took place.
Under normal operating conditions, a pump control valve should open and close in 10 or more critical periods, allowing for gradual changes in fluid velocity and minimizing the potential for surge-related issues. This is generally done by starting a pump against a closed valve. When the pump is generating enough pressure to meet the static head the pump control panel will send a signal to the valve to open. Similarly, the valve is closed at a speed of 10 critical periods or greater with the pump running. When the valve is closed the pump is shut down. There are of course many different scenarios but this is the most common.
In emergency situations, however, the pump control valve must close within one critical period to prevent the surge wave from causing damage to equipment. If there is a power failure for instance, the pump will come to a stop quickly inducing a system surge wave. Pump control valves must be able to close rapidly so that this surge wave cannot return and damage the pump. The rapid closure of the valve itself can generate a surge wave, requiring additional mitigation measures.
Surge Relief Valves for Emergency Situations
To protect equipment during emergency valve closures, surge relief valves are often used in tandem with pump control valves. These relief valves are designed to open when a pressure wave generated by the rapid closure of the pump control valve reaches a predetermined threshold, allowing excess pressure to be safely vented from the system.
By venting the pressure, surge relief valves help to reduce the amplitude of the surge wave, mitigating the potential for damage to equipment and ensuring the stability and safety of the fluid system.
The Importance of Proper Valve Selection and Sizing
Choosing the appropriate pump control and surge relief valves for a given application is essential to ensure adequate equipment protection from surge-related damage. Factors to consider when selecting and sizing these valves include the system's operating pressure, flow rate, pipe diameter, and the specific characteristics of the fluid being handled.
Working with experienced valve manufacturers and engineers can help ensure that the correct valves are chosen and that they are properly sized and configured for the specific application. This is where your local DeZURIK rep comes in. They are experts at designing pump control valves and the associated systems which often include not only pump control and surge valves but also isolation and air valves.
Pump control valves play a vital role in protecting equipment from the damaging effects of surge and water hammer in fluid systems. By carefully controlling their opening and closing times, these valves mitigate the risk of equipment damage due to rapid changes in fluid velocity. In emergency situations, surge relief valves provide an additional layer of protection by venting excess pressure and reducing the amplitude of the surge wave.
This is one of the most critical systems of a treatment plant. A damaged pump or pipeline rupture will cost many times over the design and installation of a proper valve system for a pump station or main sewage pump. The potential for a poorly designed system to injure personnel is an even greater concern.
DeZURIK has an entire program designed for just this application which can be found here: https://www.dezurik.com/products/industry/pump-stations/
Organizations can ensure the safety, efficiency, and longevity of their fluid handling systems by understanding the principles behind pump control valve operation and working with experienced professionals to select and size the appropriate valves.