Keeping Drinking Water Safe.
“Keeping Drinking Water Safe” seems like a simple goal that everyone would agree is crucial to the safety and well-being of all consumers of public drinking water.
With this simple mission, it might seem that since this straight forward goal, it would be a relatively manageable task. On the surface, it might be, but there are many parts of a water distribution system that can present risks to the goal of maintaining safe drinking water.
Many respected industry professionals have spent a good deal of time assessing various points of potential contamination in water supply systems. An internet search for “contamination of public water” or “drinking water pathogen intrusion” will populate several pages of your browser with numerous articles.
While there are many points of vulnerability in a water system, we will address some of the more common areas to consider, as well as to provide some ideas to reduce the risk of water contamination in a water utility distribution system.
Many distribution pipelines use “bell and spigot” type of connection for connecting the individual lengths of pipe. This type of pipe joint have been an industry standard for nearly a century and while it is still common today, the rubber seal used for this pipe joint is designed to withstand pressure from within the pipe, or internal pipe pressure. The bell and spigot connection has evolved over the decades and is considered a reliable pipe joint sealing method.
The weakness in this type of pipe connection is when the pipeline experiences a pressure surge that includes momentary negative pressure. Under certain conditions, fluid column separation may occur, causing a momentary vacuum within the pipeline. Vacuum conditions are also referred to as a “negative pressure”, these hydraulic forces can cause a great deal of stress on the pipe walls, since the pipes are designed for positive internal pressures, not negative internal pressures. Under a negative pressure condition, the rubber seals at the pipe joint are disrupted from their normal position, and under extreme, or repeated, negative pressure conditions the seals at any affected pipe joint can become a point of intrusion to the water supply. There is no practical means to change all of the seals on all of the piping connections in a water utility, nor is there a practical means to change the type of pipe joints in a water distribution system.
The most effective means to mitigate these potential points of contamination is to undertake a thorough study of the distribution system. This requires hydraulic modeling of the water distribution system, including the pumps, air valves, and all points in the system. Pressure surges can occur in any size system and in both low head and high head systems. Virtually no system is totally immune from potential for pressure surges. The first step is in understanding the causes of pressure surges. Once, a water utility has an understanding of the areas within their system with the greatest vulnerability of experiencing negative pressures due to pressure surges.
Below Grade Control Valves
Many water utilities have multiple pressure gradients and have control valves including pressure reducing, pressure sustaining, rate of flow control, relief valves. Many systems include elevated tanks with level control valves (altitude valves). Some systems have below grade pumping systems with pump control valves. While each of these control valves would be selected for a specific purpose, some control valve manufacturers use a design where the valve has “air cushion vents” or“packing vents” on the side or bottom of the valve body. If your control valve includes these “design features”, by now you are probably well aware of their presence.
When water is discharging from one of these “vents” it becomes clear that there is a flow path from the drinking water supply to atmosphere. Normal control valve operations include modulation action to perform the valves designed purpose. When the valve opens and closes, or when it modulates, this movement causes fluctuating forces on the packing inside the valve. Even when there is no water discharging from the “vent hole” the vulnerability remains a silent and virtually invisible threat to the safety of the drinking water in the pipeline.
A real threat to the drinking water supply exists when these “vents” become submerged in non-potable water that collects in the below grade chambers (vaults) where many valves are located. Once a control valve is submerged, a “cross connection” exists. The term cross connection is used when potable water is in contact with non-potable, or untreated water. Water can collect in below grade vaults for many reasons; the most common can be due to rain water that finds its way into the vault through the access hatch, manhole cover, or even due to a rising water table and permeable walls. Rainwater in and of itself is not typically considered non-potable, but as it travels, it can come into contact with a wide variety of “non-potable material”.
If there is control valves located below grade in a system, there is not a problem, until there is a problem. Many water systems have control valves in below grade vaults. Is it time to evaluate the risks of contamination caused by control valves in your system?
Harper Control Solutions represents Cla-Val Automatic Control Valves; these valves do not include a “vent” in the valve body. These are a diaphragm type control valve and along with a “vent-free body design” they also have extremely low maintenance requirements. So, not only do these control valves have a lower cost of ownership, they also help to “Keep Drinking Water Safe”.
If you are ready to evaluate how you can lower your control valve maintenance costs as well as taking a step towards “Keeping Drinking Water Safe” in your system,contact Harper Control Solutions to learn how we can help.
Please note, that the ideas presented in this article may not represent every potential risk of contamination within a water distribution system. There are certainly other areas in potable water distribution systems that should be evaluated for their potential risks to the water supply. If you have questions about various equipment within your system, it’s time to contact Harper Control Solutions.
Challenges in Water Systems:
Water production facilities and water distribution networks include an intricate assembly of pipes, control valves, instrumentation, and automated control systems. Those in the industry know there are plenty of challenges to keeping everything running properly; ensuring safe drinking water throughout the water utility’s system.
Harper Control Solutions knows what works best for varying requirements in water production and distribution systems.
Some Common Challenges in Water Systems:
- Gravity storage tanks being filled by a nearby higher pressure gradient. Potential cavitation and a valve with adjustable flow rate control can be advantageous and be integrated with a solenoid shutoff function.
- Interconnection of pressure zones or neighboring utility. Flow rate control, along with back-pressure control, should fire flow demand indicate need for a flow rate over-ride? Harper Control Solutions knows the challenges in water systems.
- Booster pumps drawing from ground storage tank supplementing other sources. The bleed down control valve should include solenoid shutoff, back-pressure control, and relief override. What about the pressure drop across the valve, will the valve experience cavitation? Harper Control Solutions has the knowledge you’ve been looking for.
Call Harper Control Solutions to discuss your challenges.