How to Select the Right Check Valve in a Waste Water Application
There are many questions you should ask to determine which check valve is best for your application
Check valves are often one of the most overlooked and misunderstood components of a water flow system, but using the proper size and style is essential for efficient operation.
Simply stated, check valves are designed to allow flow only in one direction and prevent back flow or reverse flow. Improper sizing or selecting the wrong valve can pose serious hydrodynamic issues on the pumping system performance and possible failure.
To choose the right check valve, it’s important to analyze the system hydrodynamics from the beginning. Jim Tucci, National Sales Manager for Flomatic Valves, says, “It’s all too often that people order the wrong valve because they aren’t assessing the system as a whole when choosing the valve size or type”. It is crucial to use a “system approach” when selecting size and type valve because the hydraulic conditions of each and every system are different.
When selecting a check valve, the following series of questions can help establish the application needs and find the proper size and type of check valve needed.
- What is the flow rate or anticipated flow rates of the system (GPM)?
- What are the pressures, under both static and pumping conditions (PSI or FEET)?
- What is the pipeline diameter size?
- What is the media (Potable water, wastewater, slurries etc.)?
- What potential chemicals will be used in the system?
- What size solids will the system deal with, if any?
- Is it a multiple pump application?
- Is it a header system?
- Where and how far is the discharge pipeline going (Feet)?
- Open or closed discharge line?
How water will flow through the system directly affects check valve size and type. “A lot of times people don’t realize it’s so important to know the answer to all these questions,” Tucci says. “But it is very important for a trouble free system operation. If all that isn’t taken into consideration, you can have potential problems.”
Specific information on what media is used, the type of water and size of solids that will be passing through will dictate the size and style needed to handle the debris. “If you’re running grey water or regular sewage, you want to specify a full port check valve to allow solids and stringy material to pass easily and avoid the hinge arm of the swing check valve to get stuck.”
Internal components, like the seat trim, may also vary depending on the circumstances unique to each system and application. “As far as materials, that is dependent on a lot of things, like if there are any additives that may be in the flow stream or where it is in the treatment process,” Tucci says. “Another important factor to know is where the valve is going to be located. Is it outdoors in a coastal environment? If you have really salty air, you want to make sure you have stainless steel components.”
Where and approximately how far the pipeline is going is information needed to calculate head pressure and surge potentials. It’s important to know whether the water or wastewater flow will be open discharge in a gravity system or a pressurized closed system. Each variable impacts the calculations and may require different valve type with an external assisted closing system.
Knowing your flow rate and pipe size are particularly important. “I often ask the customer what their flow velocity is, and they can’t answer that question. If they provide us flow rate and pipe size, we can calculate it.” Tucci explains that it’s all based on flow velocity. “Certain check valves have certain velocity ranges and certain acceptable head parameters. If they aren’t sized properly, you’re going to have maintenance issues with the system.
“With increased flow velocity, you have increased surge potential if a pump were to fail. You will have the possibility for greater slamming potential or waterhammer if something goes wrong.” Surges will travel down the pipeline providing another example of why it is so important to think of the system as a whole, and how a wrong sized valve can impact more than just the area or pipe where it is located.
Too-low velocity can result in chattering of the internals, depending on the style of the valve, causing the spring or closing mechanism inside the valve to wear away at a faster than normal rate. The valve may barely open under low-flow conditions which will eat away the seating components, also leading to shorter lifespan.
“Check valves want that sweet spot,” Tucci says. “If you’re too low or too high, you have the potential to wear that valve out.
Swing style check valves like Flomatic’s model 745 AIS are common across the spectrum of water systems and ideal for systems where flow is constant to minimize pressure drop.
“It’s a great overall check valve for wastewater applications or clean water applications. It’s a full port check valve and it has a broad range of acceptable velocities.”
Check valves that are factory compatible with optional features allow operators more control and monitoring over the valve’s functions. Add-ons like a position indicator provide a visual indication of the internal disc’s location during operation and shutdown. Another option to consider is a backflow device. These devices can be installed in check valves and manually operated when backflow, pump priming, line draining or system tests are required. Limit switches are also extremely useful for remote indication of valve position and a positive sign of flow.
Check Valves are Designed to Protect The System
“Check valves are designed to protect your system and pump. You want check valves closing smoothly, you want the system be happy and to protect the pump,” Tucci says. “When you get outside the recommended operating conditions the system becomes unhappy and things are going to prematurely cause grief. It might be as minor as having to replace the seal, but it could also be as major as the side of a valve blowing out and dumping 30,000 gallons of waste on the ground.”
Taking the time to establish the needs using the “system approach” of your application will help ensure you always select the right check valve for the job.