When, where, and why.
By Laura Jensen
There are multiple resources regarding the installation of submersible check valves within the water well industry, and one question that often sparks debate is the installation of one check valve versus multiple check valves for a submersible pump.
Here’s one take on it.
In a submersible pump, check valves are critical to stop water from flowing downward in the pipe and returning into the well when the pump is turned off. To reduce the long-term risks and damage to a pump, I think it is critically important to install multiple check valves, rather than just one check valve, in submersible pumps.
Proper Placement
Most high-quality submersible pumps will have a check valve built in from the manufacturer at the discharge. This check valve will be the first check valve installed. The second check valve should be placed above the pump and no more than 25 feet above the water pumping level in a well. This will ensure that if the check valve at the pump fails, the second check valve in the system will hold the vacuum below it.
Think about a drinking straw in a glass of water. When you place your finger over the top of a drinking straw, you can lift the straw out of the glass and the liquid that was in the straw remains inside. The maximum range or length of straw that could hold water is roughly 32 feet at sea level. Anything higher than 32 feet cannot physically be held by the vacuum, thus the water would fall out of the straw. The same holds true in a submersible pump installation.
Above this initial valve, submersible check valves should be placed every 200 feet in the drop pipe as permitted by well depth. Outside the hole, many states require an additional check valve above ground that is commonly positioned near the pressure tank.
For example, let’s look at a 750-foot-deep well with the water level at 700 feet. This situation requires a total of five or six check valves to be installed. The system will have a check valve positioned at the pump discharge followed by another at 675 feet deep. Above the installation of these valves there should be three more check valves installed every 200 feet on the drop pipe below ground, putting them at 475 feet, 275 feet, and 75 feet deep. The sixth and final check valve, if necessary, is positioned at the surface.
Note that the ideal recommended installation location for the first check valve is one pipe length above the submersible pump. A valve in this position will be subject to laminar flow and isolated from the very turbulent conditions near the pump discharge.
Misconceptions
The use of high-quality check valves are vital components for the correct usage of submersible pump systems worldwide. A common misconception is that just one submersible check valve is necessary for the entire system.
High-quality check valves built to last are pressure rated to 400 PSI or 923 feet of head pressure. However, that does not imply that just one valve can be placed at 923 feet in a standalone unit.
For every foot per second of velocity change in a steel pipe, 54 pounds per square inch of backpressure is created. This means in a common well drop pipe at 1 inch in diameter and a flow of only 10 gallons per minute, a backpressure of 370 psi or more could be created when the pump turns off and the water column reverses. In a 4-inch pipe, a flow of 350 gpm could create a backpressure of 860 psi, resulting in more than what stock pump check valves are made to handle.
Staging check valves at even intervals along the riser pipe reduces hydraulic shock in stages, which protects the lifespan of valves, the pump, and its pipes. Each check valve installed at 200 feet or less protects the one below it. The installation of numerous check valves allows for the system to absorb and lessen the shock above and below each check valve.
Proper design and planning of a water well system is important to keep in mind when determining pump size along with pump depth, drop pipe diameter, piping elbows, and the number of check valves.
When selecting the proper submersible check valves, it is important to be sure the valves are sized properly and according to pipe flow velocities. The sizing of valves is vital and can be overlooked when installing submersible check valves or selecting the sizing of a valve based on friction loss rather than system flow.
Potential Consequences
When a pump system is not properly designed, there are many potential issues and concerns associated with it—a shorter lifespan for the system in the short term as well as higher costs and maintenance expenses in the long term.
Multiple submersible check valves also provide a smooth application. Following are a few conditions that multiple submersible check valves help to maintain and control.
Backspin, that occurs when water flows backwards through the pump, causing the pump impellers to spin in the reverse direction from their intended use. If the pump turns back on while spinning backwards, it will put a tremendous amount of torque on the pump assembly. This pressure on the pump may cause the pump shaft to break or cause severe damage to the motor thrust bearing.
Upthrust, that occurs when the pump turns on in a low head condition which results in an uplifting action on the impeller shaft assembly. Repeated upthrust in a system can result in premature wear and pump failure.
Water hammer, that is undesirable noise and damage. Water pumped and flowing through a piping system has a certain amount of energy (weight × velocity). If the pumping is stopped, the water continues to move, and its remaining energy must be absorbed in some way. This absorption of energy can sometimes create the noise and damage called water hammer.
Water hammer can destroy piping systems, valves, and related equipment. Water hammer varies in intensity depending on the velocity with which the water is traveling when the pump shuts down. It is important for installers to realize the potential of water hammer, and they must take this into consideration when sizing the system and deciding what material the valves should be made from.
Water hammer can result under certain hydraulic conditions if properly sized check valves are not installed.
Multiple Reasons for Multiple Check Valves
With regard to flow and maximum system pressures, there are many different types of submersible check valves to consider for different applications. Material, size, and construction all make a significant difference in performance and are important to consider for years of trouble-free operation.
To properly absorb hydraulic water shock associated with water well pumping and maintenance-free operation, installing multiple submersible check valves is highly important to provide a well system the greatest chance of long-time functionality without repair.
Nearly all well-known pump manufacturers recommend the installation of multiple check valves in water well systems—thus acknowledging the placement of checks at multiple stages along the drop pipe is the best way to protect their product and increase longevity.
When working on submersible pumps, do your research on check valves and their placement as it is critical to the life of the water well system.
Laura Jensen was marketing communications specialist at Flomatic Valves. For nearly 90 years, Flomatic Valves has been an innovator in the water and wastewater industry, designing and developing a wide variety of valve products. From check valves to automatic control valves, Flomatic Valves is associated with some of the largest water and wastewater projects in the world.