Shallow Wells always elicit this question because of the elevation of the pump in relationship to it being located above ground, as well as being able to easily access the check valve when needed for service.
The short answer is 'yes', but under two specific conditions which ultimately dictate whether or not a shallow well pump retains prime to operate when it is no longer running.
Quick answer: In answer to the initial question, 'Yes, Check Valves may be installed on the surface at the top of a Shallow Well installation; there must be two things that exist before they will be able to operate correctly: a) The check valve must be located close enough to the inlet of the pump (less than 300 mm) and b) The entire suction line needs to be airtight from the check valve to the pump.
Based on standard practice, the check valve used for a shallow well would typically be placed as a foot valve at the bottom of the suction pipe to maintain water in the pipe so that when the pump is restarted, the water is still in the pipe and it will continue to have water. The fact that the pump does not need to be primed on start up allows for a check valve to be installed at the well head for a Self-Priming & Rotary-type Pump if located within approximately 300 mm of the pump inlet and the suction lift is less than 7.5 m.
Most of the calls for service regarding lost prime situations on a shallower well with a non-self-priming pump are caused by the improper placement of a check valve at the family well head.
The Short Answer, it works, but there are two conditions
A check valve located above the well head will perform its intended function, which is to stop water from flowing backwards through the pump when it is OFF. However, it does not provide the opportunity for the suction pipe to remain full; since the portion of the suction pipe that is located below the check valve (the well) will drain out immediately after the pumping ceases.
Understanding this distinction is key to getting your installation right. A check valve at the well head will prevent back siphonage of water from the well to the pump. However, a check valve installed at the bottom (foot) of your suction pipe will provide for both prevention of back siphonage of water as well as maintaining the prime in your suction line. In order to determine which check valve type you need, you must determine whether or not your pump has the ability to be re-primed.
The two conditions that must be met for an above ground installation of your check valve: The pump must be a self-primer ( able to remove air from the suction pipe and re-establish water flow) and the check valve must be positioned relatively close (enough) to the inlet of the pump to allow the volume of air between the check valve and the pump to be minimal so that the pump can unblock (clear) the priming air.
There is a practical limit of approximately 300 millimeters (mm) that should be kept between the pump and the Well while positioning them, but closer is better.
Why Position Is More Important Than The Valve
A shallow well pump works by creating an area of low pressure inside the pump at its inlet, which allows atmospheric pressure to force water up the suction line. The maximum lift from a shallow well pump at sea level is approximately 10.3 meters (m), but in practice will generally only lift around 7.5 m since there are friction losses and vapour pressure effects. Therefore, every element between the pump and well can either support or impede the pumps performance, with position being the most significant single factor.
When the pump shuts down, three different things can occur to the water in the suction line depending on what type of check valve/recirculation system is installed. A foot valve will hold enough water in the suction line and allow the pump to restart against water. A check valve will cause the suction line to drain down to the static water level where the pump will have to restart against a column of air. If the pump does not have either a foot valve or a check valve, then the suction line will drain to the static water level and the pump will lose water in its casing.
Although restarting against air is not necessarily a failure, a self-priming pump is designed to restart and clear air from the suction line and to re-prime in 30 seconds to 2 minutes. A self-priming pump depends on having water in its casing to recirculate and thereby clear out the air volume. For example, with a check valve located 3 m above the static water level, there would be a 3 m column of air to clear, and most pumps will not be able to do that.
Thus, the basic design of a shallow well is to place a foot valve at the bottom of the suction pipe (about 12 to 20 cm above the bottom of the well: If your foot valve is installed at or below the very bottom of the well (usually referred to as "well bottom"), you will likely find that it fills with sediment.) This foot valve serves two functions: First, it prevents the backflow of water into or out of the foot valve and secondly, to keep the suction line (also called the column of pipe above the foot valve) full of water.
Foot Valves & Standard Shallow Well Installation
Above the foot valve is a suction pipe, a pump (if applicable) located above the foot valve, a discharge check valve, if necessary, between the pressure tank and the service line, and a pressure tank. A check valve on the discharge side of the pump is installed to prevent the flow of water from the pressure tank back through the pump. This check valve serves a different function than the foot valve and the suction pipe.
The success of the shallow well design depends on three specific factors: the correct sized foot valve for the flow of water being pulled from the well, the open area of the strainer must not restrict flow anywhere in the suction line, and the suction pipe must be filled with water continuously without the use of a pump.
For the pump to work properly, there should not be any air leaks in the suction line. A tiny hole in the suction pipe allows air to come into the pipe instead of letting water leak out. When this happens and there is too much air in the suction line, the prime of the pump will be lost. The layout provided above should be used unless otherwise necessary; the only reasons to change the layout are access to repair it or an entry restricted to a pump room. If a foot valve fails, then you must pull the suction pipe. Therefore, in most cases, installers will install a check valve above ground and pay the penalty of having a pump that will not prime itself as efficiently.
How to install your check valve above the well head
If you must use an above-ground check valve, five items must be considered for it to function effectively:
- The pump is a self-priming unit. A jet pump or a self-services centrifugal (centrifugal) unit can eliminate the air from the suction line; other centrifugal models will operate dry, causing the unit to wear out prematurely.
- The check valve should be located as close to the pump inlet as possible (Practical distance = approximately 300 millimetres). The further away from the pump inlet you place the check valve, the longer the length of pipe connecting them will be; therefore, any length of pipe will require the pump to remove the air that occupies that pipe to create the required pressure to prime itself.
- The maximum lift capacity of the suction lift should conform to the manufacturer's flow range, which is typically rated 7.5 metres with the premise that the valve is installed within the manufacturer's recommended length of pipe.
- The length of pipe used for suction must be airtight. Thread sealant or a suitable gasket must be used to seal every joint on plumbing lines that are submerged underwater, and the piping must be able to withstand high-pressure. A suction line will always lose its prime due to an air-leakage condition regardless of where you place the check valve on the pipe.
- The check valve is meant to be installed perpendicular to the direction of fluid flow (Process Flow Default), although its flow may be upward. A swing-check valve is designed to be installed with the fall of the water over the closed flap, and as a result it can only be installed in the vertical position. A ball-check valve can be installed in any orientation as long as the direction of the fluid flow is upward.
Common installation errors that are made when the swing-check valve is installed too low are that it will continually leak by because it can not close properly, where it was designed for horizontal or vertical flow.
For applications where cleanliness is important (i.e., food processing), ANSI-AI, Sanitary Standard, and associated standards should apply to the surface finish (e.g., smooth) and joint design; therefore, the design characteristics must be referenced at the time of inspection.
If any one or more of these five factors is missing, the designated solution would be to utilize a foot valve instead of moving the check valve to the elevation of the storage tank or a sump. This practice (placing a check valve on a higher elevation than the pump itself) can create more problems in terms of maintenance for the pump and, therefore will reduce primes. Moving a check valve to a higher elevation is a choice made for ease; the factor of cost will be calculated and accounted for when making the decision to move the valve.
Check Valve Types and Their Application
| Type | Orientation | Best Position | Precautions |
|---|---|---|---|
| Swing check | Horizontal or vertical upward flow | Suction side of pump outlet | No vertical downward installation allowed |
| Ball check | Any orientation, upward flow only | Suction side near pump | can rattle at low flow |
| Spring check | Any orientation | Vertical piping and tight areas | Spring applies cracking pressure |
| Wafer check | Between flanges, either horizontal or vertical | Compact installation | No maintenance access unless breaking joint |
| Foot valve | Vertical, bottom of pipe | suction line bottom | Strainer must not be buried in sediment |
Swing checks are the preferred style for applications where fluid is discharged since they have virtually no flow resistance when opened and provide a good seal when closed. Ball checks, on the other hand, are more commonly used for suction lines since they are designed for the general orientation the pipe runs and are better able to tolerate debri than swing checks. Spring checks are ideal for applications where the valve needs to close immediately to eliminate water hammer and also provide very little pressure drop.
The comparison between swing and ball check valves is detailed further in the article "Comparison of Swing vs. Ball Check Valve Designs" as well as details on how each valve performs under low flow conditions, and which valve is less likely to create a slam.
One term that can reduce confusion when ordering: Check valve, non-return valve, one-way valve, and reflux valve are the same device and are basically the same as each other except that the specifications for the locations of the valves are slightly different and reflect the types of valves as a catalogue; they are primarily labelled according to what standard they have been built to, not how they operate. Apart from the standard and region in which a particular valve is manufactured, All these terms are clearly defined when considering whether to make a purchase; please refer to the descriptions of the check valve and non-return valve before placing an order against only one name.
Requirements When Installing Sanitary Check Valves
Sanitary check valves have been designed for easy cleaning and not for use with water from wells; therefore, replacing a well water valve with a brass valve that is not easy to clean defeats the point of having a sanitary check valve installed.
There are three installation rules that apply to sanitary check valves. All sanitary check valves must have a means to drain completely, usually by having a slight slope towards the outlet of the valve, and not a straight-line connection. All sanitary check valves must have a removable method for cleaning, which is why tri-clamp ends are now standard, and not welded ends. The gasket material must also meet the needs of the cleaning method; for example, for the caustic and acid cleaning methods, EPDM is recommended, while PTFE is best suited for cleaning at higher temperatures.
The orientation of sanitary check valves is more important than for industrial check valves. Most sanitary check valves are built to allow for either upward flow or horizontal flow via the vertical orientation of the seat; if a sanitary check valve is installed upside down, the valve will not seat properly, and it will hold product in the valve. The instructions that accompany sanitary check valves will provide specific instructions regarding this, and it is advisable to read the instructions before tightening down the clamp.
Another important consideration in the use of sanitary check valves is that they have a potential for dead-legging. A valve located at the end of a piping run creates a trapped space where cleaning fluids cannot reach, therefore sanitary designs should use inline valve bodies and not tie into branch piping. Sanitary check valve operation is dependent upon the internal geometry of the valve, which plays a vital role in cleaning capabilities.
The 3rd item on the list is the surface finish. Standard Ra 0.8 µm (micro-meters) for food contact surfaces, and the rougher the finish on a valve body the more likely it will retain particulate, regardless of its orientation. This standard has been established based on the sanitary standards used in dairy and pharmaceutical industries; confirm rather than assume a valve’s finish prior to purchase ordering.
Brass and Threaded Check Valves
Brass check valves are commonly employed in residential and light commercial applications and have different installation guidelines than their sanitary counterparts.
Thread standards are the first consideration. Incompatible BSP and NPT threads may appear similar and will jam after three turns of threading, damaging both components. Always confirm the standard prior to placing a valve order and specify it on the PO, not via a conversation.
The second consideration is thread sealants. A brass check valve on a suction side must be airtight, not watertight, as a suction piping system draws air rather than leaks liquid. Use PTFE tape or liquid type sealants, and do not rely on the proper tensioning of the pipe threads to hold an airtight joint.
The final consideration is orientation.
A brass swing check valved with a threaded body is designed to work with horizontal or vertical flow (upward) through the body of the valve, while the arrow on the body indicates which way the flow should go. The most common error that occurs when installing a brass check valve in residential applications is to install it vertically (downwards) rather than having the valve face upwards. When a customer experiences a check valve that closes each time the pump begins to run rather than each time the pump stops running, they should consider checking to see if the valve has been installed improperly.
The fourth issue is that of dezincification, which occurs primarily with standard yellow brass fittings when aggressive water conditions exist. Under those conditions yellow brass fittings leach out zinc from the brass, thus causing them to become pinkish in color and breaking apart. DZR brass is recommended for all wells located in a high-chloride or low pH environment, since the cost difference is minuscule compared to replacing a failed valve installed inside a wall.
Five Common Mistakes that cause most installations to be unsuccessful
In total, five errors account for the majority of check valve failures.
- A check valve installed above a non-self-priming pump. Each time the pump stops, it loses its prime, which to the owner results in the perception of a defective pump. In such instances, a foot valve or self-priming pump is required; the installation of a new check valve will not resolve the problem.
- A valve that was installed too far from the pump. For every three metres of vertical pipe placed above a check valve, the pump must "lift" three metres of air out of that pipe before it can clear the check valve. Either install the check valve with the inlet pipe being within 300 mm of the inlet to the pump or accept that the pump will take longer to prime, and make sure to select a pump rated for that longer priming time.
- A swing check valve installed vertically downwards. Due to gravity, the flapper may not seal when closed. Always check the orientation of the check valve and be sure to confirm it is tightened down in the correct orientation.
- An air leak in the suction line. If a joint exists below the level of the water and is not properly sealed, it will draw air into the suction line, resulting in the destruction of the prime faster than would occur via a failed valve. Suction lines shall be pressure-tested prior to starting the pump.
- A suction strainer can become clogged with silt and will hold the foot valve open. This can be prevented by suspending the strainer 300mm to 500mm above the bottom of the well and ensuring that it is clear at least once at the end of the first season.
The decision process of selecting a sanitary-style check valve for your process line is important to read before specifying a check valve for your installation. The same criteria that applied to the sanitary-style check valve will also apply to sanitary-style check valves for use in the well.
How To Choose An Eagle Check Valve
Eagle Products is a manufacturer of stainless steel valves and fittings in the 304 and 316L grades and produces check valves in the welded and clamped pattern for use in sanitary-style applications with EPDM, PTFE and FKM seats. Eagle Products' customers are fabricators, contractors in the municipal and water treatment fields and OEMs, and as such, their discussions with Eagle Products are primarily regarding the process and the standards that are applicable to the products and not about the replacement of a single component.
Eagle Products recommends a stainless steel check valve to be used in a shallow well located on a farm or in a process water system where the water is aggressive or the check valve can be difficult to reach. In cases of poor water conditions, a brass check valve will fail and will require excavation. However, for potable municipal water where the check valve can be reached easily, brass will be the best option, and we indicate as such in writing.
If you're specifying a clean water system, provide the flow rates, pipe sizes and cleaning method of the system, we'll determine what valve type and what orientation you'll need for installation; this is much cheaper than having to excavate a second time.
Frequently Asked Questions
Can I put a check valve above the well-head?
Yes, but the pump has to be self-priming and the check valve needs to be within approximately 300mm from the pump inlet. At that point, the air volume that the pump has to remove becomes too huge for most pumps and causes a loss of prime every time the pump is stopped. A check valve will prevent backflow at the well-head, but will not keep the suction pipe full as a foot valve would.
Do I require a check valve or a foot valve on a shallow well?
A foot valve is typically installed at the bottom of the suction pipe, typically 300mm to 500mm above the well bottom, and the purpose of a foot valve is to retain the water in the suction pipe and prevent backflow. A check valve is used to prevent water from entering the pump and returning to the pressure tank after the pump has stopped.
Why does my check valve cause my pump to lose prime?
Because the check valve is located on the end of the pipe above ground level, the water has to drain back through the pipe to the well before the pump can restart and it does so with the added burden of having to push air ahead of it. To get around this: either change the check valve location to be at the bottom end of the suction pipe (as a foot valve), or install a self-priming pump and move the check valve to within 300mm of where it connects to the pump. A leak in the suction line will cause the same symptoms; therefore, it should be checked first.
How should the valves be positioned?
The check valve should have the arrow on the body aligned in the direction of flow. A swing check valve must have horizontal flow, or vertical flow from below to above, so that gravity helps close the flapper valve. If you install one with the flapper pointing down, there is no way to seal it. Ball check valves do not require any particular orientation other than to be used in conjunction with upwards flow. Spring or wafer check valves are not as sensitive to orientation as the others, but they do create a small amount of pressure before they will open.
References
- Swagelok - Check Valve Selection and Installation Practices
- Alfa Laval - Hygienic Check Valves & Flow Equipment
- American Society of Mechanical Engineers - B1.20 Pipe Threads & B31 Piping Codes
- Copper Development Association - Brass Alloys and Their Dezincification Properties
- ASTM International - Stainless Steel & Copper Alloys Specifications
Conclusion
A check valve located above ground level on a shallow well serves a different purpose than a foot valve; its function is to stop backflow and not to maintain a full suction line. Therefore whether or not this configuration is permissible is dependent on whether or not the pump will self-prime as well as how much air might sit between the check valve and the inlet.
If the check valve is accessible, and the pump is self-priming, the best solution may be to install it within 300mm of the outlet of the pump, since that will allow for easier maintenance. If the pump is a traditional centrifugal pump, then it would be better to use a foot valve at the bottom end of the suction line, since it will be easier to pull the suction line with just one effort than to attempt to re-prime the pump every day.
