Check valve failures result from wrong installation techniques, poor maintenance practices, and inadequate research before valve application, among other reasons. These failures prevent the valves from functioning properly and may damage the pipe systems, pumps, and well equipment.
Check valves, also called non-return valves, are devices through which fluid flows in only one direction. They function to prevent the reversal of fluid flow (backflow) in the system to which they are applied. Therefore a well check valve failure may result in fluid flowing back into the well.
For check valve failures to be prevented, the valves need to be installed correctly, regularly tested for quick notice of impending valve failures, and maintained properly.
This post discusses how to test, install and assemble check valves. It also highlights some check valve failures, with their symptoms, causes, and solutions.
Tests are required to prevent check valve failure. Checking the valves for seal integrity or leakages in the seat and shell ensures that problems in the valves are noticed quickly, and the system is protected from failure.
The success of many operations depends on the working of the check valve in the system. Therefore check valves should be tested regularly to avoid backflow, water hammer, and other consequences of failed check valves.
For proper testing, check valves should be subjected to MSS SP-61. The MSS SP-61 is an ANSI standard that issues the proper requirements for testing shell and seat closure in a check valve.
Below are the ways check valves can be properly tested:
For the Shell test, the test fluid is water, and the valves are tested at a pressure greater than or equal to 1.5 times the 100-degree Fahrenheit rating, rounded to the next 25psi increment. The valve sizes and their test time are:
Valve SizesTest Time< 2inches 15 seconds2.5 to 6 inches60 seconds 8 to 12 inches120 seconds 14 inches and above300 secondsFor a successful result, there should be no leakages in the valve.
For this seat closure test, the test fluid is water, and the valves are tested at a pressure greater than or equal to 1.1 times the 100-degree Fahrenheit rating, rounded to the next 25psi increment. The valve sizes and their test time are:
Valve SizesTest Time< 2 inches 15 seconds2.5 to 8 inches30 seconds 10 to 18 inches60 seconds 20 inches and above120 secondsThe max leakage allowed for metal seated valves is 40 ml/hr of water per inch of nominal valve size. No leakage is allowed for soft seated valves.
Max leakage allowed after one hour is 80 ml for 2 inches, 240 ml for 6 inches, 560 ml for 14 inches, and 800 ml for 20 inches.
For the seat closure test, the test fluid is air, and the valves are tested at an air pressure greater than or equal to 80 PSIG. The valve sizes and their test time are:
Valve SizesTest Time< 2 inches15 seconds3 inches30 secondsThe max allowable leakage for metal seated valves is 0.4 SCFH/inch of inlet size. For soft seated valves, no leakage is allowed.
Lift-type and Swing check valves can also be tested using the pressure test. The axis of the lift check valve’s closure element is positioned perpendicular to the horizontal surface. In contrast, the axis of the swing check valve’s closure element and the channel is positioned almost parallel to the surface.
The pressure test involves two tests: The strength test, which tests for leakages in the valve body, and the cover and sealing test, which tests for leakages around the sealing surface.
The test fluid is introduced from the inlet, and the outlet is closed. If there is no observable leakage from the valve body and cover, the valve passes the test.
The test fluid is introduced from the outlet, and the valve is shut. If there is no observable leakage from the sealing surface, gasket, and packing, the valve passes the test.
Check valves, even though solidly constructed and properly structured, are like every other piece of equipment in their need for careful use, tests, and maintenance.
If the check valve is not tested or maintained as often as it should, it may develop problems that worsen with time and eventually lead to the check valve failure.
Pump check valve failure may result from the piling up of suspended particles in the check valve, and well check valve failure may result from the use of the valve in functions with incompatible materials, leading to the slow destruction of the valve parts. Hence, different modes of check valve failures exist in their different functions and are usually caused by poor research, wrong installation, and irregular maintenance.
Non-return valve failures vary as check valves are of different types and, in some cases, different parts. However, below are some common check valve failures:
Some check valve failures in pipe systems, wells, and pumps include:
A reverse flow occurs when water flows back from the outlet to the inlet area. Check valves are one-way valves, and a reverse flow is an indication of the check valve failure.
The backflow is especially disadvantageous when it occurs in discharge pump operations, as the backflow of fluid into the pump may cause the impeller to spin in a different direction, resulting in pump damage.
Debris can be deposited in the check valves by fluids moving through the pipeline, causing the valve to get stuck in an open or closed position. Irregular check valve maintenance encourages the accumulation of debris over a long period.
Also, debris moving in the fluid at high speed may damage the valve’s internal parts. These broken internal parts of the valve then contribute to the accumulation of debris.
A water hammer occurs when fluid flowing through the pipe is suddenly restricted or forced to move in another direction. It is a pressure surge or vibration which damages pipes, fittings, and the check valve.
This is a common swing check valve failure, in which fluid backflow causes the valve to shut off suddenly, resulting in pressure vibrations throughout the pipe.
Check valve discs, balls, or plugs are sealed to the seats using seals such as elastomer rings to ensure proper shutoff. This sealing happens when the inlet pressure falls below the valve cracking pressure, or a fluid backflow occurs.
These sealing materials lose their ability to seal properly over time due to constant friction and frequent use. With decreasing sealing integrity, fluids seep through the shutoff valves, resulting in the check valve failure.
Check valve failure can lead to flow disruptions and fluctuations in the valve. Check valves ensure a constant fluid flow in one direction until the fluid is shut off. Therefore, any flow stoppage or inconsistency in flow indicates a failed check valve.
Source: Pro Boat Mag
Alt text: Check Valve Operation
Troubleshooting of well pump check valve failures and other modes of check valve failures indicate that valve failures are caused by the actions and conditions below.
The Installation, assembly, and maintenance of check valves, if done wrongly, may lead to serious damage to the valve. Improper installation causes premature wear and tear in the valve, which could result in the valve failing at the early stage of operations.
High temperatures cause the expansion of valve parts and contribute to their quick degradation. It also negatively affects valve sealing integrity, leading to leakages in the valve. Therefore, high-temperature conditions result in check valve failure.
Check Valves function properly with adequate pressure. The insufficient pressure of the fluids causes the valves to open and close frequently, resulting in wear out of the valve parts.
Also, low pressure caused by clogged or wide pipelines affects the valves negatively and could lead to their failure.
Check valve failures can cause irreparable damage to the valves and the pipes. However, they show symptoms that, if noticed and attended to, can prevent serious damage. Some of these symptoms are:
Water hammer, backflow, and other check valve failures can be prevented by following these maintenance guides:
Other check valve maintenance and preventive measures include considerations in selecting appropriate valve sizes, material compatibility, and reaction speeds of the valves.
For the safety of your valves and to prevent the non-return valve failures from transforming into system failures and more costly repairs, you may need to replace the valve parts or the entire valve.
But in less critical cases, the valve could be repaired by tightening bolts or removing debris. Some solutions to check valve failures include:
Check valves should first be tested and troubleshot to know the exact areas of the valve leaking and the causes of the valve leakages. For example, swing check valve leakages may be caused by loosened bolts, damaged gaskets, or bad flappers. Bolts should be tightened in the necessary cases, and replaceable valve parts should be replaced.
Check valve parts can be replaced if a part is ineffective and cannot be repaired. In some cases, as soon as the valve part malfunctions, it’s safer to change the part at once to prevent that part from affecting the entire valve operation.
There could also be a need to replace the entire valve. In situations where the valve size, type, closing assembly, or reaction speed is inappropriate for the operation, it’s best to replace the entire valve.
Water hammer can be prevented using the preventive and maintenance guides above. Still, in cases where a water hammer occurs, regardless of the procedures, the pipe where the water hammer occurs should first be located.
When discovered, some of the various solutions that can be implemented are the installation of water hammer arresters, the release of air pockets in the valve, replacement of intake connections, installation of pressure limiting valves, etc.
Obstruction of valve opening and closing may be caused by accumulated debris in the pipeline. Other causes include stuck parts, wrongly installed valves, or the use of wrong valve sizes.
Valves should be disassembled for proper analysis of the problem. The debris in the valves should be cleaned, lubricated, and the valve size should be confirmed with the pipe size before reinstallation.
Different modes of check valve failures occur due to improper assembly and installation of the valves. For valves to be installed properly, valve installation rules and guidelines must be followed.
Below are three pipe design rules that must be followed for effective installation and operation of check valves:
Pipes connected to the check valves should be designed straight, upstream, and downstream, as valves work best with smooth and non-turbulent (laminar) flow.
Five times the nominal pipe size (NPS) of straight pipe is recommended. However, some check valves can be installed with fewer straight pipes.
For optimum operation of check valves, appropriately sized valves are important. The sizing rules applied to check valves differ from on-off and control valve sizing rules.
Nominal valve and nominal pipe sizes should not always be assumed to match, and sizing calculations should be done for minimum, maximum, and normal flow conditions.
Installing the valve connected to a horizontal or vertical line matters for the smooth operation of the valve. Horizontal lines are usually preferred because of the absence of gravity effect on the valves.
Also, even though many valves work when connected to horizontal pipelines, silent or axial flow check valves are best on vertical lines.
Error in the installation of the valves results in check valve failure and possible damage to the pipe system. Check valves differ in types and parts. Hence installation depends on the check valve type.
However, below are some installation best practices for flapper-type swing check valves:
Qualified and licensed professionals should handle the installation of industrial check valves.
Valve seats are essential parts of the check valve. The closure elements of check valves seal against the valve seats to ensure proper shutoff.
Valves seats are replaced for reasons such as:
If valve seats are not replaced, the damaged seats can cause leakages in the valve, backflow, and ultimately, non-return valve failure.
Check valve seats can be replaced by following these steps:
Check valves, unlike other valves, mostly work automatically and do not require an on-site or remote control. Hence, most check valves do not have handles, stems, or actuators.
Check valves are mostly influenced by the fluid pressure to open or close. When the inlet fluid pressure is above the valve cracking pressure, the valve opens, and when the inlet fluid pressure is lower than the cracking pressure or there is backflow, the valve closes.
However, the stop check valve has a handle and can be controlled externally. Stop check valves are used to isolate and throttle fluid flow, as well as shut it off.
Handles on stop check valves can be replaced following these steps:
Check valve failures are preventable when adequate attention is given to the operations of the valve. With proper installation, testing, and maintenance practices, costly failures such as well or pump check valve failures can be avoided.
In this post, test procedures, installation guidelines, and proper maintenance practices of check valves were outlined. Also check valve failures, their symptoms, causes, and solutions were highlighted in the post.
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