Pressure Testing Methods and Precautions for Common Valves

In the industrial sector, valves play a vital role as key components in piping systems, and their performance and safety are of utmost importance. Whether in the fields of petroleum, chemical engineering, pharmaceuticals, or water treatment, valves are indispensable. They not only control the flow of fluids but also ensure the system's sealing and safety. However, valves must undergo rigorous testing both before leaving the factory and after installation to ensure they can withstand the pressures and media encountered during actual operation. Valve pressure testing is a crucial part of this process. It not only checks the valve's strength and sealing but also identifies potential defects in a timely manner, preventing failures during actual operation that could cause unnecessary losses and safety hazards.

Next, we will delve into the specific pressure testing methods for various common valves. Mastering these methods is essential for ensuring the safety and reliability of valves in practical applications. Different types of valves, due to their varying structures and working principles, have different pressure testing methods. Here are the pressure testing methods and steps for several common valves.

Pneumatic ball valves are a common type of valve, and their pressure testing method is relatively simple. During the strength test, the ball should be placed in a semi-open position, and the test medium should be introduced from one end to the specified pressure, with the other end closed, to check for any leakage in the valve body and cover. For the sealing test, the valve should be in a semi-open position, with the test medium introduced from one end and the other end closed. After rotating the ball several times and closing the valve, open the closed end to check the sealing performance, and also check for any leakage at the packing and gasket areas. If there is no leakage at both ends, it indicates that the valve has good sealing performance.

The pressure testing methods for floating and fixed ball valves are slightly different. For the sealing test of a floating ball valve, the valve should be in a semi-open position, with the test medium introduced from one end and the other end closed. After rotating the ball several times and closing the valve, open the closed end to check the sealing performance, and also check for any leakage at the packing and gasket areas. For a fixed ball valve, the ball should be rotated several times without load before the test, then the valve should be placed in a closed position, and the test medium should be introduced from one end to the specified value, with a pressure gauge of 0.5–1 grade accuracy used for inspection. If there is no pressure drop within the specified time, the valve is considered qualified. Then, introduce the test medium from the other end and repeat the above test. Finally, place the valve in a semi-open position, close both ends, fill the cavity with the medium, and check for any leakage at the packing and gasket areas under the test pressure.

The pressure testing of a three-way ball valve requires sealing tests at each position. This is because the structure of a three-way ball valve is more complex, with multiple channels, and it is necessary to ensure that the sealing performance of each channel meets the requirements. During pressure testing, sealing tests should be conducted on each channel separately to ensure that the valve can effectively prevent medium leakage under different working conditions.

The pressure testing state of a check valve varies depending on its type. For a lift check valve, the valve disc axis should be in a position perpendicular to the horizontal plane, while for a swing check valve, the channel axis and the valve disc axis should be in a position approximately parallel to the horizontal line. During the strength test, introduce the test medium from the inlet end to the specified value, with the other end closed, to check for any leakage in the valve body and cover. For the sealing test, introduce the test medium from the outlet end and check for any leakage at the sealing surface, packing, and gasket areas on the inlet end.

The strength test of a globe valve usually involves placing the assembled valve in a test frame, opening the valve disc, injecting the medium to the specified value, and checking for any leakage in the valve body and cover. For the sealing test, the valve stem of the globe valve should be in a vertical position, with the valve disc open, and the medium introduced from the end below the valve disc to the specified value, to check for any leakage at the packing and gasket areas. If the valve needs to undergo both strength and sealing tests simultaneously, the strength test can be performed first, then the pressure can be reduced to the specified value for the sealing test, to check for any leakage at the packing and gasket areas; then close the valve disc and open the outlet end to check for any leakage at the sealing surface.

The strength test of a pneumatic butterfly valve is similar to that of a globe valve. The sealing performance test of a butterfly valve should involve introducing the test medium from the end where the medium flows in, with the butterfly plate open and the other end closed, and injecting the pressure to the specified value. After checking for any leakage at the packing and other sealing areas, close the butterfly plate, open the other end, and check for any leakage at the butterfly plate sealing area. It should be noted that butterfly valves used for regulating flow can be exempted from the sealing performance test.

During the strength test of a plug valve, the medium is introduced from one end, with the other passages closed, and the plug is rotated to each fully open working position in sequence for testing, with no leakage in the valve body indicating qualification. For the sealing test, a straight-through plug valve should maintain equal pressure inside the cavity and in the passage, with the plug rotated to the closed position and checked from the other end, then the plug rotated 180° to repeat the above test; for three-way or four-way plug valves, the pressure inside the cavity should be equal to the pressure at one end of the passage, with the plug rotated to the closed position in sequence, the pressure introduced from the right-angle end, and checks performed simultaneously from the other ends. Before testing a plug valve, it is permissible to apply a layer of non-acidic light lubricating oil to the sealing surface. If no leakage or expanding droplets are found within the specified time, the valve is considered qualified. The testing time for a plug valve can be shorter, generally specified as 1–3 minutes according to the nominal diameter. For plug valves used with gas, an air sealing test should be conducted at 1.25 times the working pressure.

The strength test of a gate valve is similar to that of a globe valve. There are two methods for the sealing test of a gate valve. One method involves opening the gate to allow the pressure inside the valve to rise to the specified value; then close the gate, immediately remove the gate valve, and check for any leakage at the sealing areas on both sides of the gate, or directly inject the test medium into the plug on the valve cover to the specified value and check the sealing areas on both sides of the gate. This method is called intermediate pressure testing, but it is not applicable to gate valves with a nominal diameter of less than DN32mm. The other method involves opening the gate to allow the valve test pressure to rise to the specified value; then close the gate, open one end blind plate, and check for any leakage at the sealing surface. Repeat the above test by reversing the direction until the valve is qualified. For pneumatic gate valves, the sealing test of the packing and gasket areas should be conducted before the gate sealing test.

During the valve pressure testing process, to ensure the accuracy and safety of the test, it is important to pay attention to some common technical issues and details. The following are some key precautions, which are crucial for ensuring the smooth progress of the pressure testing process.

During hydraulic testing, it is important to expel as much air as possible from inside the valve to ensure the accuracy of the test results. The valve should be installed in a position that is easy to inspect during the test to facilitate the observation of any leakage. For cast iron valves, during the strength test, the valve body and cover can be gently tapped with a copper hammer to check for any leakage. For valves with a welded connection, if blind plate testing is not feasible, a conical seal or O-ring seal can be used for the test.

After the valve pressure test is completed, any accumulated water inside the valve should be promptly drained and the valve wiped clean. A record of the test should also be kept. The pressure should be gradually increased during the test, and sudden or rapid increases in pressure are not allowed. Except for plug valves, which are permitted to apply oil to the sealing surface during testing, no other valves should be tested with oil on the sealing surface. Throttle valves do not undergo a closing element sealing test, but they should be tested for strength and sealing at the packing and gasket areas.

During the pressure testing process, the closing force of the valve should only be within the normal physical strength of one person, without the use of levers or other tools to apply additional force (except for torque wrenches). When the handwheel diameter is greater than or equal to 320mm, two people are allowed to close the valve together. When testing the valve, the clamping force of the blind plate on the valve should not be too great to avoid deformation of the valve, which could affect the test results. This is especially important for cast iron valves, as excessive pressure could lead to valve damage.

For valves equipped with actuating devices, the sealing test should be conducted using the actuating device to close the valve. For manually operated actuating devices, a manual closing test of the valve should also be performed.

During strength and sealing tests, the bypass valve installed on the main valve should also be opened when the main valve's closing element is open. Safety valves should undergo strength and sealing tests before installation. For low-pressure safety valves, a random check of 20% should be conducted, and if any are不合格, then a 100% check should be performed; for medium and high-pressure safety valves, a 100% check is required.

For valves with upper seals, the packing should be removed for a sealing test. After the upper seal is closed, check for any leakage. When using gas for the test, fill the packing gland with water for inspection. During the packing sealing test, the upper seal should not be in a closed position.

The duration of strength and sealing tests is generally 2–3 minutes, with important and special valves lasting 5 minutes. The testing time for small-diameter valves can be shorter, while that for large-diameter valves can be longer. If there are doubts during the test, the testing time can be extended.

During the strength test, no sweating or leakage should occur in the valve body and cover. For the sealing test, general valves are usually tested only once, while important valves such as safety valves and high-pressure valves require two tests. For low-pressure, large-diameter, and less important valves, as well as valves that are allowed to have some leakage according to regulations, a small amount of leakage is permitted. Since general valves, power station valves, marine valves, and other types of valves have different requirements, the leakage requirements should be followed according to the relevant regulations.

Valve pressure testing is a crucial step in ensuring the safe and reliable operation of valves in practical use. By understanding the pressure testing methods and precautions for various common valves, potential safety accidents caused by valve quality issues can be effectively avoided, the service life of valves can be extended, and the smooth progress of industrial production can be ensured. When conducting valve pressure testing, it is essential to strictly follow the relevant standards and specifications to ensure the accuracy and reliability of the test results. We hope this article has been helpful to you. If you have any other questions, feel free to consult us at any time.