- Principle
The water pressure test uses the incompressibility and good fluidity of water. By applying a certain pressure of water to the inside of the valve, the valve is observed to see if there is leakage under pressure, so as to judge its sealing performance. As a common and relatively safe medium, water can stably transmit pressure during the test, and once a leak occurs, it is easy to observe due to the visibility of water.
- Operation steps
1. Preparation
Install the valve to be tested on a special test device to ensure that the valve is in a closed state. The test device should have a reliable connection interface to connect with the pressure test pump and other auxiliary equipment. For example, in an industrial pipeline valve testing workshop, a gate valve with a nominal diameter of DN50 is tested and installed on the test bench. Both ends are firmly connected to the test pipeline through flanges. An exhaust hole is set at the highest point of the valve to smoothly exhaust the air in the pipeline and valve during the water injection process. If the air is not exhausted, it will affect the accuracy of the pressure test, because the compressibility of air will cause unstable pressure fluctuations.
2. Water injection and exhaust
Use a pressure test pump to slowly inject water into the valve and connecting pipeline. During the water injection process, the water injection speed should be kept moderate to avoid excessive air being introduced due to excessive water flow. At the same time, observe the exhaust hole. When there is continuous water flow and no bubbles, it means that the air has been exhausted. For example, when injecting water into a large stop valve, the operator can judge whether the air has been exhausted by observing the water flow at the outlet of the exhaust valve installed on the top of the valve. If a large number of bubbles are discharged with the water flow at the outlet of the exhaust valve at the beginning, as the water injection continues, the bubbles gradually decrease until only continuous water flows out, at this time the air has been basically exhausted.
3. Pressure increase and pressure maintenance
Start the pressure test pump and continue to slowly increase the pressure to the specified test pressure. The test pressure is usually determined according to the nominal pressure (PN) of the valve and the relevant standards, and is generally 1.5 times the nominal pressure. For example, for a ball valve with a nominal pressure of PN16, the test pressure should be 24 bar. After reaching the test pressure, keep the pressure stable for a period of time, generally 10-30 minutes, depending on the valve type and standard requirements. During the pressure holding process, closely observe the pressure indication to ensure that the pressure fluctuation is within the allowable range. If the pressure drops too quickly, it may mean that there is a leak in the valve or a problem in the pressure test system, which needs to be checked in time.
4. Check for leaks
After the pressure holding time is over, conduct a comprehensive inspection of the valve to observe whether there is any water droplet seepage. The key inspection areas include the valve stem, the connection between the valve body and the valve cover, the sealing surface, and other areas that may have leakage risks. Taking a butterfly valve as an example, you can use a clean white cloth or filter paper to wipe the various connection parts and sealing surfaces of the valve during the inspection. If there are obvious water stains on the white cloth or filter paper, it means that there is a leak in this area. For some minor leaks, you may need to use tools such as a magnifying glass for careful observation.
- Application scenarios
Hydraulic pressure tests are widely used in various types of valves, especially for valve testing in pipeline systems for the transportation of water or other liquid media. For example, in urban water supply pipeline systems, newly installed valves must be subjected to hydraulic pressure tests before they are put into use to ensure that they can be reliably sealed under water supply pressure to prevent water resource leakage and waste and damage to the pipeline system. In the building water supply and drainage system, faucets, stop valves and other valves in the bathroom, kitchen and other areas also need to undergo water pressure testing to ensure that there will be no leakage during daily water use and to provide residents with a good water environment.