What causes a wafer-type check valve to fail to hold back water?
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This post was last edited by Xin Cheng on 2018-6-25 at 18:01. Hello, experts and teachers. I have a question to ask: there are 3 pipelines in a system, and sometimes certain check valves fail to prevent water from flowing back, while at other times all of the check valves fail to do so. Upon inspecting the pipelines, no foreign objects were found inside the check valves. However, when these valves are installed in the pipelines, water flows back, meaning the check valves cannot prevent water from flowing back. What causes this? All check valves are brand new check valves. The outlet pressure is sufficient, all above 0.4 MP. The check valve is located at the outlet of the water pump; when the pump stops operating, the pressure in the pipeline system causes water to flow back into the tank behind the pump. The initial water pressure in the tank was around 0.3 MPa.
The sealing of a check valve is determined by the pressure difference between the front and back sides. Please analyze the reasons: 1. When performing its check function, the pressure acting on the check valve is not sufficient to ensure sealing； 2. The sealing grade of the check valve itself is much lower, and it cannot be compared to that of valves and similar components ； 3. In the event of significant water leakage, check the condition of the valve plate and also verify whether there are any issues with its installation.
The pressure is above 0.4 MPa
1 The pressure received is sufficient, all above 4 kilograms. The sealing rating of the 2-valve body is 16 kilograms, and the maximum outlet pressure does not exceed 10 kilograms. The 3-check valve is located at the outlet of the water pump; when the pump stops operating, the pressure in the outlet pipeline flows back into the tank behind the pump
Your check valve appears to be of the disc type; when checking it, water needs to be injected to see if there is any leakage. These types of valves have springs inside them; it is essential to pay close attention to the operating principle of the valve during installation, as it is easy to install them incorrectly. Check it out and take a look. Also, check whether the valve seat is damaged and whether it needs grinding or machining. It would be best to send another photo after disassembly, to confirm whether the installation was correct.
Yes, there are springs inside the valve body; make sure that the entire valve body is installed correctly. I’ll re-upload a photo of the valve body in a moment
It can be said that no check valve is completely leak-free; as long as the leakage amount is within the specified limit, it is considered acceptable. Is it leaking drop by drop, or is the water flow leaking? You calculate how many milliliters there will be in the next minute. There are acceptance criteria. If it exceeds the limit, it is due to inadequate grinding of the check valve body and the valve disc. It needs to be ground again. These are Senior Kaichuan’s experiences. I’ve sent it to you in a summary
This post was last edited by sdwfsgyykai on 2018-6-25 10:34 to discuss check valves. Check whether the guide rod is smooth with no jamming, and whether there is excessive swinging of the valve head. Try to check for leaks by pouring water in the direction of the outlet. Is grinding necessary?
The possibility of incorrect installation is low. In my opinion, after the pump starts operating, before it stops, there might be a valve or a pressure source in front of the pump, which creates negative pressure and prevents the check valve from functioning properly (according to standards, pressure gauges or high/low pressure protection devices should be installed either in front of or behind the pump)