What is this on top of the check valve?
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Circulating water pump outlet check valve, the one on top looks like an oil cylinder? Are there any sea friends who understand?
It looks similar to an oil cup. The copper pipe and small valve are used for filling oil.
In order to reduce the impact force caused by the instantaneous fluid cutoff, this type of valve uses this device as a buffer to prevent the valve from being damaged due to impact. This kind of valve is called a slow-acting check valve.
It is best to use a multi-functional control valve, which can better prevent "water hammer" and damage the valve.
For slow-closing check valves, a small hole is opened in the large valve core and a small valve core is installed. When the pressure in front of the valve is lost, the large valve core closes, and the small valve core does not close temporarily. As the pressure difference between the front and rear of the large valve is equalized, the small valve core closes again. The thing in your picture is to control the small valve core, and it is controlled by taking the pressure in front of the valve. This kind of valve reduces the impact force caused by the instantaneous closing of the check valve.