Problems with check valves
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Should a valve or a check valve be installed first at the pump outlet? In our company, a check valve is installed first; I personally think this is not good, as it may lead to pressure buildup. Dear sea friends, please help check if this is okay.
Install the check valve first, then the valve, to prevent backflow and avoid pressure buildup
If the material is not removed from between that check valve and the valve, especially materials that are prone to vaporization, it will cause pressure buildup in that section. (Also, our company doesn’t have a bypass installed) After all, it’s not possible to discharge waste outside in this section.
Our factory installs the check valve first, and then the outlet valve. 1. In this way, if the single-valve fails, closing the outlet valve allows for disassembly and inspection. 2. If the outlet valve leaks, the check valve prevents the material from flowing back. 3. If, as mentioned by the poster, the vaporization of the material causes pressure buildup in the section comprising the check valve and the outlet valve, it is sufficient to open the outlet valve and connect it to the outlet pipeline. It’s similar to when the material between the inlet and outlet valves (inside the volute) vaporizes; in that case, you can open the volute drain valve to release it. Personal opinion, for reference only
What was said on the 5th floor is very practical; to add, if there is a concern that the valve might be closed due to accidental operation. To prevent overpressure due to material vaporization, a safety valve can be installed between the check valve and the outlet to ensure safety.
I think it depends on what type of pump it is. For the centrifugal pumps in our systems, a check valve is installed first, followed by another valve; whereas for the positive displacement pumps used in the unit’s oil stations, a safety valve comes first, then a check valve, and finally an outlet valve
The pumps with check valves in our unit have a drain line between the check valve and the shut-off valve, which can solve the problem you mentioned. Additionally, we have some pumps as backups; the check valves on these pumps are designed to have bypasses, which are used to warm the pump when it is in backup mode.
Install the check valve first, then the gate valve; that’s how all the pumps I’ve seen are built.