Should a check valve or a shut-off valve be installed first at the outlet of a centrifugal pump?

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I’ve seen it, but the explanation isn’t clear; I hope there are standard guidelines available for reference.

This post was last edited by ylb913 on 2018-8-8 at 19:57. At the outlets of all centrifugal pumps in our factory, a check valve should be installed first, followed by a shut-off valve; there is an independent check valve in front of the outlet valve for each pump. Whether an additional check valve is needed on the main pipeline at the pump outlet depends on the operating conditions But in cases where there are multiple branches after the pump outlet valve, it is also common to add check valves to each branch. Regarding the identification of high-risk and low-hazard scenarios, HAZOP analysis indicates that not a single check valve can be considered effective in reducing risks; only when two check valves operating on different principles are installed on a pipeline can it be regarded as an effective line of defense. Of course, there are also many centrifugal pumps whose outlets are not vulnerable to backflow, such as the top-of-tower reflux pumps; they all operate at the same pressure level and with the same type of fluid. In such cases, the check valve located before the pump outlet valve might be redundant, but we still install check valves in front of the outlet valves of each pump in accordance with the standard requirements for pump outlet piping.

In my opinion, installing the check valve in front of the shut-off valve helps to protect the pump and also makes it easier to service the check valve. However, some people say that installing a check valve after the shut-off valve can protect both the pump and the shut-off valve, and it also makes it easier to open and close the shut-off valve. Does this make sense? Some others say there are design specifications: one-way valves with large diameters are installed in front of the shut-off valve, while those with small diameters are installed behind it. Is there such a saying? Are there any corresponding design specifications?

This post was last edited by ylb913 on 2018-8-12 07:17. SH/T 3122-2000, \"Code for the Design of Process Piping in Refining Units\", states clearly that \"a check valve should be installed on the outlet pipe of each centrifugal pump or vortex pump; it is advisable to place the check valve between the pump’s outlet nozzle and the pump’s outlet isolation valve.\" All the drawings in this standard follow this principle as well； There is also a statement that \"when the pump outlet pipe has multiple branches, it is advisable to install a check valve on the main pump outlet pipe.\" In addition, many large design institutes also have regulations for pump piping design; the main reason for these regulations is to prevent the impeller of the pump from rotating in reverse. Although it is not stated that \"each pump should be equipped with an independent check valve located before the outlet valve,\" the drawings show this to be the case (which is equivalent to common sense). As specified in SEI (Sinopec Engineering Construction Company)’s SEPD 0111 \"Specifications for Pump Piping Design\", a check valve should be installed at the pump outlet to prevent backflow of fluid and subsequent reversal of the pump’s impeller. ”The specific piping is also indicated in the accompanying drawings ； The ‘Pump Piping Design Regulations’ issued by the Ocean Chemical Engineering Design Institute are identical to those of SEI; ‘to prevent backflow of fluid in the pump from causing the pump impeller to rotate in the reverse direction, a check valve is generally installed at the pump outlet.’ ”. ——In fact, check valves are not only necessary for the piping at the pump outlet; to prevent backflow, check valves are also installed before many types of fluids enter the equipment, as well as before various utility fluids are introduced into the pipelines (to stop these fluids from flowing back into the pipelines leading to water, gas, air supply points and thus entering the utility network system). They are also used, as mentioned earlier, to prevent high-pressure fluids from reaching low-pressure areas (to avoid overpressure in low-pressure equipment and resulting accidents). Take the example of the check valves installed at the pump outlets in our facility: In the workshop where I used to work, there was an amine liquid pump whose outlet had multiple branches leading to desulfurization towers operating at different pressure levels (all dealing with gases or liquefied gases). Some of these towers operated at 1.0 MPa, others at 0.6 MPa, and still others at near-atmospheric pressure. Initially, check valves were installed in front of the outlet valve of each pump as required by the standards; however, no check valves were placed on the main pipe at the pump outlet. Instead, check valves were later installed on the branches leading to the equipment operating at 1.0 MPa and 0.6 MPa levels. In one case, a quick-shut off valve was also installed (since that equipment was located in another workshop). This was done not only to prevent liquefied gases from flowing back into the pump inlet in the event of a sudden shutdown, but also to avoid high-pressure media from entering low-pressure equipment due to faulty control valves in certain branches. It’s important to note that it’s not only the equipment connected to the pump inlet that can be considered low-pressure; the equipment connected to the various pump outlets can also have different pressure levels. ——Standards are also updated as our understanding evolves. With the increasing speed of media dissemination and rising demands for safety and environmental protection, many new safety incidents that are emerging today are challenging the old standards or those that are still in use.

In my opinion, cut-off valves should be installed at both the inlet and outlet of every pump in order to ensure a complete shutdown of flow! As Gong said, for check valves, it is necessary to take into account the specific processes and parameters of the subsequent stage It can be installed on the main pipeline if there are no strict requirements; otherwise, it should be installed on the branch pipelines as needed!