Should a check valve be installed first at the pump’s outlet, or is a butterfly (ball) valve better?

Sure, it’s the check valve first, to prevent the material from flowing back.

To understand this issue at its root, one must first understand why a check valve is installed at the pump outlet. A check valve is used to prevent water from flowing back, and the ultimate purpose of preventing backflow is to stop the pump from rotating in the reverse direction. There are two forces in the opposite direction: the first is due to the inherent pressure of the pump outlet pipeline ； The second is the expansion pressure of the liquid itself. If only the first factor is considered, then the order of installation of check valves, gate valves, and butterfly valves has little impact. However, if the reverse impact on the pump caused by the expansion of the liquid being pumped is taken into account, it is necessary to keep the distance between the pump outlet and the check valve as small as possible. I think this is why, at the outlet of a pump, whether it’s a large or small pump, as long as a check valve is installed, a check valve is installed first, followed by a gate valve or ball valve, without exception.

By design, a check valve should be installed at the outlet of a centrifugal pump, followed by a shut-off valve； Furthermore, the check valve is designed with a bypass line, and a globe valve should be installed on this bypass line. The purpose of installing a check valve is to prevent the material from flowing back inside the pump, as such backflow can cause the pump motor to rotate in the reverse direction. Reversing the pump will damage the motor.

1. Install the check valve first, and then the gate valve or butterfly valve. Advantage: It protects the check valve, especially in parallel pump systems; when one pump stops operating while the other starts, the impact forces are absorbed by the gate valve or butterfly valve. Disadvantage: Then who will protect the gate valve or the check valve? There was once a case in which the valve disc of a butterfly valve was broken. 2. Install the gate valve or butterfly valve first, and then the check valve; advantage: this protects the butterfly valve or gate valve, as the impact forces are absorbed by the check valve. Disadvantage: Who will protect the check valve? The check valve operates based on pressure differences – it closes when the pressure in the main pipe is high and opens when the pressure from the pump is high. If the flow rate used is unstable, the check valve will open and close repeatedly, which can affect its lifespan. Personal opinion: Regarding the design of check valves, their performance is constantly evolving; many of them now are slow-closing check valves. This allows the impact force to be distributed across two sources. Since the gate valves or butterfly valves at the outlet are not fully open, it is possible to install the check valve behind them. If it is not a slow-closing check valve, it is still best to place it behind the gate valve or butterfly valve.

First, install the check valve, and then the gate valve or butterfly valve. However, to save costs, gate valves are generally used; personally, I think butterfly valves are easier to operate, which facilitates work for the workers.

On the outlet of a pump, a check valve is usually installed first, followed by an outlet valve. Gate valves are chosen for these outlet valves, as they allow for the immediate shutdown of the flow of material during maintenance work. This is applicable to pumps used for transporting water as well. Additionally, gate valves can be used to regulate flow rates. Butterfly valves perform poorly in such applications, and especially in situations where there is frequent use of the equipment, it should not be used just because it is cheaper – as this could create problems in future operations.

I believe that when installing gate valves, ball valves, butterfly valves, etc., it is necessary to consider the flow rate and the nature of the medium being transported. Gate valves provide good sealing, but impurities tend to accumulate in them. Butterfly valves are used for high-flow applications and require little installation space. Ball valves have good sealing performance and fast operation, require a large installation distance, and are suitable for media containing many particles. As for the sequence of the check valve and the shut-off valve, it is usually the check valve first and then the shut-off valve, because during automatic operation, these shut-off valves do not need to be closed, allowing for the switching of the pump from the control room. Close the isolation valve during maintenance. Check valves can prevent the pump from reversing, but when preheating or precooling is required, some of the fluid must flow in reverse; therefore, the check valve does not remain completely closed, and sometimes holes even need to be made in the valve disc.

It depends on the medium and the usage environment, hehe

We first install the check valve and then the gate valve

Reply to 8# sunday9084: The following statement by this person is debatable – as for the sequence of installing the check valve and the shut-off valve, it is usually the check valve first and then the shut-off valve, because during automatic operation, these shut-off valves do not need to be closed, and pump switching can be carried out from the control room. Under normal circumstances, the outlet isolation valve of a centrifugal pump must be closed before it is started. The reasons are as follows: 1. When the pump starts up, the current drawn by the motor is very high, usually about 7 times that during normal operation. If the pump tries to deliver energy outward at this time, it will further increase the current and damage the motor. 2. If the shut-off valve is not closed when the pump starts, it can cause the pipeline to be suddenly subjected to high-flow water hammer impacts, leading to damage. The standard procedure is to gradually open the outlet isolation valve after starting the pump.