Is it necessary to install a shut-off valve and a check valve at the pump’s outlet? What is its function?
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This post was last edited by jocc_bobo on 2009-7-9 09:41. I’ve seen on several drawings that there are stop valves and check valves at the outlet end of the pump – what is their purpose? ? 2. Are flow meters also one-way? ? What will happen if the fluid flows back in the opposite direction? Does the flow meter also need to be equipped with a check valve? 3. Do check valves and stop valves serve the same purpose? ? Hehe, I hope everyone can help me and discuss this together! I’ve seen check valves that don’t have a valve stem; they don’t require manual operation and possess the ability to prevent flow in the reverse direction on their own. What about the stop valve? There is also an arrow on the valve body indicating the flow direction of the fluid, but since it has a valve stem, can the fluid flow in both directions when the valve is open?
1. The stop valve is primarily used to facilitate disassembly and assembly, as well as to prevent pressure buildup when the centrifugal pump starts, thereby reducing the load on the motor； A check valve prevents fluid from flowing back ； 2. If the flow meter is a rotameter, it is unidirectional ； Ordinary household water meters charge for both forward and reverse flow! Do you mean it’s one-way? 3. Check valves and globe valves serve different purposes; as the name implies, a globe valve is used for shutting off flow in both directions ； A check valve provides one-way flow restriction, but its sealing performance is not strong.
At the pump outlet, the function of the stop valve is primarily to shut off the flow at the pump outlet and regulate the flow rate. Without a stop valve, when the pump is started, it will exert maximum pressure on the pipelines and equipment downstream. The pump outlet also needs to be closed when the pump or check valve is under maintenance. The main function of a check valve is to prevent the material in the pipeline from flowing back and hitting the pump when the pump stops suddenly, thereby avoiding reverse rotation of the pump. Flow meters are generally unidirectional, especially those with rotors. As for whether a check valve is needed, I haven’t seen any cases where it’s required; this is clearer in high-pressure systems.
Of course, a stop valve should be installed. The purposes are: 1. To isolate the pump body when it is under maintenance； 2. When starting the pump, the outlet stop valve should be closed, and the minimum reflux valve should be opened to start it ；
Since it is used to isolate the pump during maintenance, can’t a regular gate valve be used? A regular gate valve combined with a check valve should also suffice to achieve the purposes of isolating the pump during maintenance and preventing backflow, right? ? Hehe, I’m not sure if what I said is correct ?
Check valves also come with valve stems. Gate valves generally have only two states: open and closed, whereas globe valves can be used to regulate flow; that’s why globe valves are installed at the pump outlet instead of gate valves.
It is necessary to install a check valve in order to prevent the fluid from flowing back into the pump in case of pressure imbalances. As for which type of valve to choose, it depends on the specific process conditions; for use in water systems, a regular butterfly valve is usually sufficient.
Two additional points: A shut-off valve is installed before the pump. 1: Before starting the pump, close the valve located before it. According to the curve relating flow rate, head, and shaft power, it can be seen that when the flow rate is zero, the head is at its maximum while the shaft power is at its minimum, thereby reducing the load on the motor； 2: If the valve before the pump is open or no valve is installed, air will accumulate at the center of the impeller when the pump starts, preventing the creation of a sufficient vacuum. This hinders the pump’s ability to draw in water and affects its proper operation; therefore, the valve before the pump must be closed to create pressure.
Check valves are used to reduce the severe impact exerted on the pump impeller and the stop valve (check valve) due to water backflow when the pump is stopped. A stop valve (check valve) is used to prevent water from flowing back.
The stop valve is used to enable startup under light load, preventing excessive current from damaging the motor
Gate valves are generally used to shut off media containing granular materials. Its sealing performance is the worst. Gate valves are typically suitable for applications where frequent opening and closing are not required, and where the gate plate needs to remain fully open or fully closed. Not suitable for use as a regulator or throttle. Globe valves can effectively regulate flow rate; they are suitable only for fluids, and their sealing performance is also acceptable. It can be seen from the above that gate valves are not used at the pump outlet.