Why is it so difficult to open the pump outlet valve?
Thread Content
I have a question: When operating our equipment, we often need to start a pump (a centrifugal pump). The current consumption during normal operation is 120A, the pressure at the pump’s outlet is around 1.5 MPa, and the medium being transported is coking water containing a small amount of impurities; the diameter of the outlet pipe is 350 mm. It’s particularly difficult to start the pump each time; usually, two people need to use the F gun together with force in order to get it running. What could be the reason for this? Is it possible to replace it with an electric valve?
The reason why the valve is difficult to open is likely that the pump outlet pressure is around 1.5 MPa, which is a bit high； Additionally, the outlet pipe has a diameter of 350 mm, resulting in a large flow area. Therefore, the force acting on the valve core (force = pressure × area) is relatively large, so it is normal for it to be difficult to open. It is recommended to switch to an electric valve!
Are the valves you export gate valves? You can apply some oil to the valve stem and clean out any impurities from it. Our factory has also encountered this situation with you; cleaning and refueling will fix it.
High pressure and the presence of impurities can both cause difficulties in opening it. Either replacing the electric or starting mechanism will work.
It might be due to an excessive pressure difference before and after the valve, or impurities getting stuck in the rotating parts
It might be due to an excessive pressure difference before and after the valve, or impurities getting stuck in the rotating parts
With pipes of such large size, high pressure, and media containing impurities, it is quite difficult to operate any valve manually； Even for a manual gate valve, it would likely take hundreds of turns to open it, which is equally labor-intensive; it’s better to use an electric valve instead.
A large pressure difference before and after the valve, or impurities in the rotating parts, can make it difficult to open the valve – this is normal； It would be better to use an electric or hydraulic version.
Switch to a globe valve or butterfly valve, and it will be easier
Is the packing compressed too tightly? This has happened before; loosening the packing makes things work much better. Of course, this is done without causing any leaks.
The ultimate goal is to eliminate the pressure difference on either side of the valve, and then everything will be fine. A DN50 ball valve can be installed alongside the main line valve as a balance valve.
Suggestions for the poster: 1. Apply lubricant to the valve stem regularly； 2. Install bypass pipelines with a diameter of 25 CM in front of and behind the valve, to be controlled by small hand valves ； 3. Switch to a butterfly valve. 4. Switch to electric valves: When switching to electric valves, it is essential to pay attention to the selection process – the valves should be simple to use and effective.
The valve behind the centrifugal pump should be slowly opened only after the pump has started operating properly. Due to its large diameter, considerable force is required to open it, and other factors make it difficult to open the valve. I feel that changing it to an electric version is not appropriate. It is very difficult to open it manually; by using an electric motor, no effort is required from humans, but the motor needs to be larger in size, and the underlying problem remains unresolved. It is recommended to first identify and eliminate the reasons why it is difficult to open, before considering whether to switch to an electric version. There are many reasons mentioned above for its formation, and I basically agree with them. No repetition.
When the medium contains impurities, it is difficult to open the valve; applying oil to the valve stem can reduce resistance, or an electric valve can be used instead.
If the pressure difference between the front and back is large, you can add a small auxiliary valve.
It could be that the valve packing is too tight, or the valve stem is rusty and lacks proper lubrication; an excessive pressure difference before and after the valve, or impurities in the rotating parts, can all make it difficult to open the valve. If the pressure difference before and after the valve is too large, the outlet valve of the pump can be slightly opened first when starting the pump.
There could be two reasons: 1. The pressure at the pump outlet is high, and the pipe diameter is large, so the force acting on the valve core is significant, making it difficult to open. 2. The filler is compressed too tightly or is of poor quality. Graphite filler is preferred, and the valve stem should be lubricated with grease regularly.
High pressure and a large flow area are the main reasons for difficulty in opening. It is recommended to use a butterfly valve or create a bypass to relieve pressure through a secondary valve; this approach results in low modification costs, and it is not necessary to use electric valves.
With such a large pressure difference between the inlet and outlet, and a large pipe diameter, it’s inevitable that it will be difficult to operate; it is recommended to add a small bypass valve. First, open the small valve; wait until the pressure on the front and back is balanced before opening it further, and things will be much better.