Why Discharge Valve Closed During Starting of Centrifugal Pump ?

 >By closing the discharge valve, we can reduce the starting current

>As you know,the current will be high during the starting of any motor. If you start the pump with discharge valve open, the discharge head will act on the pump ie, more resistance, so the motor has to give more starting torque to the pump which means more current is drawn by the motor. 

>If you start the pump discharge valve closed, it means no discharge head minimum resistance to the pump and minimum current drawn. Even though current taken during startup is more than normal, by closing discharge valve you can avoid extra load on the pump

>If you have a check valve, then the discharge valve can be opened. Without a check valve, you need to have the discharge valve closed if there is pressure on the discharge side at the time of startup.

>Thinking on a different way , If there is pressure on the discharge side of the pump,prior to start up, it can flow back  through the pump, causing a backward spin and may draw more current, thereby causing damage to  the pump. It can also be prevented by keeping the discharge valve closed.

Must Read:> Centrifugal Pump Components And Functions With A Simple Diagram

Explanation Using Pump Characteristics

>The discharge valve of the pump has to be closed during startup. This is maintained so, inorder  to prevent sudden load on the power system, if the valve is open. If you look at the characteristics of the pump, the power required ,increases with flow rate. If the valve is open and the pump is switched on, there is a sudden power load corresponding to the flow rate. If the valve is closed (zero flow) the power load is minimum ie minimum current.

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  1. very nice .Thanks for sharing this information. thanks marine site.

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  2. How will be come to know about backward spin???

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    Replies
    1. The motor fan will be seend rotating in opposite direction

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  3. Perfect explanation ..thanx

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  5. Just saying thanks will not just be sufficient, for the fantasti c lucidity in your writing. I will instantly grab your rss feed to stay informed of any updates. best artificial christmas trees

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  6. But closing the valve will cause the churning in the pump as pump is still trying to push the water. In that case won't the load on pump increase? please explain.

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  7. I have learnt a lot because at times we miss out this especially on pump start up (We start while discharge valve is open)but I also educate others.

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    Replies
    1. I meant I'll be there for other who do not to make sure I'll share the information with them

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  8. Thank you for giving such valuable information

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  9. can i close The valve on the suction side to control the flow and reduce curent

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