Starting operation of a metering pump
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I would like to ask the experts: why is it necessary to open the connection valve between the pump’s inlet and outlet before starting the metering pump, and then gradually close this valve after the pump has started?
In my analysis, metering pumps generally cannot hold pressure; at the time of startup, no pressure can be generated. Only by applying air pressure can the flow in the rear section be established, and this also serves to supplement the inlet pressure at the outlet
Positive displacement pumps generally cannot withstand pressure buildup; the bypass valve is opened to prevent pressure buildup behind the outlet valve.
OP, first you need to understand the characteristics of metering pumps. Metering pumps are of the positive displacement type and have the ability to draw in liquid without any fluid present; their theoretical pressure can be extremely high. Therefore, before starting the pump, the outlet must be opened, and the pump should be started at a low flow rate. When stopping the pump, it is necessary to reduce the flow rate first before shutting it down – this is the standard operating procedure!