Must the outlet valve be closed when the Centrifugal Pump is started
Nov 17, 2021|View:157
Centrifugal Pump requires a lot of attention when starting up, but is it necessary to close the outlet valve when starting up Centrifugal Pump? Let's find out together.
Why is it necessary to close the outlet valve when Centrifugal Pump starts?
When Centrifugal Pump starts, there is no water in the pump outlet pipeline, so there is no pipeline resistance and lifting height resistance yet. and line damage, so start to close the outlet valve in order to make the pump run normally.
If the pump with axial flow is the opposite, must be open valve start, at this time the motor power minimum for a short period of time because there is no resistance, will be biased large flow operation, often pump vibration, noise, and even motor overload operation, the motor will be burned. Close the outlet valve, equal to artificially set the pipe resistance pressure, with the normal operation of the pump, slowly start the valve, so that the pump along its performance curve law gradually normal work.
Centrifugal Pump must ensure two points before starting:
1, the pump casing will be filled with water, the purpose is to form a vacuum;
2. The gate valve on the outlet pipe must be closed, so that the pump does not form a flow, which can reduce the motor starting current and facilitate the smooth start of the pump.
Centrifugal Pump relies on the impeller centrifugal force to form vacuum suction to lift the water, so when the centrifugal pump is started, the outlet valve must be closed first and the water filled. The water level exceeds above the impeller part and discharges the air in the centrifugal pump before it can be started. After starting, a vacuum is formed around the impeller to suck the water upward, and its can be opened automatically to lift the water. Therefore, the outlet valve must be closed first.
About Centrifugal Pump
Centrifugal Pump is a kind of vane pump, relying on the rotating impeller in the process of rotation, due to the interaction between the vanes and the liquid, the vanes will transfer mechanical energy to the liquid, so that the pressure energy of the liquid increases, to achieve the purpose of transporting liquid. Centrifugal pumps work with the following characteristics.
①Centrifugal Pump has a limited value of the head produced at a certain speed. The working point flow rate and shaft power depend on the condition of the device system connected to the pump (level difference, pressure difference and piping loss). The head varies with the flow rate.
②Stable operation, continuous delivery, no pulsation of flow and pressure.
③Usually there is no self-priming ability, so the pump needs to be filled with liquid or pumped into vacuum before it can start working.
④Centrifugal pump is started when the valve of discharge line is closed, and vortex pump and axial flow pump are started when the valve is fully open to reduce the starting power.
Before the pump starts, the pump casing is filled with the liquid being conveyed; after starting, the impeller is driven by the shaft to rotate at high speed, and the liquid between the vanes must also rotate with it. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and gain energy to leave the outer edge of the impeller at high speed into the worm-shaped pump casing.
In the worm casing, the liquid decelerates due to the gradual expansion of the flow channel, and transforms part of the kinetic energy into static pressure energy, and finally flows into the discharge pipe at a higher pressure and is sent to the required place. When the liquid flows from the center of the impeller to the outer edge, a certain vacuum is formed in the center of the impeller, and the liquid is continuously pressed into the impeller because the pressure above the liquid surface of the reservoir is greater than the pressure at the entrance of the pump. It can be seen that as long as the impeller keeps rotating, the liquid will be continuously sucked and discharged.
Other Centrifugal Pump start-ups
The above mentioned are Centrifugal Pump, for other types of pumps, the situation is as follows:
1、High flow starting characteristics of axial pumps - full open valve starting
Axial flow pumps have the maximum shaft power at zero flow condition, 140%~200% of rated shaft power, and the minimum power at maximum flow, so in order to start the minimum current, the starting characteristics of shaft power should be high flow starting (i.e. full open valve starting).
2, mixed-flow pump starting characteristics - full open valve start
Mixed-flow pumps in zero flow conditions when the shaft power between the above two pumps, 100% to 130% of the rated power, so the starting characteristics of mixed-flow pumps should also be between the above two pumps, the best full open-valve start.
3, vortex pump starting characteristics - full open valve start
Vortex pump in zero flow conditions when the shaft power is the largest, 130% ~ 190% of the rated shaft power, so similar to the axial flow pump, the starting characteristics of the vortex pump should be a high flow start (i.e. full open valve start).