Start-up and shutdown procedures for pumps with high back pressure
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There is a centrifugal pump available, with a back pressure of 750 m and a head capacity of 800 m； During debugging, our procedure is to close the valve near the backpressure device, open the vent, measure the outlet pressure at 8.0 MPa, then close the vent again and gradually open the valve that was closed ； Following the above procedures, two problems were encountered: 1. The flow rate would not increase; no matter how far the valve was opened to 4.8 cubic meters per second, the flow rate remained unchanged ； 2. When the flow rate is 4.8 cubic meters per minute, the system shuts down after 5 minutes of operation; the current remains stable at 76A during operation, but suddenly it rises to 130A, and this happens several times ； I would like to ask those present here about the operation procedures and processes, as well as the two problems I’ve encountered…… Thank you.
The inlet valve should be fully open. Is there a minimum flow line? When the outlet valve is closed, the medium will heat up and vaporize!
This post was last edited by 3983596_FPPZ on 2019-1-24 at 13:40. I guess the reason is as follows: 1. Due to excessive back pressure, when the pump operates beyond its rated flow rate, its head will also be less than 800 m. Adding in the losses caused by the valves in the outlet pipeline, it’s very likely that the outlet pressure at this point is already roughly equal to the back pressure. This is why the flow rate cannot increase any further even after it reaches 4.8； 2. When the flow rate is set to 4.8, the motor trips for a short period of time, and there may even be a sudden increase in current. This is likely due to the failure of the axial force balancing mechanism to maintain balance, resulting in excessive stress on the bearings; or it could be that the high axial force causes the bearings to lose their positioning ability, leading to axial displacement of the rotor and subsequent friction between the moving and stationary parts. Both of these situations can cause an increase in current, or even a sudden spike in current levels
The flow rate is very low; no minimum flow threshold has been set, and the operations take place over short periods of time, ensuring that vaporization due to heat generation does not occur
Thank you. The first point is likely to be the issue; as for the second point, I’m not sure yet. Choosing the right motor is indeed a challenge – at home we measured the terminal current, and it never exceeded the allowable level. Yet at the site, the power keeps failing frequently. Our first thought is that there might be high losses at the site
Is there a cross-sectional view with a pump? Upload it and study it
Is the testing at home an inlet pressure test? If not, there will be differences between the conditions at home and those at the actual site
It’s most likely a problem caused by axial force
I have another question: when selecting equipment for high backpressure applications, is it necessary to take into account an additional head margin? Instead, just choose one that doesn’t exceed the back pressure?
Screw shell pumps are also classified as centrifugal pumps