Key operating points of multi-stage pumps
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This post was last edited by lxq700918 on 2010-7-15 at 13:02. By reviewing literature and consulting other manufacturers, it was found that when starting a multi-stage pump, it is necessary to slightly open the outlet before starting the motor, and to wait until the operation stabilizes before fully opening the outlet valve. The main purpose of this is to protect the pump; what damage could occur to the pump if I close the outlet while starting it up? The opposite is true when the pump is stopped. But I also consulted some people who work with equipment. It doesn’t matter much whether it can be said or not. So I’m conflicted – should I open it or not? I assume many of you who are in the marine industry also use multi-stage pumps. May I ask how you operate your multi-stage pumps?
When starting a multi-stage pump, it is essential to open the minimum flow valve – this prevents the impeller from rotating in reverse and thus protects the blades as well as the mechanical seal. In our operations, we usually keep the valve at 30% open~
I have a question: Why does the impeller rotate in reverse after a multi-stage pump is started, if the outlet valve is not opened?
For the pumps mentioned by the original poster, the manufacturers specify requirements for starting the pumps; if the outlet valve is not opened slightly when starting the pump, both the temperature and pressure of the fluid will rise rapidly. This is not to prevent reverse rotation – the motor controls the direction of rotation.
Agree with what was said above. Multistage pumps generate a large amount of work; if this heat is not removed in time, it causes the temperature of the fluid to rise, increasing the risk of vaporization. In fact, even with conventional pumps, if the medium has a high volatility (such as liquid ammonia or ammonium hydroxide), vaporization can easily occur during sealing.
I wonder if there is a check valve at the outlet of your pump? If so, the outlet valve needs to be slightly opened.
Reply to 3# cthlj2007: The outlet valve is closed or the outlet opening is too small; due to the high outlet pressure, flow reverses at the outlet of the subsequent impellers, resulting in intense shock and significant fluctuations in rotation speed, which is particularly evident when compressing gases~~
I. Startup: 1. Before starting the water pump, it is necessary to verify whether the rotation direction of the motor is correct and whether the pump rotates smoothly； 2. Close the gate valve on the discharge pipeline and fill the pump with water ； 3. Start the water pump and open the pressure gauge as well as the vacuum gauge valves. Gradually open the outlet gate valve until the pressure gauge indicates the desired value. If the pump cannot achieve the required pressure, stop it immediately to prevent wear on the sleeve and the balancing mechanism ； II. Operation 1. Blocking of the balance pipe is strictly prohibited ； 2. While the pump is in operation, pay attention to the temperature of the bearings; the maximum temperature of rolling bearings should not exceed 70°C. Rolling bearings should be replaced after 1000 hours of operation with dry oil. 3. Check that the axial movement of the pump shaft is greater than 1.5 millimeters, and ensure that the packing is compressed evenly so as to allow a leak of water at a rate of 10–20 drops per minute. 4. The water pump should be inspected after operating for a certain period of time (1000 hours). III. Shutdown: Slowly close the outlet valve, the pressure gauge, and the vacuum gauge plug, then turn off the motor
Reply to 6# Xinji: Some have it, some don’t
Reply to 9# Ran Hongyang: The reasoning was explained on floor 7; I’m not sure if you understood it! An outlet check valve must be installed.
I agree quite a bit with what was said on floors 4 and 5; before starting our factory’s high-pressure ammonia pumps and high-pressure ammonium hydroxide pumps, we open all the outlet valves to prevent backpressure and pump vaporization. For our multi-stage piston pumps, the outlet valve is also opened fully before starting; for other smaller pumps (centrifugal pumps), the outlet valve is generally opened slightly first before starting.