How should a plunger pump be shut down?
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We use the CO2 stripping method; for both high-pressure liquid ammonia pumps and high-pressure ammonium methoxide pumps, triple-plunger pumps equipped with frequency converters for regulation are employed. During the shutdown of these pumps, our usual procedure is to go to the operation site and directly press the power-off button for the pump’s motor (no actions are required on the DCS computer screen). Once the pump has come to a complete stop, we then turn off the frequency converter on the DCS computer screen, and finally close the last outlet valve of the pump – the valve that is located near the high-pressure system. However, during today’s operations, since the frequency converter of the high-pressure ammonium pump was damaged yesterday (the exact reason is not clear; a new frequency converter was installed today), our workshop supervisor requested that in future operations, especially when shutting down the pump, we first turn off its frequency converter using the computer on the DCS screen, and then press the stop button for the motor’s power supply at the site. I don’t understand this new requirement at all. The workshop supervisor explained that when the button to stop the motor power is pressed, a brief reverse current is generated, and this current can very likely cause damage to the electronic components of the inverter. I have the following questions now: 1. How is the triple-plunger pump in your factory shut down? 2. May this backflow current cause damage to the inverter when the triple-plunger pump is shut down? 3. If anyone can help explain the working principle of the frequency converter, or how to adjust and operate it in order to prevent more accidents related to this type of frequency converter. Thank you all here! Thank you so much! ! ! !
Why isn’t anyone helping me think of a solution? Even just providing the shutdown procedures for your factory’s plunger pumps would be helpful! Waiting here!
In our plant, the pump operator presses the stop button for the motor’s power supply on-site; only afterwards is the power supply to the pump turned off and the frequency of the inverter stopped via the DCS interface. As for how the inverter was burned out, it needs to be explained by a specialist in that field. But at least that’s how things have been done in our factory, and the frequency converters have never had any problems.
Back to floor 3: Yes! We have been doing this for almost a decade now, and we don’t understand why the workshop supervisor is asking for this now. As for the inverters getting damaged, there’s no way we can know the reason; even when professionals explain it to us, we still don’t understand. Thank you!
The owner’s system is highly automated; the DCS can also shut down the high-pressure pump. How do you operate the pump in reverse? Can’t the pump outlet valve be closed using DCS in this case? We perform pump shutdowns manually on-site: 1. Slightly open the pump bypass valve to maintain pressure ； 2. Close the pump outlet valve ； 3. Fully open the bypass valve ； 4. Press the on-site pump stop button to halt the pump’s operation.
Fifth floor, correct. Reciprocating machinery must never be stopped while under pressure! However, controllers such as regulating valves are also not allowed to be exported, because if the valve closes erroneously during the operation of the pump, it can cause the machine to stop due to overpressure in mild cases, or it may damage the motor, and even ruin the pump’s cylinder, leading to equipment and safety hazards for personnel. The master control is connected to the DCS emergency stop button, which is used for emergency shutdown. This post was last edited by jetlee_78 on 2008-11-7 22:30.]
We sometimes do things in this way as well. What I want to ask is: when stopping a reciprocating pump on-site, should the operation be carried out on-site or via the computer DCS? Also, I’m not sure whether either method causes any damage to the frequency converter. What I don’t understand is why the workshop supervisor requires us to carry out the operation via the computer DCS first, and then press the power-off button for the pump’s motor on-site.
Is that so? Stopping the machine while it is under pressure is strictly prohibited. What damage does this cause to the pump body, the reducer, or the motor? I have this question, which is why I’m here to ask the experts for advice, hoping to resolve it. As for the method mentioned on floor 4, I would like to use that approach as well, but our workshop doesn’t have any regulations regarding this type of operation! If it’s handled solely by our operation team, it can definitely be achieved. Well, let’s return to my initial question: what are the hazards of stopping a vehicle under pressure? I hope to get some advice from everyone! ! ! !
Personally, I think stopping the pump under pressure will not cause damage to the inverter. When we press the stop button, what actually happens is that the switch in the control circuit is turned off, which results in the power supply being disconnected. When we stop the pump, in emergency situations the main controller is used to do so directly; if it’s not an emergency, we first switch to the bypass line on site before stopping the pump. The concern here is protecting the check valve from shock, not the frequency converter. According to professionals, it is prohibited to start an inverter under pressure.
Borrowing from someone else’s response, I personally believe that when stopping a plunger pump under pressure, it is the check valve or combination valve that suffers the most damage; reverse rotation of the gears is not likely to occur. What our workshop supervisor said about a reverse current occurring during pump shutdown – could it be that the gears rotated in the opposite direction for a moment, which caused a sudden high-voltage current to be generated in the motor? I still need to ask the forum members!
It certainly isn’t stopping the pump while it’s under pressure; no company would do such a thing.