The master is not here; I seek guidance from experts regarding the issue of pump interlock at low pressure

Since the pressure has returned to normal, it’s pointless to underreport it – so why is there still a start signal? I find this very hard to understand

There is something wrong with your description: when the pressure is low or extremely low, the instrument control system sends a high-level signal, which enables the pump to start. The pulse duration is between 2 seconds and 5 seconds, as specified in the electrical specifications; after that time, this signal disappears. When the pressure returns to normal, the operator clicks to stop the pump. Once the pressure drops to low or ultra-low levels again, the pump will start up once more.

Your pressure gauge readings have increased, and the interlock has been automatically disabled – so what is the connection to the electrical system?

The pressure has returned to normal, so the interlock condition is no longer met; the interlock state is lifted. Then why is there still a pump-start signal sent to the electrical system?

First, I spent a long time looking but didn’t understand what you were asking. I only see one problem: What to do? ? Can I just say that the people in electrical engineering are stupid? The so-called interlock is triggered only when the conditions are met; once the pressure returns to normal, the interlock conditions are no longer satisfied and the signal disappears accordingly. His electrical system should be turned off – what does secondary startup mean? ? If there is no signal and a second start attempt fails, check the wiring by yourself. Some of the experts above said it’s a trigger signal. I can’t agree with that. This interlock must be a continuous signal to be correct. If the pressure is low and the pump starts, someone presses the stop button; when they do so, the pump stops, but once they release the button, the pump starts again. The prerequisite is low pressure.

This post was last edited by HEJIYUER on 2015-7-22 at 14:37. Analyzing your description (which requires careful consideration:dizzy:), I can roughly guess the original design intent: 1. The RS flip-flop sent from PSL locks the DCS, enabling the DCS’s self-protection; a \"high voltage\" signal is sent to the electrical system, and that system does not have any self-protection mechanism for PSL. 2. To stop the pump, a “low level” signal must be sent to the electrical system; two conditions must be met simultaneously: the pressure must return to normal, and the “manual reset” function on the DCS must be activated. So this reset button actually stops the pump in the DCS. 3. The outdoor operation is normal according to the on-site pressure indication, and the on-site button stops the pump. . . . 4. Under normal operating conditions, the selector switch on the electrical control panel should be set to “automatic mode”. If 2 fails to reset = the DCS keeps the power supply at a high level, and the pulse signal from button 3 stops the pump, then a \"secondary pump start\" will occur. The core of this question is: How do the operating procedures specify when to stop the pump? For this type of “pump shutdown method” with self-starting capability, two options can be considered: 1. For particularly important process materials, DCS pump shutdown is generally not used; instead, the pumps are stopped via the on-site control panel. The DCS sends a start pulse for electrical self-protection. If it is necessary to stop the pump via the DCS, that is also possible: once the pressure returns to normal and the “manual pump stop button” on the DCS is pressed, both conditions being met will send a \"stop pulse\" to the electrical system, thereby preventing the DCS from stopping the pump accidentally. If the pump stops accidentally on site, it is necessary for PSL to restart the pump. . . 2. It is relatively unimportant; automatic shutdown can be set in the DCS as long as the pressure returns to normal, and there is no need to arrange for manual reset. “Both the “start/stop” signals are voltage levels, ensuring DCS self-protection. If you don’t want to change anything, then modify the rules for stopping the pump on-site: the operator should first switch the on-site switch to the “manual” mode (at this point, the DCS commands to start the pump are ineffective), and then stop the pump on-site. Then, perform an outdoor check to confirm whether the DCS has been “reset”? If YES, the operator can switch the on-site switch back to \"automatic mode\" (otherwise it would be a \"second start\"), and the pump will then wait for the next start command.

Thank you! But I was thinking, is it possible to make the start signal a short-term one, meaning that the signal disappears once the pump starts, and it won’t cause the pump to restart even if the pressure returns to normal and the pump is manually stopped? How can this message be reflected in the design?

Big bro, stop causing trouble, okay? !

1. A short signal is what is known as a pulse signal. If there is no DCS or if implementation on-site is desired, a delay relay is used. 2. If it is implemented using a simple method such as a pressure switch, meaning that the signal can either be sent to the DCS or not, a changeover switch can be connected in series between the low-low signals from the pressure switch. With this switch in the on or off position, it can be indicated as interlock or bypass mode; in bypass mode, the start and stop of the pump are entirely controlled manually, which is quite convenient. If the switch cannot be moved arbitrarily, a locked switch can be chosen. 3. This situation is particularly suitable when: the pump starts at normal pressure, but the pressure required for it to start is very low. Avoid frequent start-stop of the pump.

This post was last edited by HEJIYUER on 2015-7-22 at 15:01. Could the start signal be made a short-term signal, so that it disappears once the pump starts? It can be made into a short signal to ensure self-protection on the electrical side. So, the electrical extraction cabinet needs to have its wiring modified so that the start signal is set to \"self-protection\" mode. And when the pressure returns to normal and the pump is manually stopped, it won’t cause it to restart either? How can this message be reflected in the design? When 1 is fixed, only the PSL controls the pump’s startup. If the pump stops and then starts again, it means the PSL has dropped again. I think you should be aware of the requirements for DCS pump shutdowns in terms of process operations: 1. When the pressure returns to normal, the pump stops automatically. 2. The pressure returned to normal, and by pressing the DCS “manual reset” button, both conditions were met, resulting in the pump being stopped. 3. The pressure observed during internal operation is normal; the pump can be stopped manually. Pressure is determined purely by manual judgment. Once the requirements are clear, discuss with the electrical team how to implement them, while checking for any bugs.