Do I need to turn off the heat pump circuit when cutting the oil pump? Why?

I believe that if it is turned on, it will operate in parallel with the pump outlet; if the medium pumped contains particles (such as in the pumps at the bottom of catalytic fractionation towers), this can cause wear on the preheating valve. Also, if it is turned on, in the event of a pump failure, forgetting to close the preheating valve while shutting down the pump can lead to accidents. So it’s best to turn it off.

I think the heating pump circuit should be turned off immediately after cutting the hot oil pump.

The standby machine is kept on to be ready for immediate startup. . . That is, when the conditions for starting the pump are met, the standby pump here even has its inlet valve open, ready to take over at any time. . After all, the diameter of the heat pump pipeline is small; imagine that under the same pressure, the flow velocity in a pipe with a smaller diameter is much higher than that in a pipe with a larger diameter, which could lead to turbulent fluctuations Or turbulence?

The preheating line for high-temperature pumps and the precooling line for low-temperature pumps are usually installed in series after the check valve at the pump outlet and on the outlet valve with a smaller diameter; these lines must be closed while the pumps are running, mainly because they cause unnecessary energy losses, in other words, they increase power consumption. The preheating and precooling lines have nothing to do with the minimum flow rate requirements for the pumps specified in the process; since their functions are different, they cannot be confused. The minimum flow line is a pipeline that runs from the pump outlet back to the bottom of the tower or container before the suction outlet; it is a process pipeline designed to prevent the liquid level in the tower or container from dropping too low, which could lead to the pump running dry and disrupt the normal operation of the process. The pre-heating line runs from the outlet valve to the check valve and then back to the pump; it is designed to prevent heavy oils from becoming more viscous or even solidifying at normal temperatures. During the startup of the standby pump, the high starting current can cause damage to the motor and shaft. Additionally, blockages in the sealing lines can lead to poor lubrication, which in turn can result in sealing issues and leakage of hot oil at high temperatures ； The pre-heating line of the hot water pump is designed to prevent sudden inflow of hot water into the cold pump body, which could lead to the formation of gas inside the pump and result in vacuum conditions, preventing the pump from starting ； Similarly, the pre-cooling line is intended to prevent the low-temperature medium from vaporizing at normal temperatures; when the pump starts, there is often gas inside the pump casing, which leads to vacuum conditions and prevents the pump from starting. For the standby pump of a high-temperature pump, the preheating wire remains connected at all times to ensure it can be started immediately; once the pump begins operating, the preheating wire ceases to function. As a result, some of the fluid returns to the low-pressure side, leading to energy losses for the pump and a reduction in the effective flow rate of fluid delivered. Especially for slurry pumps, there are inevitably tar substances and catalyst particles present in the slurry. During preheating, in order to ensure an effective preheating effect while preventing the impeller from rotating in reverse and causing the set screws to loosen or fall out, the flow rate of the medium inside the preheating pipeline is low, which has little impact. However, once the pump starts operating and pressure rises, the flow rate of the medium containing particles in the preheating pipeline increases, which leads to increased wear on the relatively thin pipe walls, fittings (mainly elbows), and valves. Leaks are likely to occur in these areas. The oil slurry has a low auto-ignition point; once it leaks out and comes into contact with air, it ignites immediately, resulting in a fire. In mild cases, there will be a loss of oil ； Secondly, due to a leak, the device stopped operating, resulting in localized shutdown for emergency repairs ； Worse still, it may lead to fire accidents and casualties.

It must be turned off. There are two types of preheating lines: one is self-preheating, and the other is externally supplied heat. If the preheater does not turn off after the pump is started, the medium will flow into the external preheater.

Of course it needs to be turned off; it’s specified in these operating procedures. In some units, the slurry pumps use refinery oil as a preheating medium in order to reduce wear on the preheating lines; as a result, these lines are relatively long, and flushing oil is needed to push the fluid through them before shutting them down.

It is necessary to prevent reversal, as it can damage the equipment

There’s no need to turn it off; firstly, this helps prevent issues such as vibration when the pump starts. Once the pump is running properly, it can be turned down to prevent premature condensation on the heating line