Questions about gear pumps

I think there’s no problem with doing it this way; as long as the outlet valve isn’t closed, the motor can be turned on!

Gear pumps belong to the category of positive-displacement pumps, so their operating method is naturally different from that of ordinary centrifugal pumps! If the motor is started before the outlet is opened, two situations may occur. 1. Sealing leakage. Since it is a positive-displacement type and the liquid is incompressible, if the outlet is not opened in time, the pressure in the sealed chamber continues to rise, which can very likely lead to seal leakage. Mechanical seal face specific pressure. 2. Noise from the pump body, motor trips and stops. In most cases, it’s due to excessive current; when you block the outlet and prevent the medium from exiting, the load on the motor keeps increasing until it can no longer rotate. The correct procedure is to open both the inlet and outlet of the gear pump before starting the motor; if you are concerned about excessive starting current, you can partially open or leave the outlet valve at half its position. Aside: When our factory shuts down the lubrication pump of large-scale units, if Pump A is in operation, it is necessary to first switch to Pump B to prevent shutdowns that could result from fluctuations in oil pressure. The steps are as follows: 1. Manually adjust the positions of columns A and B, start pump B, and observe the pressure in the main pipe. 2. Slowly close the inlet valve of pump A, paying attention to pressure fluctuations. 3. Turn off Pump A completely, stop it, and set its control lever to the automatic position. 4. Set the B pump control column to the automatic position to complete the pump switching process.

Gear pumps are positive-displacement pumps; it is crucial to be careful not to start them or open their inlet valves with the outlet valve closed.

It’s not a big issue to open both the inlet and outlet before starting the motor; the key factor is the inlet pressure. Opening the outlet first, starting the motor, and then opening the inlet allows the incoming medium to be discharged immediately, thereby preventing damage to the equipment due to high inlet pressure.

From the perspective of the structural principle of gear pumps, it is necessary to first open the inlet and outlet; as for the motor, there is no major issue. Moreover, this is the way in which most positive displacement pumps are operated

The inlet valve should be opened first, followed by the bypass valve; after startup, the outlet valve should be opened and the bypass valve should be gradually closed

Should I turn on the valve first or the motor first? I think there shouldn’t be any problems in the short term. But sometimes the decision should be based on the conditions on site; for example, in cases where heat tracing is available, we should first open the inlet valve to allow the material to enter the pump, then rotate the pump before starting it, and only after confirming that the pump can operate should we start the motor. It is important to avoid a situation where, due to insufficient preheating from the pump’s heating system, the material solidifies as soon as it enters the pump; attempting to force operation in such conditions can cause damage to the equipment.

3# yxmqh: For safety reasons, it is also possible to consider disabling the interlock

““Prevent equipment damage caused by pressure buildup due to high import pressure” – isn’t that wrong? To achieve this goal, we should open the entrance first! ! For positive displacement pumps, the inlet and outlet connection valves must be opened first; after startup, these connection valves are used to regulate pressure and flow.