Sealing Oil Main Pump HSN280-43NZ: Tips for Non-Disruptive Switching Between Main and Standby Pumps

The core task of a generator seal oil station is to supply oil at a stable pressure to the seal pads. This oil pressure seals the hydrogen gas inside the generator. Hydrogen leaks can compromise unit safety, while unstable oil pressure can damage the seal pads. The HSN280-43NZ main oil pump is a three-screw pump with stable flow and low noise, making it ideal as a main pump. However, a main pump alone is not enough; a backup pump is necessary to quickly take over in the event of a main pump failure. However, switching between pumps can easily lead to problems: hydrogen leakage during an oil outage or a sudden surge in oil pressure that can damage the seal pads. The following discusses how to achieve bumpless and smooth switching between primary and standby pumps and how to avoid oil pressure surges during switching.

1. The Key to Smooth Switching

Switching between primary and standby pumps requires more than simply stopping the main pump and starting the backup pump; it must be seamless. During the switchover process, the oil supply pressure to the sealing pads must not fluctuate significantly, and oil supply interruptions are strictly prohibited. The HSN280-43NZ main oil pump (three-screw pump) maintains a stable flow rate, laying the foundation for the switchover. However, this also requires a coordinated system.

First, real-time pressure monitoring is required. Pressure sensors are installed in the oil supply lines of the sealing oil station to continuously monitor the oil pressure within the lines. During normal operation, the main HSN280-43NZ screw pump supplies oil and maintains the pressure within the set range. If a problem occurs with the main pump, such as a drop in flow or a drop in pressure below the set value, the sensor immediately transmits a signal to the control cabinet. The control cabinet does not immediately shut down the main pump but instead starts the backup pump.

After starting, the backup pump does not immediately operate at full capacity. Instead, it gradually increases its output. For example, speed control can be achieved through a frequency converter (VFD) or by adjusting the pressure regulating valve at the pump outlet to gradually increase the backup pump’s supply pressure until it reaches a level with the main pump’s current pressure. At this point, the oil pressure in the pipeline remains stable because the main pump is still supplying oil, and the backup pump is slowly catching up. The pressure won’t jump when both pump oil together.

After the backup pump’s output has fully caught up and the pressure has stabilized, the control cabinet slowly shuts down the main pump. The main pump doesn’t stop abruptly, but rather gradually reduces its speed and output until it stops completely. Throughout this process, there’s no interruption in oil supply and no significant fluctuations in oil pressure. This is known as “bumpless switching.”

If your power plant’s sealed oil station frequently loses oil during a switchover, it’s likely due to inadequate pressure monitoring or a lack of “soft start” on the backup pump. Contact us to check the response speed of the pressure sensor or install a compatible inverter on the backup pump for more stable switching.

2. Key Components for Bumpless Switching

Smooth switching between the main and backup pumps relies not on a single component but on the coordinated efforts of several key components. If anyone is missing, switching problems may occur.

The first is the pressure sensor. Choose one with fast response and sufficient accuracy. Don’t wait for the main pump’s pressure to drop significantly before triggering an alarm. For example, if the HSN280-43NZ main pump’s oil supply pressure is set at 0.3 MPa, the sensor must send a signal when the pressure drops to 0.28 MPa, allowing enough time for the backup pump to activate. If the sensor reacts slowly and the pressure drops to 0.25 MPa before it activates, the backup pump will not have caught up, resulting in insufficient oil pressure and possible hydrogen leakage from the sealing ring.

The second issue is the control cabinet’s logic program. The program must specify the “pressure value for activating the backup pump,” “the backup pump pressure ramp-up time,” and “when to shut down the main pump.” For example, after the backup pump starts, the ramp-up time might be set to 30 seconds, allowing the pressure to slowly rise from 0 to 0.3 MPa to match the main pump’s pressure. If the program is set to a rapid 10-second ramp-up, the backup pump will suddenly surge, causing the oil pressure to jump. Some older power plants often have poorly optimized control cabinet programs, leading to frequent switchover issues. These issues can be resolved by adjusting the program parameters. We offer program debugging services.

The third issue is the backup pump’s regulating device. The HSN280-43NZ main pump is a three-screw pump, and its flow rate is proportional to its speed. If the backup pump is the same model, it’s best to equip it with a frequency converter. By adjusting the speed, flow and pressure can be controlled. This is more stable than using valves for throttling and saves energy. If the backup pump is a different model, an adjustable pressure-regulating valve should be installed at the outlet. Open the valve slowly to allow the oil flow to increase steadily.

Check valves should also be installed at the outlets of both the main and backup pumps to prevent oil backflow. For example, when the backup pump is started while the main pump is still running, the check valve prevents oil from flowing back to the backup pump, nor does it prevent oil from flowing back to the main pump. This ensures that the oil flows from both sides are independent and the pressure is stable.

3. How to Avoid Oil Pressure Surge

Oil pressure surges during switching are mostly caused by the backup pump suddenly reaching full capacity, the main pump suddenly stopping, or oil hitting a wall in the pipeline. To avoid surges, design considerations should be made regarding backup pump startup, main pump shutdown, and pipeline buffering.

The backup pump should be soft-started. Don’t start the pump at full speed immediately after powering it on. Although a three-screw pump provides a steady flow rate, sudden startup can still cause a surge in oil flow. If using a frequency converter (VFD), slowly increase the starting frequency from 0 to 50Hz. The speed will increase accordingly, and the flow rate and pressure will rise steadily, avoiding a sudden surge. If you don’t have a VFD, adjust the outlet pressure regulating valve: first close the valve completely, then start the backup pump, then slowly open it to allow oil to enter the pipeline bit by bit. This will naturally prevent pressure spikes.

The main pump should be shut down “softly.” You can’t just shut it down, especially with a three-screw pump like the HSN280-43NZ. Sudden shutdowns can cause the oil flow in the pipeline to slow down instantly, causing “oil hammer,” similar to water hammer caused by suddenly closing a valve in a water pipe. This can cause a sudden increase in oil pressure and damage the seals. The correct approach is to reduce the speed of the main pump (if using a VFD) before shutting it down, or slowly close the main pump outlet valve to gradually reduce the flow rate. Wait until the backup pump has fully taken over the oil supply before completely shutting down the main pump. This way, the oil flow won’t be suddenly interrupted and the pressure won’t surge. Furthermore, piping layout is also important. Try to avoid right-angle bends in the outlet piping of the main and backup pumps. This reduces resistance to oil flow during turns and reduces the risk of eddies and pressure fluctuations. Tighten joints to prevent leaks. Air entering the piping will cause air resistance during switching, leading to oil pressure fluctuations.

4. Debugging and Inspection During Actual Switching

Design alone isn’t enough; debugging before actual use and daily inspections are required to ensure consistent switching stability.

During debugging, measure “switching time.” For example, simulate a main pump failure by manually lowering the main pump pressure to see how long it takes for the sensor to send a signal, how long it takes for the backup pump to start, how long it takes for the pressure to stabilize after the backup pump starts, and how long it takes for the main pump to shut down. The entire process should ideally be kept within 1 minute, and oil pressure fluctuations should not exceed 0.02 MPa—exceeding this range may affect the sealing ring. If the time is too long or the fluctuation is large, adjust the parameters: for example, set the sensor alarm value higher to activate the backup pump earlier, or increase the backup pump’s pressure build-up time.

Daily inspections should focus on “critical components.” Check the accuracy of the pressure sensor daily by comparing it with a pressure gauge. Calibrate if inaccurate. Check the backup pump’s inverter or pressure regulating valve for any sticking. If they are unable to rotate, lubricate them. Regularly remove the check valve to check for wear on the sealing surface. Wear can cause leakage, which can lead to oil backflow during switching and unstable oil pressure. The screw of the HSN280-43NZ main pump should also be inspected regularly. Wear can lead to reduced flow and unstable pressure, increasing the switching frequency and causing seal ring problems.

Also, don’t wait until the main pump breaks down before testing the backup pump. It’s best to manually start the backup pump once a week and let it run for 10 minutes to see if it can build pressure normally and switch smoothly with the main pump. Many power plants have backup pumps that are not used for long periods of time. When the main pump breaks down, the backup pump may not start because it hasn’t been tested regularly. If you’re unsure how to develop an inspection plan, we can help you create a maintenance checklist.

5. Why is the HSN280-43NZ main pump suitable for this switching method?

Not all oil pumps can switch between them so smoothly. The HSN280-43NZ, as a three-screw pump, has inherent advantages. Its rotors rotate in meshing motion, ensuring continuous oil flow through the pump, without pulsation. Unlike gear pumps, where flow can fluctuate intermittently, this ensures stable pressure during the primary pump’s oil supply. Once the backup pump is activated, the oil flows from the two pumps are easily matched, preventing pressure fluctuations caused by pump pulsation.

Furthermore, the HSN280-43NZ has a relatively flat head curve, resulting in minimal pressure fluctuations with even small speed changes. This makes it ideal for speed control of the backup pump using a frequency converter. Precise speed control is unnecessary; slight adjustments can maintain stable pressure. A centrifugal pump, with its steeper head curve, can cause pressure fluctuations with even slight speed changes, making it difficult to control during switchover.

Thus, when choosing a primary pump, a three-screw pump like the HSN280-43NZ is naturally suited for switching between primary and backup pumps in sealed oil stations. If your power plant is struggling to choose the right oil pump for its main pump, balancing switching stability and oil supply efficiency, please contact us for recommended compatible models.

If your generator sealed oil station is experiencing oil pressure surges, oil shutoffs, or hydrogen leaks during the switchover between the main and standby pumps, or if your HSN280-43NZ main pump requires selection or maintenance, please contact us. We offer not only genuine HSN280-43NZ three-screw pumps, but also a variety of genuine pump repair parts to ensure full compatibility with the pump.
E-mail: sales@yoyik.com
Tel: +86-838-2226655
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