Dingchuang fans are used in sand filters, membrane tanks, water plants, etc. for air backwashing, also known as backwashing fans, including Roots blowers and screw blowers. When designing and installing the backwash fan, the following precautions should be taken:

One System working principle and design guarantee

The backwashing system of the filter usually adopts a combination of "water flushing" and "air flushing", and Dingchuang fan is responsible for providing the air source.

1. Physical isolation: The outlet pipe of Dingchuang backwashing fan is connected to the aeration pipeline at the bottom of the filter tank. The outlet pipe of the backwash water pump is connected to the water pipeline at the bottom of the filter tank. Although they may be very close at the bottom of the filter, there is no direct pipeline connection between the fan outlet side and the pump outlet side.

2. Pressure difference protection: This is the most critical protection mechanism.

3. The outlet pressure of the backwash fan is usually high (several tens of kPa depending on water depth and resistance), but it provides gas pressure.

4. The outlet pressure of the backwash water pump is higher (usually much higher than the fan pressure, reaching several hundred kPa), and it provides liquid pressure.

During normal operation, even if two pipelines intersect at the bottom of the filter, higher pressure water will effectively prevent air from flowing back, and it is even less likely for water to flow back into the lower pressure fan air duct. The pressure of water will firmly "seal" the outlet of the trachea.

II Serious consequences of water entering the fan

The entry of water into the backwash fan is a catastrophic failure, as Roots blowers and screw blowers are positive displacement fans with very small internal clearances.

1. Impeller stuck: Water is an almost incompressible liquid. Once a large amount of water enters the casing, it will cause the impeller to fail to rotate and freeze instantly.

2. Motor burnout: Impeller jamming can cause a sharp increase in motor load, leading to motor overload and stalling, and quickly burning out the coil.

3. Component damage: The enormous impact force may cause damage or even breakage to the impeller, gears, and bearings.

4. Corrosion: Even a small amount of water entering can cause rusting of precision components inside the fan, increasing wear and affecting performance and lifespan.

III How to effectively prevent water from entering the fan?

To prevent such serious accidents, the system design must include multiple protective measures:

1. Strict start stop program control (most importantly!):

Start sequence: Start the fan first, then start the water pump.

Shutdown sequence: Stop the water pump first, delay for a period of time (blowing time), and then stop the fan.

This logic must be automatically implemented through PLC (Programmable Logic Controller) instead of manual operation.

2. Install check valve:

A check valve must be installed on the outlet pipe of the backwash fan to prevent fluid from flowing in the opposite direction.

3. Install vacuum breaking valve/solenoid valve:

A vacuum breaker valve or an electromagnetic valve controlled by PLC can be installed on the pipeline between the check valve and the fan. When the fan stops, this valve automatically opens to allow air to enter the pipeline, breaking the possible vacuum and preventing water from being "sucked" into the pipeline.

4. Install drainage system:

Install an automatic drain or manual drain valve at the low point of the air pipeline to regularly remove condensed water from the pipeline and reduce the risk of water accumulation.

5. Equipment alarm and linkage:

Set up sensors for pressure, liquid level, etc. When an abnormal shutdown of the fan is detected, the system should be able to immediately interlock and stop the operation of the water pump.

4 summary

Under normal circumstances, water will not enter the fan due to the pump pressure being much higher than the fan pressure.

2. In abnormal situations, such as incorrect shutdown, equipment failure, or failure of protective measures, water backflow can occur, causing serious damage to the fan.

The key to prevention lies in the correct automatic start stop program (start the water pump first, then stop the fan and delay), reliable check valves, and additional protective devices (such as vacuum rupture valves).

Ensuring that the automation control program of the backwash system is correct and reliable, and regularly maintaining and inspecting protective components such as valves, is fundamental to avoiding such accidents.