Application of vacuum self - priming pump theory analysis

The vacuum self-priming pump is designed to initiate pumping under negative pressure conditions. To start the pump, a vacuum pump must first be activated to evacuate air from the suction pipe and fill it with water before the pump can begin operation. Additionally, the pump should only be started once the valves are fully open. It’s important to ensure that the vacuum self-priming pump and the centrifugal pump operate smoothly, so two vacuum pumps with different exhaust volumes (ranging from 2m³/min to -10m³/min depending on the pipeline length) are installed. Our technical team can help select the appropriate option based on your needs, ensuring a vacuum degree of 0 to 200 hPa. The vacuum self-priming pump group can be centrally controlled either from the pump station's operator station or operated locally. The pump is designed with an automatic interlock mechanism, meaning if one pump fails, the backup pump will automatically activate. The vacuum pump and water pump are programmed to start automatically in sequence. Normal shutdown occurs when the electric butterfly valve at the pump outlet is fully closed, triggering an automatic pump shutdown. The pump and motor are mounted horizontally on the same base. The pump performance curve must meet the design conditions for flow, lift, and efficiency, ensuring no negative deviations and a head deviation of no more than 5%. The flow-head curve should rise gradually from the design flow to zero flow, with the pump structure designed to accommodate a motor speed variation of up to 20%. At the rated operating condition, the efficiency should be within the optimal range. To prevent damage from reverse flow, the pump should not exceed 120% of the rated speed when reversing, and the pump (and motor) can be started as long as the reverse speed is below 20% of the rated speed. The pump’s Q-H curve must be smooth from the design point to the shut-off head, with the shut-off head exceeding the design point head to ensure it meets system resistance requirements. Under various conditions, including when the pump is closed or running in reverse, the pump generates horizontal, vertical, and torque forces, including those caused by earthquakes and temperature changes. These forces must be absorbed by the pump unit and transferred to the base. The pump requires no pre-lubrication or external water supply for bearings and seals, allowing for transient dry starts. After startup, the required lubrication water is drawn from the pump outlet pipe, filtered, and used to lubricate/cool the bearing and shaft seal assembly. Mechanical seals are used for the pump body. During normal operation, the pump must maintain excellent cavitation resistance to avoid cavitation and vibration issues. The pump material includes a cast iron body, high-quality SKF bearings, wear-resistant 304 stainless steel impellers, and other components selected based on standard materials. An automatic exhaust valve is installed on the pump housing. The pump is connected to the motor via a rigid coupling, which includes a removable and sturdy protective cover. The pump should continue to operate efficiently even when the Net Positive Suction Head (NPSH) is 5 meters. For the motor, it must be a three-phase asynchronous motor. The motor’s basic performance tolerances include an efficiency tolerance of -0.1 (1-h), a power factor tolerance of -(1-cosf)/6, a maximum starting current of 20% over the guaranteed value, and a maximum starting torque of -15% of the guaranteed value. The motor should output the rated power when the frequency is rated and the voltage deviation is within ±5%. The motor’s rated power must exceed the capacity needed for long-term continuous operation and meet GB755 standards for overload values during full-voltage direct start. The motor operates at 380V and 50Hz, capable of starting at 85-100% of the rated voltage and power, with acceleration features. The motor must withstand thermal and mechanical stresses at the design ambient temperature and maintain satisfactory performance at 100% of its rated voltage. The stall current of the motor should not exceed 750% of the full-load current without consent. The motor layout uses an IP54 protection class with self-cooling. The motor housing should be properly grounded, with a grounding device installed in the main terminal box. The motor should have Class F insulation (with a temperature rise assessed as Class B) and a junction box protection class of at least IP55. The motor bearings should be sealed to prevent dirt and moisture intrusion, and the housing and base should have anti-rust measures. The critical speed of the shaft should be at least 25% higher than the rated speed. Equipment noise levels should comply with industrial hygiene standards, with noise levels not exceeding 85 dB(A) at 1.0m height and 1.2m distance from the pump casing. The maximum vibration amplitude for the dual-pump vacuum self-priming pump group should adhere to existing relevant standards.

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