1. Bibliogrpahy
- Centrifugal Pump(CP)와 Positive Displacement Pump(PDP)의 원리, 용도 등을 잘 설명해놓은 곳 (Link: https://www.castlepumps.com/info-hub/positive-displacement-vs-centrifugal-pumps)
- Chemresources No.12답변 (Link: https://www.cheresources.com/invision/topic/17427-can-pump-suction-presure-be-higher-than-discharge-pressure/
- 미국 정부가 정리해주는 엔지니어링 지식 (Link, Link2) - 아주 이해하기 쉽게 잘 정리되어 있음!!
2. 비교
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Centrifugal pump |
Positive displacement pump |
원리 |
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Discharge pressure |
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Performance |
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Viscosity |
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장비 |
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용도 |
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종류 |
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3. Centrifugal Pump Operation Summary
There are three indications that a centrifugal pump is cavitating.
- Noise
- Fluctuating discharge pressure and flow
- Fluctuating pump motor current
Steps that can be taken to stop pump cavitation include:
- Increase the pressure at the suction of the pump.
- Reduce the temperature of the liquid being pumped.
- Reduce head losses in the pump suction piping.
- Reduce the flow rate through the pump.
- Reduce the speed of the pump impeller.
Three effects of pump cavitation are:
- Degraded pump performance
- Excessive pump vibration
- Damage to pump impeller, bearings, wearing rings, and seals
To avoid pump cavitation, the net positive suction head available must be greater than the net positive suction head required.
Net positive suction head available is the difference between the pump suction pressure and the saturation pressure for the liquid being pumped.
Cavitation is the process of the formation and subsequent collapse of vapor bubbles in a pump.
Gas binding of a centrifugal pump is a condition where the pump casing is filled with gases or vapors to the point where the impeller is no longer able to contact enough fluid to function correctly.
Shutoff head is the maximum head that can be developed by a centrifugal pump operating at a set speed.
Pump runout is the maximum flow that can be developed by a centrifugal pump without damaging the pump.
The greater the head against which a centrifugal pump operates, the lower the flow rate through the pump. The relationship between pump flow rate and head is illustrated by the characteristic curve for the pump.
Centrifugal pumps are protected from dead-heading by providing a recirculation from the pump discharge back to the supply source of the pump.
Centrifugal pumps are protected from runout by placing an orifice or throttle valve immediately downstream of the pump discharge and through proper piping system design.
4. Positive Displacement Pumps Summary
The flow delivered by a centrifugal pump during one revolution of the impeller depends upon the head against which the pump is operating. The positive displacement pump delivers a definite volume of fluid for each cycle of pump operation regardless of the head against which the pump is operating.
Positive displacement pumps may be classified in the following ways:
- Reciprocating piston pump
- Gear-type rotary pump
- Lobe-type rotary pump
- Screw-type rotary pump
- Moving vane pump
- Diaphragm pump
As the viscosity of a liquid increases, the maximum speed at which a reciprocating positive displacement pump can properly operate decreases. Therefore, as viscosity increases, the maximum flow rate through the pump decreases.
The characteristic curve for a positive displacement pump operating at a certain speed is a vertical line on a graph of head versus flow.
Slippage is the rate at which liquid leaks from the discharge of the pump back to the pump suction.
Positive displacement pumps are protected from overpressurization by a relief valve on the upstream side of the pump discharge valve.
