Pumps and their Applications Flashcards
What are the types of positive displacement pump?
What are the types of velocity pump?
What is a pump?
A machine that imparts energy into a fluid to:
- Increase potential energy
- Increase kinetic energy
- Incrtease internal pressure energy
- Overcome friction losses
How is the pump rating usually goven for a pump? Fill in the gaps below with SI units.
On the inlet of a pump, is it sucking the water up?
- No, pumps cause the inlet pipe to go below atmospheric pressure.
- The pressure acting on the source pushed the fluid into the pump.
What is theoretically the highest suction head a pump can have?
- 10.3 m
- Equivelent to 1 bar in meters head.
- Atmoshpheric pressure is pushing the water in to the pump.
What factors effect a pumps suction?
- Pipe and fitting friction
- Dissolved gasses
- Air leakes
- Altitude
- Density of fluid
- Vapour pressure
- Manufacturing limitations
What is crucial to ensure with inlet pipes to a pump?
- That they gradually increase to inlet side of pump to stop air gaps.
- Being level, with certain fittings is also acceptable, such as in the picture attached.
What are the general charcteristics os a PD pump?
- Output is directly proportional to speed of pump and indepependent of head.
- Operate at low speeds with gearing.
- High efficiency but low throughput at high head.
- Self priming
- Should never be started against a closed valve.
What are some advantages of a PD pump?
- Good suction lift
- Head dependent on power from prime mover - only limited by pipes and fittings.
- Constant volume regardless of pressure - theoretically
- High efficiency - >80% usually
What are the disadvantages of PD pumps?
- Low throughputs
- High torque on start up
- Expensive to purchase, maintain and repair
- Nature of flow is pulsational
- Potentially shorter lifespan due to start/stop nature
Draw a typical head against flow diagram for a PD pump.
Give a brief description as to what each component of a PD pump system does.
Suction vessel:
- Promotes even flow to the pump from inlet - helps prevent cavitation
- Usually fitted when a pump has high suction lift or long suction pipe.
Pulsation damper:
- On the delivery side. Promotes an even flow, reducing the chance of water hammer and shocks.
- Usually considered essential
PRF:
- An essential component for systems with PD pumps.
- Limits the amount of pressure obtainable by the system, therefore reducing the risk of injury or damage.
What are the characteristics of a velocity pump?
- No simple relationship between head and flow
- Speed change results in head and flow change
- Change in head results in a change in flow
- Change in flow results in a change in available head
Draw a diagram of a typical centrifugal pump curve on a head against flwo diagram.
Describe what some of the typical fittings of a centrifugal pump system do.
Strainer:
- Essential fitting for all pumps.
- Stops suspended matter in a fluid from damaging the pump.
Footvalve:
- No return valve at the base of the suction pipe.
- Stops the need of the pump having to be re primed when stopped.
System bypass valve:
- Allows the pump to be started up against a low delivery head if the rising main is full of liquid.
- Slowly closed to increase the liquid speed in the rising main once started.
Check valve:
- One way valve which prevents fluid from getting back into the pump when it is stopped.
- Protects pump from the potential pressure damage.
