Why a reciprocating pump produce high head but low discharge?
First of all we need to generalize the question. Its not just Reciprocating Pump, High Head and Low Capacity is a characteristic of a more general class of pumps i.e. Positive Displacement(PD) Pump. Recip. pump is one of the several types of PD pumps like Gear Pump, Vane Pump, Lobe Pump etc in class of PD pumps.Though its not so straight forward, in a pump selection chart, Reciprocating pump(as metering pump, plunger pump in selection guide chart) is in High Head(H) and low Capacity(Q). Where as Centrifugal pump generally stays in High Capacity and Low head region.It is because of their different principle to create Flow(Q) and Head(H).PD/Reciprocating Pump: This type of pump squeezes/pressurize the fluid by reciprocating action of Piston in Cylinder with help of valves. So, here fluid is first pressurized and the increased pressure/head(Head=Pressure/fluid density) in fluid causes the fluid to flow to low pressure destination. High Pressure/Head is converted to flow of fluid. As a result theoretically a recip pump can provide infinite level of pressure/head if leakage/material failure is not considered.Centrifugal Pump:Kinetic energy(motion or flow) is provided by pump impeller to the fluid by rotating/centrifugal action. That flow energy is converted to pressure energy(head) in the pump casing volute. Conversion of kinetic energy to pressure energy/pressure head is in line with Bernoulli theorem.So the head generated is always limited by the capability of casing volute design. Ideal centrifugal pump with only centrifugal action produces only flow with no head.The different characteristics of PD pump and Centrifugal pump can be seen in the pump characteristic curves.
Why a centrifugal pump produces high discharge but low head?
Centrifugal pumps are one of the easiest to build and modify pumps currently used. The beauty of their design lies in its simplicity: a single rotating component connected to a suction nozzle and a discharge nozzle. Applications for centrifugal pumps range from conveying crushed coal to powering sewage water plants. Although you can build each component of a centrifugal pump from scratch, much higher efficiency levels are achieved by building your pump from easily available commercially manufactured parts. You will need to adapt these generic instructions to your particular requirements and the specifications of the pipe system you connect to the pump. Step 1Decide what materials you need to pump and at what speed. The specific gravity and viscosity of a material as well as how corrosive or abrasive it is will inform the type of impeller or turbine you will need.Step 2Build a turbine by connecting an electric motor to a shaft and an impeller. There are two main impeller models: the closed type and the open type impeller. Open impellers, which look similar to the rotor blades of a submarine, do not clog as often as closed impellers. Step 3Connect the turbine to a solid casing. The casing must have a discharge nozzle and a suction nozzle that matches the pipe sizes of the rest of your system. If you can't find or afford a custom made casing, you can cut an opening into a standard pipe bend and connect your turbine to it. In this case, the turbine must be smaller than the pipe diameter and you will have to seal the turbine to avoid leaks and maintain pressure.Step 4Attach your pipe system to the suction and discharge nozzles of your centrifugal pump.
Is a 0.5 HP water pump able to lift 50 ft?
This can be found out by referring the characteristic curves of the pump. They show the variation of discharge wrt head and also the maximum head that a pump can generate and the maximum discharge.The discharge of a centrifugal pump decreases as the head increases. To know why this happens, refer to my answer toWhy can a centrifugal pump deliver water to lower head better than a reciprocating pump?It's difficult to say whether a 0.5 HP pump can deliver water to 50 ft since the 0.5 HP is the power input to the pump. The output depends largely upon how efficient the pump design is. The pump performance is affected by various parameters some of which are listed below:Diameter of pump impellerImpeller vane angleConstruction of impellerHead loss within the pumpDiameters of the suction and discharge portsSpeed of the pump (RPM)
If water can be pumped to a maximum of 10m, how can pumps in home can pump water of more that 10m?
Centrifugal pump never pull the liquid, it push the liquid. This is very important concept for the working of centrifugal pump.So, water which is coming in the pump should posses enough energy that they can go inside pump. Water in a pipe is not sucked up by a pump, is actually being pushed up by the source pressure in which it is stored. I will assume that we want to "lift" water from well. To lift the water (density=1000 kg/m3) from 10 m height, atmospheric pressure shall be 10*9.81*1000=98100 Pa (0.981 bar). let us assume atmospheric pressure is 1 atm (1.01325 bar), then height from which water can be lifted is THEORETICALLY (1.01325*10^5)/(9.81*1000) = 10.328 m (not more than this). I used the word "Theoretically" because when i specify 10.328 m, i didn't mention the flow rate of water. For the definite flow rate, we have to consider additional frictional and dynamic losses in the suction pipe. In any of these case, NPSHa and so cavitation will play a very crucial role.In any suction lift at any flowrate of water, if static pressure at the pump impeller eye drop below the vapour pressure, water will vaporized and form the vapor bubble which result in cavitation.So to avoid this, calculate the suction static pressure (Ps) based on the suction lift and flowrate. Calculate the NPSHa;NPSHa = (Ps - Pv)/ρgPv = Vapour pressure of liquid at the operating conditionρ = density of liquid at the operating conditiong = acceleration due to gravityNPSHa should be always positive value and it should be greater than NPSHr by minimum 1 m. Pump shall be selected accordingly.