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In the picture shown for the reciprocating pump, there is an error in labeling. What is labeled "CAM" is not in fact a cam at all, but rather it is a crank.

What is labeled "HEAD" is in fact simply the pump cylinder wall. The head would be further to the right. The valving is usually in the head.

The piston is shown extremely elongated; why?

The connecting rod is not labeled at all.

The implication seems to be that the seal is embedded in the cylinder wall and does not reciprocate. I see no reason why the seal cannot be embedded in the piston and reciprocate with it.

Overall, this is not a very good picture.

You don't really say in words what the difference it; you only show pictures. One of the very important differences, operationally, is that the centrifugal machine provides a continuous flow whereas the reciprocating pump provides a pulsating flow only. There are also major differences in the pressure difference across the pump that the two types can support.

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Arvind Laad: Major difference is the type of flow & the working principle. In a single acting reciprocating pump (recip) the flow is intermittent in semi-sinusoidal  form with gaps in between. In a centrifugal pump the flow is continuous. If a Recip is connected to a long pipeline, this can set up surges & resultant vibration & noise due to intermittent flow. Therefore it is necessary to provide surge protection equipment like a surge tank or surge vessel to prevent damage to the pipeline. The pipeline is more prone to what is known as Water Hammer (this subject is too vast to be described here)

Another important consideration is that inadvertent closure of valve in the discharge line for a recip can cause severe damage because it is a positive displacement pump due to overpressure. So a pressure relief arrangement is essential. In the centrifugal pump also, a damage can take place, but not due to overpressure. The line does not get over-pressurized like in case of a recip, but the fluid gets churned & gets slowly overheated. The damage therefore is delayed, but due to heating & not by over-pressure.

 

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Good comment, Arvind.

In the USA, reciprocating compressors are used in a vast network of pipelines to transport natural gas from the sources in the southwest to the more heavily populated northeast. It is not possible to simply raise the gas to high pressure at the source and expect it to travel several thousand miles through the pipe without further pumping. Consequently, natural gas pipe lines have compressor stations every 10 to 15 miles, and the entire volume of gas comes out of the ground and passes through a recip compressor at each compressor station. Usually the compressors are powered by natural gas, taken from the pipeline flow, and burned in a diesel engine converted for spark ignition.

You are certainly correct about the need for surge chambers and proper consideration of the pulsations. The pulsation damping chambers must be properly designed -- not just any old tank -- so that pulsating pressure does not shake the piping and cause fatigue failures.

To the best of my knowledge, I don't think centrifugal machines are ever used in this service.

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In a Centrifugal compressors there are impellers which rotate with a very high velocity to provide high pressure head where as in reciprocating compressors there is a piston and a rotar to provide necessary high pressure.

one of the major difference between the two are:

reciprocating compressors provide high pressure head with low volumetric flow where as centrifugal compressors provide low pressure and high volumetric flow.

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the above quotes is correct. its not a piston, its a plunger see the diameter and length ratio for piston and plunger. so call plunger pump.its not  cam  its crank. however its a positive displacement pump. it pumps into large head. also priming is not needed. for getting large volume  discharge we needed big size pumps. the centrifugal pump is a high volume low pressure discharge. in volume discharge the centrifugal pump is in front.  we can use multi stage centrifugal pumps for achieving high discharge pressure and high volume is required through the arrangement of parallel or series arrangement of impellers ..the delivery valve of the centrifugal pumps being closed at starting to get maximum efficiency and reduce effort and cavitation phenomen  and the delivery valve of the reciprocating pump being opened at the starting of the pump.

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We cannot simply equate centrifugal and reciprocating pump. Its just like comparing brandy to whisky... Its just a matter of understanding the application where thos pump is to be used, for example at high head, centrifugal will be the best pump to used, but as to metering the output by any means ( e.g. Volume, pressure, etc.) reciprocating pump is best to use.

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Centrifugal pumps rotate fluid, continue transfer momentum to the fluid and create centrifugal force through impeller blades so that it can continue flow in radially outward direction. Because of these properties, it is used where a continue large amount of flow at low pressure is desirable whereas reciprocating pumps positively displaced the fluid in a forward direction using reciprocating motion of the piston. It means if we stop the pump, there will be no reverse flow of the fluid. It contains suction and discharge valves that enables pump to create a high pressure in the fluid in cylinder during compression stroke so it is used where less amount of flow only in one direction at high pressure head is required and discrete flow has no any bad impact.

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