Variation of flow-rate in reciprocating pumps

Is it crankshaft-driven or swashplate driven?

What is the fluid, its temperature and pressure?

"How can i determine the variation of flow rate ..."

By measuring it.

Did you mean something else?

Are you referring to the variation per cycle, or over an extended time period?

Are you concerned about the flow rate to use for friction calculations?

I need the flow rate to determine the accleration head of the pump

Nalu - you're really not helping yourself here.

Please give all the information you have about the pump (or a link to it), and explain carefully what you want to calculate or measure.

There are two ways:

a theoretical approach

a practical measurement

In the 1st case you can assume (witha sliaght error and not function of crankshaft or swashplate) that each piston delivers over 180° of rotation and that its delivery is a sinus function. The pump flow is the sum of all piston deliveries considering the angular shift between the pistons θ= 180/ z where z= number of pistons.

So that the delivery is at every moment Q= Σ A*S*sin(φ+(n-1)*θ) from n=1 to n=z.

This for 180° of rotation. Having this function you can define the average and the extreme values and compute the nonunifiormity of flow

In the second case you rae related with flow so that the flow measurement should consider the dynamic aspect, this means that you flow metere MUST have the possibility to define the instantaneuous flow at every moment. having the reccord you can as above compute the average value and having the peaks compute again your flow dynamics.

Which ever the mechanical part of the pump is the piston movement is well approximated with a sinus function. Of course if you hace long stroke pistons with a hydraulic cylinder as motor the corve is not any more a sinus.

Hope it will help quantitavely

If you look at the discharge flow patterns( or curve) for reciprocating pumps, you'll see how the pressure fluctuates above and below the mean. For instance the quintuplex reciprocating pump has a variation of about 1.8% above mean and 5.2% below mean which is a total of 7% variation.How did they arrive at these values? That's my problem.

Sorry but I did not succeed to copy it was necessary to scan and paste it as picture.

I tried once with RTF for text only and it worked but it does not for pictures.

Thanks for the effort.

can you give me the link? can't see it clearly.

I have no "link", I made it myself in order to explain it to you but as you see it is not possible to communicate the right way.

Sorry, any way you see the principle and you could make yourself the computations considering the flows in 1st approximation as a sinus curve and sum the effects of all cylinders active at same time. If you have EXCEL or any other spread sheet you can do it very easily.

The graphs are for single acting, in case of double acting you divide the phase difference by 2 (in this case it becomes 36°). If the piston areas are not equal in both directions then you introduce a coefficient for one side as ratio of the 2 areas.

Even if you are not yet a full engineer you can make use of the principle and obtain sufficient informations.

In general those informations are required for the choice of the pulsations damper.

In fact the principle was already explained in my previous mail and you had also an indication about the equations to be used.

I've ploted the graph using the excel sheet but I have not been able to plot the relative flow delivery curve (like the blue line in the second picture).and

In the equation you gave me in the 6th comment, what does the A,S and φ stand for? Is φ=ωt ?

φ= ω*t

A piston area

S stroke

The blue curve is the delivered flow i.e. the sum of all the partial flows from the pistons active at same time exactly as indicated in the 1st figure last message.