How to maintain flowrate and pressure head in a pump?

[Nitheeswar]

Pump is supply fluid to the 35 nozzles through 3 inch pipe and manifold.At nozzle the pressure is 32 m and pressure at pump outlet is 30 m .The flow rate required at nozzles is 500 lpm. Pump can deliver 860 lpm at 24 m head.pump size 100x100 mm
1)how delivary pipe size affects the pressure head?
2)how required flow rate is maintained?

 

[erobz]

Do you have any ideas about how it works?

 

[erobz]

@Nitheeswar 's Reply.

Yes, we developed it, the pump is capable of delivering 860 lpm at 24 m head, we are maintaining pump delivary pressure 32m and we are getting 30 pressure at nozzles.we only considered pressure .Required flowrate is maintained by designing nozzle . But pump is delivering around 600 lpm more volume and nozzle is delivering less volume 500 lpm.what is effect of remaining volume?

 

[erobz]

Your pump performance spec is probably at operation point of best efficiency (BEP). The actual pump curve is something like the following (red line). The purple lines are two theoretical system curves. $S_1$ is less restrictive than $S_2$.

But pump is delivering around 600 lpm more volume and nozzle is delivering less volume 500 lpm.what is effect of remaining volume?

This part of the reply does not make sense to me. Show us a simple diagram of the piping system.

 

[Mark44]

Thread temporarily locked for moderation.

 

[berkeman]

Thread unlocked and moved to the ME forum for now.

 

[erobz]

Thread unlocked and moved to the ME forum for now.

Did I do something? The OP replied to me privately, I just copied that here and it got locked.

 

[berkeman]

No, you did nothing wrong. There was an account issue with the OP, where they had started multiple accounts while trying to register here at PF. We just needed to clear that all up.

 

[Nitheeswar]

 

[Nitheeswar]

Let say pump is delivering 650 lpm at 32 m
What is the delivary that I get in nozzles?

 

[erobz]

What is the delivary that I get in nozzles?

650 lpm. The flow is incompressible. Unless you are not showing a branch in the network that the takes flow somewhere else, or a portion of the flow is accumulating somewhere that is not shown…the answer is 650 lpm.

 

[Nitheeswar]

But the nozzle is designed as at 30 m it can supply only 15 lpm , for all nozzles it is 500 lpm, so the nozzles supply 500 lpm

 

[Nitheeswar]

I have shown side view the nozzles are connected to tube which is connected to manifold

 

[erobz]

But the nozzle is designed as at 30 m it can supply only 15 lpm , for all nozzles it is 500 lpm, so the nozzles supply 500 lpm

I don’t know what to tell you. What does your performance curve for the pump tell you the output is supposed to be at approximately 32 meters differential? To that point about the differential pressure, what is the pressure measure on the pump inlet?

 

[Nitheeswar]

I don’t know what to tell you. What does your performance curve for the pump tell you the output is supposed to be at approximately 32 meters differential? To that point about the differential pressure, what is the pressure measure on the pump inlet?

650 lpm

 

[erobz]

What are the inlet conditions of the pump? You just have a box drawn. Is it a tank?

 

[Nitheeswar]

650 lpm at 32 m pump outlet

 

[Nitheeswar]

What are the inlet conditions of the pump? You just have a box drawn. Is it a tank?

Inlet is connected to tank

 

[erobz]

650 lpm at 32 m pump outlet

I asked what is the head at the inlet of the pump, not the discharge. It’s the differential pressure that is important, not just a discharge, it’s probably a small correction, but it’s better if you just come out with it.

 

[erobz]

Inlet is connected to tank

Then calculate the cross section of the tank, and measure the change in height over some reasonable time interval, see if it’s measuring about 650 lpm.

 

[erobz]

Another thing: is the fluid water at the temp of the pump curve performance data?

 

[Nitheeswar]

Irrespective of pump output conditions, if we are maintaining pressure 30 m at nozzles, we are getting the 500 lpm, the flowrate only changes if pressure is below 30m

 

[erobz]

Irrespective of pump output conditions, if we are maintaining pressure 30 m at nozzles, we are getting the 500 lpm, the flowrate only changes if pressure is below 30m

How do you know what you are getting at the nozzles. Are you catching it in a bucket?

 

[Nitheeswar]

How do you know what you are getting at the nozzles. Are you catching it in a bucket?

Yes we measured for a minute

 

[erobz]

Yes we measured for a minute

all of them together??Or just 1 nozzle multiplied by 30?

 

[Nitheeswar]

Just one nozzle multiplied by 30

 

[erobz]

Just one nozzle multiplied by 30

Bad idea, they are all going to be different.

 

[erobz]

like I said, measure the inlet tank change in volume over a minute.

 

[Nitheeswar]

So,Irrespective of nozzle design, we will get the delivary what pump is capable of delivering

 

[erobz]

So,Irrespective of nozzle design, we will get the delivary what pump is capable of delivering

Yes. But If you take some nozzles out ( blocking them) the purple curve I show gets steeper, reducing the flow rate of the pump. But… with an incompressible flow and no place for flow to go elsewhere…what goes in must come out. That is that.

You need to give me the inlet conditions ( head), tank fluid, temperate, and a pump curve would be nice. There are too many paths to take with this little bit of info to troubleshoot.

 

[erobz]

You need to give me the inlet conditions ( head), tank fluid, temperate, and a pump curve would be nice. There are too many paths to take with this little bit of info to troubleshoot.

On second thought, just tell me about the fluid properties, no need to tell me what’s it is exactly. Your pump performance curve is tested with water(likely) . If the fluid has a viscosity different from water the performance curve could need adjustment.

To get the inlet conditions without a guage, need to know the tank water height and where the pump is physically placed relative to the water level.

 

[Nitheeswar]

The relative height between pump and water level in tank is 1.6 m

 

[erobz]

The relative height between pump and water level in tank is 1.6 m

Ok, so subtract 1.6 m from 32m. Your differential is about 30.4 m. What flow rate does your pump curve suggest it is running at 30.4 m?

 

[Nitheeswar]

We are using old pump, there are no pump curve for that. It has only head range and flow rate at particular lpm.please find attached image

 

[erobz]

We are using old pump, there are no pump curve for that. It has only head range and flow rate at particular lpm.please find attached image

If your tank has a regular cross-sectional area its a simple matter to determine the average flow rate. You mark the top of the water, let it run for a minute (if tank capacity permits). And measure the height again.

$$ \bar Q = \frac{A_{tank} \Delta h }{ \Delta t } $$

Since you don't have a pump curve, or cant find one. Its old, perhaps modified from nameplate. It would be a challenge to verify its performance with so little information. As far as I can tell you are already operating outside of nameplate head range.

 

[Lnewqban]

Irrespective of pump output conditions, if we are maintaining pressure 30 m at nozzles, we are getting the 500 lpm, the flowrate only changes if pressure is below 30m

What is the problem with that?
Is the pump satisfying the nozzles or not?

The nameplate of your pump states that it can deliver 14 lps (840 lpm) at a head of 24 m.
If a gauge located at the discharge of the pump shows 32 m of water column (45.5 psi), then it can only deliver less than 840 lpm (let's assume 630 lpm).

In actuality, it will deliver only the amount of water that the nozzles let go through.
The motor will consume less electricity (Amps) and the water may get a little warm.

Please, see how similar pumps behave.
Note the ranges of delivery pressures and volumes.

Copied from:
https://www.crompton.co.in/product/...agricultural-pumps/centrifugal-monoset-pumps/

 

[Nitheeswar]

If we assume it is delivering 630 lpm ,the nozzle can only permit 500 lpm.
What is effect of that 130 lpm?

 

[erobz]

If we assume it is delivering 630 lpm ,the nozzle can only permit 500 lpm.
What is effect of that 130 lpm?

If we assume the pump is delivering 630 lpm, the nozzle are dischaging 630 lpm. You are really hung up on this idea that the nozzels are designed to only output 500 lpm. No one cares what you think the design specs are for your nozzles!

Nozzle: “Hey pump, destroy mass because some engineer miss-designed me!"

Pump: “…”

 

[Lnewqban]

If we assume it is delivering 630 lpm ,the nozzle can only permit 500 lpm.
What is effect of that 130 lpm?

There is no effect, because those 130 lpm are not happening.

Please, take a look at the red curve in the diagram shown in post #4.
Q is the volume of liquid that is delivered by the pump at different pressures.

Note how the pump produces a maximum discharge pressure when Q=0, and it remains close to that value for small amount of flow.
Our pump may be working in a similar flexible area of performance, in which the flow self-adjusts according to the restriction of the nozzles, keeping a maximum discharge pressure.

That is how centrifugal pumps work.
You can fully close the discharge using a gate valve (Q=0 condition), and your gauge will still show the maximum discharge pressure that the pump can produce.

Because the power taken from the motor is proportional to the product of pressure and flow (P x Q), our pump will consume less power in that zero-flow condition.

Your nozzles are acting as a partially open valve, limiting the flow.
Your pump will naturally adjust to that limited flow, increasing the pressure accordingly (which is good for the performance of your nozzles).

All you need to do is to watch the temperature of the water downstream the pump, which tends to increase in those conditions.
If it gets warm, there is no problem.
If it gets too hot, it could damage the seals and the bearings of the pump.