Spill Back System (Recirculate line)

[Loo Kian Sing]

Kindly refer to the image uploaded.

May I know, what is the percentage range of the capacity that can be spilled back to the suction of the pump through the recirculate line (restrict orifice located at the recirculate line)?

Can i maximize the capacity of spill back by installing a flow control valve at B (discharge line)?

Thank you for anyone who are willing to help me.

 

[LittleInch]

Can be 100%, but with your restrict orifice that will limit the flow.

Installing a great restriction at B will change the flow, but not by a lot.

Looks like a student question to me unless you provide some proper numbers.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

OP - do some research in Engtips, recirc. lines have been done to death.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Loo Kian Sing]

Thank you for your response.
I apologize for my not professional question.
For your information, this spill back system has been design to allow some of the liquid spill back to the suction of pump when not enough liquid from suction source. As I am not the one to design this system, I am not sure the reason of insufficient liquid mention and I am not sure if this is a good design. Some one told me the maximum of the capacity to spill back through restrict orifice is 30 percent (the flow is 0.45m3/hr). As these things confusing me, so I would like to gather more information from experience or professional engineer and I asked those question. I thought it is common design, but I think I am wrong.
I use search tool by typing "recircul", but nothing found. I found page by page in pipeline Piping and fluid mechanism forum but I still cannot find it. Maybe my effort is not enough. Maybe it has been done to death as no one ask about recirculate anymore.
Thank you again for spending your time in this unprofessional thread.

 

[Artisi]

If you have insufficient fluid coming into the pump inlet, how can you recirculate flow back to the inlet to make up the short-fall of flow.
What you are saying is if X amount of fluid is supplied from the source, and you divert some of that flow from the pump discharge back to the inlet the total pump output will now be X plus - well I think that's what you are saying.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[mk3223]

The 30% recirculation could be the original design specifically for your system. There were discussions in the Pump Engineering Forums to use a restrict orifice on the pump recirculation or bypass line. As it may be a simple and cheap solution, the downside is that you won't be able to control it since the flow rate is pretty much fixed.

 

[Loo Kian Sing]

"If you have insufficient fluid coming into the pump inlet, how can you recirculate flow back to the inlet to make up the short-fall of flow."
Is this statement true? As per my understanding, flow can be controlled by restrict orifice. And whenever there is a separate line (from one line to two lines), if the pressure of both lines are low enough, fluid will flow to both lines. Is my understanding correct?

So if a restrict orifice is installed at the circulation line, the maximum capacity can be 100 percent (but depend on the system)?

 

[lilliput1]

If the equipment served by the pump have 2 way modulating valve, the recirc line would prevent dead heading the pump if all the control valves are off. The design gpm through this recirc should be above the minimum flow recommended for the pump as shown on the pump curve. The design pressure drop through the orifice should match that shown on the pump curve at minimum flow.

 

[Artisi]

This thread is an extension of a thread in pump engineering and needs to be read in conjunction with each other. Otherwise just further confusion will reign.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[mk3223]

So if a restrict orifice is installed at the circulation line, the maximum capacity can be 100 percent (but depend on the system)?

Unlike a control valve, the restrict orifice is calculated for a single flow based on the required pressure drop. So, the flow of the RO is somewhat fixed at one rate and can't be modulated.

 

[Loo Kian Sing]

Artisi,
Yes, I agree I am lazy to do research on engtips as other situation might not same with mine. You have mentioned twice. I thought this is a forum to post the question and seem like engtips does not have the rule of posting the question.
However, thank you for your reminder. Thank you.
I will try to do some research next time before I want to ask something.

Dear lilliput1 and mk3223,
Thank you for sharing your understanding. I have a better understanding now.

 

[Artisi]

Loo Kian Sing;
Too lazy, well that's your problem not ours. And yes you can post questions and people if they have a mind to will answer with advise for free - because we are big hearted -- but what we won't do is lead you by the hand or do your job for you.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Loo Kian Sing]

I never say is your fault or others. Please dont assume in your own way. I am not too lazy as I got many things to do also like everyone, I just want to ask and in the same time do some research. I dont know much about engineering. But I know there are many difference situations in difference cases. As I am new, I dont know whether the one has posted related to the one I want to ask. Yes, you can don't leave your comment if you feel the question is repeat. I never want anyone lead me by hand or do job for me, I just want to have better understanding (I know I am stupid). As you are big heart, you know what to do, like advise me, I am appreciate with that. I will do more research before I ask. Thank you.

 

[Artisi]

First up stop apologising and saying you're stupid, it is appreciated you are probably out of your depth - but supply a sketch and installation data so we can assist. This has been asked for a number times in your pump engineering post, but not supplied.
You have a basic simple installation problem, not a complicated hydraulic problem.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Looking at you other thread, you have a situation where the inflow into your tank is led than pump capacity. Installing a flow control valve downstream of pump B will reduce flow. If you close it enough then you can stabilise the level in the tank and prevent the inlet line from being exposed and getting air in toy system. Some water will go back via your orifice but in the main the active point on the pump curve will just move left.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Loo Kian Sing]

Dear Artisi,
Noted and thank you for your advise.

Dear LittleInch,
Appreciate of your explanation. From you explanation, I know that we can install a control valve at downstream of pump B to reduce the flow, and prevent pump B to go dry (if possible).
In this situation (if the pump not necessary to be function all the time), can I install a pressure gauge or flow indicator at the upstream of the pump instead of using the bypass line (when the pressure or flow is not enough, the pump will stop automatically)?

 

[LittleInch]

you would be far better off with a level control on your tank to switch off the pump on low level and then switch it back on at high level IMO.

Pressure indication is essentially the same as a level control and in some cases you can use a sensitive pressure transmitter at the bottom of the tank as a level indicator, but on a pump inlet it is difficult to get the setting right.

Flow indicators are again not easy to set up and in my experience are often quite simple devices which can malfunction and not work properly.

If you're going to add anything, add level switches or transmitters in the tank you're pulling liquid out of.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.