How to decrease pump flow???

[Bio-boy]

Is it simply a case of restricting the flow into the pump i.e. could you use a valve and partially close it?
I have a pump capable of flowing 350L/min at 6m head and would like to know how, if possible the flow rate could safely be restricted.
I'm thinking by partially restricting the flow via a valve it would act in a similar fashion to increasing the head. Would I be wrong in thinking this? I appreciate that there would come a point that too greater a restriction would damage the pump due to excessive load.

[knighty]

you want to restrict the flow into the pump, not the flow out of it

how much do you want to restrict it by ?

[therecklessengineer]

No you don't. If you restrict flow into the pump, you run the risk of cavitation.

Restrict the flow out of the pump with a valve.

Or...use a variable speed drive (assuming the motor is 3 phase).

Restricting the pump does not cause an increase current draw in the motor. The power delivered is a product of head and flow rate. Reduce the flow rate, you reduce the power required by the impeller - thus the current drawn by the motor.

You will, initially see a rise in current as you start to increase head. But it will drop off when you go too far. You can't overload a pump by throttling it. In fact, the only way I can really think of is by either pumping a fluid that's viscous, or by running it too fast - but again, you'll need a VSD for that.

[Tony]

Totally agree, you're pretty much guaranteed cavitation with methanol in the mix and restricting the input flow

The only risk with restricting the output is heating the pumped liquid, so long as there is some flow you will be OK.

[julianf]

You could loop the flow back to the feed.  That way you would not actually restrict the pump movement at all, but reduce your flow all the same.

[dgs]

Bio Boy,
It may be an idea to try to measure the flow before you start to think about restricting it. With most bio/oil mixes the pump flow is about 50% of the quoted amount with water. Drum tested his 105 at 29lpm and my 120 is down to 34lpm with cold oil.

May I ask you what sort of pump is it.

[therecklessengineer]

Mr engineer and Tony, I'm sure I have seen some posts on infopop where some say cavitation produces better mixing.

I find that surprising, but not unbelievable.

Certainly though you'll find your impeller erodes with cavitation.

[knighty]

I was told a long time ago by an engineer to always limit on the input if you can



but as julian said, if it's your mixing pump... put a loop between the input and output (with a valve on it)


slower flow through your reactor tank

but max flow through the pump for max in pump mixing :-)

[Julian]

Mr engineer and Tony, I'm sure I have seen some posts on infopop where some say cavitation produces better mixing.

I find that surprising, but not unbelievable.

Certainly though you'll find your impeller erodes with cavitation.

This appeared on youtube a while back ...

https://youtu.be/Abw3dG0SB0g

and

https://youtu.be/6BXy_vTNju8

[Bio-boy]

Bio Boy,
It may be an idea to try to measure the flow before you start to think about restricting it. With most bio/oil mixes the pump flow is about 50% of the quoted amount with water. Drum tested his 105 at 29lpm and my 120 is down to 34lpm with cold oil.

May I ask you what sort of pump is it.

http://www.oilybits.com/pumps-for-liquids-/pedrollo-pro-nga-open-impeller-316-stainless-steel-centrifugal-pump.html

[knighty]

so.... why do you want to limit the flow ?

[therecklessengineer]

so.... why do you want to limit the flow ?

That is a good question...

[Bio-boy]

As it flows 300+ litres per minute and I have concerns that whilst it will be OK for the reaction it may be too much for the drying/filtering stage as at 6Bar will it not simply crush the cartridge filter see below:

http://www.oilybits.com/filters/elements-complete-with-housings/pentek-20-big-blue-polypropylene-filter-housing-1-5-bsp-ports.html

If you all think it will be fine then happy days. That's why I thought I would ask the question as there is a lot of knowledge on this forum.

[Tony]

From the specs it looks to be a low pressure high flow pump.  The 6 bar is almost certainly the rating for if this is used as a booster pump in an already pressurised system, I very much doubt it will push 6 bar on its own, but without a datasheet showing the pump curves it's impossible to tell.  It is very much a pump that a small amount of restriction will slow the output considerably.

What process are you planning to use (why do you want to filter the processor's discharge?)

[dgs]

Filtration systems always work more efficiently at lower flows. I would consider purchasing a low flow pump for your filtration. I did consider getting a pump similar to yours for my new set up, but having had a word with jamesrl he told me to go with lower flow and higher pressure for the process pump, so I went with the TAM 120 and a 1/2'' eductor and my goodness, does it work well.

For my filtration pump I use an adjustable flow geared pump, I have it set on 4.3 litres/min to go through 1 and 0.5 micron filters.