Eductor pump at saturation point - can it work?!

[Duncan Mek-Tek]

Hello there,

I'm designing a pumping system. Before my Centrifugal pump, I want to increase the pressure of the flow (to reduce cavitation, so the pump lives longer).
We thought to do this with an Eductor pump!

I'm worried however, that there will be vapourisation in the Eductor pump. The suction liquid is essentially at vapourisation pressure already. surely if I run it through an Eductor pump (that causes a temporary drop in pressure) I will have vapourisation? Cavitation?
If so, will that make the whole system unpredictable?

Any help would be greatly appreciated!

 

[Artisi]

Sounds like dog chasing tail to me. A suction inducer is usual the remedy for low suction pressure.

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]

IMO, it comes down with the actual NPSHa at the suction of the centrifugal pump. But, it may not be a good idea to have the stream saturated with vapor before enter the pump suction without a safe margin, no matter how it's been predicted or controlled.

 

[Duncan Mek-Tek]

Thanks for the help

Artisi - I totally agree, an inducer is usually what I go for. Unfortunately, we really can't design one that will operate without cavitation, when the liquid is so close to saturation. So we're looking into some small addition...

mk3223 - yeah, there's basically no margin. Was hoping the Eductor could give that to us. Perhaps if it can operate with some vapourisation in a stable way? But I can't find any literature on it.

 

[EdStainless]

Instead look at a low NPSH inducer on the front of your pump impeller.
With the eductor you are very likely to end up with 2 phase flow and more pump issues.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

Duncan,

You can't beat physics.

All you can do is lower friction, lower temperature, lower the pump or add some pressure on the surface of the liquid.

Or maybe buy a different pump.

If you're using an eductor then you must have a higher pressure source of the same liquid??

Can't you use this further down the inlet line somewhere?

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

 

[Duncan Mek-Tek]

Ed - I fear there's not such thing as an Inducer capable of negligible cavitation at saturation point . But maybe we can make something good enough!

LittleInch - Haha, yup, that would all work! Is there no sneaky, less heavy/expensive way?
and yes we do have a higher pressure source - after our centrifugal pump. How can we use that further down the inlet line??

Thanks guys,
Duncna

 

[1503-44]

What liquid and temperature? You don't see where actually say what it is.