Suction line diameter of saturated liquids

[virk]

Hello!

I have one question which some of you perhaps can answer: We often design suction line of saturated liquids like ammonia in a way that the velocity in this suction pipe is about 0,8 m/s. Additionally we consider NPSH issues. We never had problems.
My problem is that I do not know why it should not be possible to design the suction line with a diameter of 1,8 m/s. Are there any other parameters I should consider besides NPSH?
In my opinion the valve in the suction line is creating a large part of the pressure loss. Until now we nearly always used globe valves which cause a much bigger pressure loss than for example butterfly valves.
So, what do you think? What is to be taken into account besides NPSH?

Any hint or links appreciated

Kind regards virk

 

[ChrisConley]

I do not know why it should not be possible to design the suction line with a diameter of 1,8 m/s.

Double negative intended as reversal, or as amplified negative?

 

[virk]

Hi Chris!

Probably it is a bit confusing. What I wanted to ask:
Is it possible to design the suction line diameter for a suction line speed of approx. 1,8 m/s. What parameters I have to consider?

Kind regards virk

 

[Compositepro]

If you have a saturated liquid then you basically have zero npsh. Saturated liquids are tricky to pump and sensisitive to turbulence. An example is carbonated water.
The pressure in bubbles is higher than ambient pressure due to surface tension. It takes more vapor pressure to nucleate a bubble than to grow one after it has formed. Low flow velocity will minimize turbulence that can nucleate bubbles.

 

[virk]

Hi Compositepro! If you have saturated liquid you at the most have the suction column as NPSH.
I also think the lower the suction velocity the better. But is gets more expensive. Does anyone have any experience in designing a suction line diameter with more than 1m/s for saturated liquids (here ammonia)? Who can give some practical hints?

Kind regards virk

 

[Compositepro]

Virk, you are correct in what you say, but the way I look at it if you have more than zero NPSH then the liquid at the pump suction is not saturated. It may be saturated at the surface of your feed tank but that is not really relenvant. If you have plenty of NPSH then there is no reason to limit flow velocity.