suction nozzle bigger than available nozzle of the tank. 1

[jor1492]

Hello
I have to do the connection arrangement of a centrifugal pump for cryogenic service with a cryogenic tank (source), the fluid is liquid oxygen and I have this case , the nozzle of my tank is 1" and the suction nozzle of my pump is 2 1/2". Is there problem in the performance of the pump if I just put a 1 x 2 1/2" coupling to do the connection of these equipment?

thanks in advance.

 

[bimr]

Without the required information such as the flow, length of pipe, fluid properties, etc. to make an evaluation, the answer would be just a guess. How did you size the pump? Do you own the tank?

 

[QualityTime]

I would talk to the pump manufacturer. But in general the suction piping should as a minimum be the same size as the pump suction and/or one size larger. You will get weird flow patterns into the pump suction. The optics (aka common sense) alone are all wrong....a 1" pipe into a 2.5" suction....You are asking for trouble

 

[Lnewqban]

It doesn't sound good.
Maybe the pump you are using is too big and its speed could be reduced to harmonize with the 1" outlet and pipe?

I would consult the manufacturer of the pump for that specific application.
If the response is positive, I would ask about the recommended type of reducer and its location respect to the suction of the pump.

"Engineering is achieving function while avoiding failure." - Henry Petroski

 

[Artisi]

Distance from tank outlet to pump inlet is???

The pump doesn't care what the size of the tank outlet is, what is important is flow behaviour at its inlet and into the eye of the impeller.

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]

jor1492,

Is there a problem doing what you're doing?

Maybe, maybe not. The missing data you need to know or advise includes:

Flow rate
Pump NPSHR
other frictional losses from tank to pump
temperature of the liquid
Height of the liquid above the pump centre line
Pressure above the liquid in the tank
Vapour pressure of the liquid at that pressure and temperature
density of the liquid (to convert pressure to head)

Then calculate the NPSHA for your system. Note nozzle exit losses need to be calculated.

If it's greater than min required, normally by more than 1m, then you should be ok.

Gut feel is that it doesn't sound good, but there is much we don't know so can't say one way or another.

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

 

[jor1492]

Thanks everyone
below the process information.
I did the math and by the operation pressure of the tank the NPSHA is bigger than NPSHR.

Flow rate =120 GPM
Pump NPSHR = 4.9 ft
Line from nozzle tank to pump= 8.2 ft
temperature of the liquid=-361.4 °F
Height of the liquid above the pump centre line= 3.9 ft
Pressure above the liquid in the tank=50 psig
Vapour pressure of the liquid at that pressure and temperature=1.12 mm Hg
density of the liquid=71.17 lbs/ft3

 

[EdStainless]

The pressure in the tank is what lets you get away with this.
It is very easy to cavitate in liquid gases, I would suggest a pressure sensor in the inlet line linked to a shut off.
Cavatating LOX can lead to very serious results (like fires).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[QualityTime]

Let me ask a stupid question. Why design something on the basis there is something not quite right? Why would anyone want to take this chance when it is in your power to do something about it now? We are not talking about installing a dipshit 2-1/2" nozzle and ripping out the 1" nozzle. Why are we even contemplating keeping the 1" nozzle? Cripes! Do you like going to bed thinking about whether you made the right engineering decision? Play it safe and put in a bigger tank nozzle

 

[Artisi]

Simply increase the 1" fitting by using a 1" to 2 1/2" fitting at the tank discharge and then run 2 1/2" pipe to the pump inlet, it's not rocket science just normal common sense.

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]

That's also 0.4 F above its freezing point. Looks far too close to me. ..[pre][/pre]

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

 

[moltenmetal]

Is liquid N2 at those conditions really denser than water?