HELP with Pressure Blanket required for Pump

[ChemDCPD]

Hi Forum,
Need your help and advice for this,
At our facility, we use gear pump to transfer product from storage vessel to the truck container. We replace our pressure regulator on the vessel by a new one, and since then our blanket couldn't keep up with the pump when it pump out.
Can anyone show me the detail to calculate the amount of CFM to keep up with the pump so i can increase the size of the pressure regulator orifice.

Nitrogen Pressure Blanket : 6 in W.C
Gear Pump with 3''ID suction and outlet
Pump is 6ft below the vessel
NPSHR: 5 ft
Pump inlet pressure: 7 PSIG
Pump Outlet Pressure: 48 PSIG
Pump RPM: 378.52 with 85 GPM
Truck Container : 25 PSIG

 

[EdStainless]

Just use your max flow rate, convert to CFM (about 11.5 CFM, but you need some margin) and then look at the regulator specs.
Make use to correct for the pressure (both supply and delivery).

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P.E. Metallurgy, Plymouth Tube

 

[ChemDCPD]

Regulator specs have range from 2 -7 in W.C , which is the specs design for the vessel. The pressure regulator have maximum allow 200 psig,due to the vessel is low pressure, maximum 12 in W.C . We supply 14 PSIG to the regulator, in case the regulator broke, i dont want any high pressure flow into the vessel and damage it. I check the manual and spec sheet of the regulator it doesn't list the minimum require for it to operate.
and as soon as i turn on the pump, it ran for a couple minutes and the pressure blanket drop real fast from 7 to -0.5 and then it shut the pump. My guess would be the orifice size that couldn't keep up with the pump suction pressure. from what i got from the specs sheet, currently it has 1/8'' and provide 325 SCFH. i can increase up to 9/16'' and provide 1863 SCFH, but i want to make sure it can keep up with the pump or i have to change to another model.

 

[LittleInch]

Kind of curious as to why you couldn't figure out that the volume of blanket gas at that sort of pressure is virtually the same as the volume of liquid leaving the tank - As ed says 85gpm = 11.5 CFM = 660 scfh.

So if you currently can input only 325, then you will run out pretty fast.

Probably 3/8" orifice would be enough?

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

 

[ChemDCPD]

oh, that is more clear now. Thank a lot for helps. i were stuck and recalculate many time for pressure inside vessel base on volume and dimension, and get field check for every elbow, and valve to make sure i didnt miss anything. turn out the answer is right in front of me. so technical i just need to convert from GPM to CFM . and 3/8'' would give me 1653 SCFH with 14 PSIG supply.
Thank you very much