Convering inches of oil to NIPA
Convering inches of oil to NIPA
(OP)
I have a positive displacement pump at the top of a tank with a suction piping going into it. I know the oil operating level and have determined that the suction piping is 5 inches under the normal operating level.
My question is how do I convert the 5 inches of oil level to Net Inlet Pressure Avaliable? I've looked around online and cannot find a straight forward answer and I'm sure it's a simple equation. The tank does operate at a slightly negative pressure but normally it is atmospheric.
And NO this is not a homework question, it's a real issue!
My question is how do I convert the 5 inches of oil level to Net Inlet Pressure Avaliable? I've looked around online and cannot find a straight forward answer and I'm sure it's a simple equation. The tank does operate at a slightly negative pressure but normally it is atmospheric.
And NO this is not a homework question, it's a real issue!





RE: Convering inches of oil to NIPA
DOL
RE: Convering inches of oil to NIPA
Since this pump is only 32 gpm I think the only other consideration we need to take into account is the pressure drop across the strainer, what is an approximate loss??
Also, can we not use this equation? Pressure=0.434*Head*SG where head is the 5 inches?
Maybe I'm only confusing myself..
RE: Convering inches of oil to NIPA
Can't really answer your question about the loss across the strainer: how big is the strainer? how fine is the mesh? what is the viscosity of your fluid? How clogged is the strainer? Does the strainer have a bypass valve? If so, how strong is the spring?
The flow rate is an important consideration: but calling it "only 32 gpm" isn't really fair, especially if your suction pipe is only 1/2" diameter (how big is the pipe?). If I were you, I wouldn't neglect the fluid friction in the suction line.
Post some numbers and I'll do a quick calculation for you. Please be specific about your units - which size "gallon" are you using?
DOL
RE: Convering inches of oil to NIPA
You mean net suction head, that's 5" no matter if it's oil or water.
For a small pump strainer, 5 psi would be too much.
That's 5 psi * 62.4/144 / SG_oil in feet of head terms.
0.434 ft/psi is for water only. Divide that by SG of the oil to get feet head of oil.
Hope you're not running a nuc plant.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Convering inches of oil to NIPA
We are actually installing a vacuum dehydrator oil purification kidney loop to the lube oil tanks. Would this in theory improve the suction if the lube oil pump? Less sludge on suction strainer and less crude going into the screw pump. Thanks for the help so far.
RE: Convering inches of oil to NIPA
I found out the the NIPR of the pumps (depends on the temperature of the oil), but since this is based in PSI, I was trying to convert it to inches of head.
If we are increasing the oil level above the suction of the pipe (inches of oil level), how would I can I convert this to psi?
RE: Convering inches of oil to NIPA
http://www.engineeringtoolbox.com/static-pressure-...
Ted
RE: Convering inches of oil to NIPA
http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Pr...
Ted
RE: Convering inches of oil to NIPA
62.4 pcf density of water
144 in2/ft2
Hope you're not running a nuc plant.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Convering inches of oil to NIPA
Simply a learning engineer
RE: Convering inches of oil to NIPA
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Convering inches of oil to NIPA
For example if I have 17 inches (1.416 feet) of liquid between the bottom of the suction piping and top of the liquid level, that would give me 17 inches of head...
pressure = (1.416*0.9)/(2.31) = 0.551 psia
This doesn't seem right at all.....has to be way too low....do I need to add 14.7 psia (atmospheric)??
Big Inch, should I use 0.434 in place of the 2.31 like you said above??
RE: Convering inches of oil to NIPA
Maybe it should be (a homework question).
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.)
RE: Convering inches of oil to NIPA
Ted
RE: Convering inches of oil to NIPA
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.)
RE: Convering inches of oil to NIPA
NIPR is in units of psia. That is why I'm thinking my 2.31 conversion number may in error....should it be the 0.434 number instead?
RE: Convering inches of oil to NIPA
At the pump inlet 5" above the fluid level, pressure is 14.7 - (5/12)*(1/2.31)*0.9 = 14.7 - 0.16 = 14.54psia, static pressure. Does not account for flow losses when the pump is running.
1/2.31 = 0.43 like biginch said.
Ted
RE: Convering inches of oil to NIPA
I may just be confusing myself so here is a quick sketch of my situation to clear the air. Pressure at the bottom of the suction pipe would be Static Pressure PLUS Atmospheric....correct?
I read that NIPR is measured in PSIA, but I need to confirm.
RE: Convering inches of oil to NIPA
It is of no interest what the pressure is at the suction pipe inlet. The pressure due to fluid in the pipe back up to the tank fluid level is balanced(canceled) by the depth to which the pipe inlet is below that fluid level. Static pressure concern is only with the distance the pump inlet is above the tank fluid level. Go back and re-read other references given to you.
Ted
RE: Convering inches of oil to NIPA
So L2 doesn't matter at all. L1 needs to be from the oil level to the suction flange of the PD pump or the middle of the screws? I need to check to see if there are any elbows towards the suction flange (shouldn't be, but need to text).
if the inlet pipe is 3" in diameter would it be worth calculating the head loss of that?
RE: Convering inches of oil to NIPA
Search for inlet nozzle loss coefficients.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Convering inches of oil to NIPA
Since the strainer is below the oil level, this would impact how much net inlet pressure available there is?
RE: Convering inches of oil to NIPA
Minus the effective head of the fluid = L1 x r x g
I need to convert the effective head of the fluid to psia correct?
It is so weird I would use L1...I guess this is why PD pumps are so different than centrifugal pumps.
RE: Convering inches of oil to NIPA
There is no difference between a PD and centrifugal in that regard. PDs, especially diaphram and reciprocating cylinder pumps have additional acceleration head losses, because each time the diaphram, or cylinder is full, the cylinder or diaphram reverses stopping all velocity for a second, so the velocity head must be energized again and again at the beginning of each new cylinder cycle. If there are 3 or more diaphrams, then one diaphram is always filling as each diaphram is offset in cyclic period by 2 pi/3, as opposed to 2 pi/2 for a 2 diaphram pump, or 2 pi/1 for a 1 diaphram pump. The dead zones are less pronounced as the number of cylinders, or diaphrams increase.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Convering inches of oil to NIPA
Just seems like NIPA would decrease with a dirty strainer....
RE: Convering inches of oil to NIPA
Net Inlet Pressure Available = P(tank)-P(static)-DP(strainer)-DP(pipe)
P(tank) in this case is atmospheric, but sometimes a slightly negative pressure, due to fans inside.