Scavenge pump check 2

[slickstyles5]

Hi,

I am trying to check if the pump that I plan to use for a scavenge system is adequate for my system. I have calculated the NPSHA (10.2 ft.). The pump model is NDP-20BAV (Yamada) and it says that the max dry suction lift is 18 ft. What does this mean and how can I check if my pump will work?

Notes: I am pumping an air/oil mixture (scavenge). I took hvpa to be 0 ft. because it is oil.

Thank you for any advice.

Gabriel

 

[JRLAKE]

Suction lift refers to an air operated double diaphragm's ability to pull a suction lift during prime. Don't confuse this with NPSHr.

Therefore. If I installed the pump on the top of a sump and the liquid level is 17.9 feet BELOW the pump, this pump could suck it up the pipe during the priming cycle.

Don't rely on this number. It is performed under lab conditions with perfect seating of the balls and seats. As soon as these items begin to wear, this suction lift ability drops off. Also, your diaphragm life will be reduced if it has to pull an 18' suction lift. The vacuum created on the suction stroke will eventually fatigue the diaphragm.

 

[JRLAKE]

Oh yea, to answer your other question, if NPSHa > NPSHr, the pump will "work" in terms of NPSH. Other than that you are on your own because we don't know desired flow rate, desired head, compressed air pressure, solids content, system curve, piping design, temperature, etc, etc.

 

[slickstyles5]

Thank you JRLAKE!

This answered some of my questions. Will the manufacturer be able to provide the NPSHR? Is this a fixed value or does it depend on some variables?

Also, is it ok to assume that the vapor pressure of oil is equal to zero? (I have MIL-23699 Oil at 160 deg F).

Thanks again!

 

[JRLAKE]

NPSHr should be on the pump curve. Remember pump curves are normally in terms of water. There are performance adjustments needed for different viscosities.

I can't answer your question on the vapor pressure because I don't know anything about that oil. However, I normally don't assume this kind of information at elevated temperatures.

 

[slickstyles5]

The only information I have in terms of curves lies in the document I have attached. Does this document provide the NPSHR? How would I go about figuring that out?

I know my flow of 15.4 gpm. Other than that I have no idea.

Sorry if I don't know too much about design for pumps. I don't usually do too much work on pumps.

 

[JRLAKE]

Usually there is another curve provided showing varying suction lift with increasing air inlet pressure. These should be treated as NPSHr curves. Be careful because each diaphragm material has its own suction lift curve.

 

[slickstyles5]

I have contacted the manufacturer so see if these curves are available.

Thanks for all your help!

 

[slickstyles5]

For my scavenge system, is there any other way to determine if my pump will work? I am basically pumping from an air/oil mixture from a manifold through some hose (with elbows) into the pump. I am only calculating the suction part because the discharge is directly into a tank. I determined my NPSHA and I will compare it to the NPSHR. Is there any other verification I can do?

Thanks for any advice!

 

[Artisi]

galeblanc

to answer your question - there are no suction capabilities shown on the curves you have posted.
The curve is clearly marked as "curve data is based on one-foot flooded suction; ambient temperature"

Contact the suppler with your problem - they should be able to help you.

JRLAKE - pumps don't suck - (maybe you can say that when they don't work)

" this pump could suck it up the pipe during the priming cycle."

 

[slickstyles5]

I determined my NPSHA and I will compare it to the NPSHR. Is there any other verification I can do for my application?

 

[Artisi]

Do you have the NPSHr curve?

 

[slickstyles5]

Nope. This pump is an air powered diaphragm pump, so I am assuming that the best way to check if my pump will work is to calculate the losses first. Then, I can calculate the suction head = static height - losses. Then I can calculate the total discharge head = discharge head (lossses) - suction head.

Finally i could compare this to the manufacturers max discharge pressure.

Do you think this would be good? Because is there even an NPSHR for this type of pump?

 

[slickstyles5]

I found the maximum discharge pressure which is 5 bar (72.52 psi). My total discharge pressure is 11 psi, so I assume my pump is ok?

 

[slickstyles5]

What is maximum dy suction lift?

 

[Artisi]

1. Total Suction head is total losses PLUS static head if negative or MINUS static head if positive.
2. Total head is discharge static head PLUS losses PLUS total suction losses.

You are currently running in circles, advise the total picture - inlet configuration and heights, inlet pipe details etc - discharge config.etc and NPSHr info for the pump.

You can assume what you like - but wishful thinking won't make it work if you have exceeded its limitations.

 

[JRLAKE]

Artisi, with all do respect, an AODD pump does "suck" quite well.

 

[Artisi]

JRLAKE, just as I am at the moment - sucking ice-cold coffee thru a straw, actually I am lowering the pressure in the straw and atmospheric pressure is forcing the coffee up the straw so that I can drink it. Until this is understood the concept of NPSHr and NPSHa will not be understood.

 

[JRLAKE]

An air operated double diaphragm pump creates one hell of a vacuum in the suction line by exerting a suction force, which by definition is sucking. However, I see the point you are making.