PUMP DISCHARGE HEAD

[ryuchangmyong]

Dear sir,

Demiwater pump have 8m of suction head below storage tank, and pump discharge head is of 80m, in this case, is this suction head(8m) have to be included in a total head calculation of pump as to 88m.

 

[Artisi]

From what you have described - it sounds like yes, although what you have described is a little vague, can you attach a sketch for clarification. Also an 8 metre lift, if this is what you have is pushing the limits.


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.)

 

[ryuchangmyong]

Dear Artisi

Pls refer to attached file for for this clarification.

 

[EmmanuelTop]

TDH stands for total differential head (discharge head minus suction head), and it should be derived from corresponding suction and discharge pressures in consistent units.
If the tank contains non-boiling liquid at storage pressure, the suction head will be higher than 8m.

See

http://www.pumpfundamentals.com/tutorial3.htm

and

http://www.mcnallyinstitute.com/07-html/7-01.html

Dejan IVANOVIC
Process Engineer, MSChE

 

[LittleInch]

Ryuchang,

As noted above, be very careful in your wording and read carefully the data given by you and the pump vendor.

Pump discharge head is exactly that. In many cases this could be taken as already including the inlet head.

Most pump data sheets or curves give you Developed Head in which to get the Discharge head, you add the inlet head. As emmanueltop says very well, use the same units and be consistent in the use of your units.

If what you mean in your OP is that the Pump developed or differential head is 80m, then you are correct, but need to add the atmospheric pressure (or whatever the absolute pressure is on top of the liquid) to the inlet and then convert to absolute pressure from the final discharge head.

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

 

[Artisi]

Come on guys, I know the intention is good but the OP is confused and unsure of what is what - so lets keep it simple.

The sketch doesn't really clarify much other than there is 8 metres positive head on the pump. The 80 metre discharge head is still confusing -- is it 80 meters total head at the discharge (72 being developed by the pump Hd + 8 Hs+ = 80) or is it 80 metres developed by the pump to give a total of 88 (8+80=88).

OP - please clarify the 80 meters at the pump discharge - or do we assume it is the total head at the pump discharge? -- if yes - the answer to your question is "the total discharge head is 80m" and the sketch should say 80m total head.



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.)

 

[bimr]

Ryuchang,

System head = total discharge head - total suction head

See the example:

http://www.mcnallyinstitute.com/07-html/7-01.html

 

[LittleInch]

Bimr, sorry but IMHO I'm not sure that adds anything. I've never heard of pump developed head called total system head before now or "friction head". Friction losses yes, but this example seems to be one persons take on a subject different to just about everything else I've ever seen.

Referring to negative feet head is also a new concept as is feet of head absolute or guage.

If you do it all in absolute then there is no confusion and pump developed head is quite clear - "system" could mean anything....

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

 

[bimr]

LittleInch, just realized that JEmmanuelTop posted the same link. Most people find the McNally articles to be helpful.

 

[LittleInch]

There's a lot of good stuff in there, but there's also some odd ways of calling things. In order to try and make it make sense in a lecture type setting and with simple systems, some of the wording strays into some non technical language which in this instance I think confuses things.

The pump fundamentals link is a bit more like it, but even that gets a bit too simplistic at times, IMHO.

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

 

[Artisi]

LitleInch: Total system head and friction head to me are very common and understood terms and do not cause any confusion (to me).

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.)