How to increase the head

[sree555]

I have a diesel engine driven pump for my blast furnace. The pump has a discharge rate of 800m3/hr at 50Mts head. The pump is connectd to an emergency Overhead tank which is at an height of 40Mts. The problem I face is the water is not discharged with full volume. The suction pipe is 350 Dia and the delivery pipe is 250 Dia. No. of bends in the delivery line is 10. (All 90 degree)
The horizontal length of the delivery pipe is 35 Mts and the vertical length of the pipe is 42 Mts.
What is the frticitional losses developed by the pump and whether the pump can deliver at the present height with rated volume.
If not please help me out so tha the pump will deliver at least with 80% of its rated volume.

 

[BigInch]

How much flow can you get now?

If those are mm diameters, it looks like they may be pretty small for 800 m3/h.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[FloThru]

Every one of the 90 degree bends is killing your efficiency. If they can be replaced with 22.5 or even 45 degree bends, you will see an immediate rise in the volume that the pump can deliver.

 

[rzrbk]

Is this a new installation; if not did this pump put up full flow in the past?
Has speed of diesel drive been checked?

 

[Artisi]

Following on from rzrbk's question - if it is a new installation and you have checked the engine speed and it is correct -- then the following is required -- is the water level in the supply tank 40 metres above the inlet of the pump and what is the length of the 350 dia inlet pipe - any bends etc.?
Having this information we can calculate the approx friction loss thru' your pipework.

However I think something else is amiss unless we don't have all the information - if the inlet pressure is 40 metres " Overhead tank which is at an height of 40Mts." and the pump is rated at 50 metres head, then the difference in head is only 5 metres less any friction losses and if this is the case then pump is probably cavitating as there is insufficient head on the pump discharge.

 

[BigInch]

I think the pump rated head is differential head not discharge.

I simply don't think there is any way to get 800 m3/h through a 350 mm D, never mind 250 mm D, with any kind of pump, so I want to get those units straight first.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Artisi]

800m3hr is approx 3500 USgpm and the head loss thru a 250dia (10") is round 6.5 - 7 ft /100. With the info given so far seems the discharge pipe length is 35 + 42 + 10 90deg bends - for argument lets say 100 feet total pipe run so we can assume the head loss from friction on the discharge is next to nothing.
I think we are missing some info here or else the problem is mis-represented.

 

[MikeHalloran]

That's 35 + 42 METRES of pipe.



Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

Mike
You beat me to it, I just logged on to fix the error which came to me about 5 minutes ago. The problem of working in mixed terms, or too many easter eggs and hot-cross buns or just stupidity. Anyway the friction head loss is still not all that great maybe 6 /7 metres.

 

[BigInch]

OK. Looks like I'm losing a 0 or two myself.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[sree555]

This is a new installation and the engine rpm was checked and found to be 1500.The engine performance is good.
The present water flow is some where around 175m3/hr.
The height of the suction pipe from the top level of the water in the sump is 3.5 mts and the sump volume is 350m3. The delivery pipe is 250mm and the suction pipe is 350mm with a bend in the suction ( 45 deg)

 

[BigInch]

Should work.

So, is the motor turning the right direcion?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Artisi]

It's a diesel drive - so the motor is in the right direction - BUT is the pump the right hand?

 

[Artisi]

I should say engine - not motor.

Is the inlet to the pump 3.5 metres above the sump level?
If yes, then the head across the pump will be getting somewhere near to the 50m head rating you advised, so in theory it should be ok.

BUT:

you are pumping 800m3h from a 350m3 sump - how is the sump replenished at 800m3h

 

[sree555]

This is recirculation system. Water pumped by the diesel pump goes to the overhead tank from where it flows by gravity to our blast furnace for cooling.
After heat transfer it again comes back to the sump.

 

[Artisi]

How does the water enter the sump - is it free falling into the sump or is it piped in with the discharge below the pump water level.

If it is free falling into the sump it is probably driving huge amounts of air into the pumpage which is putting your pump "off" performance.

 

[davsy]

sree555

800m3/hr is 13333 lpm and using table B-13 in Crane 410M for a 250NB(10") pipe gives a velocity ~4m/s and a pressure drop of ~0.55 Bar/100m which gives a head loss for the 77m of piping of around 4.6m.

Additional to that is the head loss for the elbows. you also do not mention any valves or other in line components, if any.

From your recent post you said

The height of the suction pipe from the top level of the water in the sump is 3.5 mts and the sump volume is 350m3

I read that as though you have a suction lift (i.e. the water level is 3.5m below the pump centre line) is that correct or did I read it wrong.

For the 350NB(14") suction line Crane 410M gives a velocity of ~2.5m/s and a pressure drop of ~0.15 Bar/100m.

How long is the 350NB suction pipe and are there any valves or fitigs in it.

Do you have a pump curve for the pump, what are the NPSH requirements for it.

Have you a pressure gauge anywhere in the discharge piping, if you had a gauge just above the pump, what does it read at dead head and what does it read when it is pumping the 175m3/hr. Do any of the readings correspond points on to the pump curve.

Answers to these points may give a better indication of where the problem may be.

 

[lilliput1]

What is the temperature of the water.

 

[sree555]

The water level in the sump is above the pump centre by 3.5mts. The suction pipe of 350mm is for a length of 6mts with a 45 degree bend with a gate valve in suction and a butterfly valve and a nrv in the delivery system.
The problem is there is no pump characterstic curve in hand.
We have checked the pressure in the delivery after the deivery valve. It is 5.2 Kg/cm2.

 

[sree555]

The water temp is 95 deg Far