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15 comments
Associate

Join Date: Nov 2009
Location: india punjab
Posts: 28

Balancing the Leak-Off Line in a Boiler Feed Pump

02/12/2010 4:00 AM

what is the function of a balance leak off line in a feed pump of a boiler ? explain please. balancing line is given in casing not in delievry line. And

there is a ARC valve ( automatic recirculation ) in delievery line of feed pump whose outlet is in de-aerator of boiler. then what is the purpose of balance leak off line ?

and there is increase in pressure in balancing line. initially it was upto 5 kg/sq.cm and now it is upto 8 to 10 kg/sq.cm. whAT is reason of increase in pressure does it have any bad effect on pump ?

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Power-User

Join Date: Feb 2009
Location: India
Posts: 156
#1

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/12/2010 10:35 PM

In multi stage pumps end thrust is created. This is balanced by the balance leak off. Check with the pump supplier reg the designed value of balance pressure. It has to be greater than that of dearator pressure.

ARC is for minimum re-circulation. If the load falls, BFP's excess flow will be diverted by the ARC.

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Associate

Join Date: Nov 2009
Location: india punjab
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#4
In reply to #1

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/13/2010 5:20 AM

k thank u sir for ur concern.

how this axial thrust is balanced by this line and what is the reason behind the increase in pressure of balancing line and upto what extent this is permissible and what are the effects of increase or decrease of balancing line pressure on pump ?

i will be very thank u to u if u give ur valuable time for me on this query.

i have a KSB - HD 65/14 MODEL AND 30 CUBIC M CAPACITY AND 995 M HEAD MULTISTAGE FEED PUMP

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Power-User

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#7
In reply to #4

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/14/2010 10:21 PM

All have given good hints. You should now read good text books or google search.

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Anonymous Poster
#2

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/12/2010 11:00 PM

Have you checked the injector quill going from the pump to the tank? Could be corroded.

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Associate

Join Date: Nov 2009
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#3
In reply to #2

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/13/2010 5:08 AM

what is injector quill ?. there are 2 nrv present in line WHICH ARE TIMELY CHECKED AND CLEANED. THEY ARE IN GUD CONDITIONS

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Active Contributor

Join Date: Dec 2009
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Good Answers: 1
#5

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/13/2010 9:57 AM

The balance leakoff pressure acts on balancing disc attached to the shaft and works aganist pump thrust load. Check the pump manual for the limit. The balance leak off pressure may vary due to change in clearances or wear in the balancing disk. It is necessary to go for pump overhaul, if the balance leakoff pressure goes beyond the limits.

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Guru
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#6
In reply to #5

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/13/2010 12:15 PM

Well said...

If abcpaper requires more explanation on this, I can bring in some relevant pictorials...

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Associate

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#8
In reply to #6

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/15/2010 8:34 AM

it will be very good and helpful to me if u provide me that.

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#9
In reply to #8

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/15/2010 12:37 PM

Thrust balancing in a centrifugal compressor principally works in the same way as in a multi stage centrifugal pump. So the following sketches (from a centrifugal compressor training module) should help in better understanding.

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Associate

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#12
In reply to #9

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/19/2010 9:54 AM

thank u mr. yesyen, that was very gud demonstration. it has cleared a lot of doubts.thx. but u still miss one thing.

in my set up, the leak off line is from pump discharge side to de-aerator but in ur set up the line goes from pump discharge side to suction side of pump.

nd there is one more doubt which remained unawnsered what is the reason for increase in pressure in this line ?

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Guru
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#14
In reply to #12

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/20/2010 10:52 PM

The sketches that I have inserted explain the typical thrust blanching arrangement in centrifugal compressors, principally the same as in a multi-stage centrifugal pump.

The balance piston is supposed to counter the axial forces crated by the set of impellers. The impellers have suction pressure on side and discharge pressure on the other side; the intermediate pressures get cancelled themselves, by and large. The balance piston is supposed have the same set of pressures, i.e., discharge pressure on one side and suction pressure on the other side, but in the opposite direction. One side gets the discharge pressure automatically. The other side can be led to suction pipe or to a pressure where suction pressure exists.

" in my set up, the leak off line is from pump discharge side to de-aerator" If the suction pressure and the de-aerator pressure are more or less the same, the thrust balance is taken care off by and large. This should ensure less load for the thrust bearing.

This pressure could go more in case:

- As indicated, if there is an orifice and got blocked. This could happen if the fluid has grids or solids. Cleaning this orifice would help.

- If the circumferential clearance around the balance piston/drum peripheral got increased. There can be many reasons for this: again grids in fluid, wear due to rotor wobbling (the cause for rotor wobbling could be imbalance or even worn radial bearings.)

So it is important to analyze the root-cause and resolving one by one from simpler ones to extensive causes.

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Participant

Join Date: Dec 2011
Posts: 2
#15
In reply to #12

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

01/09/2012 8:53 PM

LEAK-OFF ACT ON A DISK MOUNTING AT DISCHARGE SIDE,THEN LEAK WATER LINE CONNECTED TO SUCTION SIDE IS NOTHING BUT REUSE OF WATER.

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Power-User

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#10

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/15/2010 2:17 PM

The leak off line allows for a small amount of water to be recirculated through the pumps and back to the de-aerator even if there is no demand by the boilers. This flow is typically controlled by the use of an orifice sized for your specific pumps. This circulation prevents the pumps from cavitating and burning up. If pressure is building up the orifice could be partially blocked and you risk pump damage.

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Power-User

Join Date: Feb 2009
Location: India
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#11
In reply to #10

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/17/2010 10:41 AM

Flow demand control is by ARC minimum re-circulation and not by balance drum leak off.

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Participant

Join Date: Jul 2008
Location: ludhiana,india
Posts: 4
#13

Re: Balancing the Leak-Off Line in a Boiler Feed Pump

02/20/2010 2:10 AM

Increased pressure in balancing line means clearance in between rotating and stationary balancing disc has increased may be due to wear.For that you need to replace both the discs.

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Users who posted comments:

abcpaper (4); anildigra (1); Anonymous Poster (1); b v rao (3); beriberi (1); SNEHAL PATEL (1); Vanam (1); yesyen (3)

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