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Help with oil combustion settings

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RayPlumb

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About 12 days ago attended a boiler lock out. Apparently another plumber was there a week before to and adjusted the photo cell. ..
It is a grant wall 16/21 about 10yrs old. The ones where there is no room to move ...! Doesn't look like serviced much. Opened up and heavily sooted. Bottom baffle warped and 3 tabulators completely stuck. Managed to get stuck damaged tabulators out and replaced as well as new baffles. Gave it a good clean and added 2xnew longlife hoses (still had original braided ones) added filters on fuel line as had non.
New Nozzle set combustion as per MI (air a little higher than I normally have for these) but CO2 11.8% Exess air 31.4% co 16ppm temp 68deg.
Thought all good probably just needed a proper service.
Over weekend it locked out. Went today and sooted again (not as bad as before) but nozzle and blast tube black. Checked and small oil stream from nozzle after shut down. Presumed this is the sooting problem. Pump filter not great so just changed the pump with coil. and new nozzle.
Went to set it up to MI and with mid 19.3 KW setting at 10 bar, I had to open air damper right up past 8 (normally about 3 for this boiler) to get 12.2% co2. Smoke settings OK.
After adjusting for a while and lowering pressure a bit to get fair readings but was unsettled by air setting still being way near fully open.
I ended up lowering the pressure to 7 bar as the 17 KW range had the same size nozzle @ 7 bar and air damper back down to about 3. Got readings of Co2 11.2, Co 23ppm, Flue temp 75.4 Deg (bit higher than MI max) Xair 37.5 96.9 % efficiency. Good smoke setting 0-1
Anyone with any ideas why I struggled to get good readings at the MI 10 Bar pressure setting. I thought it might be a poor nozzle?
Could a worn / slipping fan produce less air than normal but same oil pressure?
I have offered to go back next week and recheck.
Any Thoughts.
Thanks
 
The fan won’t be slipping and causing that but you could have dirt/crap in air intake to fan.
Did you check for hairline crack in the nozzle assembly? How do you know there was a small stream of oil after the coil closes?
 
SJB060685 said:
The fan won’t be slipping and causing that but you could have dirt/crap in air intake to fan.
Did you check for hairline crack in the nozzle assembly? How do you know there was a small stream of oil after the coil closes?
Click to expand...
Didn't check for crack. The small stream out the nozzle - burner shut off spray off 1- 2 seconds later small stream of oil out nozzle and lasted 2-3 seconds. I took burner out and disconnected made safe electrodes, covered photocell pointed the nozzle to a small tub and switched on.
 
When the coil de energises there should be no more fuel leaving the nozzle. If that’s happening every time the burner shuts down you will have oil on the refractory base. This will cause footing.
 
I have since changed the pump and coil. Big improvement but still a few drops as shut down.
If there was an air bubble in the oil line between the coil and the nozzle, will this work its way out ?
 
Should do but not always. When the oil u set pressure is flowing through the nozzle assembly an air bubble would compress, when the coil shuts this bubble would expand and force oil through the nozzle. I’m not saying that is the cause but when the coil de energises no more oil should reach the chamber.
 
If there is a small crack on the brass oil nozzle assembly allowing a small amount of oil through where it is not wanted, how would I test this. Could you blank off where the nozzle goes and see it any leaks. Would this have an affect on the danfoss BFP11 pump . Any one experienced similar. ?
 
You wouldn’t want to blank the nozzle outlet off as it might blow the pump seals. Internal by pass should prevent that but I still wouldn’t try my luck.
Just whip the burner out and take the nozzle assembly off and visually inspect it. A hairline crack/fracture will be easily spotted
 
Went back last week and new nozzle starting to blacken up. Bit of soot again in chamber Cleaned nozzle holder and there was a tiny crack down the top of the nozzle holder. Ordered new part and replacing tomorrow. Ill probably have to give the chamber another clean...
 
Looks like not solved this problem yet. Started sooting up again after week, still mainly around the nozzle and blackening the photocell ...lockout.. Ive checked the nozzle again and back to a small squirt at end shut down. Presume drawing air in somewhere, but it is on a tigerloop. This should bleed air out, but could air still be drawn into the nozzle oil line causing it to compress and then squirt when expanded.?
New issue today was tigerloop was empty boiler been off for day and half. No sign of leaks presume check valve passing ?. Could this draw in air..?
Phoned grant Friday for advice and the tec said the cleaning door seal could of compressed over the years and caused the door to sit further in causing the long drip plate just under the tubulators to touch the door insulation causing the an air flow restriction which end in sooting.. There is some evidence of this with a black soot line on the door insulation.
But would this cause sooting on nozzle and photocell?
Turning into nightmare...
 
The door seal problem is known yes. Trying cutting a shallow 25mm grove into the insulation to allow proper passage of flue gases.
The tiger loop sounds like the NRV has failed. Either put a small 10mm NRV on the suction line before the loop or replace the loop with a current regs metal one. It is possible the oil feed line and flexi is drawing in air. See through hoses help to diagnose this problem.
 
So went out today and tiger loop still holding oil after a day ( burner been off).
Cut chanel in door insulation and added some more door seal rope around seal.
Removed the burner and checked electrodes and while it was out. With a container of oil checked the burner. Littler after squirt. Flushed out air in nozzle oil line. Ran on and off quite a few cycles and no after drip or squirt at shut down. No evidence of any oil leak on oil line from tigerloop to burner, so presume the day it was empty it had drained back to tank.
Added a non return valve just before tigerloop on supply side. Also added a clear oil hose on the suction side to pump.
Connected all up and flushed all air out oil lines with coil disconnected. Clear oil suction hose nice and clear with no air flowing through. Although every 1.5 - 2 minutes a small bubble comes through the return line.. ran for about 10 min and still small bubble every 1.5 - 2 min. The flow hose is still clear no air. (although flow rate quite high would I even notice?)
Could it be cavitation in the pump ? or is there a small leak sucking in air. Is it enough to worry about. ?
There is two isolation valves on the suction and return, but cant see any leaks.?
 
Last edited:
What’s the total suction height from base of tank to burner? As you know a tiger loop or any other deaerator is a sub gravity system. I think at about -0.4 bar gases can be extracted from the fuel, that’s the purpose of the deaeration. If the suction head is more than 3.5-4m this can happen.
An air bubble appearing in the return chamber rather than the feed chamber still suggests a leakage after the loop and before the pump inlet, the return is pressurised.
 
SJB060685 said:
What’s the total suction height from base of tank to burner? As you know a tiger loop or any other deaerator is a sub gravity system. I think at about -0.4 bar gases can be extracted from the fuel, that’s the purpose of the deaeration. If the suction head is more than 3.5-4m this can happen.
An air bubble appearing in the return chamber rather than the feed chamber still suggests a leakage after the loop and before the pump inlet, the return is pressurised.
Click to expand...
The tank is about 10 mtrs away from the tigerloop and burner is about 1 mtr above the bottom of the tank. Flow rate through oil line is quite good, but slows a bit through fire valve, but more than burner nozzle would need.
 
RayPlumb said:
SJB060685 said:
What’s the total suction height from base of tank to burner? As you know a tiger loop or any other deaerator is a sub gravity system. I think at about -0.4 bar gases can be extracted from the fuel, that’s the purpose of the deaeration. If the suction head is more than 3.5-4m this can happen.
An air bubble appearing in the return chamber rather than the feed chamber still suggests a leakage after the loop and before the pump inlet, the return is pressurised.
Click to expand...
Click to expand...
So if there is no air in the clear inlet hose could that rule out all before the hose including the isolation valve. Which would only leave the connection of the clear hose to the pump and the new pump itself.
 
If the tank base is only 1m below the burner then most of the time when the tank is full/near full the suction line will be under a positive pressure. Only the oil line above tank fill level would be subject to less than atmospheric pressure. That’s where you would expect air being drawn in.
I’ve always approached like this. If air/bubbles can be seen entering the bottom chamber of loop from tank then there’s a leak somewhere between tank outlet and loop entrance. If no air/bubbles at that point it any air ingress would be on the suction side of the pump.
 
SJB060685 said:
If the tank base is only 1m below the burner then most of the time when the tank is full/near full the suction line will be under a positive pressure. Only the oil line above tank fill level would be subject to less than atmospheric pressure. That’s where you would expect air being drawn in.
I’ve always approached like this. If air/bubbles can be seen entering the bottom chamber of loop from tank then there’s a leak somewhere between tank outlet and loop entrance. If no air/bubbles at that point it any air ingress would be on the suction side of the pump.
Click to expand...
The only connections that would be under negative pressure it the check valve I installed below the tiger loop.
Bubbles definitely entering from the side where the return pipe enters the tigerloop. I did tighten all the suction side connections, could pressure test but would that not necessarily show up if it a suction issue. Looks like a revisit...
 
When I was setting up I ran the boiler with the solenoid connection off and photocell out so I could flush out any air in pipework before coil is connected. So effectively the pump just circulating the same oil round from the pump to the tiger loop in a constant loop and not drawing in any new oil as coil is not is not sending any to nozzle.
On one occasion while trying to figure out where this 2 min bubble was coming from I switched the burner on but had left the isolator near the fire valve on the supply line before the tiger loop closed. Instantly there was loads of air filling the clear suction line...?.
I opened the isolator and the air started to clear the hose filling back up with oil..
Surely with the oil just circulating pump- tigerloop - pump and coil not connected there was no additional oil drawn into the loop, then having the isolator before the tigerloop open or closed should not make a difference...??
 
Was the tiger loop completely full? As in top chamber full? I doubt it based on your description.
With that isolation valve closed you would experience a hard vacuum which as I said above can cause gases to be extracted to be pull from the solution, hence why I asked about a vacuum test.
A vacuum test enables you to see the sorts of pressure on the suction line.
 
Vaccum test from pump just under 0.1bar . On switch off drops a fraction and holds
I also removed both suction and return lines from the tiger loop and pressure tested to pump at 2 bar and no leaks.
Changed the suction line connection at the tiger loop as no inserts and the isolation valve on the suction line.
Reconnected and flushed air from lines. Fired up boiler and 2 min later small bubble popping up from return. .....!
Boiler is running fine and good combustion results.
 

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