Tiger Loop / oil feed problem

Discussion in 'Plumbers' Talk' started by mikes, Apr 19, 2012.

  1. mikes

    mikes Guest

    Hello all, I have a problem with a tiger loop, it may not be the tiger loop itself, but problem is as follows.

    New WB boiler with Riello burner. Tank level is not that far below burner level but as old WB boiler had burner at bottom of jacket (i.e. just above floor level) the nominal oil level is now about 300 mm below burner whereas before it was about 300 above (no tiger loop). BTW this is a new tiger loop Bio for internal with the vent to out side.

    On first start up there were persistent lock outs with lots of foam air being release from the bleed/suction port. Initial start was with the flexi hoses in a tub of oil; and seemed to be pulling ok so connected to 10 mm pipes.

    Fed burner with single hose directly from container ? no problem ? bled a bit of air then runs and runs.

    Tried tiger loop again ? locking out persistently ? and air dragged in. btw the feed return connections have not been swapped as have checked and ran oil from the tiger outlet to the boiler and it ran fine.

    Connected container to outlet of tiger loop (valve on outlet feed = off) again no problem ? runs and runs. Boiler has now run about 50 lit from containers no problem regardless of whether run with lots of stops or starts or long and hard, either first thing in the morning (cold) or after running most of day. So happy with boiler ignition process etc etc

    By using the container to flood up all the lines I did get it working via the tiger loop and it ran fine after a small amount of air was bled from the pump. It ran for 2 days about 10 hours of burning before locked out. A restart produced a lot of air from the bleed at the pump ? locking out persistently. Reverted to container and all is fine again.

    The lay out is as follows

    Floor level Inlet pipe 10 mm from tank about 25m away.
    Valve
    Bowl filter
    Valve
    Oil meter (aqua metro VZ04)
    Valve
    Line up to tiger loop main inlet Tiger loop about 200 mm above top of boiler
    Line to boiler with valve on exit of tiger loop then flexi hose with boiler casing
    Return from boiler with valve on return inlet to tiger loop (flexi hose with boiler casing)

    I can understand difficulty in getting the first prime and bleed but once running I?m surprised it ran as long as it did.

    It may be dragging in air. I would think this would have to be in the section from tiger loop to boiler as anywhere else would (in theory) be expelled by the tiger loop.
    There are no obvious leaks everything is very tight and when running from the container most but not all of the same pipe work is used. I am concerned that A) maybe compression fittings or the 10 mm valves are under pump suction allowing air ingress, or B) the tiger loop was/is defective ? other than that I can?t see what else.

    My next test is to connect the container to the incoming supply line and raise it above the level of the tiger loop. This will give a slight positive pressure on the bottom inlet to the tiger loop and ensure oil flow / bleed occurs naturally. ? any problems with doing this??. Then repeat with the container lower. If the tiger loop cannot pull properly will air get dragged in? These are not great heights so I cant see how the tiger loop will be struggling.

    Sorry for the long post but I like to give as much precise technical detail as possible so you experts don?t waste your time.

    Thanks in advance

    Mike
  2. heatyman

    heatyman Member

    First question; have you fitted the by pass screw to the pump? (Don't be offended, you haven't  mentioned it in your comprehensive summary)
    If you have, then do not discount the run from the tank to the tiger loop. If this leaks, then the tiger loop will not expel air as it will not pull up oil. The only air it will expel is that created by 'stirring up ' in the pump. All your successful temporary runs are with a positive head to the loop, which points to a fault in the feed to the loop. When priming, I never use the bleed port, let the tiger loop expel the air through the return port. If you are still getting air after a short run ( 1-2 mins) then you are pulling air in somewhere.
  3. mikes

    mikes Guest

    Hi Heatyman,
    Many thanks, but yes I have ?screwed in? the bypass, it?s a good point to make as we can all miss the obvious. I agree all my attempts have involved positive head. I am pulling a fair suction from the pump as it?s new and I forgot to remove the air hole bung in the canister and started crumping down a 2 gal plastic drum. I say screwed in because the instructions iaw WB are remove blanking plug and ?screw in? the bypass screw ? inwards = clockwise.

    To test this today instead of doing what I stated above I popped off the feed inlet to the Tiger Loop, this was full to the top of the pipe which is above the tank level, oil ran out emptying the T/L chamber so = full. I disconnected the return to the T/L and fed the boiler pump from the canister, again oil ran out of the T/L from return line and I ran about ½ lit from the return line with the boiler on and firing.

    I tapped the canister feed into the T/L feed to the boiler with a T piece and fired up with the return valve to the T/L open and the T/L outlet open. So the canister was providing some head and the return line was running in and out through the T/L. The only valve closed was on the main inlet to the filter ? so it?s not pulling from the tank but was (I hope) reticulating via the T/L. So far so good. Gave it about 5 mins then opened the inlet valve and It kept running, after about 30 seconds (felt longer) indicator on meter started turning so waited a few mins and closed valve on canister so am drawing from tank again. Been running about 2 hours so far. I nipped up all the joints.

    It may of course be a day or so before repeat so we?ll see.

    Thanks

    Mike
  4. heatyman

    heatyman Member

    What level of oil is the tiger loop retaining? There should be enough to allow the boiler to run and replenish even if you do have some run back during off periods. Even with small leaks, I've always managed to prime tiger loops without any assistance, especially on such short lifts. Even after fuel run outs, a couple of resets is all that has been needed. It is easy to test the non return valve by sucking against it from the feed port, and if there is a bit of muck holding it open, this can be cleared by forcing a quantity of oil through the inlet with a pump.
  5. mikes

    mikes Guest

    Hi,

    Cant tell, as its a new one and they are all solid. Some say it looks like R2D2 so we cant see inside at all.
    I'm waiting to see what happens.

    Mike
  6. mikes

    mikes Guest

    Hi,

    After a while I thought this had resolved itself. We seem to have returned to the persistent lock out with air being bled from the vac gauge port on re-start up.
    I?m beginning to think it?s a dicky tiger loop not pulling.
    The oil tank level is quite low about 5 inches above the outlet so not a huge head but definitely not letting air in,  I estimate this level to be about 400mm below the burner (which is about 400mm below the TL).
    To get the boiler going I left the ?T? in the line from the TL to boiler flexi feed, to this the canister is connected. So if I open the canister isolation valves (there?s a few so I can break the line and keep it sealed) I am flowing directly to the boiler, I leave the isolation valve on the return from the boiler pump return point open so we are circulating via the TL. I have also been leaving all of the supply isolation valve trough the filter and to the TL main inlet open. When running like this the meter on the inlet does not turn.
    After about 5 mins of running close canister isolation valve so we must be drawing from the TL. After about a few mins the meter on the inlet begins to turn. The time for this to occur is roughly calculated as the time to deplete the TL bowl and thus be pulling in the supply - hold breath ? fine works, and works through a variety of on/off cycles. The volume passed seems correct.
    But after 2-3 days same again.

    Either air is being drawn in or the TL is not sucking sufficiently, or possibly not expelling air?

    If the TL was allowing the level to fall back that would be a fault within the TL ? there is a small check valve on the bottom inlet.

    If a totally gross amount of air was returned to the TL it?s possible that it couldn?t expel it.

    If anyone is interested I have a cross section diagram (I will attach separate) through the TL casing so can see a ball poppet in the lowest of the 3 chambers. But as mentioned the height difference is not great but equally that should mean that there is less to reverse flow so should hold the prime.

    The isolation valve I've used is the 10mm mini ball valve (pn 79038) looking at the detail it doesn?t specifically mention oil whereas some of the peglar ones do state oil. I used these because they were 10mm. I know there is a brass type with a thumb wheel, excuse my ignorance but is there a special type more suitable?

    Any suggestions? Tiger Loops seem pretty reliable although they say it will self prime it didn?t from the outset. It might have done but the lock out occurs quite quickly after firing so how many lock outs would have been necessary to prime the line? I flooded up as much of the lines as possible by running through a bowl.

    Another thought was that the flexibles run over the top of the burner to the service hole on the casing (this is an outside boiler WB green star combi located within a shelter/shed) they feel quite warm, is it possible that the heat is causing some off-gassing? Should they be re-routed round/under the burner?

    So any suggestions ? experimental or otherwise.

    Many thanks
    Mikes
  7. mikes

    mikes Guest

    Hi,
    This is the cut through of a tiger loop. I may be wrong in suggesting that its at fault. But it is interesting to see whats in side.

    [​IMG]

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