Hi all, Just thought I would put up a photo or 2 of my recently acquired Primus 744 roarer burner. Tried firing it up as is but won’t hold any pressure in the tanks. Replaced the washers on the filler lid and pump lid and fitted a new leather pump cap to no avail. Seemed to be relatively clean in the tank before I refuelled it. Having few problems getting the NRV out at the moment. Any tips please? Awaiting washers to replace on all the burners. Got the “flame rings/spreaders?” from a local fabricator I know, not the exact size but should suffice for now. Surprisingly, the stove came cleaned-up like this. Some fuel is coming through on one burners but will not light. Could the burners be blocked up. Thanks in advance
Take care with the NRV. The best bet is to use a steel rod the same diameter as a snug fit in the pump tube (eg a bolt); with a slot cut 5mm wide and 5mm deep across the bottom of the rod. Use some acetone and or penetrating oil down the pump tube overnight before unscrewing the NRV. A lot of downward pressure while applying and lateral torque. Tony
Good Morning, I have been successful in removing NRVs with my selfmade tool. Might be worth a try. You can see it here: New member and how to remove stuck NRV when the NRV head is damaged. Normally, changing the burner washers is not neccessary unless the connections between burner and riser tubes are leaking fuel. Did you clean the jets? If the jets are blocked, it may explain that there is only one burner emitting fuel. You have to preheat sufficiently, because the burners are of the large type, especially your very heavy flame ring spreaders take a lot of heat unless they reach working temperature. That may explain, why the fuel does not ignite. And if the pump and NRV is working correctly, you have to pump a lot, because it is a large tank capacity.
Thanks Tony, I will try to acetone the night before as you suggested. I have the NRV removal too so should have some luck. Best regards Kev.
Hi Jack Tar, The tank is not holding pressure despite me replaced the filler cap washer and NRV cap washer. Pricked out all the jets, one of which let a bit of fuel through, which gets me thinking possible blockages in the burners heads themselves. I will admit I did leave my “home-made” flame rings/spreaders” on whilst trying to get them to flame, so probably a significant mistake there on my part. Also I am sure I did not pressurise the tank enough, in hindsight. I am really looking forward to getting this working as I hear that it is quite noisey and powerful. It will not fit into my old Hestia Primus-powered oven; too big, and would probably start warping the metal. Thanks for the advice. Once working I will put some photos on the site for your delectation.
A lot of these furnaces lived a hard working life, so there is a possibility the burners may be fairly clogged with carbon deposits. Try everything else first but there is a possibility you may need to remove but ers, remove nipples from burners and decoke.
If the burners are clogged by coaked fuel residues, there will be problems in fuel emitting, causing poor performance, when the tank is pressurized properly. Coaked burners do not cause a loss of pressure in the tank. Perhaps there is still a leak somewhere? Or a low fuel level, allowing the air venting through one of the burners?
Yes, thanks Guys, appreciate the input. I do have an ultrasonic cleaner, though I hear you have to be careful you don’t strip the metal if in the citric acid/detergent mix too long, so I will leave burner removal as a last resort.
Yes, my post regards blocked burners was in response to the question posed in post #1, which asked if the burners could be blocked. Indeed they could, especially if fuel is only issuing from one of four. Regards pressure loss, we haven't yet covered all bases: There are two seals in the area of the pump valve (NRV)- one which seals the valve assembly to the end of the pump tube, but seldom gives trouble unless disturbed and often no trouble even after being disturbed. The other is the seal within the valve itself, much more likely to cause a pressure loss and easy to diagnose by immersing the (empty) pressurised tank, or pumping like mad, removing pump and filling the tube with water...
Thanks Blackdog. I have plenty of info to get my teeth into. Best regards all round for all your help. Kev.
Without wanting to appear contentious, how would heating the tool help? By warming the valve body slightly, it will only expand and tighten into the pump tube end, if anything. My experience of very stuck pump valves (ones where the solder joint has failed between the pump tube and end, before the valve broke loose) is that at least one cycle of red heat and cooling has been required, sometimes several. It's hard to imagine how heating to 100° or so could help.
@Blackdog The heat expands the flat surface of the Nrv while the flat surface of the pump tube is not immediately affected and does not expand. I have used this method several times on stubborn nrv's and it has worked for me. The threads on the nrv don't seize up as much as those two surfaces. Penatrating oil will be more effective for the thread on an nrv if applied from inside the stove tank ( enough to submerge the bottom end of the pump tube)
I completely agree that if penetrating oil is going to be used, putting it down the pump tube is illogical- before the fluid could reach the threads, it would have to get past a joint which is designed to resist a fairly penetrating liquid (paraffin/kero) under ~15psi pressure. Get it to the threads from inside the tank and it has a chance of penetrating. Interesting thought regards the face friction between valve body and pump tube end. Although in a lot of cases there is a sealing washer, providing the stove manufacturer did things properly and subsequent rebuilders took due care!
Unfortunately, there were some periods, when some factorys mounted the NRV without any washers. Just a small brass rim in the pump tube bottom, which deforms to form a seal to the NRV. I had several attempts with putting the (empty) stove in a freezer, then pouring hot water in the pump tube. But I can not find any difference with or without temperature treatment. Perhaps the "hot tool method" can provide the heat more targeted. I have to try it next time.
