Sealing pipe threads

Discussion in 'Help Wanted' started by picklesquirt, May 10, 2020.

  1. picklesquirt

    picklesquirt Member

    Evening everyone,

    Having trouble sealing pipe threads for the starting air for the Blackstone. Using PTFE tape most of the threaded joints give small bubbles at 300 psi with soapy water. Although the compressor gets there it's not what I would like.
    Having Googled hemp as a sealant it suggests it swells when wet so I presume it is best suited to water service.
    Just wondered what other folk have found to be the best sealant for air at this pressure. Pipe is 1in BSP

    Many thanks
  2. campingstoveman

    campingstoveman Active Member

    When I was working we used PTFE on compressed air, only up to 10 bar and never had an issue, I was taught to wind on the tape in the opposite direction to when you were doing the thread up so that the thread didnt push the tape off and to always cover the threads, until they disapeared. According to the RS website PTFE can be used of fuel injection systems which are high bar.

  3. picklesquirt

    picklesquirt Member

    Thanks Martin,

    Your comment of , cover the threads until they disappear is interesting . I am going to strip it down and will reassemble with more generous dose of tape.

  4. hourlapa

    hourlapa Administrator Staff Member

    We use PTFE tape for pretty much everything, water, steam, air although the brush on PTFE is good as well if a little pricey. We buy tape in bulk and apply heavily, don't just stick on a couple of turns :)
  5. Dazzla

    Dazzla Member

    For anything above 1” BSP I prefer to use Bosswhite and hemp. It works well and I’ve never had any problems. It needs a bit more thought when applying than ptfe tape though.

  6. picklesquirt

    picklesquirt Member

    Thanks Gents,

    I have stripped it all down and reassembled with more PTFE tape. Can't test it at present as more pipeing is required to reconnect the compressor in a new location but will let you know the success or otherwise. I've done many trouble free joints with PTFE and normally use about 5 or 6 turns but on radiator tails and small stuff not larger steel pipe.

  7. robtheplumb

    robtheplumb Member

    There is a chart somewhere that gives number of wraps for different size pipes and we all follow that don't we...

    Normally PTFE is fine, you can get PTFE string that is better than the tape on black iron pipe, if you do still have problems after putting the tape on smear a little Boss White, Heldtite or LSX on the tread before making the joint.
  8. picklesquirt

    picklesquirt Member

    Many thanks for all your comments. Have now got there just using more tape and a bit more porridge when tightening up, all is ok at 350psi which turns the engine over 20 revs on a tank of air.
    Split the brass non return valve between the compressor and the tank by overtightening it ( it was rather thin walled ) and is not rated for this pressure - more abuse !! It is silver soldered up and is ok at present.

    Now for some exhaust pipe using a length of field irrigation pipe very thin walled 4in dia galvanised - should rattle well. Will make expansion vessel from an old gas bottle.

    Then it will need some cooling- Hoping it will thermosyphon to a high level tank. 2in dia steel pipe this time but will be able to see the leaks ! Fortunately the pressure is much lower.
    Not put any fuel near it yet, it has a floor standing fuel tank with lift off lid all in cast iron, guess 10 gals. Jolly heavy .

    There is a nice video of a very similar engine if you Google " Blackstone engine at Denver windmill.

    Cheers for now
    Ewan p.p Heath Robinson
  9. picklesquirt

    picklesquirt Member

    Things have moved on a bit
    After stripping down the metering pump and found the plunger stuck, drove it out and honed it with some very fine grinding paste. o.k now
    Then the injector nozzles holes , four of them and the injector valve full of crud cleaned out.
    Now she runs , eureka ! no cooling as yet but enough encouragement to pipe it up when we can get some 2in stocks and dies.
    She needs 300psi air to start her. Have been talking to the people at Denver Mill, they have a very similar engine and say it starts on 150 psi. Theirs is 1932 where as the on we have is 1923.
    It appears from studying their video that the starting air cam is much longer on the younger engine. The cam on ours is about 3/4 in base and no more than a triangle with the top rounded. They also have a much larger air receiver. The handbook talks of a low pressure starting engine 250 psi or high pressure 400 psi any ideas why they offered two options? Or simply did it change over time.

    Happy days in lockdown

    P.S Many thanks to Paul for sorting out a handbook.
    robtheplumb likes this.

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